Method and apparatus for contactlessly determining the temperature of a stream of conveyed material, and granulation device having such a contactless temperature determination apparatus

Abstract

The present invention relates to a method and an apparatus for contactlessly determining the temperature of stranded and / or granular objects in a stream of conveyed material, for instance at the dryer outlet of a granulator, in which infrared sensors are used to capture the radiation field of the stream of conveyed material flowing past against a background, and the temperature of the stranded or granular objects is determined from the measurement signal from the infrared sensors, wherein the temperature of the background, against which the stream of conveyed material to be measured flows past, is varied in terms of time and / or location by means of a temperature control apparatus, wherein degrees of fluctuation are determined from the measurement signal from the infrared sensors for different background temperatures and the position of a minimum fluctuation is determined from these degrees of fluctuation, wherein the object temperature is determined from the value of the measurement signal at the time / location of the minimum fluctuation.

Description

[0001] Maag Germany GmbH

[0002] Method and device for contactless temperature determination of a conveyed material flow and granulation device with such a contactless temperature determination device

[0003] The present invention relates to a method and a device for the contactless temperature determination of strand- and / or granular objects in a conveyed material flow, wherein an infrared sensor is used for the temperature determination to determine the temperature of the particles or strands in the conveyed material flow. The invention further relates to the use of such a contactless temperature determination device in a granulation device, in particular at the outlet of a granulate dryer or a strand granulator of a granulating device.

[0004] For the processing of granules and their precursors and intermediate products, precise temperature determination is both important and difficult. Since temperatures of the strands or granules being processed that are too high or too low can cause problems in the process, precise temperature determination is essential. The most accurate knowledge of the respective temperatures at various points is required in order to be able to control the process in a targeted manner. In each upstream process section, various control variables such as melt temperature, water temperatures, water velocities, air velocities, cooling water nozzle flow rates, surface-to-volume ratio of the granules or strands, residence times, and many more can be adjusted in order to specifically change the temperature of the objects at the measuring location.Many of these manipulated variables exhibit linearizable correlations with the object temperature at operating points, and it can be considered that changes only become effective after a certain delay at the measurement location. For temperature control, the manipulated variables and response times are not a problem. Sometimes, the aim is not to control to a setpoint temperature at all, but rather to maintain a temperature window, since other important process variables also need to be monitored. However, the difficulty so far has been that without a reliable, accurate temperature measurement, temperature control within a temperature window is not possible, which this invention aims to change.

[0005] Granulation processes can be used to produce plastic granules, whereby a plastic melt is usually forced through nozzle-like holes to produce plastic strands. Depending on the granulation technology, the resulting strands can be cut off immediately at the outlet of a perforated plate by a rotating knife, as is known in underwater granulation or dry granulation, whereby in underwater granulation the pellets or granules are dried in a downstream dryer. Alternatively, in strand granulation the plastic strands can first be passed through a cooling section in strand form and then fed to a strand granulator, where the strands are then cut into granules between a stationary knife bar and a rotating cutting rotor. However, such granulation processes are not only used for plastics orIt's used not only for plastic melting, but also in the pharmaceutical industry for the production of tablets and pills, and even in the food industry. To achieve high-quality products, precise temperature control of the processed masses is necessary.

[0006] For example, the cutting quality can be impaired if the temperature or the cross-sectional temperature profile in the strands yet to be granulated is incorrect, so that precise temperature determination of the plastic or material strands may be required at various positions between the die plate and the strand granulator. From measurements of the longitudinal temperature gradient or temperature measurements in two or more evaluation sections along the material flow path, conclusions can be drawn about the core state of the strands, which must not consist of a hot, low-viscosity melt for cutting. On the other hand, process problems can also arise after comminution if the temperature of the granules deviates too much from the specified temperature window. For example, crystallizable plastic pellets or-granules reach a specific temperature, which can be sufficiently high to initiate an energy-efficient self-crystallization process using their own heat, but must not be too high to prevent the plastic granules from sticking together. In particular, the granules should reach the predetermined temperature at the outlet of a granule dryer before being fed into a corresponding post-treatment section or station, such as a vibrating conveyor or a reaction vessel.

[0007] However, determining the temperature of such strands and granules is difficult for a variety of reasons and has so far been difficult and not sufficiently accurate. This is due, on the one hand, to the fundamental problem that temperature measurement is performed on a moving object. The plastic strands or granules are in motion while the temperature is being measured. For example, at the outlet of a centrifugal dryer, for example, there is no leisurely, densely packed stream of granules flowing past, but rather granules swirled by the air stream that more or less fly past. Depending on the material, the granules should remain fluidized during the temperature measurement process, as otherwise agglomerations may form. This applies in particular to plastic granules made from sticky plastics, but can also be the case with pharmaceutical or food-grade granules.

[0008] Secondly, the strands and granules whose temperature is to be measured are often very small, so the sensors used require a sensitive, highly dynamic response to adequately address the correspondingly small amounts of heat or radiation emanating from these small objects, particularly given the sometimes high speed at which the granules flow past the sensors and the rapid transverse vibrations of the strands, whose oscillations are stimulated by the granulation process. Depending on the material, the strands and granules often have diameters of only a few millimeters or even fractions thereof, for example, less than 7 mm and often less than 4 mm, so the objects are very small compared to the size of the detection range of an infrared sensor.

[0009] For this reason, contact temperature sensors, which are arranged in the product stream with a thermocouple, have been predominantly used to date. However, this is usually problematic because only a small amount of heat is transferred from the product stream or the passing objects to the thermal sensor. When the object comes into contact with the thermal sensor, the Hertzian contact areas are very small, the contact time is very short, and the thermal conductivity of the material, which is usually a plastic, is very low. In contrast, the surface of the thermal sensor continuously radiates heat into the environment and simultaneously absorbs ambient heat radiation. Furthermore, it is in convective exchange with the air. If one considers a conventional granulate dryer with a vacuum fan, the flowing pellets move out of the outlet together with warmed, moist air boundary layers.Cool, dry ambient air is drawn in against this flow, which flows into the dryer at the outlet in a countercurrent to the particle flow. The ratio of the swirling air currents of the cooler countercurrent air flow and the warmed air carried along with the pellets depends on many parameters and is difficult to adjust reproducibly. Therefore, the result of the contact temperature measurement is often ultimately just a measurement result derived from the air temperatures of the various air flows, the product temperature, and the outlet pipe temperature.

[0010] Furthermore, non-contact temperature measurement has also been attempted. For example, infrared sensors can be used for plastic granules in the range of 20°C to 150°C. These sensors evaluate the radiation emission of the granules or strands in a wavelength range of approximately 8 to 14 pm. Pyrometers and bolometric infrared cameras can be used for this purpose. The fastest currently available sensors have a response time of slightly less than 10 ms. This means that granules or particles flowing through the measuring spot of the infrared sensors generate detectable measurement signals as peaks. However, the residence time in the measuring spot is far from sufficient for the pyrometer or individual pixels of the bolometric infrared camera to be controlled to the full particle or granule temperature.The situation is comparable with vibrating strands, which, due to their narrow width, can only be partially detected by a pyrometer or pixel. The maximum temperatures of the individual peaks are significantly colder than the actual object temperature, which is measured by temporary accumulation or agglomeration, in an unacceptable and barely useful way. As mentioned, such compaction of the product stream is not permitted, especially for strands and plastic granules, due to the risk of agglomeration. It is only possible under laboratory conditions or for testing purposes, but not during the ongoing process in large-scale plants.

[0011] Direct infrared measurement is only possible if a compact, sloping bed forms in the outlet pipe or chute at a high product fill level, which is undesirable or even impossible for many products. Similar problems arise with strand temperature measurement, where, due to the thinness of the strands, a very high resolution of a very expensive infrared camera is required, or several cameras must be installed on a scanner beam at considerable expense.

[0012] Even with powerful infrared sensors in the form of pyrometers and bolometers with only average resolution, one obtains significant signal noise, with the longer response times preventing the sensors from fully adjusting to the granule temperature. The granules fly past the sensor or through its measuring spot too quickly to allow the sensor to respond sufficiently. Both ultimately stem from Boltzmann's law, according to which the radiant power arriving at the sensor depends on the area and temperature of the granules and the measuring distance, more precisely, Psensor = 8 x 6 x A x T 4 / r 2, where 8 denotes the emissivity of the plastic, 6 is the Stefan-Boltzmann constant, A denotes the area of ​​the granule, T is the granule temperature, and r is the distance of the sensor from the granule. The temperature of the pellets in the range of approximately 40°C to 120°C is very low for an infrared sensor, and the radiating surface of the granules or strands is very small. In addition, the distance of the sensor is usually very large compared to the pellet size. The 1 / r 2The distance dependence therefore leads to very weak measurement signals. The small size of the granules and strands leads to the problem that pixels only partially receive the radiation from the object in low-resolution infrared cameras. Only with continuous, full coverage of the pixels does an asymptotic approach to the actual granule or strand temperature occur, with a simultaneous decrease in signal noise, provided the granule or strand remains close to the sensor for a sufficient length of time. This, however, is not the case in large-scale processes with high throughput.

[0013] The document DE 10 2016 115 348 A1 attempts to achieve non-contact temperature measurement of fiber optic strands using a thermal imaging sensor. The problem of movement of the very thin strand relative to the significantly larger pixels of the thermal sensor and of only small temperature differences between the strands and the background are to be compensated for by integrating the thermal sensor's measurement signal over a longer period of time and comparing the resulting integral with a reference value that can be determined from a correspondingly long measurement of the background without passing fibers. A blackbody radiator is used as the background radiator, whose reflectivity should be at least approximately 0 to prevent any reflections of thermal radiation in the sensor's thermal image.By forming the integral, a mean value is determined, so to speak, which is intended to be more accurate than the maximum value of the heat sensor's measurement signal at a specific time. However, the use of a blackbody radiator permanently located near the strand is hardly feasible in practice in large-scale plants due to the problem of contamination. Furthermore, the necessary reference measurement inevitably results in greater or lesser inaccuracies if fluctuations in the process control cause the actual temperature of the measurement background to change compared to the reference measurement, which is often the case in large-scale processes.

[0014] Document WO 2014 / 090994 A2 attempts to measure the temperature of metal strands, which are to be coated with an insulating plastic sheath, in a non-contact manner using a radiation sensor that performs a spatially resolved thermal radiation measurement from the interior of a tube through which the metal strand passes. Here, too, the tube is designed as a black cavity radiator. With a sufficiently long tube, edge losses can be minimized to such an extent that a measurement under specular inclusion conditions is possible in the center. The document is based on the finding that when the temperature of the metal strand and the cavity radiator are identical, the metal strand is no longer visible against the background formed by the inner wall of the tube, and therefore no significant deviation occurs in the spatially resolved thermal sensor image in the area of ​​the moving metal strand.This knowledge is used, on the one hand, to determine the temperature deviation of the metal strand from the known pipe temperature based on the deviation of the radiation sensor signal compared to a reference measurement at a known pipe temperature. On the other hand, this knowledge is used to control the temperature. The hollow radiator, which is designed as a tube and whose temperature is easy to measure, is heated to the desired setpoint temperature. Process parameters that influence the metal strand temperature are then adjusted if the measurement signal from the heat sensor exceeds or falls short of the corresponding setpoint, which occurs at a metal strand temperature that corresponds to the pipe temperature. While this approach can be used to adjust the temperature of the strand to a setpoint temperature, it cannot be used to measure the temperature of a strand when it is not at the setpoint temperature.Only a non-calibrated measure of the deviation from the background temperature is determined, i.e., slightly hotter or cooler than the background. If the object cross-sections and occupancy densities of the objects to be measured are unknown, a quantifiable calibration to the object temperature is not possible. Precise measurement of temperatures that do not correspond to the target temperature is not possible. Therefore, it is not possible to monitor whether a temperature window is being maintained.

[0015] The present invention is based on the object of creating an improved method and an improved device of the type mentioned above, avoiding the disadvantages of the prior art and advantageously developing the latter. Preferably, not only a deviation from a background temperature per se should be determined, but also quantified in order to be able to output or display the actual object temperature as an absolute temperature value.

[0016] In particular, even with infrared sensors with limited resolution and response time, sufficiently precise non-contact temperature measurement should be possible for conveying streams containing small, fast-moving objects such as plastic strands from strand pelletizers and plastic granules in large-scale pelletizing plants, especially in plant sections with short overall lengths, such as the outlet of a pellet dryer, where the objects move rapidly without a high fill level and can be kept sufficiently fluidized. Known solutions for infrared measurement under gloss confinement often cannot be used in large-scale plants due to their long overall length, so special solutions are required. The temperature measurement result should be suitable for temperature control, in particular for maintaining a temperature window.In order to keep the control technology simple, it is desirable to obtain a low-noise quasi-continuous measurement signal with a short and stable known measurement delay time.

[0017] According to the invention, the stated object is achieved by a method according to claim 1 and a device according to claim 21, as well as a granulating device according to claim 34. Preferred embodiments of the invention are the subject of the dependent claims. It is therefore proposed to engage with signal fluctuations, so to speak, and to examine the intensity of the measurement signal fluctuations more closely. The cause of the fluctuations is that infrared radiation emissions emanate alternately from the objects to be measured and from the background. In the case of strands, local intensity fluctuations occur in particular, while in the case of granules, temporal fluctuations occur in particular. Surprisingly, from the fluctuation intensity of the sensor signal with a simultaneous change in the radiation background, it can be determined what the sensor would measure if granular objects were actually located in the measuring spot of the sensor for long enough.Strands would be so wide that there would be no problems with partial coverage of sensor pixels. The temperature of the background, in front of which the material to be measured flows, is varied temporally and / or spatially using a temperature control device, with the intensity of signal fluctuations in the resulting measurement signal from the infrared sensor being evaluated by an evaluation device. In the simplest version, signal fluctuation minima can be searched for, with infrared measurement signals in these fluctuation minima directly representing the object temperature. At the infrared contrast minimum, the infrared sensor receives infrared radiation of equal intensity from the objects and from the background, evaluated with its spectral sensitivity characteristics, so that the measurement signal directly reflects the object temperature.

[0018] This measurement signal is generally suitable for process control and monitoring a temperature window in an industrial plant. However, with purely temporal variations of the background, this simple method only updates the measurement result at certain times, and small jumps may occur because measurement noise makes it uncertain to locate fluctuation minima. A simple control technique would have to be designed relatively conservatively and slowly. For more dynamic control, a more complex prediction model would have to be trained. For a simple way to dynamically control the process within a temperature window, a quasi-continuous measurement signal is desirable.Further challenges lie in precise temperature measurement with infrared sensors, as the temperatures to be measured differ only slightly from the infrared sensor housing temperature, meaning the sensor element also receives thermal radiation from its own electronics and housing. The transmission of conventional infrared optics is also extremely temperature-dependent. Therefore, infrared sensor manufacturers invest considerable effort in calculating such influences from the measurement signal using self-temperature monitoring sensors and compensation methods with correction curves. This compensation does not work perfectly, especially with temperature gradients in the sensor head, and degrades with age.

[0019] In advantageous embodiments, measures are therefore provided to improve the infrared sensor accuracy, for example by sensor head temperature control, methods for reducing the emissivity influence without the need for complex two-color pyrometry, additional temperature measurement of the background with independent measuring methodology for online temperature compensation of the measuring signal, whereby the online updating of the temperature compensation value is possible in the presence of the conveyed material flow or even during production breaks, a calibration station with a black radiator, onto which the infrared sensor system can be briefly positioned.

[0020] Furthermore, various statistical methods are included that, on the one hand, robustly quantify signal fluctuations, but on the other hand, also filter out the effects of measurement noise and, with a reference temperature calculated for the measurement background, provide a low-noise temperature parameter for regression models. Regression models enable the reliable detection of minima via interpolation or extrapolation with verifiable quality, allowing a reliable, precise object temperature to be determined quasi-continuously.

[0021] Furthermore, various devices are described that are well suited to temperature-regulating the background and the enclosure in such a way that the objects to be measured are placed in temporally and / or spatially varying infrared contrast situations against the measurement background, allowing objects to be measured in a confined space under conditions virtually equivalent to specular inclusion. If local temperature differences and longitudinal temperature gradients of objects are to be analyzed in the measurement area, locally varying backgrounds can also be varied over time and / or multiple evaluation sections can be defined, in which object temperatures and precise measurement positions are determined locally for each section using individual regression models.

[0022] The central starting point for temperature measurement or determination is the analysis of the infrared sensor signal for fluctuations and the change in these fluctuations in relation to the background temperature, whereby the infrared sensor is aligned to the material flow in such a way that it also receives infrared radiation from the background, at least briefly or for some areas of the measuring field.

[0023] If, based on the spectral sensitivity characteristics of the infrared sensor, an infrared contrast exists between the objects to be measured and the background, the infrared measurement signal for rapidly moving granular objects exhibits highly dynamic temporal fluctuations because a different object density is present in the measurement spot(s) at any given moment. The material flow of strand-like objects, on the other hand, occurs in the longitudinal direction, whereby the strands in the transverse position can be either steady or strongly oscillating, depending on their position and mechanical guidance. With an infrared contrast between the background and the strands and an infrared sensor in the form of a line-scan or area-scan camera, local intensity fluctuations in particular occur transversely to the strands.At one pixel, there's more background in the image, while at another pixel, the object is more prominent. The object may be smaller than the resolution of the infrared camera, but the corresponding sensor pixels are still controlled differently. Oscillations in strands also produce highly dynamic temporal intensity fluctuations in the measurement signal, similar to granular moving objects.

[0024] If, based on the spectral sensitivity characteristics of the infrared sensor, there is no infrared contrast between the objects to be measured and the background, the temporal and / or spatial fluctuation of the measurement signal is minimal because the infrared sensor can stabilize at the object temperature over an extended period. The infrared radiation from the background controls the sensor element(s) with just as much intensity as the infrared radiation emitted by the object to be measured. If the measurement is carried out in an environment that creates specular confinement conditions with homogeneous infrared radiation from a blackbody radiator at object temperature from all spatial directions, it is no longer a problem if the emissivity of the object to be measured is not ideally E = 1, but, for example, only E = 0.9. In this case, the object emits only 90% of the infrared radiation.However, the missing 10% is completely compensated for by specular reflection from neighboring objects or the equally intense surroundings, resulting in a total emission of 100%, so that the emissivity no longer influences the measurement. Furthermore, sensor response times, partial pixel coverage, object area densities, and the dynamic motion of the objects being measured have virtually no influence on the measurement signal at the infrared contrast minimum, which stabilizes at the object temperature.

[0025] The two described situations, with and without infrared contrast, differ only in the degree of infrared contrast, which is measured by the extent to which the infrared radiation emanating from the background differs from the infrared radiation emanating from objects. If the temperature radiation of the background is higher or lower than that of the object, fluctuations in the measurement signal occur. If the temperatures are identical, the radiation is also identical, and the fluctuations become minimal. Since the cause of the fluctuations is the temporary or regional alternation of infrared radiation from the object and the background, the intensities of the fluctuations are, to a good approximation, linear to the temperature difference between the object and the background.The greater the temperature difference, the greater the fluctuations; the smaller the temperature difference, the smaller the fluctuations become, until they reach their fluctuation minimum when the temperature difference vanishes.

[0026] For the analysis of precisely these measurement signal fluctuations, it is therefore advantageous to maintain the linearity of the fluctuation intensity to the temperature difference in the method for determining a fluctuation intensity measure. Furthermore, the calculation of a fluctuation measure can be used to reduce a large amount of raw data from measurement signal values ​​to a few key figures. In order to be able to determine a low-noise fluctuation measure of the sensor signal for a background temperature, a larger amount of sensor data can advantageously be used, which can then be analyzed using statistical methods. If a pyrometer is used as the infrared sensor, which, as a 1-pixel infrared camera, always only delivers a single measured value, this data is usually recorded over a certain period of time (temporal evaluation zone) and evaluated for temporal fluctuations.

[0027] With a line-scan infrared camera aimed at strands or granules against a uniformly tempered background, a fluctuation measure can be calculated directly from each exposure in an evaluation zone that includes, for example, the entire line scan. Most data is obtained with an area-scan infrared camera, particularly when the background is tempered as a temperature gradient field. Here, several different local evaluation zones can be defined so that different fluctuation measures against different background temperatures can be determined from a single infrared image. The evaluation can also summarize several exposures recorded under comparable conditions. Since each evaluation zone now has a spatial and temporal extent, the respective fluctuation measures can be determined from a larger amount of measurement signal data and thus with less noise.

[0028] The following considerations are used to summarize data in an evaluation zone: A certain amount of measurement signal data is required to determine a degree of fluctuation, for example, using statistical methods. All measurement signal data are recorded under similar infrared contrast conditions, especially against a similar background temperature. For the purpose of temperature determination, the many elementary events in the measurement signal, such as receiving more or less radiation from the object, are not individually relevant and can be described with a few key figures for an evaluation zone: - Degree of fluctuation of the infrared measurement signal (e.g., signal amplitude; various other options are described below).

[0029] - Background reference temperature (e.g. background temperature or a reference temperature described below)

[0030] - Location (especially position in the direction of the material flow in the spatial center of the evaluation zone)

[0031] - Time (especially the average between the start and end of recording)

[0032] - Key figures from the frequency distribution of the temperature measurement signal, in particular: o Mean value of the temperature measurement signal o Statistical key figures o If necessary, further key figures for the maxima of the distribution.

[0033] The design of the spatial boundaries for an evaluation zone can be as complex as desired in order to encompass only the data points within a narrow background temperature window as precisely as possible. However, if the above-mentioned parameters subsequently serve as input data for regression models that have no problems with noisy parameters, it makes little sense to invest a lot of effort in defining the boundaries of evaluation zones. For a very inhomogeneous temperature background, a grid of evaluation zones can simply be defined. In extreme cases, an evaluation zone can also be considered a single data point. In this case, the measure of fluctuation is the measured signal value itself, because regressions can be calculated even for this degenerate shape of an evaluation zone.Only for a purely temporal variation of the background temperature during direct minimum search without regression modeling is it necessary for the evaluation zone to contain multiple data points. Apart from these rather theoretical extreme examples, it is particularly useful to use evaluation zones to reduce the measurement signal data to a few key values ​​at an early stage.

[0034] In the following, the intensity of fluctuation can be understood as a measure that is essentially linearly correlated with the temperature difference between the object and the background. The signal amplitude or range of the measured signal is generally suitable as such a measure. For greater robustness against outlier measurements, a small portion of the largest and smallest measured data can be omitted and the interdecile range or a trimmed range, for example, used as the measure. The interquartile range is typically less suitable because it excludes information-bearing data points as outliers. The standard deviation has proven to be a particularly suitable linear measure of fluctuation. It is less sensitive to individual outliers than the signal amplitude, takes all data points into account, and is easy to calculate without internal rank sorting.

[0035] An evaluation zone is characterized in particular by the background temperature for which measurement signal data is recorded. The boundaries of an evaluation zone are selected so that only negligible differences in background temperatures occur. Therefore, it is useful to determine an average background reference temperature for an evaluation zone. Because no measured background temperature is available in some designs, this reference temperature is referred to below as the reference temperature, whereby a background temperature can be a reference temperature.

[0036] In order to make it possible to use the reference temperature as a reference value for regression models, non-linear distortions compared to the background temperature should be avoided so that simple functions can be used for regression models. The following requirements are therefore preferably placed on the reference temperature: a) The reference temperature should have an essentially linear relationship with the background temperature; in particular, higher background temperatures should result in higher reference temperatures, which can, however, differ by a positive scaling factor; b) For the situation of the infrared contrast minimum, in which the infrared radiation emitted by objects and the background becomes indistinguishable for the infrared sensor, the reference temperature should, within the scope of technical possibilities, assume the value of the true background temperature and thus the object temperature as closely as possible.Furthermore, it is advantageous if the value for the reference temperature is determined as noise-free and stable as possible for a temporal and / or spatial evaluation zone, which is characterized by maintaining a narrow temperature window for the background temperature.

[0037] There are a variety of options for determining the specific reference temperature in a temporal and / or spatial evaluation zone, which differ primarily in the effort required for sensor technology and mathematical modeling. If the evaluation zone covers a certain period of data acquisition, it is always assumed that temporal averaging or similar filtering is used to determine the reference temperature, although this is not mentioned below. To reduce noise or model the reference temperature using more detailed regression models, data from neighboring evaluation zones can also be used if necessary. The background temperature is the surface temperature of the background to which the infrared sensor is directed.

[0038] The following concepts can be used as reference temperatures, possibly in combination with each other:

[0039] 1 ) a directly contacting background temperature, e.g. in the form of a foil temperature sensor glued to the background,

[0040] 2) an indirectly non-contact measured background temperature, e.g. in the form of an additional infrared sensor mounted on the rear,

[0041] 3) the infrared measurement signal, which, although exhibiting significant temporal and / or spatial fluctuations, can be filtered over an evaluation zone or several adjacent evaluation zones temporally and / or spatially before and after the evaluation zone currently being processed, by: a) averaging the data of the zone or zones or filtering them appropriately, which in particular averages out the short-term and local fluctuations, but reduces the variation of the reference temperature by a reference factor (1 - A ob Yes tot ) downscaled, thus especially at higher relative object area density A obj / A totin the conveyed material flow varies less than the background temperature, b) using statistical or image processing methods, data points of the measurement signal of the zone or zones are selected that probably represent particularly low radiation components from object surfaces and high radiation components from the background. From this, a reference temperature value can be determined using further statistical methods, the reference scaling factor for the background temperature being significantly closer to 1 than with the averaging described under a), which is particularly possible with quietly running strands against a background. ) an indirect back-contacting background temperature measurement, e.g. in the form of a resistance thermocouple or a thermocouple. During heating and cooling cycles of the temperature control device, a certain temperature gradient is created due to non-ideal heat conduction in the wall thickness of the background, which is why the background temperature lags behind the externally measured temperature.and a systematic measurement error arises. This can be minimized using various methods, which is particularly relevant for time-varying measurement backgrounds: a) Simulation of the heat flow through the background wall and estimation of the reference and background temperatures based on a model of the assumed heat flow and an assumed or optimized heat diffusion coefficient in the wall; b) Additional measurement of the heat flow of the temperature control device on the back of the background with a heat flow sensor and simulation of the reference and background temperatures based on a model of the measured heat flow and an assumed or optimized heat diffusion coefficient in the wall; c) Symmetrization of heating and cooling cycles with comparable temperature change rates when passing through the situation of minimal infrared contrast;where a FIFO data buffer always contains the same number of fluctuation minima from heating cycles as from cooling cycles, whereby the regression model automatically compensates for the fact that the reference temperature is sometimes slightly too high and sometimes slightly too low,

[0042] 5) Furthermore, the redundancy that a reference temperature can be determined both from measurement data from contacting or otherwise non-contact temperature sensors and non-contact from the infrared sensor system can be used for greater accuracy, better stability, mutual monitoring of the sensors, co-calibration, and analysis of the density of the material flow. In particular, the reference temperature can be determined: a) as a weighted arithmetic mean of concepts 3 and 4, b) by using measurement data according to concept 3 to optimize parameters of the heat conduction-based simulation models 4a or 4b in such a way that a temporal / spatial offset is minimized. As a result, reference temperatures determined according to concept 3 differ from reference temperatures determined with optimized concepts 4a or 4b only by a scaling factor.A weighted arithmetic mean of Concept 2 and an optimized Concept 4a or 4b can be used as the reference temperature for the regression. This includes the option of using only Concept 3 or only one of the optimized Concepts 4a or 4b.

[0043] Variant 5b is particularly advantageous because, once the two independent reference temperature methods have been aligned, the same reference temperatures should be determined independently of each other at the contrast minimum. In particular, after model adjustment of concept 4a or 4b, the more reliable temperature measurement can be used to determine temperature compensation values ​​T at regular intervals. c (temperature compensation) in order to adjust the measurement signal of the infrared sensor to the more reliably determined reference temperatures, see Figure 3 and description.

[0044] Functional models that can be determined by approximation from a point cloud of noisy fluctuation data, e.g., using regression calculations and the least squares minimization method, as well as models based on machine learning, are particularly well suited for the precise localization of fluctuation minima. Minima for such functional models can be calculated directly using mathematical methods. Advantageously, the background of the measurement objects varies over time and / or space, which is why it is obvious to set up regression models in which, for example, fluctuation amplitudes are plotted against time or space. This is possible, but has the following disadvantages: The desired result, the object temperature, cannot be determined directly from the regression, but can be read off in a second step from the measurement signal at the time / location of the determined minimum.Because the measurement signal is known to be noisy, it is often helpful to apply a suitable data filtering method, whereby recorded data of the measurement signal around the found time or location of the fluctuation minimum is used for filtering, e.g. by averaging. In addition, the fluctuation minimum must be included in the recorded data, because simple extrapolation is not possible. A further disadvantage of direct regression against time or location is that the functional relationship between measurement signal fluctuation and time or location can be distorted by nonlinearities in the temporal or spatial temperature variation, so that more complex and therefore potentially less stable models are helpful for a good functional approximation. A selection can also be made as to which data is suitable for a functional approximation for minimum search.It is possible to calculate simple direct regression models for the signal fluctuations versus time or location, especially if the temporal variation of the background is realized via temperature ramps with temporally constant rates of change, or the local variation with a homogeneous temperature gradient field.

[0045] It is more advantageous to choose a reference temperature, e.g., the background temperature, for the regression modeling of the fluctuation measures. The fluctuation measure, e.g., the fluctuation amplitude, reacts largely linearly to the infrared contrast ratio of the object-to-background temperatures. A regression model with the reference temperature defined above as the reference value makes it possible for the position of the functionally determined fluctuation minimum to correspond directly to the determined object temperature. Each data point in the point cloud for the regression calculation now exhibits two scatters: the uncertainty of the determination of the fluctuation measure in the ordinate direction, and the uncertainty of the reference temperature determination in the abscissa direction. The more data available, the more accurately the minimum can be determined. At stable object temperatures, redundantly collected data points are close to one another.If the background temperature varies over time, multiple heating / cooling cycles can be represented in the point cloud, albeit at the expense of a longer delay time. If the background temperature, starting from a temperature lower than the object temperature, increases and approaches the object temperature, the fluctuation amplitude decreases with the increase in the background temperature. A fluctuation minimum is reached at the infrared contrast minimum of equal object and background temperatures, and as the background temperature continues to rise, the fluctuation amplitudes increase again. This applies to a temporal progression within a heating cycle as well as to a spatial progression against the temperature gradient. The fluctuation measures plotted against the reference temperature form a point cloud with a minimum.In the left area of ​​colder background temperatures, the fluctuation intensity decreases with higher background temperatures, while in the right area it increases.

[0046] If, for various reasons, the background temperature should not be changed to the point where the minimum fluctuation intensity is reached and passed through, the background temperature at which the fluctuation minimum would occur can nevertheless be determined by extrapolation. The point cloud of fluctuation intensities at the reference temperatures no longer contains a minimum. Nevertheless, a regression analysis can be performed. The object temperature is output as the background temperature at which the fluctuation intensity extrapolated from the functional relationship would reach zero or a predeterminable value.

[0047] For processes where sudden changes in object temperature must be measured in a highly dynamic manner, an area-scan infrared camera with a gradient background should be used. This configuration allows for instantaneous measurement evaluation for each exposure, as a single image contains the entire point cloud for a regression model.

[0048] If the local change in the object temperature within the measuring area is to be determined, which can be particularly relevant along the direction of the conveyed material flow, several sections can be provided, each of which determines the object temperature and the exact measurement position. Furthermore, Figure 9 describes a method for determining longitudinal temperature gradients using temporal and spatial temperature variation.

[0049] In many infrared temperature measurement methods, the emissivity, a material property of the objects being measured, must be compensated using multiplicative emissivity correction or expensive two-color infrared measurement technology must be used. Although plastics typically have high emissivity values ​​of 85–95%, these values ​​still need to be compensated for accurate measurements. It requires considerable laboratory effort to determine the emissivity of each formulation and transfer this data to the system. An ideal blackbody radiator has an emissivity of 100% and a reflectance of 0%. Using Boltzmann's law, the radiator temperature can be directly calculated from the infrared radiation emission. A plastic object with, for example, 90% emissivity reflects 10% of the radiation at its surface as gloss.The strand- or granular-shaped objects in the conveyed material flow are typically convex, so the infrared sensors detect thermal radiation reflected from the various surfaces of the objects being measured, coming from very different directions. At the edges of the objects, a glancing angle constellation sometimes occurs, reflecting the radiation emitted by neighboring objects of almost the same temperature. This self-illumination, which acts like an increase in emissivity, can possibly be compensated for in regularly arranged strands; however, in chaotically fluidized granular flow streams, the self-illumination situation is uncontrollable.

[0050] As is known from devices for measuring under gloss confinement, the influence of emissivity can be virtually eliminated. For this purpose, the immediate surroundings of the measuring spot are heated to a temperature nearly equivalent to that of a blackbody radiator at object temperature using a housing. Ideally, a balanced radiation exchange takes place between the housing and the objects, so that all surfaces emit as much energy as they receive. For wear-resistant surfaces exposed to product abrasion dust, a housing with a blackbody radiator cannot be implemented. Edge effects due to limited installation space and the portion of infrared radiation reflected by the housing must be taken into account.Ideally, the inner surface of the measurement background and the enclosure temperature control should be homogeneously diffusely scattering, non-polarizing, and have an emissivity of > 85%, but preferably at least > 70%. If necessary, these properties can be achieved with special coatings. Advantageously, the measurement background to be temperature-controlled and / or the surrounding surfaces of the guide body or the enclosure for guiding the conveyed material flow can be provided with a suitable coating, preferably made of plastic or a plastic-like material that possesses the aforementioned high emissivity. Advantageously, a lacquer coating and / or a non-stick coating, for example made of fluoropolymers and / or silicones, can be provided on the aforementioned guide body surfaces.

[0051] The measurement background already irradiates the inside of the enclosure temperature control with almost the correct infrared radiation, which minimizes the error influence of an irradiation of the enclosure temperature control that deviates from the object temperature. Radiation edge losses in the inlet and outlet zones of the enclosure temperature control are more problematic because in most systems, only a limited length is available for the enclosure temperature control. Radiation losses also occur when the enclosure temperature control cannot be seamlessly adjacent to the temperature-controlled background, as is the case with a water bath with a background heating bar arranged transversely beneath the strands. All radiation losses together result in the enclosure temperature control being irradiated from the inside with slightly less radiation intensity than would be the case with an ideal radiation field for measurements with glare exclusion.To compensate for the non-ideal emissivity of the interior of the enclosure temperature control as well as the radiation losses in edge zones, the enclosure temperature control is regulated to a temperature slightly above the determined object temperature.

[0052] In order to reduce edge effects and increase the effective emissivity of the surrounding surfaces of the guide body or the measuring background or to bring it even closer to 1 and to save energy, the measuring background and / or the said guide body as well as the housing temperature control can have thermal insulation. Alternatively or additionally, the said temperature control device can have large-area heating and / or cooling elements on the background or guide body surfaces to be temperature-controlled in order to be able to temperature-control the said surfaces efficiently and quickly in order to achieve fast cycles to reach a desired setpoint temperature. In particular, the said flat heating and / or cooling elements on the surfaces of the measuring background or guide body to be temperature-controlled can determine the temporal and / or local temperature gradient orachieve the desired spatial or temporal variation of the background temperature, during which the fluctuation of the measurement signal is then analyzed in the manner described.

[0053] Devices that measure moving objects against a temperature-controlled background typically require adaptation to the specific conditions of the production facility. The background can be formed, for example, by a tubular or trough-shaped guide body through which the material is conveyed, but can also be implemented in sliding surfaces, side surfaces, cover surfaces, freely suspended, or immersed in water.

[0054] A device for temporally varying the background temperature, for example, means that the background temperature in the measuring range of the infrared sensor can be varied during heating and cooling cycles, particularly around the object temperature, using a temperature control device. A pyrometer is preferably used as the infrared sensor for this purpose. If an infrared line-scan or area-scan camera is used as the infrared sensor, a wider measuring area can be analyzed against a background. This background can be varied in temperature purely over time and maintained at a uniform temperature.

[0055] However, for faster measurement results, particularly with an infrared area camera, it is advantageous if the background has different temperatures, for which devices for locally varying the background temperature are suitable. A local temperature change means, for example, that along the path covered by the material flow to be measured, the background is brought to different temperatures by means of the temperature control device, or that a temperature gradient is established along the path of the material flow, for example, that the guide device in the background, through which the material flow is conveyed, is warmer upstream than downstream, or conversely, that an upstream guide device section is colder than a downstream section.If both implementation options are arranged directly one after the other, two evaluation sections can be implemented. From their two temperature measurements, the temperature change of the conveyed material flow can be determined, which can allow conclusions to be drawn about cooling measures, core temperatures of the objects, or exothermic reactions. To detect fluctuations in the sensor signal at different sections of the measuring section, the infrared sensor can also have several sensor elements distributed in the direction of the conveyed material flow, along the measuring section, or in the direction of the temperature gradient.

[0056] The temperature gradients in the background can also assume any other angle with respect to the conveyed material flow, for example, perpendicular to it. Inhomogeneous, circular, or periodic temperature fields with temperature gradients in different directions are also possible.

[0057] The aforementioned creation of temperature gradients along the conveying flow direction can be achieved using heating and / or cooling elements of the temperature control device, which can be distributed along the background. Given the heat conduction occurring in the background material, it may also be sufficient to heat or cool only a short section of the guide device to provide two opposing temperature gradient fields for two evaluation sections along the conveying flow direction in the measuring section of interest.

[0058] The temperature control device can advantageously comprise one or more temperature sensors, by means of which the temperature of the measurement background or of the conducting body or tubular body can be measured, wherein said temperature sensors can operate in a contact-type manner. Background temperatures between the temperature sensors can be determined, at appropriate distances, by interpolating two adjacent sensor readings. Alternatively or additionally, non-contact measuring sensors can also be provided for determining or calibrating the background temperature fields. Depending on the measured background temperatures, the temperature control device can be controlled such that a desired spatial and / or temporal temperature gradient is created, which can include a temperature in a central section approximately identical to the object temperature to be measured.

[0059] The measurement background can also be realized using an infrared radiator that shines through a window material sufficiently transparent for infrared radiation. If transmission losses occur, the infrared radiator can be operated at a higher temperature. The background temperature for such a radiator is referred to as the sensor-evaluated infrared radiation emission, which is evaluated identically to a normally emitting background with a nearly ideal emissivity that is tempered to this same background temperature. To allow the infrared radiator to be considered as an emitting background at different temperatures, the radiator can be calibrated with a suitable characteristic curve.

[0060] A device for the targeted temporal and spatial variation of the background temperature has, for example, a temperature gradient field, wherein the temperature control device varies the average temperature of the entire temperature field in heating and cooling cycles. Such a device enables, in particular, the measurement of longitudinal temperature gradients in objects. The control of the temperature control device and, in particular, the highest and lowest temperatures of the temporal and / or spatial variation should be automatically coordinated with the evaluation device. Typically, a certain range around the object temperature is defined for the variation, which range should be adjusted as symmetrically as possible to the determined object temperature. By means of the aforementioned temperature control device, the average target temperature of the measurement background can advantageously be readjusted orbe adjusted so that the objects flowing past in the material flow stand out brightly against the colder background areas and generate a clearer fluctuation signal, in the background areas with medium temperature the fluctuation of the sensor signal is minimized and in front of the hot background areas the objects stand out with a darker signal and thus stronger fluctuations in the infrared signal arise.

[0061] In a further development of the invention, a tube can be used as the measuring background and guide body. This tube can be mounted so that it can rotate about its longitudinal axis and rotated manually or by a rotary drive around its longitudinal axis in order to enable a contrast measurement with the background even in denser conveyed material flows. For this purpose, the tube can be placed in a laterally rotated position. Likewise, the aperture for the infrared sensor can be arranged offset laterally from the central axis, making it possible to align the measuring spot with the nearby pipe flank. If the infrared sensor has a front-side mounting flange with a helix angle to the optical axis, the optical axis can be moved along a conical surface simply by rotating the sensor head flange.This makes it possible to align the measuring spot to different zones of the material flow, so that a relative object area density in the range of 15-80%, or better 25-70%, can be achieved for the measuring area.

[0062] In an advantageous development of the invention, the infrared sensor measuring head can be kept at a nearly constant temperature using a temperature control device. Despite fluctuating ambient conditions, the sensor can thus be operated within a narrow, predetermined temperature window. High and fluctuating ambient temperatures enable greater measurement accuracy, improved long-term stability, and a longer service life. Such a temperature control device for the infrared sensor can advantageously comprise, for example, one or more temperature control elements on the sensor head of the infrared sensor. For example, a liquid temperature control body, for example in the form of a water sleeve, can be provided on the sensor head to cool or heat the sensor head and thereby maintain it within the desired temperature window.

[0063] To calibrate the infrared sensor, it can be provided that the sensor head can be relocated, ideally without interrupting the power supply and temperature control, from the measuring position at operating temperature to a nearby calibration station with a largely ideal black body reference, which is very precisely and homogeneously regulated to a relevant operating point temperature at the measuring spot position and optionally also the infrared scattered light field is modeled on that of the measuring situation, whereby in the relocated calibration position the infrared sensor is calibrated to the operating point temperature.

[0064] If there are no objects to be measured in the measuring field after the infrared sensors have been repositioned, a transfer calibration to the temperature-controlled measuring background can be carried out directly after the aforementioned absolute operating point calibration, whereby the background is ideally regulated to a stable level at the same working temperature as the blackbody reference, whereby a second parallel measurement is then carried out with the infrared sensors repositioned at the measuring location, in which the infrared radiation of the background is measured simultaneously and the background temperature is recorded with contact temperature sensors, so that the emissivity of the temperature-controlled background environment can be determined from the results of the second parallel measurement and saved as a calibration parameter for this operating point without material flow.

[0065] To improve the accuracy of temperature determination, in phases when there are no objects to be measured, the background and the environment can be tempered to an operating point temperature suitable for the next production, and the temperature compensation in the aforementioned evaluation module can be updated using the calibration parameter for an operating point without material flow, so that objects can be measured directly with high absolute accuracy when production starts up, without the need for manual absolute calibration using the calibration station and the blackbody reference.

[0066] The invention is explained in more detail below with reference to preferred embodiments and the accompanying drawings. In the drawings:

[0067] Fig. 1 : a schematic side view of an underwater granulation plant with an underwater granulator, a downstream centrifugal dryer, at the outlet of which a device for contactless temperature measurement of the outgoing granulate stream is provided,

[0068] Fig. 2: a schematic side view of a dry-cut strand pelletizing plant with a water bath, with two possible positions of a device for non-contact temperature measurement on strands and a device for non-contact temperature measurement at the outlet of the classifying screen,

[0069] Fig. 3: a perspective side view of an outlet and the contactless temperature measuring device provided there from a previous figure, with the infrared sensor looking through a cutout on the lateral surface into the outlet pipe, including the basic scheme of the measurement signal data processing, which applies to all subsequent figures,

[0070] Fig. 4: a perspective side view of the outlet similar to Figure 3, wherein the beam path of the infrared sensor is folded over a movable deflection mirror, so that a scanning movement in the outlet is enabled, which is carried along with the conveyed material flow. Fig. 5: a sectional view of the outlet with the attached infrared sensor and the mounted devices for tempering the measuring spot background and the tubular housing.

[0071] Fig. 6: the temporal course of the measurement signal of an infrared sensor with a circular measuring spot (pyrometer) from Figures 3-5, the deliberately time-varying measurement background temperature, as well as the fluctuation intensities, and the determined object temperatures,

[0072] Fig. 7: a representation of moving objects against a temperature gradient background measured by an infrared sensor with an area sensor (infrared camera) from Figures 3-5 with temperature frequency distributions in evaluation zones,

[0073] Fig. 8: in Figure 8 A a perspective view of an infrared sensor with an area sensor (infrared camera) for measuring the temperature of strands, there is a background with, for example, a temperature gradient field under the strands and the measuring area is optionally surrounded by a housing temperature control to minimize the emissivity effect, whereby Figure 8 B shows a more complex design of a background with two temperature gradient fields, which serves to simultaneously determine the object temperature in two sections along the conveyed material flow direction,

[0074] Fig. 9: a representation of the locally varying degree of fluctuation of the measurement signal of an infrared sensor from Figure 8 when using an infrared camera, the background having a temperature gradient field,

[0075] Fig. 10: a perspective view of an infrared sensor system on strands, where a line infrared camera or an area infrared camera is used as the sensor, an infrared radiating background is located under the strands, which can also be immersed in a water bath, and the measuring area is optionally surrounded by a housing temperature control to minimize the emissivity effect,

[0076] As the figures show, non-contact temperature measurement can be used at various positions in large-scale granulation plants. The sensor technology is suitable for both dry and wet strand granulation systems, as well as underwater granulation systems. The sensor technology can also be used in these and other plants at various measurement positions other than those shown as examples.

[0077] Figure 1 shows a typical extrusion line with an underwater pelletizer 12. A melt feeder 15 forces a polymer melt through a die plate 14 into the cutting chamber 16 of an underwater pelletizer 13, where the emerging strand material is cut into pellets by a rotating blade in the water and conveyed via a pipeline to the pellet dryer 17. There, the pellet-water mixture is separated. The separated pellets are dried and then exit the outlet 18, from where the pellets are typically fed to a further processing station such as a sizing screen, vibrating chute, or thermal container, for example, to carry out a crystallization or self-crystallization process of the pellets.

[0078] The temperature of the granules exiting the granule dryer 17 at outlet 18 should be within a process temperature window. If the granules are too cold, the residual heat may not be sufficient to evaporate the residual surface moisture. If the granules are too hot, agglomeration may occur due to welding. For polymers that are specifically intended to retain a high level of residual heat so that sufficient energy remains to initiate a subsequent crystallization, the process temperature window is particularly narrow. For some polymers, only temperature deviations of a few degrees Celsius are permissible; otherwise, rejects will be produced. Non-contact temperature measurement can be carried out in particular in the aforementioned outlet 18, through which the dried granules exit in the form of a conveyed material stream 2.The granular objects of the conveyed material stream 2 do not usually emerge in the form of a sluggishly flowing, compact granular stream, but rather fly more or less spaced from one another and fluidized through the tubular outlet 18. Warm, moist air from the granular dryer 17 can also be entrained in the boundary layer of the granules. In typical operation, a slight negative pressure is created in the granular dryer 17 using an extraction fan, so that a drying counter-air stream is sucked into the outlet 18, opposite to the exiting conveyed material stream 2. Overall, complex flow conditions can therefore prevail in the outlet 18 with different air streams of different temperatures, which are guided through the outlet 18 in addition to the granular objects of the conveyed material stream 2.

[0079] The infrared sensor 1 can be assigned to the said outlet 18 and look into its interior in order to be able to measure the temperature of the objects 3 flowing past.

[0080] The inner wall of the outlet 18 forms the background 4 for the temperature measurement, whereby in the case of a preferably circular-cylindrical outlet pipe, the pipe inner surface forms the said background 4 of the temperature measurement, cf. Figures 3-5.

[0081] Figure 2 shows a classic dry-cut granulation system in which a melt feeder 15 presses polymer or other materials through a die plate 14, forming parallel strands 7 which are first passed through a water bath 8 before being cut in a granulating device 12. Various further processing stations can be arranged downstream, as explained in relation to Figure 1. Shown here is a classifying screen 9, from which the material stream 2 is fed into an outlet pipe 18. Two exemplary positions for the sensors are shown for measuring the temperature of strands 7: a first infrared sensor 1a is arranged above the water bath 8 (see Figure 10), with a temperature-controlled background infrared radiator in the water bath 8, and the strands 7 still in the water being measured by the infrared sensor 1a.A further infrared sensor 1b, preferably with a temperature gradient background, is arranged in the inlet zone to the granulating device, see Figure 8A. From an infrared image of the strands 7 against a temperature gradient background, the individual temperatures of all strands 7 can be measured precisely and with high dynamics, even if the strands should oscillate dynamically there. With a two-section temperature gradient background, see Figure 8B, it can be checked whether short-term strand temperature changes occur between two evaluation sections along the direction of the conveyed material flow, e.g. due to the heating of the strand outer skin by a hot strand. With an infrared sensor 1c in the outlet 3, the temperature of the granules after cutting in a fluidized conveyed material flow 2 can be measured, see also Figures 1 and 3-5.

[0082] Various other strand pelletizing systems with automatic strand infeed in wet and dry cutting, not all of which are shown individually here, can also be equipped with non-contact temperature measurement technology on strands and cut pellets, whereby the sensor technology on strands can be used particularly in chute areas, where small zones of the chute can be designed as heated backgrounds or where background infrared radiators are used in water-sprayed areas.

[0083] As Figure 3 shows, the infrared sensor system 1 can view the interior of the outlet 18 through an aperture 19, so that the infrared sensor system 1 has at least one measuring spot 20 inside the outlet 18 through which the conveyed material flow 2 moves. If an infrared camera is used as the infrared sensor system 1, a larger measuring area is captured, with each pixel or pixel group measuring a separate measuring spot 20. As an example, a moving granular object 3 is shown in the measuring spot 20 of the infrared sensor system 1.

[0084] The inner surface of the outlet 18 and thus the background 4 is advantageously provided with a high emissivity, which can be achieved by a corresponding design of the outlet wall and / or a suitable coating of the wall surface, which forms the measurement background 4 and the area of ​​a housing temperature control 22. For example, the outlet 18 can be coated on the inner wall side with a plastic-like coating, a varnish, or in particular a non-stick coating made of fluoropolymers or silicones, which have high emissivity.

[0085] The outlet 18 and thus the background 4 can be tempered by a tempering device 6 at least in the region of the measuring spot(s) 20, wherein the said tempering device 6 can comprise at least one heating and / or cooling element 21 which is mounted on the wall of the outlet 18.

[0086] Preferably, an enclosure temperature control 22 can be mounted in the vicinity of the temperature control device 6, for example in the form of a heating sleeve, which encloses the outlet 18 at least in sections and can optionally have several zones in order to generate different temperatures in different sections of the outlet 18.

[0087] In particular, the aforementioned temperature control device 6 can be designed to vary the temperature of the background 4 spatially and / or temporally during the measurement of the infrared sensor system 1. The temperature of the entire outlet 18 can also be uniformly increased and decreased via the housing temperature control 22. With a local variation in the temperature of the background 4, the temperature control device 6 can heat and / or cool different background zones 4a-c of the outlet 18 in different ways, for example to set different temperature fields along the path of the conveyed material flow 2. For this purpose, temperature fields can take on any shape, have any number of zones, temperature minima and maxima, and temperature jumps, as long as different background temperatures occur simultaneously depending on the location. The temperature fields can also change over time.An independent measurement of the background temperature 25 can be carried out using contact or non-contact temperature measurement technology, which can optionally be supported by temperature simulation models into which measurement data from various locations on the background 4 can be incorporated. A measurement of the background temperature 25 is not required, but can nevertheless be provided. The conveyed material flow 2 does not usually completely cover the background 4, so that a reference temperature 38 can be determined from the measurement signal 29 alone, which reference temperature is at least partially influenced by the background temperature 25. For an inhomogeneously tempered background 4, for example, starting from any grid of evaluation zones 45, reference temperatures can be determined individually for all zones.There is then the option of combining evaluation zones 45 of similar reference temperature 38 into larger evaluation zones 45 and subsequently using these larger evaluation zones 45 to determine fluctuation measures 32 and reference temperatures 38 for them.

[0088] The temperature of the background 4 can be controlled by the temperature control device 6, wherein one or more temperature sensors 23 can measure the temperature of the outlet 18, depending on which the temperature control device 6 can then be controlled.

[0089] The data processing of the measurement signal 29 takes place in an evaluation device 30. If there is more than one evaluation section 51, see Figure 8 B or Figure 9, the respective subsets of measurement data are assigned to each section 51 in a first preprocessing step.

[0090] In a second preprocessing step, the measurement signal 29 is optionally corrected with a temperature compensation value Tc 40.

[0091] Subsequently, a single complete data processing is carried out for each section 51 and a determined object temperature 39 is output in each case.

[0092] The individual data processing steps are as follows: A fluctuation evaluation module 31 evaluates the fluctuation intensity of the measurement signal 29 over a certain signal data volume, which encompasses a temporal and / or spatial evaluation zone 45 of a similar background temperature, and outputs it, for example, in the form of the fluctuation amplitude as a fluctuation measure 32, which is generally proportional to the measured infrared contrast between the object and the background. Alternative methods for determining the fluctuation measure 32 are presented in the description. Additional signal data volumes from other evaluation zones 45 are evaluated in the same way, so that different fluctuation measures 32 are available for different background temperatures 25.If the background temperature 25 varies over time, a certain amount of time is required to record different evaluation zones 45. If the background temperature 25 varies locally, different evaluation zones 45 can be recorded and evaluated simultaneously. For each temporal and / or spatial evaluation zone 45, a reference temperature 38 is determined in a reference temperature determination module 37, which can be used as a reference value for the regression model 33. The reference temperature 38 can be calculated, for example, from the averaged background temperature 36 or the averaged infrared measurement signal 35, a weighted arithmetic mean thereof, and various other methods.The description presents in particular methods which, using image processing, statistics and heat diffusion models, internally determine two reference temperatures using two independent calculation methods: Modeling a - based on infrared measurement data 29 and modeling b - based on the background temperature 25 and optionally heat flow measurements 54 of a heat flow sensor 53. From the difference 4 between modeling a and b, a temperature difference T can be calculated in regular cycles for the fluctuation minimum. c 40 are determined for the described temperature compensation of the measuring signal 29 in a preprocessing step in the evaluation device 30.

[0093] In a regression module 33, the functional relationship between the fluctuation measure 32 and the reference temperature 38 is determined, and the determined object temperature 39 is determined by a minimum search 34, or in the case of extrapolation, the intersection point of a regression function with the zero axis or a predetermined value.

[0094] If the background 4 is divided into several evaluation sections 51, see Figure 8 B and Figure 9, which can be as small as pixel lines, object temperatures 39 can be determined for each section using section-specific regression models 33 for the respective section area. If the background temperature control field has, for example, complex temperature gradient curves 48 (see, for example, Figure 8 B), so that in two or more evaluation sections along the conveyed material flow path infrared contrast minima of the objects 3 to the background 4 occur, a certain spatial resolution in the direction of the conveyed material flow 2 can be achieved by determining local object temperatures 39 in spatially different sections 51. The spatial resolution becomes more finely divided, the more sections 51 with a suitably tempered background 4 are provided.

[0095] In an evaluation section, for example, an upstream section 4a of the outlet 18 can be colder than the conveyed material flow 2. A middle section 4b of the outlet 18 can be tempered at least approximately to the temperature of the conveyed material flow 2. A downstream section 4c of the outlet 18 can be brought to a temperature hotter than the conveyed material flow 2, see Figure ?.

[0096] Figure 4 shows a periodically deflected measuring spot in contrast to a stationary measuring spot according to Figure 3. The beam path of the infrared sensor 1 is folded with dynamically changing angles, e.g., via a rotating prism mirror 24. The measuring spot 20 or the measuring range of an infrared camera is moved by deflection such that it follows the flow direction of the conveyed material stream 2 at a speed as similar as possible to that of the moving objects 3. For this purpose, the aperture 19 is machined into the outlet 18 in an elongated slit-like manner in the direction of movement. The temperature control device 6 or its heating and / or cooling elements 21 are also designed to be correspondingly more elongated, as is the housing temperature control 22, in order to be able to temperature control a longer outlet section or background section.

[0097] With a continuous rotation speed of the prism mirror 24, the angular relationship or the changing distance does not result in an exactly constant scanning speed of the measuring spot 20. However, the rotation speed of the prism mirror 24 can be controlled as a function of the angle, so that the measuring spot 20 moves along the background 4 at a truly constant speed. If the scanning speed of the measuring spot 20 closely matches the speed of the conveyed material flow 2, the time at which the infrared sensors are stably aligned with a moving object 3 increases considerably. This makes it possible to individually measure the temperature of individual moving objects 3 and to determine the temperature distribution of the objects in the conveyed material flow 2.The temperature control device 6 is advantageously constructed from several separately controlled heating / cooling elements 21, so that a temperature gradient field of the background 4 is formed, particularly transversely or longitudinally of the scanning direction. The background temperature at the location where the contrast of the moving object 3 disappears indicates the temperature of this individual object.

[0098] As Figure 5 shows, the infrared sensor 1 can also view the interior of the outlet 18 at an angle. Such an oblique arrangement at an angle of, for example, 30° to 80° or 35° to 55° to the longitudinal axis of the outlet can be provided with a fixed arrangement of the measuring spot 20, but in principle also when using the aforementioned prism mirror 24. The housing temperature control 22 is designed here in the form of a heating sleeve with a recess for the temperature control device 6. A water temperature control sleeve 5 is arranged around the measuring head of the infrared sensor 1, enabling temperature-stabilized operation of the sensitive sensor.Advantageously, the infrared sensor 1 can be operated with active temperature control in a narrow temperature window, so that the sensor 1 can measure precisely with the highest accuracy in the long term despite fluctuating ambient conditions, whereby this temperature control can preferably be realized with a water temperature control sleeve 5 around the sensor head.

[0099] To protect the lens of the infrared sensor 1 from dust or contamination, finely filtered instrument air flows downwards from the purge air nozzle 27 toward the conveyed material stream 2. A combined temperature and heat flow sensor 53 can optionally be used in the heat transfer contact from the temperature control device 6 to the outlet 18. This allows the heat flow transferred to the outlet 18 during heating and cooling operation of the temperature control device 6 to be measured, and the temperature of the background 4 can be determined even more precisely from the thermal conductivity coefficient known from the wall material, as explained in the description. As Figure 6 shows, the background temperature 25 of the background 4 is varied over time, as is possible, for example, with a temperature control device 6 according to one of Figures 3-5 or 10.The infrared measurement signal 29, which is illustrated here in simplified form in the form of a thin wavy line, fluctuates very dynamically because in the measurement spot 20 of the infrared sensor 1, the infrared radiation from objects 3 or from the background 4 is received. The fluctuation amplitude 32a of the measurement signal 29 is higher, the more the background temperature 25 deviates from the object temperature 26. The measurement signal 29 practically always fluctuates only between the object temperature 26 and the background temperature 25, which gives rise to the possibility that this fluctuation almost disappears when the object temperature 26 and the background temperature 25 are the same, i.e. in the spectral evaluation of the infrared sensor 1, the radiation of the objects becomes indistinguishable from the radiation of the background 4. In this situation of a contrast minimum 42, the value for the determined object temperature 39 can be directly assigned to the measurement signal 29 or, for example, to afrom the low-pass filter averaged measurement signal 35 or the background temperature 25.

[0100] In order to regularly pass through such contrast minima 42, the background temperature 25 can, in particular, be cyclically increased and decreased again, whereby at the same time the mean value between the increases and decreases in temperature can also be varied, in particular in order to approximately approach the object temperature 26 as the mean background temperature 25. As Figure 6 illustrates, the temperature cycles are initially too low, i.e., the increase cycle is also still below the object temperature 26. However, if the mean temperature is also adjusted, the background temperature 25 and its variation can, in particular, be adjusted such that the background temperature 25 oscillates around the object temperature 26, cf. Figure 6, right half.

[0101] The degree of temperature variation of the background 4 is chosen here in particular such that, as the background temperature 25 varies, these fluctuation measures 32 vary such that the fluctuation measure 32 periodically passes through minima when the infrared contrast between the object and the background disappears. The fluctuation measure 32 is plotted on the right ordinate axis in Figure 6, where "α SD[TIR]" is proportional to the standard deviation of the infrared measurement signal. If the background temperature 25 is increased beyond the object temperature 26, the fluctuation measures 32 increase. If the increase in the background temperature 25 is reduced again, the fluctuation measures 32 decrease again until they once again reach a fluctuation minimum.If the background temperature 25 is then lowered below the object temperature 26, the fluctuation measures 32 increase again, which is then reversed when the background temperature 25 is increased again from the lowered state, so that an amplitude minimum occurs again when the background temperature 25 again reaches approximately the object temperature 26.

[0102] The measurement signal 29 of the infrared sensor 1 is evaluated by an evaluation device 30, as described in relation to Figure 3. In time-limited evaluation zones 45, the duration of which is so short that the background temperature 25 can be assumed to still be largely unchanged, a fluctuation measure 32 is calculated for each evaluation zone 45. The acquisition time in which the measurement signal 29 is recorded in order to be able to determine a fluctuation measure 32 for the evaluation zone 45 can be defined within wide limits, up to the point where it consists of only a single data point and the actual fluctuation analysis is carried out in a subsequent regression calculation. In many cases, however, it is advantageous to reduce the large amount of data from the measurement signal values ​​29 to a few characteristic values ​​at an early stage and to summarize data, for example, in the range from tenths of a second to a few seconds.The description presents various calculation options for calculating the fluctuation factor 32. The individual measured values ​​of the measurement signal 29 are recorded in short cycles to determine the fluctuation factor 32 of the measurement signal 29.

[0103] In parallel, the measured values ​​of the background temperature 25 are averaged in the same cycle. In this example, the time-synchronized data for the fluctuation measure 32 and the associated averaged background temperature 25 are temporarily stored as a reference temperature 38, e.g., in a FIFO data buffer, for regression analysis. If measurement data from one or more temperature sensors 23 are available for the background 4, independent of the infrared sensor system 1, the contrast minima 42 offer a good opportunity for co-calibrating the measurement signal 29, which is influenced by many disturbances, to the more reliably determinable background temperature 25, determined, e.g., via these same temperature sensors 23. Furthermore, in phases where the object temperatures 26 are obviously constant over a longer period of time, the background temperature 25 can be regulated as close as possible to the object temperature 26 for a certain period of time.In this stationary state of the contrast minimum, there is sufficient time for the temperature sensor signal 23 to adjust to the background temperature 25, and the difference between the infrared measurement signal 29 and the background temperature 25 measured by the temperature sensor 23 can be used directly as a temperature compensation value 40, in particular if, after the stationary phase, it has been checked by means of temperature variation of the background temperature that almost identical object temperatures 39 could be determined before and after.

[0104] Figure 7 illustrates the evaluation of a measurement signal image or a section as an image section of a multi-section measurement signal image of an infrared sensor system 1 in the form of an area infrared camera, as can be used for devices according to Figures 3-5. Figure 7 shows, in a temperature-visualizing false-color representation, moving objects 3 of a conveyed material flow 2 running in the X direction 41 against a background 4 with a homogeneous temperature gradient field 48. The background 4 is colder than the objects 3 in an upstream section 4a, has almost object temperature 26 in a middle section 4b, and is warmer than the objects 3 in a downstream section 4c.The temperature field of the background 4 can also have various and different gradient directions and considerably more complex inhomogeneous temperature fields with different temperature zones and jumps, which create the prerequisite for measuring moving objects 3 at different locations against different background temperatures 25. Evaluation zones 45, which encompass a certain background temperature window, can be realized in a homogeneous temperature gradient field in a simple form by rectangles that are approximately bounded by isotherm lines 44. For inhomogeneous background temperature fields, more complex geometries or grids can be used for the local boundaries of the evaluation zones 45, for example; see description.

[0105] Due to the short dwell time of an object 3 in the measuring spot 20 of a pixel 47 in relation to the response time of the infrared sensor 1, the measurement signal 29 in the excited pixels 47 reacts with a time delay and thus creates an afterglow trail with soft edge transitions, which is visualized here in a simplified manner as a high-contrast ellipse 3. With a device according to Figure 4, this afterglow trail can be minimized so that granules that move exactly at the scanning speed of the moving measuring spot are largely imaged with their true object contour and only short afterglow trails to the front or rear are formed for individual objects 3 that move somewhat slower or somewhat faster than the scanning speed.Thus, the dwell time of the object 3 in front of the controlled pixels 47 is long enough for the measurement signal 29 to reach full modulation, from which an individual object temperature 39 can be determined for each individually detected object 3 by simple image processing.

[0106] To determine the average object temperature 39, various fluctuation measures 32 for different evaluation zones 45 are determined from an infrared image of a measuring section. In the example shown, these fluctuation measures are formed by temperature windows of + / - 0.15°C around the respective average background temperature 25 with isotherm lines 44 as boundaries. As an example, nine evaluation zones 45 are evaluated in Figure 7. For this purpose, the measurement signals 29 of all pixels 47 within a respective evaluation zone 45 are statistically evaluated, with the standard deviation being particularly suitable for determining the fluctuation measure 32. Alternative statistical parameters such as the range or the interdecile distance are discussed in the description.To visualize the statistical scatter of the measurement signals 29 within the rectangular evaluation zones 45, temperature histograms 43 are shown at the bottom of Figure 7. These histograms refer to the data in the respective evaluation zones 45 in the infrared image above, whereby only the evaluation zone 45 is explicitly shown with reference to the histogram 43b. A reference temperature 38 is determined for each evaluation zone 45, which can be done, for example, by averaging the background temperatures 25 of this zone or by other described methods.

[0107] In the false-color image, the local infrared contrast to the center axis of each evaluation zone is represented by a dashed black line of the relative temperature Trei 46 for one pixel column, where T reiis calculated as the difference between the measurement signal 29 and the reference temperature 38 of the respective evaluation zone 45. The infrared contrast is visible in the temperature histograms 43 in the distances between the maxima 49 and 50 of the temperature distribution. All histograms 43a-i have the same axis scaling for the temperature, with only the reference temperature 38 being labeled in each case. The distances between the maxima 49 and 50 are particularly large in the downstream section 4c in histogram 43i and in the upstream section 4a. In the middle section 4b, the temperature histogram 43e only has a central maximum, because the objects 3 have an object temperature 26 that, without infrared contrast, is almost identical to the background temperature 25.In this central section 4b, the pixels 47 of the infrared sensor 1 are almost stable with their associated measuring spots 20 in balanced radiation exchange, so that, as an alternative to regression methods, the determined object temperature 39 can also be read directly from the histogram 43e with the smallest standard deviation as the temperature value at the position of the main maximum 49, 81 °C in this example. A disadvantage of this method is that during successive measurements with different positions of the objects 3, the determined object temperatures 39 can jump from measurement to measurement between different evaluation zones 45.

[0108] For the evaluation process, the angular orientation of the conveyed material flow 2 to the background temperature gradient field 48 is not relevant, provided that it can be assumed that the object temperature 26 can be approximately assumed to be constant at all locations in the infrared image or in a section of the infrared image. In the case of a non-negligible cooling of the object temperature 26 during movement over the various areas of the background 4, it can be advantageous to orient the temperature gradient 48 of the background 4 against the direction of the conveyed material flow 2. This ensures that the locally variable object temperatures 26 clearly intersect with those of the temperature gradient field 48 and do not run parallel in some zones, which can create problems when searching for the minimum 34 in zones of constant fluctuation measures 32. If it is possible that the moving objects 3 are affected by exothermic processes, such aschemical reactions or crystallization, heat up during the measurement, it may be useful to orient the temperature gradient field 48 parallel to the conveyed material flow 2.

[0109] A conveyed material flow 2a extending transversely to the temperature gradient field 48 can be used if relevant changes in the object temperature 26 in an unknown direction are expected during movement across the background 4, and homogeneous object temperatures 26 can be assumed transversely to the conveyed material flow 2. In almost all cases, it will be sufficient to set a sufficiently steep temperature gradient in the background 4 relative to the gradient resulting from changes in the object temperature 26 during the movement of the objects 3 across the background 4.

[0110] Figure 7 also implicitly depicts a special situation for background 4, namely that it is very narrow and, for example, has only the width and height of the one white-hatched evaluation zone 45 above histogram 43b as its overall dimensions. As explained above, this narrow background 4 can have any desired temperature gradient field 48, but the width should be assumed to be so narrow that any existing temperature gradient in the X direction is negligible. For the profile of the background temperature 25 in the Y direction, two relevant scenarios in particular will be discussed:

[0111] Scenario A: The white-hatched image area, which in this special situation encompasses the entire background 4 of the infrared sensor 1, or a complete section of the image, exhibits a temperature gradient oriented in the Y direction. This scenario is fully covered by the description just presented, as it is simply a representation of Figure 7 rotated by 90°, with the only difference being that the conveyed material flow 2a runs vertically and the afterglow trails of the moving objects 3 are formed accordingly in the Y direction.

[0112] Scenario B The white hatched image area, which in this special situation includes the entire background 4 of the infrared sensor 1, or a complete section of the image, is tempered homogeneously in the Y direction.

[0113] The associated histogram 43b visualizes the statistical distribution of the measurement signals 29, from which a fluctuation measure 32 that is largely linear with the infrared contrast can be determined, for example using the standard deviation method. Other statistical methods are discussed in the description. The infrared contrast situation currently visualized in the temperature histogram 43b is as follows: The background 4, which in this special situation is limited solely to the white-hatched evaluation zone 45, is homogeneously heated to 78°C. The relative object surface density in the conveyed material flow 2 is rather low, so that the maximum 49 is dominated by pixels 47, which essentially receive infrared radiation from surfaces of the background 4.

[0114] Since all pixels 47 are regularly driven by warmer objects 3 to higher measurement signal values ​​29 close to the object temperature 26 of 81°C, the dominant maximum 49 in the temperature histogram 43b lies slightly above 78°C due to afterglow effects. Likewise, the secondary maximum 50 does not quite reach the object temperature 26 and lies somewhat lower than 81°C because the pixels 47 do not receive more intense infrared radiation from the objects 3 for long enough. The fact that this is better enabled with a device according to Figure 4, and thus the maxima 49 and 50 can reach much closer to the exact values ​​of background temperature 25 and object temperature 26, has been explained in detail elsewhere.In summary, the evaluation of the measurement signal data 5 visualized in the temperature histogram 43b for this special situation of a background 4 of the size of the white-hatched evaluation zone 45 can be described as follows: the background temperature 25 is still significantly below the object temperature 26, and subsequently, for further increasing, higher background temperatures 25, the at least initially decreasing fluctuation measures 32 should be recorded in order to determine the object temperature 39 from the temporal data collection of various fluctuation measures 32 at different background temperatures 25 by regression analysis. This method is identical to the method described in Figure 6 for the temporal variation of the background temperature and the processing of fluctuation measures 32 in a regression model 33.For the analysis of the fluctuations in the measurement signal 29, it is therefore irrelevant whether these are determined via the temporal variation of a single pixel 47, i.e., the single measuring spot 20 of an infrared sensor 1 designed as a pyrometer, or via the local fluctuation in the infrared intensity, which is detected with a line-scan infrared sensor 1 over the narrow background strip described as a special situation. As an alternative to an infrared line-scan camera, an infrared area camera can also be used as the infrared sensor 1, whereby only the pixels 47 of the measuring section are read out in the form of a strip-shaped image section (Region of Interest, ROI), whose measuring spots 20 are aligned on the tempered strip-shaped background 4, as can be realized with a device according to Figure 10.

[0115] Figure 8A shows an embodiment of the infrared sensor system 1, which is in the form of an area infrared camera and is directed in the image field toward one or more strands 7, which move as a material flow 2 in the longitudinal direction of the strand. To reduce the influence of the emissivity s of the strands 7 to be measured, a housing temperature control 22 is recommended. To reduce edge effects, the aperture 19 should not be made larger than necessary. Shine from the strand surfaces captured from the camera perspective should, if possible, come from spatial directions covered by the housing temperature control 22, although certain edge effects can hardly be prevented by infrared radiation with ambient temperature 55 at the inlet and outlet.Behind the strands 7 is a measurement background 4, which, with the aid of the temperature control device 6, has a somewhat structured temperature field, so that different background temperatures 25 are present simultaneously at different locations in the image field of the infrared camera 1. Using temperature sensors 23, which can be contact or non-contact, additional temperature information 25 of the background 4 can be determined, so that from these and the information from the infrared sensor system 1, the background temperature 25 is known at least approximately for each location in the background 4. However, it is also sufficient to determine reference temperatures for temperature zones with a similar background temperature 25, as described for the data processing scheme in Figure 3.In order to be able to measure strand temperatures 26 individually, it is advantageous if the temperature gradient field 48 of the background 4 has temperature gradients oriented essentially in the direction of movement of the strands 7. If, for example, a thin layer of water still adheres to the strands 7, which causes a strong ablation cooling effect, the strand temperatures 26 fall along the direction of the conveyed material flow 2. For a stable regression model 33 for determining the temperature of the strands, it is therefore recommended that the temperature gradient field 48 in the background 4 be oriented opposite to the temperature gradient in the strands 7, i.e. warmer than the strands 7 in the downstream section 4c and colder than the strands 7 in the upstream section 4a. Oriented the other way around, the temperature gradient field 48 should have sufficiently steeper temperature gradients than the gradient of the strand temperatures 26 in the longitudinal direction of the strand.

[0116] To measure the temperature gradient of the strand temperatures 26 in the longitudinal direction of the strand, additional sections with different background temperature gradients 48 can also be used in the direction of the conveyed material flow 2. Regression models 33 assigned to the individual evaluation sections 51 then determine the respective local object temperatures 39 for the individual sections.

[0117] Figure 8B shows such a simple subdivision of the background 4 into sections 51, wherein the object temperatures 39a, 39b are determined independently of one another for two slightly overlapping evaluation sections 51a and 51b at different positions 41a, 41b of the conveyed material flow 2. Via the temperature control device 6, a low background temperature 25 is set in an upstream section 4a, a higher background temperature 25 compared to the strand temperatures 26 is set in a middle section 4b, and an even lower background temperature 25 than in section 4a is set in a downstream section 4c. In evaluation section 51a, the temperature gradient field 48a runs against the direction of the conveyed material flow 2, while in evaluation section 51b the background is designed with a more intensive temperature gradient field 48b in the direction of the conveyed flow.This allows separate evaluations to be performed for both evaluation sections 51a and 51b. As an example, a strand 7 is shown in a temperature-visualizing false color representation against the background, with the strand temperature 26 decreasing along the direction of the conveyed material flow 2. In evaluation section 51a, the fluctuation minimum and thus the determined object temperature 39a of approximately 80°C is reached in an evaluation zone at position 41a. In a separate temperature evaluation of the second evaluation section 51b, located downstream, another fluctuation minimum is evaluated at position 41b, and the object temperature 39b of approximately 76°C is determined there. The longitudinal temperature gradient in the strands 7 can now be easily determined as the temperature difference 39a to 39b divided by the distance 52 of the measuring positions 41b and 41a, whose exact position values ​​are determined for each of the evaluation sections from regressions.

[0118] Figure 9 illustrates the evaluation process for a measurement signal image from an infrared sensor 1 in the form of an area infrared camera, as can be used for a device according to Figure 8 A. This temperature-visualizing false-color image can also represent an evaluation section, i.e., an image section, so that multiple evaluations can be calculated section by section for an entire measurement signal image, see Figure 8 B. The only difference compared to Figure 7 is that here, instead of moving granular objects 3, continuous strands 7 run against the background 4. The conveyed material flow 2 essentially occurs in a continuous longitudinal movement of the strands 7 in the X direction. Depending on the measurement position and guidance of the strands 7, these shift slightly in the Y direction, but can exhibit dynamic oscillations, especially in the feed area of ​​the granulator. In production plants, dozens of parallel strands 7 often have to be measured.The background 4, which is tempered similarly to the object temperature 26 and has locally different temperatures 25 and, in this case, a temperature gradient field 48, allows the infrared sensor 1 to be placed relatively far away, so that the measurement resolution of the infrared camera 1 can just barely resolve the strands 7. For fluctuation evaluation, even in the case of vibrations of the strands 7, it is sufficient that a strand width of only one or two pixels 47 is imaged and that all pixels 47 receive thermal radiation from both a strand 7 and the background 4 in partial coverage.

[0119] Due to the slow strand speed, the strand usually cools down along the direction of the material flow 2. The detailed instructions for designing the gradient field shown in Figure 7 must be observed, especially for this application.

[0120] To meet the requirement of measuring the temperatures of individual strands 7 at a specified X-position, the background 4 can be divided into individually temperature-controlled sections in the Y-direction. This makes it possible to simultaneously set the infrared contrast minimum for all strands 7 in all sections very close to the specified X-position, despite longitudinal temperature gradients in the strands 7 and different average strand temperatures in a central section 4b.

[0121] It is also possible to define smaller sections 51a and 51b in the image, particularly to determine the temperature for individual strands 7. Since the position of strands 7 is not always static, it is recommended to use conventional image processing, and in particular threshold segmentation, to define sections 51 in the infrared image to define individual strands or strand groups. The width of sections 51 should be based on the respective width of strands 7, so that a stable relative object area density can be maintained in each zone of each section 51 for fluctuation analysis.

[0122] If strand temperatures 26 are sufficiently stable over time, there is a simpler method for precisely determining the temperature of all individual strands 7 at a given X-position. To do this, for a background 4 with a temperature gradient field 48, the average background temperature 25 is increased and decreased in cycles, and for each strand 7, a narrow evaluation section 51 following the strand is defined with a sensibly selected background area proportion. Due to the temporal and spatial variation of the background temperatures 25, the X-positions of the contrast minima a shift with the average background temperature 25 in all sections 51, so that object temperatures 39 are determined for different X-positions for each strand. Using regressions, the longitudinal temperature gradient can be determined from this for each strand 7.The respective measurement result of the determined strand temperature 39 at the target measuring position X is calculated from the currently determined object temperature 39, the measuring position 41 of the fluctuation minimum, corrected by the product of the difference between the target and measuring position with the respective longitudinal temperature gradient of the strand 7.

[0123] Figure 10 shows an infrared sensor system 1 on strands 7, similar to Figure 8A, also optionally with an enclosure temperature control system 22. However, the environmental conditions here are more challenging because the background 4 is immersed in a water bath 8 or at least flushed or sprayed with water. Direct water contact with a heated background 4 will function reliably over the long term in very few system configurations. Deposits and flaking of deposits will cause an uncontrollable emissivity of the heated surface, making reliable background infrared emission impossible.

[0124] In the detailed view of the protective housing 10, which was specially developed for water contact, it can be seen that the temperature control device 6, in the form of a temperature-controlled beam, is thermally insulated from the surrounding water. The heating and / or cooling element 21, which is centrally mounted inside the protective housing 10 and monitored by temperature sensor(s) 23 to maintain a background temperature 25, emits radiation with the surface of the background 4 through the infrared-transparent window U toward the infrared sensor system 1. Infrared-transparent polymer films are known; see, for example, Garrett Beals, Gregory Balonek, Corrie Smeaton, and Joseph Sperry, "Characterization of thin polymers for infrared windows," Proc. SPIE 12103, Advanced Optics for Imaging Applications: UV through LWIR VII, 1210309 (27 May 2022); https: / / doi.org / 10.1117 / 12.2618378, which is referred to regarding such infrared-transparent polymer films.These can be connected to a suitably designed protective housing in a watertight manner. Since the infrared-transparent window 11 absorbs part of the radiation emitted by the background 4, the internally arranged temperature control device 6 can be operated at a higher temperature, so that a background temperature 25 can be simulated according to the intensity evaluation of the infrared sensor 1. For an accurate measurement, the infrared sensor 1 can be calibrated with a calibration radiator in a comparable measurement setup. The temperature control for the temperature control device 6 can then be determined using transfer calibration.

[0125] Although the temperature control device 6 could be used to adjust a strand-specific background temperature radiation 25 by means of a plurality of heating and / or cooling elements 21 arranged transversely to the strands 7, this effort would be of little relevance for practical application. A temperature gradient field comparable to Figure 9 can be implemented more easily as a background radiation field. With a single heating and / or cooling element 21, the statistical contrast can be determined, as in a column zone in Figure 9, which can be characterized by a temperature frequency distribution. From the frequency distribution, it can be determined whether the radiation emission of the background 4 is higher or lower than that of the strands 7.

Claims

Maag Germany GmbH Method and device for contactless temperature determination of a conveyed material flow and granulating device with such a contactless temperature determination device Claims 1. Method for the contactless temperature determination of strand-shaped and / or granular objects in a conveyed material flow (2), in which an infrared sensor (1) is directed onto the conveyed material flow (2) flowing past a background (4), and the temperature (26) of the strand-shaped or granular objects (3) is determined from the measurement signal (29) of the infrared sensor (1), characterized in that the temperature (25) of the background (4) is varied temporally and / or locally by means of a tempering device (6), wherein an evaluation device (30) determines fluctuation measures (32) for different background temperatures (25) from the measurement signal (29) of the infrared sensor (1), and the position of a fluctuation minimum is determined from these fluctuation measures, wherein the object temperature (39) is determined from the value of the measurement signal (29) at the time / location of the fluctuation minimum.Method according to the preceding claim, wherein the measurement signal (29) is supplied by a regression analysis module (33) of the evaluation device (30). is subjected to a regression analysis, wherein the regression analysis module (33) determines a functional relationship between a change in the degree of fluctuation (32), in particular the fluctuation amplitudes, and the background temperature (25) which changes over time and / or place, and the evaluation device (30) uses the said determined functional relationship to determine the time and / or place at which / at which the fluctuation minimum, in particular the amplitude minimum, occurs, and the object temperature (39) is determined from the value of the measurement signal (29) at the time / at the place of the fluctuation minimum determined from the functional relationship.Method according to the preceding claim, wherein the background temperature (25) and / or an averaged measurement signal (29) and / or a reference temperature (38) is used as a reference variable for the functional relationship of the fluctuation measures (32), in particular fluctuation amplitudes, the value of which for a temporal and / or spatial zone with a minimum fluctuation measure (32) corresponds as closely as possible to that of the background temperature (25) and that of the infrared measurement signal (29), and for other temporal and / or spatial zones has a profile that is as linear as possible to the background temperature (25) with a straight line gradient proportional to the difference between the background temperature (25) and the object temperature (26).Method according to one of the two preceding claims, wherein a reference temperature (38) is used as the reference value for the regression, and fluctuation measures (32) for reference temperatures (38) are determined and / or taken into account only above or only below the object temperature (26), so that the fluctuation measure (32) does not reach its minimum value, and the determined object temperature (39) is determined by extrapolation from a regression model (33) where the fluctuation measure (32), in particular the oscillation amplitude, approaches zero or becomes smaller than a predetermined minimum fluctuation threshold. Method according to one of claims 2 to 4, wherein the time and / or location of the fluctuation minimum are determined in a further evaluation step. wherein, in particular, a data recording is used which comprises fluctuation measures (32), reference temperatures (38), and associated times and / or locations for different temporal and / or spatial evaluation zones (45), wherein coherent data groups are filtered out around fluctuation minima which have fluctuation measures (32) smaller than a predetermined threshold, and a regression of the time or location against the reference temperature (38) is performed for each data group, and the determined object temperature (39) is inserted into a respectively determined regression equation for the respective data groups, thereby determining the times and / or locations of the fluctuation minimum. Method according to one of claims 2 to 5, wherein the background temperature (25) is varied in heating and cooling cycles, wherein a heating half-cycle begins with a background temperature (25) below the object temperature (26), reaches it, and then exceeds it,and a subsequent cooling half-cycle follows, in which the initially high background temperature (25) drops, then reaches the object temperature (26) once more, then falls below it again and returns to the initial temperature, and during this time, fluctuation intensities (32) and averaged background temperatures (36) or averaged measurement signal values ​​(35) calculated for the same zones or reference temperatures (38) are recorded quasi-continuously in a data memory, in particular a FIFO memory, in temporal and / or spatial evaluation zones (45) which are limited to a temperature window for the background temperatures (25) and / or averaged measurement signal values ​​(35), wherein one or two minima of the fluctuation intensities (32) are further processed from the recorded data,With each new recorded data set, the oldest recorded data set is no longer used for evaluation, and when using the described regression models, an updated determined object temperature (39) can be output with each measurement cycle. Method according to one of claims 2 to 5, wherein the background temperature (25) varies by means of a temperature control device (6) in heating and cooling cycles, so that the background temperature (25) never reaches the object temperature (26) and meanwhile, fluctuation intensities (32) and mean background temperatures (36) calculated for the same zone or mean measurement signal values ​​(35) or reference temperatures (38) are recorded quasi-continuously in temporal and / or spatial evaluation zones (45) which are limited to a temperature window for the background temperatures (25) and / or averaged measurement signal values ​​(35) in a data memory, in particular a FIFO memory, wherein values ​​for fluctuation intensities (32) for the lowest and highest background temperatures (25) in the transitions between heating and cooling cycles are further processed from the said recorded data, and when using the described regression models used in extrapolation, an updated determined object temperature (39) is output with each measurement cycle.Method according to one of the preceding claims, wherein the heat radiation field of the background (4) is changed temporally and / or spatially by the temperature control device (6) in such a way that at specific times and / or at at least one specific location, a thermal image of the background (4) and of the conveyed material stream (2) flowing past it, provided by the infrared sensor system (1), is assessed by an evaluation unit (30) as being at least approximately contrast-free, wherein the object temperature (39) is determined from the location or time assessed as contrast-free. Method according to one of the preceding claims, wherein the background (4) is temperature-controlled by the temperature control device (6) in such a way that a temperature gradient is generated along the conveying path of the conveyed material stream (2), according to the. - the heat radiation field of the background (4) in a central section (4b) of the background (4) has a temperature (25) which corresponds at least approximately to the object temperature (26), in an upstream section (4a) has a temperature which is lower than the temperature in said central section (4b) and in a downstream section (4c) has a temperature which is greater than the temperature in said central section (4b) of the background (4), or - the heat radiation field of the background (4) has a temperature (25) in a central section (4b) of the background (4) that at least approximately corresponds to the object temperature (26), in an upstream section (4a) has a temperature that is greater than the temperature in said central section (4b), and in a downstream section (4c) has a temperature that is lower than the temperature in said central section (4b) of the background (4). Method according to one of the preceding claims, wherein the temperature control device (6) temporally or locally increases and decreases the background temperature (25) around a temporal or local mean temperature, and additionally varies or adjusts said temporal or local mean temperature such that at said mean temperature, the fluctuation amplitudes (32) in the measurement signal (29) approach zero.Method according to one of the preceding claims, wherein a product guide in the form of a tube is used as the background (4), which is rotated about its longitudinal axis into a contrast measurement position in which a contrast measurement with the background (4) is carried out by the infrared sensor system (1), wherein said contrast measurement is carried out while the conveyed material flow is continuing or has been stopped. Method according to one of the preceding claims, wherein a measuring spot (20) of the infrared sensor system (1) is carried along with the conveyed material flow (2) by means of a rotating prism mirror (24) and / or is guided along in front of the background (4) in the direction of the conveying path of the conveyed material flow. Method according to the preceding claim, wherein the rotation speed of the prism mirror (24) is readjusted based on an image evaluation such that the average size of the objects (3) depicted in the thermal image of the infrared sensor system (1) is minimized and / or minimal afterglow.Tails occur to the front and back, so that a single-object temperature measurement is performed and, if necessary, statistical statements are made about the temperature homogeneity of the product flow, wherein the measuring spot (20) is moved at an at least almost constant scanning speed, preferably with a highly dynamically varying angular velocity of the prism mirror (24). Method according to one of the preceding claims, wherein the infrared sensor system (1) along the conveying path of the conveyed material flow (2) in a plurality of measuring sections (51) determines the local object temperatures and the positions of the fluctuation minima in order to measure temperature changes and the path-related temperature change rate of the objects (3) from a plurality of measurements along the direction of the conveyed material flow (2).Method according to one of the preceding claims, wherein the locally varying temperature field of the background (4) is also varied over time, and for the objects (3) both the positions of the fluctuation minimum along the direction of the material flow are recorded, as well as the object temperatures (39) determined at these locations, so that the path-related temperature change rate of the objects (3) is determined from the resulting point cloud, e.g. by linear regression.Method according to one of the preceding claims, wherein for the individual measurement of the temperatures of strands (7) the infrared image is segmented using image processing methods and individual evaluation sections (51) are defined, in particular transversely to the direction of the conveyed material flow, for individual strands (7) or groups of adjacent strands (7), wherein an object temperature (39) is determined for each section and / or, with additional temporal variation of the background field (4), the temperature gradients in the longitudinal direction of the strand are also determined. Method according to one of the preceding claims, wherein the infrared sensor system (1) uses a plurality of sensor elements or a sensor element system. A plurality of measuring spots (20) are detected simultaneously or sequentially in a row or matrix, which are arranged distributed in the direction of the conveyed material flow. Method according to one of the preceding claims, wherein local and / or temporal situations in which objects (3) have no contrast with the background (4) are used to determine a temperature compensation (40) of the infrared sensor (1). Method according to one of the preceding claims, wherein the infrared sensor (1) is operated by means of an active temperature control device (5), preferably a water temperature control sleeve around the sensor head, even under fluctuating ambient conditions in a predetermined temperature window that is kept constant regardless of the ambient conditions. Method according to one of the preceding claims,wherein the infrared sensor (1) is relocated in a calibration step from the intended measuring position on the background (4) to a calibration station with an at least approximately black body radiator, the temperature of which in the measuring spot is regulated to an operating point temperature relevant for the objects (3) to be measured, wherein said relocation preferably takes place without interrupting the power supply and temperature control, wherein said calibration step comprises several sub-steps, namely firstly the infrared detector is directed to the black body radiator of the calibration station and calibrated to the relevant operating point with a first parallel measurement of the infrared signal and the calibration reference temperature, and following the absolute operating point calibration, a transfer calibration to the background (4) is carried out,wherein the background (4) is set at least approximately stably to the same working temperature of the black body reference, wherein then a second parallel measurement is carried out with the infrared sensor (1) placed back at the measuring position, in which simultaneously the infrared radiation of the background (4) is measured and the background temperature (25) is measured with a contact temperature sensor (23), wherein The emissivity of the tempered background environment is determined as a near-black body based on the results of the second parallel measurement and stored as a calibration parameter for this operating point. A device for contactless temperature measurement of strand- or granular-shaped objects (3) of a conveyed material stream (2), comprising an infrared sensor (1) for detecting the radiation field of the conveyed material stream (2) flowing past a background (4), a tempering device (6) for tempering said background (4), wherein conditions for the measurement with gloss inclusion can be established, in particular, via an environment, and an evaluation device (30) for evaluating the measurement signal (29) of the infrared sensor (1) and determining the object temperature from said measurement signal (29), characterized in that the tempering device (6) is designed to vary the temperature of the background (4) temporally and / or spatially.wherein the evaluation device (30) is designed to evaluate a degree of fluctuation of signal fluctuations in the measurement signal (29) of the infrared sensor (1) detected at a varying background temperature (25), and to determine the time and / or location of a fluctuation minimum, and to determine the determined object temperature (39) from the value of the measurement signal (29) at the time / location of the fluctuation minimum. Device according to the preceding claim, wherein the evaluation device (30) has a regression analysis module (33) suitable for establishing a functional relationship between the degree of fluctuation (32), in particular the fluctuation amplitudes, and time or location via regression analysis, from which the time or location at which the fluctuation minimum, in particular the amplitude minimum, occurs can be determined. Device according to the preceding claim,wherein in the evaluation device (30) boundaries for temporal and / or spatial evaluation zones (45) with assumed very similar background temperatures (25) are defined, which are preferably characterized by background temperatures (25) within a temperature window or time window or image area areas, wherein, the evaluation device (30) is preferably designed to calculate and at least temporarily store the following data for each of these evaluation zones (45) for a subsequent analysis: - a possibly transformed fluctuation measure (32) of the measurement signal (29), which is preferably quantified by evaluating the amplitude, the range, a truncated range and / or the standard deviation, - a representative temperature reference value for the evaluation zone (45), selected or calculated by averaging or filtering, in particular the background temperature (25), the averaged measurement signal (35) or a reference temperature (38), the value of which for a temporal and / or spatial zone corresponds as closely as possible to that of the background temperature (25) and that of the infrared measurement signal (29) with a minimum degree of fluctuation (32), and for other temporal and / or spatial zones has a curve that is as linear as possible to the background temperature (25) with a straight line gradient proportional to the difference between the background temperature (25) and the object temperature (26), - a value representative of the evaluation zone (45) selected for the time or calculated by averaging or filtering, which is preferably characterized by the mean value of the start and end times of the data recording for this evaluation zone (45), - a value selected for the time or calculated by suitable averaging or filtering, or a plurality of values ​​that are retained for a later precise location analysis, and / or contour lines delimiting the evaluation zone (45). Device according to one of claims 21 to 23, wherein the temperature control device (6) is designed to generate a temperature gradient along the conveying path of the conveyed material flow (2), according to which - the heat radiation field of the background (4) in a central section (4b) of the background (4) has a temperature (25) which corresponds at least approximately to the object temperature (26), in an upstream section (4a) has a temperature which is greater than the temperature in said central section (4b) and in a downstream section (4c) has a temperature which is lower than the temperature in said central section (4b) of the background (4), or - the heat radiation field of the background (4) has a temperature (25) in a central section (4b) of the background (4) that at least approximately corresponds to the object temperature (26), in an upstream section (4a) has a temperature that is lower than the temperature in said central section (4b), and in a downstream section (4c) has a temperature that is higher than the temperature in said central section (4b) of the background (4). Device according to one of claims 21 to 24, wherein the background (4) is a product guide in the form of a tube that is rotatable about its longitudinal axis into a contrast measurement position.Device according to one of claims 21 to 25, wherein the surroundings of the measuring zone, and in particular regions that can be indirectly detected by the infrared sensor system (1) via reflections at the gloss angle on the surfaces of the objects (3), emit slightly more infrared radiation via an enclosure temperature control (22) than the infrared radiation of the objects (3) with the determined object temperature (39), so that infrared radiation losses in edge zones and the measuring aperture (19) are compensated and, to a good approximation, measuring conditions for the gloss inclusion can be established in the measuring zone that minimize the influence of the infrared emissivity E of the objects (3). Device according to one of claims 21 to 26, wherein the background (4) and / or the inner wall of the enclosure temperature control (22) is provided with a coating with an emissivity with respect to infrared radiation of more than 40%, more than 70%, or more than 85%.Device according to the preceding claim, wherein the background (4) and / or the inner wall of the housing temperature control (22) is provided with a non-stick coating made of fluoropolymers or silicones. Device according to one of claims 21 to 28, wherein the infrared sensor system (1) has a plurality of measuring spots (20) along the conveying path of the material flow (2) and / or local object temperatures can be determined in a plurality of evaluation sections (51). Device according to one of claims 21 to 29, wherein the infrared sensor system (1) has a rotatably drivable prism mirror (24) for carrying the measuring spot (20) along with the material flow (2) and / or guiding the measuring spot (20) along the conveying path of the material flow (2) against the background (4).Device according to the preceding claim, wherein a control device (30) for controlling the rotational speed of the prism mirror (24) based on image analysis is designed such that the average size of the objects (3) depicted in the thermal image of the infrared sensor system (1) is minimized and / or minimal afterglow tails occur to the front and rear, and / or the measuring spot (20) is moved at an at least virtually constant scanning speed with a highly dynamically varying angular speed of the prism mirror (24). Device according to one of claims 21 to 31, wherein the infrared sensor system (1) has a plurality of sensor elements or a sensor element row or matrix with a plurality of measuring spots (20) arranged distributed in the direction of the conveyed material flow.Device according to one of claims 21 to 32, wherein an active temperature control device (5), preferably a water temperature control sleeve around the sensor head, is provided for temperature control of the infrared sensor (1) even under fluctuating ambient conditions within a predetermined temperature window that remains constant regardless of the ambient conditions. A granulation device for granulating plastics, pharmaceutical products, or foodstuffs, comprising a device for contactless temperature determination, which is designed according to one of claims 21 to 33. Granulation device according to the preceding claim, comprising an underwater granulator (13) and a granulate dryer (17) arranged downstream of the underwater granulator, wherein the infrared sensor system (1) of the device for contactless temperature determination is directed at the conveyed material flow (2) in a dryer outlet (18) of the granulate dryer (17). Granulation device according to claim 34, comprising a strand granulation head for producing strands, wherein the infrared sensor system (1) of the device for contactless temperature determination is directed at the strands (7) leaving the strand granulation head.Granulating device according to the preceding claim, wherein the tempering device (6) is designed to temper the background (4) behind the strand-like objects (3) guided by water or around which water flows only in a narrow transverse strip such that the sensor-evaluated infrared emission corresponds to the desired background temperature (25).

Images