METHOD AND DEVICE FOR SUPPRESSING NOISE IN A CONTROL SIGNAL FOR A CONTROL CIRCUIT OF A FIELD DEVICE FOR REGULATING FLUIDS IN A PROCESS ENGINEERING PLANT

Description

Field of the invention

[0001] The invention relates to a method for suppressing noise in a control signal for a position controller of a field device for regulating fluids in a process plant, as well as a corresponding device.

[0002] One of the main tasks of a position controller for a control or regulating valve is to follow the setpoint. This setpoint can be, for example, an analog current signal from a control system output card or a digital signal. It often contains interference in the form of noise. If this noise is too strong relative to the usable signal range or signal amplitude, a whole range of problems can arise: Positioner components, such as I / P converters and air power amplifiers (especially diaphragms), may experience increased wear. Transistors have a higher switching cycle rate. Piston valves may oscillate undesirably. If the noise is very loud, the positioner may even control the valve actuator to follow the noise, which impairs the process and leads to increased wear on the seals and valve actuator. Additional functions dependent on the setpoint, which may be provided in the positioner (e.g., a tight-closing function), may no longer function correctly.

[0003] In many cases, the noise cannot be eliminated, or the effort required to determine the underlying error is very high. State of the art

[0004] It is common practice to equip positioners in process plants with a fixed, constant noise filter, such as a low-pass filter. This can attenuate noise in a setpoint signal if necessary. However, this filter is always active, thus also attenuating rapid setpoint changes that are not caused by noise, and its strength cannot be adjusted to the conditions prevailing in the application. In cases of high noise, such filtering may not be sufficient.

[0005] Publication EP 2 417 502 B1 describes a rate limiter for an electropneumatic controller. This limits the current rise of the control signal or manipulated variable within the controller's control loop and can also contribute to filtering and noise suppression if necessary. Therefore, the noise suppression does not directly affect the control room's setpoint signal. Since the noise suppression takes place within the control loop, delays can occur there, which can cause unwanted oscillations. The stability of the control loop may even be compromised. Dynamic changes to the noise suppression in response to the onset of noise or its termination are not provided.

[0006] Publication US 2013 / 0041481 A1 discloses methods and devices for limiting a change in a drive variable in an electropneumatic controller. For this purpose, a controller's fluctuation limit is determined based on noise in a control or feedback signal. A drive variable is calculated based on these signals. If the difference between the current and a previous value of the drive variable is greater than the controller's fluctuation limit, the value of the drive variable is changed. Task

[0007] The object of the invention is to provide a method and / or a device which makes it possible to better detect and suppress any noise which may be present in a control signal for a position controller of a field device for regulating fluids in a process plant, without interfering in the control loop of the position controller and / or impairing the control quality. Solution

[0008] This problem is solved by the subject matter of the independent claim. Advantageous developments of the subject matter of the independent claim are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into this description.

[0009] The use of the singular shall not exclude the plural, and this shall also apply in the reverse sense unless otherwise disclosed.

[0010] Individual method steps are described in more detail below. In a preferred variant of the invention, the steps are carried out in the order specified. However, the steps do not necessarily have to be carried out in the order specified, and the method to be described may also include additional, unmentioned steps.

[0011] To solve the problem, a method for suppressing noise in a control signal for a control loop of a field device for regulating fluids in a process plant is proposed. The positioner has a control loop, and the method comprises the following steps: a) The extent of the noise in the control signal is determined. In principle, any methods or algorithms familiar to a person skilled in the art could be used for this purpose, e.g. counting the zero crossings of the first, second, or third time derivative or the local extreme values ​​of the control signal, or examining the difference between the control signal and a straight line fitted to it using linear regression or a moving average. In the present case, the extent of the noise in the control signal is determined by continuously determining local maxima of the control signal and counting each for a first predetermined period of time. If the counted number of local maxima per first predetermined period of time exceeds a predetermined number, the noise is assessed as severe.The level of noise is then determined by the maximum number of times during a second predefined period of time the level of noise is rated as high. b) If the level of noise exceeds a first predefined threshold, the noise in the control signal is reduced by a filter, resulting in a filtered control signal. For example, a day could be considered as the second predefined period of time, and the first predefined threshold could be selected such that noise suppression is switched on if, for example, the level of noise is rated as high more than 20 times during this second predefined period of time. In this way, it can be avoided that noise suppression is switched on unnecessarily, e.g. due to a one-off disturbance that does not require intervention because it does not occur continuously. c) The filtered control signal is passed on to the control loop.d) If the noise level does not exceed the first specified threshold, the unfiltered control signal is passed to the control loop.

[0012] The control loop typically controls the position of a component in the field device, e.g., the position of a valve element. If the field device is a pneumatically actuated control valve, for example, the control loop will, as always, comprise a controller, a controlled system, and a feedback loop. In the case of a pneumatically actuated control valve, the controlled system will typically comprise an I / P converter, an air power amplifier, and a pneumatic actuator for the valve element.

[0013] This makes it possible to respond flexibly to a setpoint signal affected by noise. If the noise becomes too high, such that the problems described above could occur, a suitable filter is activated to attenuate the noise or reduce it in another suitable way. In the simplest case, this could be a low-pass filter, but filters that are better adapted to the noise occurring or expected in the application are preferred.

[0014] The filtering takes place outside the control loop so that the influence on the control quality and in particular on the response and stability of the controller remains as low as possible.

[0015] A better adaptation of the noise suppression to the existing situation is achieved if the described procedure is supplemented by carrying out at least one of the following measures when the level of noise exceeds the first predetermined threshold: 1. A hardware filter is activated; 2. a software filter is used; 3. if a software filter is already in use, a software filter of a different type is switched on; and / or 4. if a software filter is already in use, a filter constant of the software filter is changed.

[0016] This ensures that increased filtering is only applied when the level of noise in the setpoint signal requires it. The measures mentioned above ensure that the optimal noise suppression is used for the respective application. Combinations of the measures mentioned are also possible. The software filters provided only require a suitably programmed processor, which can be provided, for example, in the positioner. Alternatively, it could be located on an add-on card or in a separate component or module.

[0017] The method can also provide for the output of an influence signal for switching and / or adjusting a filter, wherein the influence signal corresponds to the specific level of noise. Based on this signal, for example, it is possible to select which specific filter or setting is switched, thereby adapting the noise suppression to the specific conditions of the application.

[0018] The following is an example which is not part of the claimed invention but is merely intended to contribute to a better understanding. The extent of the noise in the control signal can be determined particularly reliably and with particularly low computational effort using the following steps: Local maxima of the control signal are continuously determined and each counted for the duration of a first predetermined time period. A predetermined number N of local maxima per first predetermined time period is selected as the first predetermined threshold for the extent of noise in the control signal. A value between one and ten seconds can preferably be selected as the first predetermined time period, particularly preferably 5 s. A value between 10 and 30, preferably 20, can be provided as the predetermined number, for example.If the number of local maxima of the control signal recorded within the first specified time period is so high, it is very likely that these are not true local maxima, i.e., changes in direction, of the setpoint, but disturbances caused by noise. This generally applies to all local extreme values ​​of the control signal. However, it is sufficient to consider either only the local maxima or only the local minima, since every local maximum is followed by a local minimum and vice versa. If all local extreme values ​​were considered, the specified number N would simply have to be multiplied by 2. This concludes the discussion of this example.

[0019] Local maxima of the control signal are preferably detected when the control signal decreases after a small, predefined increase, e.g., between 0.05 and 0.25%. This avoids the computational effort required, for example, to determine the zeros of the derivative. Alternatively, local maxima and local minima could be detected alternately.

[0020] If the control signal corresponds to a setpoint that is not static, the determination of the noise extent can be improved if the specified number of maxima and / or the specified proportion is specified as a function of an average of the time derivative of the control signal. If the control signal is not static, i.e., if it exhibits significant gradients due to intentional changes in the setpoint, the number of local maxima of the control signal that can be detected using the method described above decreases. The steeper the setpoint change, the fewer local maxima are detected. Accordingly, the number of maxima used for noise detection should decrease. Cumulatively or alternatively, the specified proportion can be reduced in order to keep the number of maxima as unchanged as possible.However, the exact nature of this dependency depends on the local conditions of the respective application and should therefore be configured during commissioning or initialization of the system. The update rate of the control signal, for example, from the control room, in relation to the speed of the respective execution of the process in question also plays a role: If this update rate is slower than 2 s -1<, for example, such a change in the specified number is generally not necessary.

[0021] The detection of potential problems and / or errors in the system is facilitated if a warning message is issued when the level of noise in the control signal exceeds a second predefined threshold. This should typically be higher than the first predefined threshold, so that such a warning message only occurs when the noise in the control signal reaches a level that experts consider to be alarming, for example, when effective noise suppression is no longer possible without compromising the control quality of the positioner's control loop.

[0022] Whether the noise level exceeds the second predefined threshold can be determined particularly efficiently using the following steps: The noise level in the filtered control signal is determined using one of the described embodiments. If the noise level in the filtered control signal exceeds the first predefined threshold, the second predefined threshold is considered to have been exceeded. For this to happen, the filtered control signal would have to be fed into the noise level determination.

[0023] Alternatively, a threshold for the noise amplitude can be specified as the second specified threshold. If the level of noise in the control signal exceeds the first specified threshold, the noise amplitude of the control signal must then be determined. This can be done, for example, using a particularly simplified procedure by determining not only the number of local maxima during the specified time period (e.g., 5 s), but also the value of the largest local maximum. This corresponds approximately to twice the noise amplitude or the noise bandwidth. However, this only applies if the setpoint remains essentially static during the specified time period.

[0024] Unnecessary calculations and possible corruption of the control signal can be avoided if the reduction of the noise in the control signal by a filter is stopped when the level of the noise remains below the first predetermined threshold for a second predetermined period of time, for example one day.

[0025] The object is further achieved by a device for suppressing noise in a control signal for a control loop of a field device for regulating fluids in a process plant. The position controller has a control loop. The device comprises a first connection for receiving the control signal, at least one switchable filter module for reducing the noise in the control signal, a setpoint receiving module for determining the extent of the noise in the received control signal and for switching the at least one filter module, and a second connection for forwarding the filtered or unfiltered control signal to the control loop. The setpoint receiving module is configured to execute the method described above.

[0026] The device mentioned can be designed as a retrofit element for any valve position controller, provided the modules are integrated circuits and / or plug-in cards and / or programmable hardware. Programmable hardware includes, for example, ASICs, DSPs, and / or FPGAs. This means that the execution of the method is not dependent on the position controller's features.

[0027] The object is also achieved by a computer program comprising instructions which cause the device already described to carry out the method steps described above.

[0028] A computer-readable medium on which the computer program just described is stored also solves the problem.

[0029] The task is also solved by a positioner for a field device, wherein the positioner comprises a device as described above. Components of the control loop can also be located outside the positioner housing.

[0030] Preferably, this is a positioner with an I / P converter and an air power amplifier, i.e. a positioner that operates electropneumatically.

[0031] The problem is further solved by a field device for regulating a fluid in a process plant with a position controller as just described, and by a process plant with at least one such field device.

[0032] Further details and features will become apparent from the following description of preferred embodiments in conjunction with the figures. The respective features can be implemented individually or in combination with one another. The possibilities for solving the problem are not limited to the embodiments. For example, range specifications always include all intermediate values ​​(not mentioned) and all conceivable sub-intervals.

[0033] The exemplary embodiments are illustrated schematically in the figures. Identical reference numerals in the individual figures denote identical or functionally equivalent elements, or elements that correspond to one another in terms of their functions. In detail: Fig. 1 shows a schematic representation of a device for suppressing noise in a control signal for a position controller of a field device for regulating fluids in a process plant, in which filter constants are set; Fig. 2 shows a schematic representation of a device for suppressing noise in a control signal for a position controller of a field device for regulating fluids in a process plant, in which different software filters are switched; Fig. 3 shows a schematic representation of a device for suppressing noise in a control signal for a position controller of a field device for regulating fluids in a process plant, in which hardware filters are switched; Fig. 4 shows a schematic representation of the algorithm for determining the extent of the noise; Fig.Fig. 5A shows a simulated example of a slightly noisy signal where the noise is not considered to be strong; Fig. 5B shows the locations where local maxima occur in the signal. Fig. 5A be detected; Fig. 5C the resulting (non-)detection of strong noise in the signal from Fig. 5A ; Fig. 6A a simulated example of a noisy signal where the noise is partially assessed as strong; Fig. 6B the locations where local maxima in the signal from Fig. 6A be detected; Fig. 6C the resulting detection of strong noise in the signal from Fig. 6A ; Fig. 7A a dynamically increasing signal to which a simulated noise is applied; Fig. 7B an essentially constant signal to which the same noise as in Fig. 7A is imposed; Fig. 8 shows a possible dependence of the first predetermined number of local maxima on the average speed of the setpoint; Fig. 9 shows a schematic representation of the algorithm for determining the extent of noise for dynamically changing setpoints; and Fig. 10 shows a simplified schematic circuit diagram of the position control of a field device with position controller, pneumatic drive and the device for suppressing noise.

[0034] Fig. 1 shows a device for suppressing noise in a control signal for a position controller of a field device for regulating fluids in a process plant. The control signal or setpoint signal w is first processed, preferably by a hardware filter 110 according to the known prior art. This is typically a first-order analog low-pass filter, e.g., with a cutoff frequency of 6 Hz. Noise from external interference signals 120 originating somewhere in the plant is thus at least partially attenuated. However, interference 125 can also occur within the circuit of the position controller, which also contributes to the noise of the control signal. This signal is digitized in an A / D converter 130.

[0035] A setpoint receiving module 140 checks the level of noise in the digitized control signal. Depending on whether sufficiently strong noise is detected, the setpoint receiving module 140 switches between two settings or filter constants 160, 165 using a switch 150. These determine how the software filter 170 processes the digitized control signal. For example, the setting for low noise could be such that the signal is not changed at all, while for high noise, a filter is provided that is designed for the noise expected for this part of the system.

[0036] The digitized control signal 180, possibly filtered, is forwarded to the control loop (not shown). In the event that particularly strong noise is detected, a warning message 190 is also provided.

[0037] Whether the extent of the detected strong noise is sufficient or not is preferably determined based on a first predefined threshold and a predefined time period. For example, one day could be considered as the predefined time period, and the predefined threshold could be selected such that the filter constants are switched if the noise is rated as strong more than 20 times during this predefined time period.

[0038] Fig. 2 shows a modification of the device from Fig. 1 Here, too, the setpoint or control signal w, which is underlaid with noise from interference signals 220, is first processed by a hardware filter 210. Further interference signals 225 can be added within the position controller. The signal is digitized by an A / D converter 230 and then checked for noise intensity by a setpoint reception module 240. Depending on whether or not strong noise is detected, the setpoint reception module 240 in this embodiment switches between two different software filters 270, 275 using switch 250, each of which filters the control signal in a different way. One of the software filters can, for example, be a standard filter, which is also useful for a signal with no or hardly any noise, while the other filter is specially tuned to the noise expected for this position controller.The filtered control signal 280 is forwarded to the control loop (not shown). In the event of particularly high noise, a warning message 290 is also provided.

[0039] A further modification of the device from Fig. 1 and Fig. 2 is in Fig. 3 shown. Here, too, a setpoint or control signal w is present, which may be noisy due to interference signals 320 from the system. However, two different (analog) hardware filters 310, 315 are present. Since these are connected upstream of the A / D converter 330, they cannot filter out interference resulting from the position controller's electronics. The control signal digitized by the A / D converter 330 is examined for the extent of the noise by a setpoint receiving module 340. Depending on whether significant noise is detected or not, the setpoint receiving module 340 switches between the hardware filters 310 and 315 using the switch 350. The digitized signal can also be further filtered by a software filter 370 - in this case, not switchable. The filtered control signal 380 is forwarded to the control loop (not shown). If necessary, a warning message 390 may be issued.

[0040] In addition to the disadvantage of not being able to specifically filter out noise caused by interference from the signal processing in the position controller, this embodiment has the advantage that, in the case of strong noise, if the setpoint receiving module 340 has been switched between the filters 310, 315 accordingly, it can automatically examine the more heavily filtered signal, thus providing a type of success check. The output of a warning message can particularly preferably be made dependent on the result of these tests, so that, for example, a warning message is output if switching to the stronger filter is not sufficient to reduce the specific amount of noise to a sufficiently low level.

[0041] Combinations and further additions to the embodiments from Fig. 1 , 2 and 3are of course possible, for example, the use of filter cascades with multiple filter stages. Different filter types such as FIR filters (finite impulse response filters), IIR filters (infinite impulse response filters), median filters, or other nonlinear filters can also be used.

[0042] In Fig. 4 is shown schematically how the extent of the noise can preferably be determined. In the control or setpoint signal w to be examined (in this case already digitized), local maxima are continuously detected 410. In principle, a wide variety of methods for extreme value detection are possible for this purpose, but it is particularly preferred that a maximum is considered to be detected when the signal w drops again after an increase of at least a predetermined proportion Δw. If a local maximum is detected, this is passed on to detect strong noise 420, whereby a simple yes / no signal y / n is sufficient for this, since only the information that a local maximum has been detected is required. This detection takes place by counting the detected local maxima. If more local maxima than a predetermined number N are present within a first predetermined time period T 1, the extent of the noise is considered to be high.Whether the noise is strong or weak is again output as a yes / no signal y / n.

[0043] Non-noise-induced peaks in the setpoint signal may arise during dynamic processing when the setpoint w changes direction. However, it is unlikely that a large number of these will occur in a short period of time.

[0044] Noise detection that functions in this way is based on particularly simple computational operations that require few resources and can run quickly. This is particularly advantageous because they can run on relatively simple or low-performance hardware, e.g., a signal processor already present in a position controller, without impairing other functions that often have to run in real time. Furthermore, there is no need to store significant amounts of data, since only "detection" and a yes / no signal need to be transmitted. Furthermore, this type of noise detection is only slightly dependent on any existing cycle time of the setpoint from the control system. This cycle time is the update rate of the setpoint in the current output circuit of the control system. Common cycle times range from 100 ms to 1,000 ms.

[0045] Fig. 5A shows an example of a simulated control signal, in this case constant 50%, to which a weak noise (noise bandwidth, ie 6 sigma of the Gaussian distributed noise signal = 0.2%) was applied. With a given proportion of Δw = 0.15%, a given number N = 20 and a first given time period T 1 = 5 s, Fig. 5B Over the entire period of 20 s shown, approximately 10 local maxima were detected. This is not enough to classify the noise as strong, which is Fig. 5C can be seen.

[0046] In Fig. 6A A simulated drive signal of constant 50% is also shown, to which a stronger noise (6 sigma of the Gaussian distributed noise signal = 0.37%) was imposed. Under the same conditions as in Fig. 5A-C , ie specified proportion Δw = 0.15%, specified number N = 20, first specified time period T 1 = 5 s are Fig. 6B Over the period of 20 s shown, many more local maxima were detected. In Fig. 6C It can be seen that the noise is therefore rated as strong in the time periods between 5 and 10 s and between 15 and 20 s.

[0047] In the case of a dynamically changing setpoint or control signal w, ie when the time derivative dw / dt is no longer small, this form of noise detection works less well, as can be seen from Fig. 7A und Fig. 7B can be seen: In Fig. 7A a dynamic setpoint curve with a gradient of 2 % / s is shown, in Fig. 7B a constant setpoint. In both cases, the same noise signal was superimposed. The local extreme values ​​detected are marked with asterisks. They were determined with the same specified proportion Δw = 0.15%. Although the same noise was superimposed, it is clearly visible that in Fig. 7A Due to the dynamic setpoint curve, fewer local extreme values ​​are detected than in Fig. 7B . The described noise detection would therefore respond less frequently.

[0048] This can be remedied by making the specified number N of local maxima in the first specified time period T 1 dependent on the speed of the setpoint dw / dt. At higher speeds, fewer maxima N are required within the specified time period T 1 to assess the noise as high. An example curve of the specified number N as a function of the speed of the setpoint is shown in Fig. 8 shown, where for a static control signal the specified number N should still be 20 at T 1 = 5 s. This curve depends on local conditions, properties of the circuits and the typically present dynamics of the setpoint signal and must therefore be specified separately for each individual case, for example when commissioning the respective system component.

[0049] In Fig. 9 It is shown schematically how the extent of noise can be preferably determined when the setpoint or control signal changes dynamically. This is an extension of the Fig. 4 In the control or setpoint signal w to be examined, local maxima are continuously detected 910. This is preferably done by considering a maximum as detected when the signal w drops again after an increase of at least a predetermined proportion Δw. If a local maximum is detected, this is passed on to detect strong noise 920, whereby a simple yes / no signal y / n is sufficient for this purpose. In addition, the time derivative DT1 of the setpoint or control signal is formed. For stabilization and to reduce any dependence on cycle times of the control system, this speed of the setpoint is averaged over a period T mean 930. Based on a predetermined dependency, as shown for example in Fig. 8 As shown, the predefined number N corresponding to the averaged setpoint speed is determined 940 and also passed on for the detection of strong noise 920. This detection occurs by counting the detected local maxima. If more local maxima than a predefined number N are present within a first predefined time period T 1 , the noise is considered strong. Whether the noise is strong or weak is again output as a yes / no signal y / n.

[0050] Fig. 10shows a schematic diagram of the position control loop of a pneumatically driven field device or control valve 1010. The dashed outline indicates which components belong to the field device's position controller 1020 in a typical application. The setpoint W or the control signal is specified by the user, a process controller, a control room, or similar device. The noise suppression device 1030 cleans or filters this signal in the manner already described. The filtered control signal W' is fed into the actual controller 1040. The - typically electrical - control signal Y of the controller 1040 is converted in this example by an I / P converter 1050 into a control pressure, which is applied to the control input of an air power amplifier 1060. The air power amplifier 1060 is supplied with a supply air pressure P z and delivers an output pressure P a to the pneumatic actuator of the control valve 1010.The position sensor 1070 on the control valve 1010 supplies the actual value X to the controller 1040 for the respective filtered setpoint W'. This results in a closed control loop 1080 (enclosed by the dot-dash line) or a control loop, which is connected downstream of the described noise suppression.

[0051] With the devices and methods described, a noisy control or setpoint signal can be clearly detected and responded to accordingly by applying more appropriate filtering than with fixed preset filters that must be suitable for all possible conditions. This can preferably be done in three steps: 1. "Good state": There is no critical noise. The standard filtering of the control signal is sufficient; no reaction occurs. 2. "Medium state" with countermeasures: There is significant noise. By switching the filtering of the control signal, as already described, the situation can be remedied, especially without impairing the positioner's control loop. If necessary, a warning message can also be issued, preferably indicating that the measures taken are sufficient. This case occurs, for example, if the level of noise lies between the first and second specified thresholds. 3. "Bad state", where countermeasures are insufficient: There is significant noise, the level of which is so high that it cannot be adequately compensated even with increased filtering, as otherwise, for example, the process control quality would suffer.In this case, the maximum possible additional filtering is activated and a corresponding warning message is issued. This occurs, for example, if the noise level exceeds the second specified threshold.

[0052] If the "good" state recurs for a longer period after the "medium" or "poor" state, the countermeasures are preferably withdrawn, for example, if the specified threshold is not exceeded within the specified period, e.g., if the noise level is rated as high fewer than 20 times on a given day. A message can also be issued about this. glossary Attachment

[0053] A plant represents a planned assembly of technical components. These components can include machines, devices, apparatus, storage facilities, lines or transport routes, and / or control or regulating elements. They can be interconnected, connected, or linked functionally, for control purposes, and / or safety reasons. Plants are operated in many different areas for a variety of purposes. These include, for example, process engineering plants, which in many cases are part of the chemical industry. The term "plant" also includes refineries, district heating systems, geothermal or solar thermal plants, food production plants, fresh water supply or wastewater disposal plants, biogas plants, etc. filter

[0054] In electrical and communications engineering, filters are circuits that change the amplitude and phase of an electrical signal depending on the frequency. This can attenuate or suppress unwanted signal components. Common examples are low-pass and high-pass filters, which attenuate high and low frequencies, respectively.

[0055] Electronic filters are called analog filters if they process signals continuously over time and amplitude. They are used either to shape signals in the desired manner or to determine which frequencies are present (signal analysis). Analog filters are constructed using passive electronic components such as capacitors, inductors, and resistors, or actively using operational amplifiers. In contrast, a digital filter is a mathematical filter for manipulating a signal, e.g., blocking or passing a specific frequency range. Digital filters are implemented, for example, using logic components such as ASICs and FPGAs, or in the form of a sequential program with a signal processor. Thus, software-based filters are always digital filters, whereas hardware-based filters can be analog or digital in nature, depending on the components and circuits used. field device

[0056] A field device is a technical device in the field of automation technology that is directly related to a production process. In automation technology, "field" refers to the area outside of control cabinets or control rooms. Field devices can therefore be both actuators (control elements, valves, etc.) and sensors (e.g., measuring transducers) in factory and process automation. I / P converter

[0057] An I / P converter is an electrical-pneumatic transducer. Depending on an electrical signal, compressed air is supplied, the output pressure of which varies with the signal's current. Such converters are used, for example, to control the actuators of pneumatically driven control valves. Noise amplitude, noise bandwidth

[0058] The noise amplitude corresponds to half the noise bandwidth and indicates the size of the noise band. This describes how much a static (but noisy) signal still changes. If the noise is caused by Gaussian-distributed disturbances, the noise bandwidth can only be determined stochastically. For example, one can require that 99.73% of all signal values ​​must always lie within the noise band. In this case, the noise bandwidth would correspond to six times the standard deviation (6 sigma) of the signal, assuming the noise has Gaussian characteristics. Alternatively, for example (as a simplification), the difference between the largest and smallest values ​​over a predefined range can be used as the noise bandwidth. control circuit, control loop

[0059] A control loop consists of a controller, a controlled system, and a feedback loop. The controlled system acts on a controlled variable X. A setpoint W is specified for this variable. The actual value of the controlled variable X is measured. From the actual value X and the setpoint W, the controller determines a manipulated variable Y according to the desired dynamics of the control loop. This manipulated variable Y acts on the controlled variable X via the controlled system with the goal of bringing the actual value X closer to the setpoint W. Positioner

[0060] A positioner is the element of a control valve that operates the actuator of the valve element to open or close the valve. Each positioner includes a control loop to regulate the position of the valve element based on a specified input, such as a signal from a control room. The actuator of the valve element—often an electric or fluidic actuator, the latter of which can be operated either hydraulically or with compressed air—is part of the control loop and is thus clearly assigned to the positioner, even if the actuator is located outside the actual positioner. Reference symbol

[0061] DT1 time derivative y / n Yes / No signal N first specified number P a output pressure P z supply air pressure T 1 specified time period T mean averaging time w, W control signal or setpoint Δw specified portion X actual value of the controlled variable Y manipulated variable 110, 210, 310, 315 hardware filter 120, 220, 320 fault signal from system 125, 225 fault from positioner 130, 230, 330 A / D converter 140, 240, 340 setpoint receiver module 150, 250, 350 switch 160, 165 filter constant 170, 270, 275, 370 software filter 180, 280, 380, W' (filtered) control signal to the control loop 190, 290, 390 Warning message 410, 910 Detection of local maxima 420, 920 Detection of strong noise 930 Averaging 940 Determination of the first specified number 1010 Pneumatically driven field device or control valve 1020 Positioner 1030 Noise suppression device 1040 Controller 1050 I / P converter 1060 Air power amplifier 1070 Position sensor 1080 Control loop cited literature

[0062] cited patent literature EP 2 417 502 B1 US 2013 / 0041481 A1

Claims

1. Method for suppressing noise (120, 125; 220, 225; 320) in a control signal (w; W) for a control loop (1080) of a field device (1010) for regulating fluids in a process plant; wherein the method comprises the following steps: 1.1 the extent of the noise in the control signal (w; W) is determined; wherein the extent of the noise in the control signal (w; W) is determined by the following steps: 1.1.1 local maxima of the control signal are continuously determined (410; 910) and each counted for the duration of a first predetermined time period (T1); 1.1.2 if the counted number of local maxima per predetermined time period (T1) exceeds a predetermined number (N), the noise is evaluated as strong; and 1.1.3 that the extent of the noise is determined by the number of times during a second predetermined time period that the noise is evaluated as strong; 1.2 when the extent of the noise exceeds a first predetermined threshold, the noise in the control signal (w; W) is reduced by a filter (170; 270, 275; 310, 315), resulting in a filtered control signal (W); 1.2.1 the filtered control signal (W) is forwarded to the control circuit (1080) (180; 280; 380); 1.3 if the extent of the noise does not exceed the first predetermined threshold, the unfiltered control signal is forwarded to the control circuit (1080).

2. Method according to the preceding claim, characterized in that 2.1 if the extent of the noise exceeds the first predetermined threshold, at least one of the following measures is carried out: 2.1.1 a hardware filter (310, 315) is switched on; 2.1.2 a software filter (170; 270, 275; 370) is applied; 2.1.3 if a software filter (270) is already in use, a software filter (275) of a different type is switched to; and / or 2.1.4 if a software filter (170) is already in use, a filter constant (160, 165) of the software filter (170) is changed.

3. Method according to one of the preceding claims, characterized in that 3.1 an influencing signal for switching and / or adjusting a filter (170; 270, 275; 310, 315) is output; 3.2 wherein the influencing signal corresponds to the determined extent of the noise.

4. Method according to one of the preceding claims, characterized in that local maxima of the control signal are recognized (410; 910) when the control signal (w; W) falls by a predetermined proportion (Δw) after an increase.

5. Method according to the immediately preceding claim, 5.1 wherein the control signal (w; W) corresponds to a setpoint value which is not static, characterized in that 5.2 the predetermined number (N) and / or 5.3 the predetermined proportion (Δw) is predetermined as a function of an average value of the time derivative (DT1) of the control signal.

6. Method according to one of the preceding claims, characterized in that if the extent of the noise in the control signal (w; W) exceeds a second predetermined threshold, a warning message (190; 290; 390) is output.

7. Method according to the immediately preceding claim, characterized in that the following steps are used to determine whether the extent of the noise exceeds the second predetermined threshold: 7.1 the extent of the noise in the filtered control signal (W) is determined; 7.2 if the extent of the noise in the filtered control signal (W) exceeds the first predetermined threshold, the second predetermined threshold is considered to be exceeded.

8. Method according to claim 6, characterized by the following additional steps: 8.1 a threshold for the noise amplitude is set as the second predetermined threshold; 8.2 if the extent of the noise in the control signal (w; W) exceeds the first predetermined threshold, the noise amplitude of the control signal is determined.

9. Method according to one of the preceding claims, characterized in that the reduction of the noise in the control signal (w; W) by a filter (170; 270, 275; 310, 315) is terminated if the extent of the noise remains below the first predetermined threshold for a second predetermined time period.

10. Device (1030) for suppressing noise (120, 125; 220, 225; 320) in a control signal (w; W) for a control loop (1080) of a field device (1010) for regulating fluids in a process plant, having 10.1 a first connection for receiving the control signal (w; W); 10.2 at least one switchable filter module (170; 270, 275; 310, 315) for reducing the noise in the control signal (w; W); 10.3 a setpoint receiving module (140; 240; 340) for determining the extent of the noise in the received control signal (w; W) and for switching the at least one filter module (170; 270, 275; 310, 315); and 10.4 a second connection for forwarding the filtered or the unfiltered control signal (180; 280; 380; W) to the control loop (1080); 10.5 wherein the setpoint receiving module (140; 240; 340) is configured to perform the method according to one of the preceding method claims.

11. Computer program comprising instructions which cause the device (1030) according to claim 10 to perform the method steps according to any one of the method claims 1 to 9.

12. Computer-readable medium on which the computer program according to the immediately preceding claim is stored.

13. Positioner (1020) for a field device (1010), wherein the positioner (1020) comprises a device (1030) according to claim 10.

14. Field device (1010) for regulating a fluid in a process plant, having a positioner (1020) according to the immediately preceding claim.

15. Process plant having at least one field device (1010) according to the immediately preceding claim.