THZ measuring device and method for measuring a measuring object

Description

[0001] The invention relates to a THz measuring device and a THz measuring method for measuring a test object. The test object can, in particular, be continuously guided through a measuring chamber of the THz measuring device. In particular, a layer thickness and / or a material property of the test object can be measured.

[0002] THz measurements are used, among other things, for the continuous measurement of conveyed objects. For example, strands such as pipes, profiles, or cables made of a material like plastic or rubber can be continuously measured for their geometric structure and potential defects after their manufacture. The THz radiation can then be reflected at interfaces and subsequently detected. If the speed of light of the THz radiation in the material is known, layer thicknesses and / or diameters can be determined from the measured differences in the transit time of the detected THz radiation. However, the speed of light in the material is sometimes not precisely known, particularly in the case of materials with unknown temperatures and material mixtures.

[0003] From WO 2016 / 139155 A1, it is known to first perform a calibration measurement of the empty measuring chamber without the object being measured. This is done by sending THz radiation through the measuring chamber to a reference mirror, and subsequently detecting the radiation reflected back from the reference mirror to the THz transceiver. This results in a measurement signal with a total internal reflection peak. Subsequently, an object measurement is performed using the same THz transceiver with a pipe in the frame. Here, the same THz transceiver again sends THz radiation through the two wall sections of the pipe to the reference mirror, which then reflects the radiation back through the object to the THz transceiver. From these measurements, layer thicknesses and material properties can subsequently be determined.

[0004] However, such measurements present difficulties, particularly when there are defects in the material or when the material absorbs more strongly than usual. Accurate alignment of the components is also complex.

[0005] DE 10 2017 125 740 A1 describes a THz measuring device for measuring at least one layer thickness of a measuring object conveyed along a conveying direction, comprising a THz main sensor for emitting a THz main beam along a first optical axis in a detection plane perpendicular to the conveying direction and for receiving THz radiation reflected along the first optical axis, as well as at least one THz auxiliary sensor for emitting an additional THz beam along a second optical axis (A2), which is located outside the detection plane and / or inclined to the detection plane, for detecting the additional THz radiation reflected back along the second optical axis. Additional reflection peaks originating from defects in the measuring object can be detected in the signal amplitude of the additional THz sensor.

[0006] DE 10 2018 124 175 A1 describes a method for controlling a production plant for plate-shaped or strand-shaped bodies, in which the body is conveyed along a conveying direction through a measuring area and irradiated with measuring radiation in the gigahertz or terahertz frequency range, wherein the measuring radiation penetrates at least partially into the body, and in which measuring radiation reflected from the body is detected and the refractive index of the body and / or the absorption of the measuring radiation by the body are determined based on the detected measuring radiation, wherein at least one production parameter of the production plant is controlled based on the refractive index determination and / or the absorption determination. Thus, layer thicknesses are also measured here by detecting the radiation reflected at interfaces.

[0007] US 2021 / 0262792 A1 describes a device for measuring a surface with first sensors distributed two-dimensionally in space, wherein the first sensors interact with the surface in a contactless manner using electromagnetic signals in the microwave range, and wherein the first sensors acquire signals from the interaction containing information about the distance between the sensors. This includes a measurement between opposing sensors without a measuring object, as well as a measurement in which the edges of a metal plate are measured from both sides to subsequently calculate the difference.

[0008] From US 2012 / 0032083 A1 it is known to generate terahertz rays based on side-domain spectroscopy, whereby a voltage is applied via a switching device having a photoconductive surface which is subsequently irradiated with light and thereby enables the generation of currents which lead to the formation of terahertz radiation.

[0009] US 2016 / 0315716 A1 describes a system for transmitting and receiving electromagnetic radiation using a beam splitter and a transceiver. The beam splitter divides an optical pulse into a pump pulse and a probe pulse. This allows a sample to be measured, and the travel time to and from the sample can then be detected using the pump pulse and the probe pulse.

[0010] US 2012 / 0217403 A1 describes the measurement of an object emitting THz radiation using a phase-sensitive THz receiver. This allows for the measurement of a time delay or phase offset caused by the object for a first frequency component, from which the material layer thickness can be determined. By using two different frequency ranges, the object can be measured, and the absorption coefficient is additionally determined. The measurement reveals an attenuation of the received signal for at least the second frequency range.

[0011] DE 10 2020 123 992 B3 describes a THz measuring device and a THz measuring method for measuring test objects, in which radiation is sent through the test object by opposing THz transceivers; the THz radiation is emitted by the two THz transceivers with different polarizations so that the radiation does not interfere with each other. The radiation emitted by each THz transceiver is reflected back to the respective transceiver by a reflector located behind the test object.

[0012] The invention is based on the objective of creating a THz measuring device and a THz measuring method for measuring objects that enable accurate measurement of objects with minimal effort.

[0013] This problem is solved by a THz measuring device and a THz measuring method according to the independent claims. Furthermore, an arrangement comprising the THz measuring device and a measured object is provided. The dependent claims describe preferred embodiments.

[0014] The THz measuring device according to the invention can be carried out in particular using a THz measuring method according to the invention. The THz measuring method according to the invention can be carried out in particular using a THz measuring device according to the invention.

[0015] The measuring arrangement according to the invention comprises the THz measuring device with measuring object, and optionally a conveying device and / or production device for producing the measuring object, e.g. an extruder.

[0016] The object to be measured can be, in particular, a strand, which can be circular or rectangular. Examples of suitable objects include: a pipe, profile, cable, hose, film, and also, for example, a semi-open profile such as a trough. The material can be plastic, rubber, cellulose, ceramic, or another material transparent to THz radiation. According to the invention, geometric properties such as wall thickness, outer diameter, and inner diameter can be determined, as well as material properties such as a refractive index and / or the speed of light. Furthermore, defects in the object being measured, such as inclusions, air bubbles, and / or deformations of the interfaces, can be detected.

[0017] The object being measured can be continuously moved through the measuring chamber and measured continuously, particularly after its manufacture, e.g., after the extrusion of the strand. Changes, deviations, and any errors can be continuously detected, especially by comparing the measurement signals.

[0018] The method according to the invention provides for successive steps of a blank measurement or calibration measurement with an empty measuring space, i.e. without a recorded object being measured, and at least one subsequent object measurement.

[0019] The device according to the invention thus comprises at least one pair of THz transceivers, i.e., a first and a second THz transceiver, arranged opposite each other with a measuring chamber between them and a common optical measuring axis. At least the second transceiver can detect the radiation emitted by the first transceiver. The two THz transceivers are synchronized by a synchronizing device to determine propagation times and / or changes in propagation times at the various steps. The synchronizing device preferably ensures the temporal alignment of the times determined and / or set by the first and second THz transceivers. For this purpose, the synchronizing device outputs synchronization signals to the first and second transceivers so that identical or comparable times can be established.According to the invention, it is particularly recognized that comparability of the measurements is more important than determining an exact time, since systematic deviations can be eliminated when calculating the difference.

[0020] In the blank measurement, THz radiation is emitted from the first THz transceiver along the optical measurement axis through the empty measurement space to the second THz transceiver, and the blank propagation time through the measurement space is determined. Thus, no reflection of the emitted THz radiation occurs to return it to the transmitting transceiver.

[0021] In the step of measuring the total transit time, the measuring device remains unchanged from the blank measurement, while the object under test is moved through the measuring chamber. Thus, the first THz transceiver outputs the THz radiation along the optical measurement axis through the measuring chamber and through the object to the second THz transceiver, which in turn determines the transit time of the THz radiation. This allows for a precise comparison of the blank measurement and the measurement with the object under test, all while maintaining the same measuring device.

[0022] Furthermore, measurements of two wall transit times of the object under test are performed, in which, in particular, the wall region opposite the THz transceiver is measured in reflection. Thus, the first and second THz transceivers each emit THz radiation, which is reflected back at the interfaces of the wall region to the THz transceiver.

[0023] According to the invention, a somewhat more complex metrological implementation of the synchronization is provided, but this also offers several advantages. In particular, compared to the aforementioned WO 2016 / 139155 A1, measurements can be carried out in which the THz radiation does not pass through the wall areas multiple times.

[0024] Thus, when measuring the total transit time, the THz radiation traverses each of the two wall sections once. By measuring each wall section opposite or closer to the first wall section during the wall transit time measurements, it is not necessary for the THz radiation to first traverse an initial wall section to perform a separate measurement of the rear wall section. This allows for reliable measurement of pipes with higher soot content and / or in damp conditions, despite absorption by the materials.

[0025] The measurement of the total propagation time can be combined with one of the two wall propagation time measurements, so that the first THz transceiver transmits the radiation to the second THz transceiver and simultaneously determines the wall propagation time of the wall segment facing it. Thus, the measurement of the total propagation time can be performed in a single measurement step along with the measurement of one of the wall propagation times.

[0026] Thus, each of the two THz transceivers can measure the wall region facing it, i.e., the front and / or area in front of it, and in particular, measure the thickness of the wall region in front of it. This also enables a more precise measurement, unlike when measuring the rear wall region, since when measuring the rear wall region, the radiation must first pass through the wall region in front of the transceiver, and the beam reflected in the rear wall region must also return through the front wall region. When measuring the thickness of the rear wall region, there is always high absorption in the object being measured, which further weakens the relatively weak reflected radiation from interfaces. According to the invention, however, a strong signal can also be obtained when measuring the wall regions.

[0027] Thus, this measurement of the front wall area by each transceiver works in conjunction with the principle of direct transmission measurement in both blank and with the object being measured, since strong measurement signals can be determined in, for example, four measurements each, which can then be evaluated together. This allows the measuring device and evaluation to be adapted to these strong signals. The measurement of the total transit time and the measurement of the first or second wall transit time by the transceivers can each be performed simultaneously, i.e., in a single measurement step.

[0028] In the method according to the invention, the measurement of the first wall transit time by the first THz transceiver and the measurement of the second wall transit time by the second THz transceiver (4) are each carried out by measuring the front wall area located in front of the THz transceiver.

[0029] In the method according to the invention, the measurement of the total transit time and the measurement of the first or the second wall transit time can be carried out together and / or in a common measurement step.

[0030] In the method according to the invention, the object being measured can be fully measured in the measuring room by: at least one pair of THz transceivers reversing or rotating around the measurement space, or a static arrangement of several pairs of first and second THz transceivers arranged around the measurement space.

[0031] A further advantage lies in the symmetry of the setup, allowing both THz transceivers to perform the blank measurement reciprocally. This enables a comparison to correct for inequalities or for compensation, for example, by using an averaged value. Thus, both the blank measurement and the total propagation time measurement can be performed from both sides to, for example, validate and / or average the measurements. A reciprocal transmission measurement of the total propagation time can be combined with the two individual wall propagation time measurements.

[0032] Furthermore, compared to, for example, mirror formations, a more precise alignment of the THz transceivers is possible.

[0033] According to the invention, defects in the object being measured can also be reliably detected, with these defects being particularly noticeable in the signal strength and / or signal shape. Upon detection of a defect, the THz transceivers can subsequently be moved to the identified defect location for further or more precise measurements.

[0034] The steps of the method according to the invention can also be carried out in a different order and repeated as often as desired.

[0035] According to advantageous designs, a complete measurement of the object being measured is carried out by a static design with several pairs of transceivers, and / or by a non-static measurement in which one or more pairs of transceivers rotate around the measuring space or reverse, i.e. move back and forth.

[0036] A further advantage of the invention lies in the ability to create different beam shapes. The THz beam can generally be focused, for example, onto a symmetry axis of the pipe. According to an alternative and advantageous embodiment, a parallel THz beam is emitted, which offers several advantages. For instance, with a THz beam focused on the symmetry axis, there are already differences in the transit times of the individual partial beams due to different path lengths, which can be largely avoided when emitting parallel THz radiation. Furthermore, according to the invention, the measurement of wall transit times is preferably improved by the parallel radiation, since focusing on the symmetry axis leads to an inaccurate measurement of the wall area located in front of the symmetry axis. The parallel THz radiation also improves detection even when the pipe is not positioned precisely.Compared to training with a mirror, the influence of multiple reflections is also reduced.

[0037] The THz beam can be emitted in a two-dimensional parallel configuration, meaning it is not only parallel in one direction and linearly focused in the other, but preferably parallel in a two-dimensional cross-section. This enables a wide coverage of the area of ​​the object being measured, with advantageous data analysis.

[0038] The first and / or second THz transceiver may in particular have a radiation optic, especially with a converging lens, for aligning the emitted THz radiation and / or for receiving parallel THz radiation.

[0039] The measurement according to the invention can be used directly in a manufacturing process, e.g. extrusion process, to control the manufacturing parameters.

[0040] The THz radiation from the two transceivers can be in a frequency range of 10 GHz to 50 THz, e.g., 10 GHz or 20 GHz to 10 THz or 4 THz, e.g., 50 GHz to 4 THz or 50 GHz to 1 THz, particularly with frequency modulation, direct time-of-flight measurement, or pulsed radiation. Thus, the THz radiation can also be wholly or partially in the range of microwave or radar radiation.

[0041] The radiation emitted by the two THz transceivers can have the same frequencies in the measuring device and / or the method according to one embodiment. Identical THz transceivers and / or identical chips can be used, which is therefore cost-effective. This also allows, for example, averaging of the measured values.

[0042] As an alternative to using THz transceivers or measurements at the same frequencies, different and / or overlapping frequency ranges or frequency bands can also be used, representing, for example, different sub-ranges of a bandwidth. This allows the measurement signals from the first and second THz transceivers to be combined into a single evaluation signal, a fundamental frequency of which can then be determined, and subsequently, one or more layer thicknesses can be calculated.

[0043] The different and / or overlapping frequency ranges offer other advantages, such as the use of multi-frequency measurement methods to achieve higher resolution of distances along the beam axis, for example, higher resolution of layer thicknesses. Different and / or overlapping frequencies or frequency bands can be selected for the measurements, representing different sub-ranges of a bandwidth, so that the measurement signals are subsequently combined into an evaluation signal. From this, a fundamental frequency of the evaluation signal can preferably be determined in order to subsequently calculate one or more layer thicknesses. Such a method is described, for example, in WO2018202696A1; it enables very high resolution of layer thicknesses. According to the invention, the advantage can be achieved that, firstly, a more accurate measurement is obtained, and secondly, the two measurements can be separated from each other.Preferably, variable-frequency THz transceivers can be used, especially fully electronic THz transceivers where frequency changes, e.g., frequency modulation, are technically feasible. This allows the use of identical first and second THz transceivers, the frequency of which can be subsequently changed.

[0044] The synchronizing device can be designed according to alternative embodiments as a) a reference oscillator for direct output of the synchronization signal, b) as a synchronized trigger, and / or c) a network, e.g. a bus system, to which the two transceivers are connected.

[0045] The determination of layer thicknesses and / or material-specific properties is carried out by a control and measurement unit that receives the measurement signals from the THz transceivers and preferably controls the THz transceivers to initiate the steps. The control and measurement unit can also be configured separately, consisting of a control unit for outputting the control signals and a separate measurement unit.

[0046] The invention will be explained in more detail below with reference to one embodiment, as shown in the accompanying drawings. The drawings show: Fig. 1 a calibration measurement of a measuring device according to an embodiment of the invention with a frequency-time diagram and a signal-time-time diagram; Fig. 2 the measuring device during the subsequent measurement of the transit time in transmission through a test object, to determine the total transit time; Fig. 3 the measuring device made of Figure 1, 2when measuring the wall transit time of a first wall section; Fig. 4 the measuring device made of Figures 1 to 3 when measuring the wall transit time of a second wall area; Fig. 5 a measurement with defects in the object being measured; Fig. 6 a measuring device of an embodiment with several transceiver pairs; Fig. 7 a flowchart of a method according to the invention.

[0047] The Figures 1 to 4 Figure 2 shows a THz measuring device 2 in several, in particular successive, measurement steps. The THz measuring device 2 has a first THz transceiver 3 and a second THz transceiver 4, between which a measuring chamber 5 is formed. The two THz transceivers 3, 4 are arranged on a common optical measuring axis B, i.e., their optical measuring axes coincide. The two THz transceivers 3, 4 are advantageously identical and / or have the same or similar transceiver chip, i.e., with the same frequency.

[0048] The THz radiation 8 is advantageously emitted in parallel, i.e., not focused on a focal point. The two THz transceivers 3, 4 are arranged at a transceiver distance L, which thus determines the width of the measurement space 5.

[0049] Furthermore, a synchronizing device 6 is provided, which synchronizes the measurements of the two THz transceivers 3, 4 as described below. The two THz transceivers 3, 4 output their measurement signals M1, M2 to a detection device 20, whereby the synchronizing device 6 and the detection device 20 can also be integrated.

[0050] Figure 1 Figure 1 shows a calibration step for calibrating the THz measuring device 2. For this purpose, the first THz transceiver 3 sends THz radiation 8 or first THz radiation 8 along an optical measuring axis B through the measuring room 5 to the second THz transceiver 4.

[0051] According to the embodiment shown here, the THz radiation 8 is output as FMCW radiation (Frequency Modulated Continuous Wave), i.e., as frequency-modulated THz radiation, in which the frequency f or core frequency of the THz radiation 8 output by the first THz transceiver 3 is temporally modulated, in particular as a sawtooth waveform or ramp waveform. Thus, a measured frequency shift in the frequency-time diagram can be correlated with a temporal shift, i.e., a time delay due to the propagation time. Instead of a measurement using such frequency modulation, a direct propagation time measurement can also be provided; furthermore, pulsed radiation can also be used, which, for example, enables a larger bandwidth of the THz radiation 8.

[0052] According to Figure 1The THz radiation 8 thus traverses the transceiver distance L and is detected at the other end of the measurement chamber 5 with a calibration propagation time T_Empty. With the frequency modulation shown according to the frequency-time diagram f(t), the corresponding frequency shift is measured and converted into the calibration propagation time T_Empty. According to the lower signal propagation time diagram of the Figure 1 The second THz transceiver 4 thus detects a measurement peak MP_Leer at the time of T_Leer.

[0053] The calibration runtime T_Empty is mathematically derived from the transceiver distance L and the speed of light (radiation speed) v_Air of the THz radiation 8 in air, where this speed of light v_Air can be equated to the speed of light c in a vacuum to a good approximation. Somit ergibt sich T _ Leer = L / v _ Luft = L / c .

[0054] Measuring room 5 is therefore calibrated. The following steps will be carried out according to... Figure 2A transmission measurement of a tube 12, inserted as the test object, is performed. The THz measuring device 2 is not changed; in particular, the THz transceivers 3 and 4 are not adjusted relative to each other. The tube 12 is made of a material transparent to the THz radiation 8, especially plastic, but also rubber, paper, ceramic, or earthenware. Plastic generally has a refractive index n12, which depends on the exact composition and can, for example, be in the range of 1.5 to 2. In this case, n12 = c / v12, where v12 is the speed of light of the THz radiation in the material of the tube 12 and n12 is the refractive index of the material. Thus, significant signal delays and suitable measurement peaks can be achieved. Advantageously, the tube 12 is continuously conveyed along an axis of symmetry A, which in particular runs perpendicularly through the measurement plane shown.In particular, the axis of symmetry A can intersect orthogonally with the optical measurement axis B.

[0055] At the in Figure 2 In the measurement of the total transit time (transmission time) T_12 with the tube shown, the first THz transceiver 3 again outputs the THz transmit beam 8, which travels along the optical measurement axis B and initially strikes the front wall section 12a of the tube 12, passes through it, through the interior 12b of the tube 12, and subsequently through the rear, i.e., second, wall section 12c of the tube 12, then continues through the measurement chamber 5 and is detected by the second THz transceiver 4. Thus, the THz transmit beam 8 is first delayed by the front wall section 12a with the first wall thickness WD1 and subsequently by the second wall section WD2.

[0056] In the case of FMCW radiation, the following results according to Figure 2The middle diagram shows a corresponding frequency shift from which the propagation time T can be determined. Accordingly, the measurement signal or measurement peak MP12 is detected within the total propagation time T_12 and is therefore delayed by a total delay ΔT_12 = T_12 - T_Empty.

[0057] Thus, the total transit time T_12 is obtained by the sum of the transit times through the free, air-filled areas, i.e. the interior 12c and the lateral areas 5_1 and 5-2 of the measuring chamber 5 to the left and right of the tube, where these transit times in air can be summed as (L-WD1-WD2) / v_air, and the wall runtimes through the wall areas 12a, 12c, where these wall runtimes can be summed as (WD1+ WD2) / v12.

[0058] The total runtime T_12 is therefore calculated as T _ 12 = L − WD 1 − WD 2 / v _ Luft + WD 1 + WD 2 / v 12 = L − WD 1 − WD 2 / c + WD 1 + WD 2 / c / n 12

[0059] The following will be according to Figs. 3 and 4The two wall regions 12a and 12c are measured to determine their wall propagation delays. These measurements are preferably performed from both sides, so that the first transceiver 3 performs a single measurement of the wall region 12a that is in front of it, and correspondingly the second THz transceiver 4 performs a single measurement of the wall region 12c that is in front of it.

[0060] In particular, the measurement can be carried out according to Figure 3 basically, e.g., also with the measurement of the total runtime T_12 from Figure 2 They are combined by the first transceiver 3 emitting the THz radiation 8 during this measurement, so that the second THz transceiver 4 can receive it accordingly. Figure 2 It detects the reflected radiation and is also the first THz transceiver 3 to measure it. For clarity, however, the measurements are shown separately in the diagrams.

[0061] According to Figure 3The first THz transceiver 3 thus emits the THz radiation 8, which is partially reflected at the interfaces 14a and 14b of the front wall region 12a. In the front wall region 12a, the outer surface 14a therefore represents the first interface, and the inner surface 14b the second interface, at which the emitted THz radiation 8 is partially reflected. According to the frequency-time diagram and the signal-time diagram of the Figure 3 This is how the following is measured: An external reflection peak MP3-1 at a first reflection time T1_1 from the transceiver 3 to the outer surface 14a of the first wall area 12a and back, an internal reflection peak MP3-2 at a second reflection time T1_2 from the transceiver 3 to the inner surface 14b of the first wall area 12a and back, and by subtracting these measured values, i.e., reflection times, with subsequent division by a factor of 2, a first wall transit time T_WD1 is obtained. The determined difference of the measured values ​​initially represents twice the value of a simple wall runtime T_WD1 represents the wall runtime, so that the (simple) wall runtime can be determined by canceling by a factor of 2.

[0062] The following system of equations results for the first wall thickness WD1 and the first wall running time T_WD1 divided by the first wall thickness WD1: WD 1 = c / 2 n * T 1 _ 2 − T 1 _ 1 = c / 2 n T _ WD 1

[0063] According to Figure 4 The corresponding measurement of the second wall area 12c, i.e., in the figures the right wall area of ​​the tube 12, is carried out by the second THz transceiver 4.

[0064] Thus, the second wall thickness WD2 and the second (simple) wall run-time T_WD2 are calculated as follows: WD 2 = c / 2 n * T 2 _ 2 − T 2 _ 1 = c / 2 n T _ WD 2

[0065] The wall transit time measurements according to Figures 3 and 4 They are therefore equivalent or symmetrical, even if the distance of the outer surface 14a from the transceivers 3, 4 may be different; this is not taken into account in this calculation of the difference.

[0066] The in Figure 1 The calibration measurement or blank measurement shown can also be performed from both sides, i.e., from the first transceiver 3 through the empty measuring chamber to the second transceiver 4, and vice versa, from the second transceiver 4 through the measuring chamber 5 along the common optical measuring axis B to the first transceiver 3, e.g., with subsequent averaging, and / or to correct or compensate for the differences in the blank measurements from the two sides, in order to determine technical differences between transceivers 1 and 2, with which, in particular, a correction or compensation of the in Figure 4 The second wall transit time measurement shown can be performed.

[0067] In the calibration measurement of the Figure 1 and the measurement of the total runtime of the Figure 2 The two THz transceivers 3, 4 are synchronized by the synchronizing device 6 using the synchronizing signals S; in the individual measurements of the Figures 3 and 4 This is not necessary, since the THz transceivers 3, 4 each act as transceivers, i.e. transmitting and receiving devices, and thus directly determine the wall delays.

[0068] From the measurements according to Figures 1 to 4 This yields both the total transit time and the wall transit times of the two wall sections 12a, 12b, so that a system of equations can be carried out to determine the three unknown quantities, i.e. the first wall thickness WD1, the second wall thickness WD2, and also the refractive index n12 (or the speed of light v12 in the material of the tube 12) based on the following system of equations GL4: T _ 12 = L − WD 1 − WD 2 / v _ Luft + WD 1 + WD 2 / v 12 = L − WD 1 − WD 2 / c + WD 1 + WD 2 / c / n = L − WD 1 + WD 2 / c + WD 1 + WD 2 / c / n → n = T _ 12 * c − L + WD 1 + WD 2 / WD 1 + WD 2 → WD 1 = c / 2 n * T _ WD 1 → WD 2 = c / 2 n * T _ WD 2 T _ Leer = L / V _ Luft = L / c L = T _ Leer * c

[0069] The following are known: T_12 = Measured value from measurement with tube 12 T_Empty = Measured value from empty measurement L = Distance between transceivers C = Speed ​​of light

[0070] The unknowns here are unknown. WD1+WD2 = wall thickness 1 + wall thickness 2 = yn = refractive index of the pipe 12

[0071] GL4 can therefore be used in the inventive method and the inventive measuring device.

[0072] The calibration measurement of the Figure 1 This can be carried out in advance, before the pipe 12 is conveyed. Subsequently, the pipe 12 can be conveyed continuously along the axis of symmetry A and according to Figure 2 , 3 and 4 The two transceivers 3 and 4 can be measured. As already explained, measurements from, for example, Figure 2 and 3 can be combined. After completion of the survey of pipe 12, a blank measurement can again be carried out. Fig. 1 This should be carried out to check for deviations from the initial blank measurement.

[0073] Figure 5 Figure 1 shows the measurement of a pipe 12 with defects 16 in or on the pipe 12. The defects 16 can be, for example, cavities, i.e., air inclusions in the wall areas WD1, WD2, or foreign bodies. Furthermore, irregularities or structures can occur on the outer surface 14a or inner surface 14b, e.g., due to material burning.

[0074] According to the signal-time diagram of the Figure 5 This results - in comparison to the measurement of the total running time according to Figure 2 - in particular a change in the measurement signal or measurement peaks MP_12, especially in the intensity and / or shape. Thus, a qualitative or quantitative evaluation of the measurement signal MP_12 can be used to detect errors 16. When detecting such errors 16, a more detailed determination can subsequently be carried out, for example, by adjusting the THz transceivers 3, 4 to the corresponding digits or around the digits.

[0075] The measuring device 2 can be designed to be static or non-static. In a static arrangement, it is advantageous according to Fig. 7 Several pairs of transceivers 3, 4 are arranged opposite each other around the measuring chamber 5. The individual pairs of transceivers 3, 4 can also emit different THz radiation, e.g., with different polarization.

[0076] In a non-static arrangement, one or more pairs of THz transceivers 3, 4 can orbit the measuring space 5, i.e., rotate; furthermore, one or more pairs of THz transceivers 3, 4 can also reverse, i.e., pivot back and forth about the axis of symmetry A. Advantageously, the THz transceivers 3, 4 or the multiple pairs of THz transceivers are arranged on a common frame 7 for fixed mechanical coupling.

[0077] Figure 7 shows a flowchart of the procedure according to the described embodiment.

[0078] After starting in step STO of providing the measurement setup 1, the following will then be Figure 1 The calibration measurement shown, i.e., blank measurement in transmission, was performed according to step ST1 and the blank propagation time T_Blank was determined. As described above, the blank measurement or calibration measurement in transmission can also be performed from both sides, so that both transceivers 3, 4 transmit THz radiation 8 once and receive it once, for example to perform an averaging; furthermore, the synchronizing device 6 can also be corrected by such a comparison, if necessary.

[0079] In step ST2, the following will be done Figure 2The measurement of the total transit time T_12 shown was performed with pipe 12. According to step ST3, the measurement of the first wall transit time T_WD1 is carried out, and in step ST4, the measurement of the second wall transit time T_WD2 is performed. In the subsequent determination step ST5, the values ​​WD1, WD2, and n12 are thus continuously determined from the measurements according to the equation system described above. Furthermore, the values ​​determined in this way can also be continuously checked and compared with each other.

[0080] According to Figure 7 The process can therefore be reset to a point before step ST2, i.e., it can be carried out continuously.

[0081] As described above, the measurements can be taken after Figures 2 to 4 These can be combined. Furthermore, the sequence of measurement steps ST2, ST3, ST4 can be varied. Reference symbol list

[0082] 1 Measuring setup 2 THz measuring device 3 First THz transceiver 4 Second THz transceiver 5 Measuring room 6 Synchronizing device 8 THz radiation 10 Reference oscillator 12 Object under test, in particular a string, e.g., a pipe 12a First wall section 12b Interior of the object under test 12 12c Second wall section 16 Error 17 Frame of the THz measuring device 2 20 Detection device A) Axis of symmetry, in particular the central axis of the object being measured 12 B) Measurement axis L) Transceiver distance M1) First measurement signal of the first THz transceiver 3 M2) Second measurement signal M2 of the second THz transceiver 4 MP) Measurement peaks MP) Empty measurement peak of the calibration measurement n12) Refractive index of the material of the object being measured 12 S) Synchronization signal T_EmptyCalibrationRuntime, Empty Runtime according to Fig. 1 T_12 Total runtime with measured object according to Fig. 2 ΔT_12 Total delay as T-12 - T_Empty v_air Speed ​​of light (radiation speed) in air (approximately c) v12 Speed ​​of light (radiation speed) in the material of the object being measured 12 WD1 first wall thickness, wall thickness left WD2 second wall thickness, wall thickness right AD Outer diameter of the object being measured 12 ID Inner diameter of the object being measured 12 T1_1 First reflection time from transceiver 3 to the outer surface 14a of the first wall section 12a and back; MP1_1 Outer reflection peak corresponding to the first reflection time T1_1 from transceiver 3 to the outer surface 14a of the first wall section 12a and back; T1_2 Second reflection time from transceiver 3 to the inner surface 14b of the first wall section 12a and back; MP1_2 Inner reflection peak corresponding to the second reflection time T1_2 from transceiver 3 to the inner surface 14b of the first wall section 12a and back. T2_1 First reflection time from transceiver 4 to the outer surface 14a of the second wall area 12c and back; MP2_1 Outer reflection peak corresponding to the first reflection time T2_1 from transceiver 4 to the outer surface 14a of the second wall area 12c and back; T2_2 Second reflection time from transceiver 3 to the inner surface 14b of the second wall area 12c and back; MP2_2 Inner reflection peak corresponding to the second reflection time T2_2 from transceiver 4 to the inner surface 14b of the second wall area 12c and back T_WD1 first wall runtime. T_WD2 second wall runtime. ST1 Step of blank measurement, calibration measurement ST2 Step of total runtime measurement ST3 Step of first wall runtime measurement ST4 Step of second wall runtime measurement ST5 Step of determination and / or calculation

Claims

1. THz measuring device (2) for measuring a measuring object (12), said THz measuring (2) device comprising: a measuring space (5) for receiving a measuring object, a first THz transceiver (3) designed to emit THz radiation (8) through the measuring space (5) and to receive THz radiation (8) , a second THz transceiver (4) designed to emit THz radiation (8) through the measuring space (5) and to receive THz radiation (8) emitted by the first THz transceiver (3), wherein the two THz transceivers (3, 4) lie opposite one another and the measuring space (5) is formed between them, a synchronising means (6) designed to synchronise emission times and / or measuring times of the two transceivers and to synchronise at least an emission time of one of the transceivers (3, 4) with the measuring time of the other of the transceiver (3, 4) at least during an empty measurement and during a measurement of the total time of flight, a determination means (20) designed to receive a first measuring signal (M1)of the first THz transceiver (3) and a second measuring signal (M2) of the second THz transceiver (4) and to determine at least one layer thickness (WD1, WD2) and / or at least one layer property (n12, v12), which can be a refraction index (n12) of the material of the measuring object or a speed of light (v12) of the THz radiation in the material of the measuring object, said determination means (20) being designed to determine the layer thickness (WD1, WD2) and the at least one layer property (n12, v12) from the following measurements: - an empty measurement, wherein the first THz transceiver (3) puts out the THz radiation (8) through the empty measuring space (5) towards the second THz transceiver (4) and the second THz transceiver (4) measures an empty time of flight (T_Leer), - a measurement of the total time of flight, wherein the first THz transceiver (3) puts out the THz radiation (8) through the measuring space (5) and through the measuring object towards the second THz transceiver (4) and the second THz transceiver (4) measures a time of flight (T_12) with a measuring object, and - at least two wall area measurements (ST3, ST4), wherein the first and the second THz transceiver (3, 4) puts out THz radiation (8) and detects the THz radiation (8) reflected at interfaces (14a, 14b) of at least one wall area (12a, 12b), wherein the two transceivers 83, 4) are arranged opposite on a common optical measuring axis extending through the measuring space (5) and, further, are arranged and designed to emit the THz radiation (8) along the common optical measuring axis into or through measuring space (5), wherein the determination means (20) is designed to control - a first wall area measurement (ST3, ST4) by the first transceiver for measuring a first wall time of flight (T_WD1) and - a second wall area measurement (ST3, ST4) by the second transceiver for measuring a second wall time of flight (T_WD2), and wherein the determination means (20) is designed to determine the first wall thickness (WD1) of the first wall area (12a) and the second wall thickness (WD2) of the second wall area (12c) , wherein each of the two transceivers (3, 4) each carries out the wall area measurement of the wall area facing it and lying in front of it,2. THz measuring device (2) according to claim 1, characterised in that the synchronising means (6) is designed as one of the following means: a) a reference oscillator for putting out a reference signal, b) a synchronised trigger for putting out a synchronising signal, and / or c) a network to which the two transceivers are connected.

3. THz measuring device (2) according to one of the preceding claims, characterised in that the determination means (20) is adapted to perform the first and second wall thickness measurement (ST3, ST4) successively by the two transceivers (3, 4).

4. THz measuring device (2) according to claim 3, characterised in that each of the two transceivers each carries out the wall area measurement of the wall area facing it and lying in front of it in a measuring step together with the measurement of the total time of flight.

5. THz measuring device (2) according to one of the preceding claims, characterised in that the determination means (20) is designed to determine both at least one layer thickness, in particular, two wall thicknesses (WD1, WD2) of the measuring object (12), and the at least one material property (n12, v12), in particular, a refraction index (n12) and / or a speed of light (v12) of the THz radiation (8) in the material of the measuring object (12).

6. THz measuring device (2) according to one of the preceding claims, characterised in that the THz measuring device (2) is designed to continuously carry out the measurement (ST2) of the total time of flight (T_12) and the measurements (ST3, ST4) of the first and second wall times of flight, and the determination means (20) is designed to continuously determine, from continuous measuring values (M1, M2) of the total time of flight (T_ 12) and the wall times of flight (T_WD1, T_WD2), the at least one layer thickness (WD1, WD2) and / or the at least one material property (12, v12), in particular, with a measuring object (12) passing continuously through the measuring space (5).

7. THz measuring device (2) according to one of the preceding claims, characterised in that the THz transceivers (3, 4) are arranged statically around the common measuring space (5), in particular, as a plurality of pairs (3, 4) each consisting of a first THz transceiver (3) and a second THz transceiver (4).

8. THz measuring device (2) according to one of the claims 1 through 6, characterised in that at least one pair of THz transceivers (3, 4) is provided on a frame (7) adjustably, in particular, reversing around the measuring space (5) or revolving around the measuring space (5) or rotating, for measuring the entire circumference of the measuring object (12) in the measuring space (5).

9. THz measuring device (2) according to one of the preceding claims, characterised in that the first and / or second THz transceiver (3, 4) is designed to emit and / or receive the THz radiation (8) parallel along the optical measuring axis (B), in particular, in a two-dimensional parallel manner.

10. THz measuring device (2) according to one of the preceding claims, characterised in that the determination means (20) is designed to determine an exterior diameter (AD) and / or interior diameter (ID) of the measuring object (12).

11. THz measuring device (2) according to one of the preceding claims, characterised in that the determination means (20) is designed to determine a first wall thickness WD1, a second wall thickness WD2, and a refraction index n of the measuring object in accordance with: n = T _ 12 * c − L + WD 1 + WD 2 / WD 1 + WD 2 WD 1 = c / 2 n * T _ WD 1 WD 2 = c / 2 n * T _ WD 2 with L = T_Leer * c wherein WD1 = wall thickness 1 WD2 = wall thickness 2 n = refraction index of the pipe 12 T_12 = measuring value from the measurement with pipe 12 T_Leer = measuring value from empty measurement L = distance of the transceivers C = speed of light T_WD1= wall time of flight through the first wall thickness 1 (WD1) T_WD2 = wall time of flight through the second wall thickness 1 (WD2) (equation system GL4)12. Measuring arrangement, comprising: a THz measuring device (2) according to one of the preceding claims, and a measuring object (12) guided through the measuring space (5) of the THz measuring device (2), in particular, a profile (12), e.g. pipe (12) and / or rectangular profile and / or semi-open profile, e.g. curved trough.

13. THz measuring method for measuring a measuring object (12), including at least the following steps: - providing a THz measuring device (2) including at least one first THz transceiver (3), a second THz transceiver (4) arranged opposite of said first THz transceiver (3), whereby a measuring space (5) is formed between the two THz transceivers (Step ST0), - empty measurement, emitting THz radiation (8) from one of the two THz transceivers (3) through the empty measuring space (5) towards the other THz transceiver (4), detecting the THz radiation (8) by the other THz transceiver (4) and determining an empty time of flight (T_Leer) (Step ST1), - introducing a measuring object (12) into the measuring space (5), - measuring a total time of flight (T_12) emitting THz radiation (8) from one of the THz transceivers (3) through the measuring space (5) and the measuring object (12) towards the other THz transceiver (4) and detecting the THz radiation (8) by the other THz transceiver (4) and determining a time of flight (T_12) with a measuring object (12) (Step ST2), - emitting THz radiation (8) by the first THz transceiver (3) through the measuring space (5) towards a first wall area of the measuring object (12) and detecting the THz radiation (8) reflected off interfaces of the first wall area by the first THz transceiver (3) and determining a first wall time of flight (Step ST3), - emitting THz radiation (8) by the second THz transceiver (4) through the measuring space (5) towards a second wall area (12c) of the measuring object (12) and detecting the THz radiation (8) reflected off interfaces (14a, 14b) of the second wall area (12c) by the second THz transceiver (4) and determining a second wall time of flight (T_WD2), (Step ST4), - determining at least one layer thickness (WD1, WD2) and / or the at least one material property (n12, v12) by a determination means (20) designed to determine at least two layer thicknesses (WD1, WD2) and a layer property from the empty measurement (ST1), the measurement of the total time of flight (ST2), and the two measurements (ST3, ST4) of the first and second wall times of flight (T_WD1, T_WD2) (Step ST5), wherein the layer property is a refraction index (n12) of the material of the measuring object or a speed of light (v12) of the THz radiation in the material of the measuring object wherein the measurements (Step ST1, Step ST2, Step ST3, Step ST4) of the two THz transceivers (3, 4) are carried out on a common optical measuring axis (B) which extends through the measuring space (5) between the two THz transceivers (3, 4), wherein a emission time of one of the two transceivers (3, 4) is synchronized with the measuring time of the other transceiver (4, 3) at least during the empty measurement and the measurement of the total time of flight.

14. Method according to one of claim 13, characterised in that as measuring object (12) a strand, e.g. a pipe (12) or rectangular profile, is guided continuously through the measuring space (5), in particular, a single layer pipe or rectangular profile, and the wall thicknesses (WD1, WD2) and / or said at least one material property (n12, v12) are determined continuously, using said at least one common empty measurement.

15. Method according to one of claim 13 to 14, characterised in that the empty measurements (ST1) are carried out repeatedly anew, for correcting or for determining changes of the transceiver distance (L).

16. Method according to one of claim 13 to 15, characterised in that the empty measurement is carried out by both THz transceivers and subsequently a comparison and / or averaging is carried out.

17. Method according to one of claim 13 to 16, characterised in that a failure in the measuring object (12) is determined as an attenuation of the intensity of the signal amplitude and / or the signal shape of a measuring signal (M, M1, M2) in the measurement of the total time of flight (T_12) and / or in measurement of the first wall area (12a) and / or in the measurement of the second wall area (12c).

18. Method to one of claim 13 to 17, characterised in that the first THz transceiver (3) and the second THz transceiver (4) are using - equal frequencies, or - different and / or overlapping frequencies and / or frequency bands representing different partial regions of a band width, wherein, subsequently the measuring signals of the first THz transceiver (3) and the second THz transceiver (4) are combined to an evaluation signal, a fundamental frequency of the evaluation signal is determined, so as to subsequently carry out a calculation of one or more layer thicknesses.