Measuring system

Abstract

To provide a measuring system capable of removing instability of displacement measurement caused by distortion of a transmitter signal due to external factors such as a change of temperature, vibrations in a real thick plate line, and the like.SOLUTION: A measuring system includes a main device, a reference device and a determination part. The main device is provided with a signal generation part, a signal division part, a main antenna part, and a main data signal processing part. The signal generation part generates a modulation signal. The signal division part divides a generated signal. The main antenna part transmits / receives a first signal to / from an object to measure. The main data signal processing part performs processing using a first signal and a third signal. The reference device is provided with a delay part and a reference data signal processing part. The delay part causes the second signal delay. The reference data signal processing part performs processing using the second signal and a third signal. The determination part measures displacement of the object to measure on the basis of a result of processing in the main device and a result of processing in the reference device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a measurement system. [Background technology]

[0002] For example, thickness measurement on a rolling line requires precision on the order of several tens to several microns. Conventional thickness measurement devices irradiate the object to be measured with X-rays or gamma rays, allowing them to pass through. However, due to issues with environmental resistance and cost, thickness measurement using millimeter-wave radar, which is inexpensive and environmentally resistant, is being researched. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] German Patent Invention No. 102019101152 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-183450 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a method for detecting dents in a thick plate in thickness measurement using millimeter wave radar or laser.

[0005] However, Patent Document 1 does not mention the effects that phase noise and vibrations on an actual line have on measurement accuracy. The following two issues are thought to be major problems when measuring minute displacements with actual millimeter-wave radar.

[0006] The first is the effect of analog distortion (phase noise, temperature characteristics, etc.) of the reference signal source, and the second is the effect of vibrations in the surrounding installation environment and vibrations during operation (vibration cannot be completely eliminated even with vibration isolation measures).

[0007] These are problems specific to radars that use frequency modulation and phase modulation, and are caused by fluctuations in the excitation of the crystal in the radar's vibration generating section due to vibrations and temperature changes. As a result, problems arise such as instability in measuring minute displacements and the inability to measure for long periods of time.

[0008] Furthermore, Patent Document 2 discloses a method for reducing noise that leaks from a transmission signal into a reception signal, as a method for removing noise components in an FMCW radar.

[0009] However, Patent Document 2 does not pay attention to the noise components that are superimposed on the transmission signal itself.

[0010] As described above, conventional minute displacement measurements using millimeter-wave radar have had the problem that the results of displacement measurements fluctuate because the excitation of the crystalline lens fluctuates due to vibrations and temperature changes.

[0011] The problem to be solved by the present invention is to provide a measurement system that can eliminate instability in displacement measurement caused by distortion of the transmission signal due to external factors such as temperature changes and vibrations in an actual thick plate production line, etc. [Means for solving the problem]

[0012] According to an embodiment, a measurement system includes a main device, a reference device, and a determination unit. The main device includes a signal generation unit, a signal division unit, a main antenna unit, and a main data signal processing unit. The signal generation unit generates a phase-modulated or frequency-modulated signal. The signal division unit divides the signal generated by the signal generation unit into multiple signals including at least a first signal, a second signal, and a third signal. The main antenna unit transmits the first signal to the measurement object and receives the first signal from the measurement object. The main data signal processing unit performs signal processing using the first signal and the third signal transmitted and received by the main antenna unit. The reference device includes a delay unit and a reference data signal processing unit. The delay unit delays the second signal supplied from the main device. The reference data signal processing unit performs signal processing using the second signal delayed by the delay unit and the third signal. The determination unit measures the displacement of the measurement object based on the signal processing result of the main data signal processing unit output from the main device and the signal processing result of the reference data signal processing unit output from the reference device. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of a measurement system according to a first embodiment. [Figure 2] FIG. 2 is a circuit diagram of the radar system in the block diagram of FIG. 1. [Figure 3] FIG. 2 is a circuit diagram of a signal generating unit included in the measurement system of the first embodiment. [Figure 4] 5A and 5B are diagrams showing a method for determining a factor of variation that appears in the measurement result of the measurement object in the measurement system of the first embodiment. [Figure 5] FIG. 2 is a diagram showing an application example of the measurement system according to the first embodiment. [Figure 6] FIG. 3 is a circuit diagram of a radar system in which the delay unit of the reference device in the measurement system of the first embodiment is configured using a reference antenna unit. [Figure 7] FIG. 10 is a diagram showing a modified example of the installation of the reference antenna unit in the measurement system of the first embodiment. [Figure 8]FIG. 10 is a diagram showing a modified example in which the measurement system of the first embodiment is used to measure the change in thickness of a measurement object. [Figure 9] FIG. 10 is a circuit diagram of a radar system in which the delay section of the reference device in the measurement system of the second embodiment is configured using a delay element. [Figure 10] FIG. 10 is a diagram showing an application example of the measurement system according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments will be described with reference to the drawings.

[0015] (First embodiment) FIG. 1 is a block diagram showing an example of the configuration of a measurement system 10 according to the first embodiment.

[0016] The measurement system 10 is a system that measures the displacement of a measurement object using a millimeter wave radar. The measurement system 10 includes a main device 100, a reference device 110, an integrated judgment unit 120, and a display unit 130.

[0017] The main unit 100 measures the object to be measured using a millimeter-wave radar. More specifically, the main unit 100 transmits a phase-modulated or frequency-modulated signal to the object to be measured, receives a signal from the object to be measured, and measures the distance to the object to be measured.

[0018] The reference device 110 is configured so that the reference signal source of the main device 100 is shared as the reference signal source for its own device, and generates reference data (signals) from the measurement results of the main device 100 to reduce frequency fluctuations due to phase distortion and vibrations when signals are generated.

[0019] More specifically, the reference device 110 receives a signal identical to the signal transmitted by the main device 100 to the object to be measured, and adds a delay equivalent to the delay in the signal caused by the measurement (transmission and reception of the signal) of the object to be measured in the main device 100. Here, the "same degree of delay" means a delay that is roughly the same, but not completely identical. To add this delay, the reference device 110 has a delay unit 1210, which will be described later.

[0020] The integrated judgment unit 120 measures the displacement of the object to be measured based on the outputs of the main unit 100 and the reference unit 110. At this time, the integrated judgment unit 120 obtains the difference between the outputs of each unit, thereby reducing the phase distortion and frequency fluctuations due to vibrations when signals are generated from the measurement results.

[0021] Display unit 130 displays the measurement result of the displacement of the measurement object output from integrated judgment unit 120. The measurement result displayed on display unit 130 may be, for example, the amount of displacement, whether or not a displacement has occurred, or the distance to the measurement object.

[0022] The main device 100 includes a signal generating section 1000 , a signal dividing section 1100 , a main antenna section 1200 , and a main data signal processing section 1300 .

[0023] The signal generating section 1000 is a reference signal source shared by the main device 100 and the reference device 110, and generates a phase-modulated or frequency-modulated signal (transmission signal).

[0024] The signal dividing unit 1100 divides the signal generated by the signal generating unit 1000 into a first signal, a second signal, and a third signal. Of these three signals, the first signal is supplied to the main antenna unit 1200, and the second and third signals are supplied to the reference device 110.

[0025] Main antenna unit 1200 transmits the first signal supplied from signal splitting unit 1100 to the object to be measured. Main antenna unit 1200 also receives the first signal from the object to be measured that has been reflected by the object to be measured.

[0026] The main data signal processing unit 1300 performs signal processing using the first signal transmitted and received by the main antenna unit 1200 and the third signal supplied from the signal dividing unit 1100 that is not transmitted or received by the main antenna unit 1200. Specifically, the main data signal processing unit 1300 performs signal processing to calculate the distance from the main antenna unit 1200 to the object 1 to be measured.

[0027] On the other hand, the reference device 110 includes a delay unit 1210 and a reference data signal processing unit 1310 .

[0028] Delay unit 1210 adds a delay to the second signal supplied from signal dividing unit 1100 of main device 100, the delay being the same as the delay of the signal (first signal) generated by measuring the object to be measured (transmitting and receiving the signal) in main device 100. Details of adding a delay to the signal by delay unit 1210 will be described later.

[0029] The reference data signal processing unit 1310 performs signal processing using the second signal to which a delay has been added by the delay unit 1210 and the third signal supplied from the signal dividing unit 1100 to which no delay has been added by the delay unit 1210. Specifically, the reference data signal processing unit 1310 performs signal processing to calculate the distance from the reference antenna unit 1211 to the reference target 3.

[0030] FIG. 2 is a circuit diagram of a radar system included in the block diagram of the measurement system 10 shown in FIG.

[0031] As described above, the phase-modulated or frequency-modulated signal (transmission signal) generated by the signal generating unit 1000 is divided by the signal dividing unit 1100 into three signals: a first signal, a second signal, and a third signal.

[0032] The first signal is supplied to main antenna unit 1200. The first signal supplied to main antenna unit 1200 is transmitted from main antenna unit 1200 to the object to be measured, reflected by the object to be measured, and received by main antenna unit 1200. Due to this transmission and reception by main antenna unit 1200, a delay occurs in the first signal.

[0033] The second signal is supplied to delay section 1210. The second signal supplied to delay section 1210 is delayed by delay section 1210 by the same amount as the delay of the first signal.

[0034] The third signal is a signal that is not transmitted or received by main antenna unit 1200, and is a signal to which no delay has been added by delay unit 1210. The first signal transmitted or received by main antenna unit 1200 and the third signal, which is a signal to which no delay has been added by main antenna unit 1200, are mixed by mixer 1400. Furthermore, the second signal to which a delay has been added by delay unit 1210 and the third signal, which is a signal to which no delay has been added by delay unit 1210, are mixed by mixer 1410.

[0035] More specifically, a first beat signal is extracted from the first signal and the third signal in mixer 1400, and a second beat signal is extracted from the second signal and the third signal in mixer 1410. The first beat signal is supplied to main data signal processing unit 1300, and the second beat signal is supplied to reference data signal processing unit 1310.

[0036] The main data signal processing unit 1300 and the reference data signal processing unit 1310 each use the supplied beat signals (first beat signal, second beat signal) to perform signal processing to derive the distance to the measurement object. The processing results are supplied to the integrated determination unit 120.

[0037] The integrated determination unit 120 removes noise components observed in both the output of the main data signal processing unit 1300 and the output of the reference data signal processing unit 1310 from the output of the main data signal processing unit 1300, and outputs the result as the measurement result (distance) of the object to be measured. These noise components are frequency fluctuations caused by phase distortion and vibration when the signal is generated.

[0038] FIG. 3 is a circuit diagram of the signal generating section 1000. As shown in FIG.

[0039] Here, an example is shown in which signal generating section 1000 generates a phase-modulated signal using phase modulator 1001 and oscillator 1002. As shown in Fig. 3, the signal generated by signal generating section 1000 may contain fluctuations due to the influence of disturbance a1 such as vibration or temperature change.

[0040] FIG. 4 is a diagram showing a method for determining the cause of fluctuations that appear in the measurement results of the main device 100 in the measurement system 10 of the first embodiment.

[0041] In the first embodiment, when a fluctuation appears in the measurement results of the main device 100 due to the aforementioned disturbance a1, the measurement system 10 having the reference device 110 can correctly determine that the fluctuation is due to the disturbance a1 and that no displacement of the object to be measured has been detected, without erroneously determining that the fluctuation has been detected.

[0042] 4(A) shows an example in which the measurement results of the main device 100 and the reference device 110 are different, and a comparison of these results indicates that displacement of the object being measured has been detected. The vertical axis of the graph showing the measurement results of the main device 100 and the reference device 110 represents displacement, and the horizontal axis represents time. The vertical axis of the graph showing the determination results represents the amount of displacement, and the horizontal axis represents time.

[0043] Fig. 4(B) shows an example in which the measurement results of the main device 100 and the reference device 110 are the same, and a comparison of these results indicates that displacement of the object being measured has been detected. The fact that the measurement results of the main device 100 and the reference device 110 are the same means that noise components are commonly observed in both. The vertical and horizontal axes of each graph in Fig. 4(B) are the same as the vertical and horizontal axes of each graph in Fig. 4(A).

[0044] 5 is a diagram showing an application example of the measurement system 10 of the first embodiment. Here, an example is shown in which the measurement system 10 is applied as a system for detecting unevenness on the surface of a measurement object (thick plate) 1.

[0045] The object to be measured (thick plate) 1 is moving in the direction A on the thick plate line 2. The measurement system 10 is installed so that the main antenna unit 1200 transmits a first signal to the object to be measured (thick plate) 1 moving on the thick plate line 2, and the main antenna unit 1200 receives the first signal from the object to be measured (thick plate) 1 that is reflected by the object to be measured (thick plate) 1.

[0046] Furthermore, in the measurement system 10 of the first embodiment, the delay unit 1210 of the reference device 110 is configured with a reference target 3 and a reference antenna unit 1211 that transmits a second signal to the reference target 3 and receives the second signal from the reference target 3 that is reflected by the reference target 3. The distance from the reference antenna unit 1211 to the reference target 3 is set to be approximately the same as, but not completely equal to, the distance from the main antenna unit 1200 to the measurement object (thick plate) 1. As a result, during transmission and reception by the reference antenna unit 1211, a delay is added to the second signal that is approximately the same as, but not completely equal to, the delay that occurs in the first signal.

[0047] FIG. 6 is a circuit diagram of a radar system in which the delay unit 1210 of the reference device 110 is configured using a reference antenna unit 1211.

[0048] As described above, signal dividing unit 1100 divides the signal generated by signal generating unit 1000 into a first signal, a second signal, and a third signal. For this division, signal dividing unit 1100 includes distributor 1101.

[0049] As described above, the second signal is supplied from the signal dividing unit 1100 to the delay unit 1210. The second signal supplied to the delay unit 1210 is transmitted from the reference antenna unit 1211 to the reference target 3, reflected by the reference target 3, and received by the reference antenna unit 1211. Due to this transmission and reception by the reference antenna unit 1211, the delay unit 1210 adds a delay to the second signal that is approximately the same as the delay of the first signal.

[0050] The first signal transmitted and received by the main antenna unit 1200 and the second signal transmitted and received by the reference antenna unit 1211 are combined by the combiner 1430. The combined signal generated by the combiner 1430 is supplied to the mixers 1400 and 1410.

[0051] The mixer 1400 extracts a first beat signal from the first signal in the combined signal supplied from the combiner 1430 and the third signal supplied from the signal generating section 1000. The first beat signal extracted by the mixer 1400 is supplied to the main data signal processing section 1300.

[0052] The mixer 1410 extracts a second beat signal from the second signal in the combined signal supplied from the combiner 1430 and the third signal supplied from the signal generating section 1000. The second beat signal extracted by the mixer 1410 is supplied to the reference data signal processing section 1310.

[0053] Next, the signal processing performed by the main data signal processing unit 1300 and the reference data signal processing unit 1310 will be described in detail.

[0054] The transmission signal (chirp signal) generated by the signal generating section 1000 can be expressed by the following equation (1).

[0055]

number

[0056] where the starting frequency of the chirp signal is f c , bandwidth B, chirp time T c , and chirp slope S. Signal dividing unit 1100 divides this signal into a main transmission signal (first signal), a reference transmission signal (second signal), and a signal (third signal) to be used when receiving the first signal and a signal to be used when receiving the second signal.

[0057] A signal that can be received by main antenna section 1200 that transmits and receives the first signal can be expressed by the following equation (2), where d is the distance to object 1 to be measured.

[0058]

number

[0059] Here, A is a coefficient including the reflection coefficient and distance attenuation, and τ=2d / c, which is the time it takes from transmission to reception when the signal hits the object 1 to be measured, and c is high speed.

[0060] Furthermore, if the distance to the reference target 3 is d, the signal that can be received by the reference antenna unit 1211 that transmits and receives the second signal can also be expressed by equation (2).

[0061] Regarding equations (1) and (2), the intermediate frequency (IF) signals (first beat signal, second beat signal) obtained by mixing using frequency mixers (mixers 1400, 1410) and passing through low-pass filters are expressed by the following equation (3).

[0062]

number

[0063] The initial phase of this signal is 2πf c τ=Φ IF , frequency is Sτ=f IF is.

[0064] The main data signal processing unit 1300 and the reference data signal processing unit 1310 receive the IF signal shown in equation (3), perform frequency analysis on this signal to find the frequency, and calculate the distance based on this to estimate the distance. The signal obtained by AD converting this IF signal is expressed by the following equations (4) to (6).

[0065]

number

[0066] where ω IF =2πf IF , 0≦n <N s and the number of sampling points is N s , sampling frequency F s is.

[0067]

number

[0068]

number

[0069] The power spectrum of X(k) is (2π / N s )k-ω IF =0, the k that satisfies this is k r Then,

[0070]

number

[0071]

number

[0072] At a distance r0 from the radar, the amplitude ad m When a range FFT is performed on an object vibrating at (t) and the phase in the range bin is obtained, it is expressed by the following equation (9).

[0073]

number

[0074]

number

[0075] That is, the processing in the main data signal processing unit 1300 and the reference data signal processing unit 1310 can be expressed as follows.

[0076] 1. After AD conversion of the input IF signal, FFT is performed to obtain range bins. 2. Extract the phase information in the acquired range bin.

[0077] Next, the details of the processing performed by the integrated judgment unit 120 will be described.

[0078] The phase information of the measurement object 1 obtained by the main data signal processing unit 1300 of the main unit 100 and the phase information of the stationary reference target 3 obtained by the reference data signal processing unit 1310 of the reference unit 110 exhibit substantially the same phase fluctuations due to distortion caused by phase noise and vibrations. The integrated determination unit 120 subtracts the phase information of the reference unit 110 from the phase information of the main unit 100 to remove the common phase fluctuations and then extracts phase information without noise components.

[0079] In this way, by performing the signal generation, transmission / reception, and signal processing described above, the measurement system 10 of the first embodiment displays only measurement results with reduced phase fluctuations on the display unit 130 at low cost, enabling stable displacement measurement over long periods of time.

[0080] That is, the measurement system 10 of the first embodiment can eliminate instability in displacement measurement caused by distortion of the transmission signal due to external factors such as temperature changes and vibrations in an actual thick plate production line or the like.

[0081] 5 shows an example of the installation of the reference antenna unit 1211 and the reference target 3, in which the reference antenna unit 1211 is installed parallel to the main antenna unit 1200 in the direction of movement (direction A) of the measurement object 1. However, the reference antenna unit 1211 and the reference target 3 can be installed in various forms as long as they can be considered to be in the same environment as the main antenna unit 1200 and the measurement object 1. FIG. 7 shows a modified example of the installation of the reference antenna unit 1211 and the reference target 3.

[0082] 5 shows an example in which the measurement system 10 of the first embodiment measures the displacement of the front surface of the object to be measured 1 moving on the thick plate line 2. As shown in FIG. 8, by further adding the measurement system 10 of the first embodiment for the purpose of measuring the displacement of the back surface of the object to be measured 1 moving on the thick plate line 2, the measurement system 10 of the first embodiment can be used to measure the displacement of the thickness of the object to be measured 1 moving on the thick plate line 2.

[0083] (Second embodiment) Next, a second embodiment will be described.

[0084] In the measurement system 10 of the first embodiment, the delay unit 1210 is configured using a reference antenna unit 1211. Specifically, a signal is transmitted from the reference antenna unit 1211 to the reference target 3, and the signal from the reference target 3 is received by the reference antenna unit 1211, thereby generating a delay of the same degree as the delay generated by the main device 100 when measuring the displacement of the object to be measured 1 (a delay associated with transmission and reception of signals between the main antenna unit 1200 and the object to be measured 1).

[0085] In contrast, the measurement system 10 of the second embodiment generates a delay using a delay element instead of the reference antenna unit 1211. Fig. 9 is a circuit diagram of a radar system in which the delay unit 1210 of the reference device 110 in the measurement system 10 of the second embodiment is configured using a delay element 1214.

[0086] In the measurement system 10 of the second embodiment, the delay unit 1210 supplies the second signal from the distributor 1101 of the signal dividing unit 1100 to the delay element 1214, thereby generating a delay of the same degree as the delay (delay associated with transmission and reception of signals between the main antenna unit 1200 and the object to be measured 1) generated by the main device 100 when measuring the displacement of the object to be measured 1. As in the first embodiment, the same degree of delay here is a delay that is roughly the same but not exactly the same.

[0087] The first signal transmitted and received by the main antenna unit 1200 and the second signal to which a delay has been added by the delay element 1214 are combined by the combiner 1430. The combined signal generated by the combiner 1430 is supplied to the mixers 1400 and 1410.

[0088] Hereinafter, similarly to the measurement system 1 of the first embodiment, the mixer 1400 extracts a first beat signal from the first signal in the combined signal supplied from the combiner 1430 and the third signal supplied from the signal generating unit 1000. The mixer 1410 extracts a second beat signal from the second signal in the combined signal supplied from the combiner 1430 and the third signal supplied from the signal generating unit 1000.

[0089] In this way, even in the measurement system 10 of the second embodiment, which generates a delay using the delay element 1214, it is possible to eliminate instability in displacement measurement caused by distortion of the transmission signal due to external factors such as temperature changes and vibrations in an actual thick plate production line, etc.

[0090] 10 is a diagram showing an application example of the measurement system 10 of the second embodiment. Here, too, an example is shown in which the measurement system 10 is applied as a system for detecting unevenness of a measurement object (thick plate) 1.

[0091] As shown in Figure 10, the measurement system 10 of the second embodiment does not require the installation of a reference antenna unit 1211 and a reference target 3, and therefore can eliminate instability in displacement measurement caused by distortion of the transmission signal due to external factors such as temperature changes and vibrations in actual thick plate production lines, etc., at a lower cost.

[0092] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0093] 1...measurement object, 2...thick plate line, 3...reference target, 10...measurement system, 100...main device, 110...reference device, 120...integrated judgment unit, 130...display unit, 1000...signal generation unit, 1100...signal division unit, 1200...main antenna unit, 1210...delay unit, 1211...reference antenna unit, 1214...delay element, 1300...main data signal processing unit, 1310...reference data signal processing unit.

Claims

1. The main device, a reference device; a determination unit, The main device is a signal generating unit that generates a phase-modulated or frequency-modulated signal; a signal dividing unit that divides the signal generated by the signal generating unit into a plurality of signals including at least a first signal, a second signal, and a third signal; a main antenna unit that transmits the first signal to an object to be measured and receives the first signal from the object to be measured; a main data signal processing unit that performs signal processing using the first signal transmitted and received by the main antenna unit and the third signal, The reference device is a delay unit that delays the second signal supplied from the main device; a reference data signal processing unit that performs signal processing using the second signal delayed by the delay unit and the third signal, The determination unit measuring a displacement of the measurement object based on a signal processing result of the main data signal processing unit output from the main device and a signal processing result of the reference data signal processing unit output from the reference device; Measurement system.

2. 2. The measurement system according to claim 1, wherein the main data signal processing unit extracts a first beat signal using the first signal and the third signal transmitted and received by the main antenna unit, and calculates frequency characteristics by spectrum analysis.

3. The delay unit A reference antenna portion is provided. transmitting the second signal from the reference antenna unit to a reference target different from the object to be measured, and receiving the second signal from the reference target by the reference antenna unit, thereby giving a delay to the second signal; The measurement system of claim 1 .

4. The measurement system according to claim 3 , wherein the distance between the reference antenna unit and the reference target differs from the distance between the main antenna unit and the object to be measured by a difference within a predetermined range.

5. The delay unit a delay element; using the delay element to impart a delay to the second signal; The measurement system of claim 1 .

6. The measurement system of claim 5, wherein the amount of delay imparted to the second signal by the delay element differs within a predetermined range from the amount of delay caused in the first signal by transmission and reception at the main antenna section in the main device.

7. 2. The measurement system according to claim 1, wherein the reference data signal processing unit extracts a second beat signal using the second signal delayed by the delay unit and the third signal, and calculates frequency characteristics by spectrum analysis.

8. 2. The measurement system according to claim 1, wherein the determination unit reduces the influence of analog distortion or vibration on the measurement result of the displacement of the object to be measured by obtaining a difference between the signal processing result of the main data signal processing unit output from the main device and the signal processing result of the reference data signal processing unit output from the reference device.

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