WO2019097761A1

WO2019097761A1 - Sensor measurement device

Info

Publication number: WO2019097761A1
Application number: PCT/JP2018/026578
Authority: WO
Inventors: 成亘小松; 礒部　敦; 優小久保; 山脇　大造; 中村　洋平
Original assignee: 日立金属株式会社
Priority date: 2017-11-15
Filing date: 2018-07-13
Publication date: 2019-05-23
Also published as: JP2019090691A

Abstract

In order to expand the delay detection range of a SAW sensor and to prevent degradation of sensitivity, the sensor measurement device is provided with: a phase comparator 21 which measures the phase difference between a reference signal and the output signal of a SAW sensor element 11; an oscillator 26 which can vary the frequency of the generated signal; a delay device 25 which can change the delay difference between the SAW sensor element and the reference signal; and a control unit 23 which controls the oscillation frequency of the oscillator, adjusts the delay amount of the delay device such that the phase difference between the reference signal and the output signal of the SAW sensor element becomes constant, and calculates the propagation delay amount of the SAW sensor from the delay amount of the delay device to calculate the physical quantity to be detected.

Description

Sensor measurement device

The present invention relates to a sensor measurement apparatus, and more particularly to a measurement apparatus using a surface acoustic wave sensor.

Surface acoustic wave sensors (SAW sensors) are known as detection sensors for various physical quantities, such as liquid sensors and temperature sensors. The SAW sensor changes the delay time in which the surface acoustic wave propagates according to the change in the physical quantity to be detected, and detects the change in the delay time to detect the change in the target physical quantity. As a method of detecting the delay amount, there is known a method of detecting a phase difference with a reference signal with a phase detector. This method can be implemented in a circuit with a smaller area than a method using TDC (Time to Digital Converter). However, since the phase detector can not distinguish the delay time exceeding one cycle of the frequency, the frequency of the propagation signal, that is, the range of the delay time that can be measured by the cycle is limited. Therefore, in order to expand the measurement range of the delay time, a technique for measuring a phase difference when the frequency is changed has been proposed (Patent Document 1).

JP, 2014-20841, A

According to the study of the inventors, it has been found that the sensitivity of the conventional SAW sensor is deteriorated as the detection range of delay is extended. However, Patent Document 1 does not mention a solution to the deterioration in sensitivity accompanying the extension of the detection range of the delay of the SAW sensor.

Therefore, an object of the present invention is to provide a sensor measurement device capable of extending the delay detection range of the SAW sensor and preventing the deterioration of the sensitivity.

In order to solve the above-mentioned problems, in a preferred embodiment according to the present invention, a phase difference between an output signal of the SAW sensor and a SAW sensor with respect to a reference signal is detected. A phase comparator, an oscillator generating an input signal of the SAW sensor and the reference signal, an oscillator having a variable oscillation frequency, a delayer capable of adjusting a delay difference between the input signal of the SAW sensor and the reference signal; Controlling the oscillation frequency of the oscillator, and controlling the delay amount of the delay device such that the phase difference between the output signal of the SAW sensor and the reference signal becomes constant, and based on the delay amount of the delay device, And a control unit configured to calculate a propagation delay amount and calculate a physical quantity to be detected.

According to the present invention, it is possible to expand the delay detection range of the SAW sensor of the sensor measurement device and prevent the deterioration of the sensitivity.

FIG. 1 is a block diagram of a surface acoustic wave sensor measurement device according to a first embodiment. FIG. 6 is a flowchart showing the processing operation of the surface acoustic wave sensor measurement device according to the first embodiment. FIG. 5 is a waveform chart of the surface acoustic wave sensor measurement device of the first embodiment. FIG. 5 is a waveform chart of the surface acoustic wave sensor measurement device of the first embodiment. FIG. 5 is a waveform chart of the surface acoustic wave sensor measurement device of the first embodiment. FIG. 5 is a waveform chart of the surface acoustic wave sensor measurement device of the first embodiment. FIG. 6 is a diagram showing an example of a circuit of a phase comparator 21 according to a second embodiment. FIG. 7 is a diagram showing an output example of the phase comparator 21 of the second embodiment. FIG. 7 is a flowchart showing the processing operation of the surface acoustic wave sensor measurement device of the second embodiment. FIG. 10 is a block diagram of a surface acoustic wave sensor measurement device according to a third embodiment. FIG. 16 is a block diagram of a surface acoustic wave sensor measurement device according to a fourth embodiment. FIG. 16 is a block diagram of a surface acoustic wave sensor measurement device according to a fifth embodiment. FIG. 16 is a block diagram of a surface acoustic wave sensor measurement device according to a sixth embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
The surface acoustic wave sensor measurement apparatus according to the following embodiment is an example using a PM sensor that measures, for example, fine particles (PM) in exhaust gas of a car.

FIG. 1 is a block diagram showing an example of a surface acoustic wave sensor measurement apparatus.
The surface acoustic wave sensor measurement apparatus is configured to include a SAW sensor 1 and a sensor control circuit 2. The output of the surface acoustic wave sensor measurement device is provided to an ECU (Electronic Control Unit) 3 and used to control an engine, other electronic devices, and the like.

The SAW sensor 1 has a SAW sensor element (hereinafter simply referred to as a sensor element) 11 in which the amount of delay of the propagation signal changes as PM adheres to the sensing portion, and the amount of delay of the propagation signal does not change due to PM adhesion. A SAW reference element (hereinafter simply referred to as a reference element) 12 for canceling the influence of manufacturing variations, and a heater 40 for burning PM attached to the surface of the sensor element 11 for refreshing the sensor element 11 are provided.

The sensor control circuit 2 compares the phase difference between the output signal 13 of the sensor element 11 and the output signal 15 of the reference element 12, and the analog digital signal converts the output voltage signal 27 of the phase comparator 21 into a digital value. A converter (ADC) 22, a micro control unit (MCU: Micro Control Unit) 23 that performs data processing of the output signal 28 of the ADC 22 and control processing of other circuits (for example, voltage generation circuit 39 etc.) 29, an input / output circuit (I / O) 24 for converting an output signal 37 to the ECU 3 and an input signal 38 to the ECU 3, and an oscillator (OSC) 26 for generating an input signal 18 to the sensor element 11. And a desired delay amount can be set to the input signal 18 to the sensor element 11 and the input signal 19 to the reference element 12 A delay unit (DELAY) 25, having a voltage generation circuit (VGEN) 39 for generating a voltage applied to the heater 40 by the control signal 41 from MCU23. The MCU 23 outputs a control signal 31 for setting the oscillation frequency of the oscillator 26, a control signal 32 for setting the delay amount of the delay unit 25, and a control signal 41 for controlling the voltage generation circuit 39. Further, reference numeral 14 denotes a GND (ground) output signal from the sensor element 11, 16 denotes a GND output signal from the reference element 12, and 17 denotes a GND input signal to the sensor element 11 and the reference element 12.

The MCU 23 controls the oscillation frequency of the oscillator 26 and controls the delay amount of the delay 25 so that the phase difference between the output signal of the sensor element 11 and the reference signal becomes constant. Then, the difference between the propagation delay amount of the sensor element 11 and the propagation delay amount of the reference element 12 is obtained from the delay amount of the delay device 25 to calculate the physical quantity (PM concentration) of the detection target. The processing operation of the MCU 23 will be described later in detail with reference to the flowchart. Here, the MCU 23 realizes a predetermined function or operation by executing a microprogram, and may be referred to as an arithmetic processing unit, a processing unit, or a control unit (in the claims, a control unit It is called).

FIG. 2 shows the processing operation by the MCU 23.
The MCU 23 controls the phase difference of each frequency and the difference of the phase difference to be 0 degree.
First, the frequency of the oscillator 26 is set to f1 (S201), and the phase difference Δφ1 of the output signals of the sensor element 11 and the reference element 12 is measured (S202). Next, the frequency of the oscillator 26 is set to f2 (S203), and the output signal Δφ2 of the sensor element 11 and the reference element 12 is measured (S204). Next, a phase difference Δφ 1 −Δφ 2 between Δφ 1 and Δφ 2 is calculated (S 205).

Here, when one of the outputs of Δφ 1 and Δφ 2 changes from 360 degrees to 0 degrees, a shift of 360 degrees occurs, so it is necessary to correct the value of Δφ 1 −Δφ 2. If the delay amount of the SAW sensor is determined to be used within the range of -180 degrees to -180 degrees (S206), then if 360 degrees is subtracted if -φ1-Δφ2> 180 degrees (S221, S222), Δφ1 If -.DELTA..phi.2 <180.degree., Adding 360.degree. (S223) enables desired correction. A value Δφ12 obtained by correcting the phase difference difference Δφ1-Δφ2 is determined (S207, S222, S223). If Δφ12 is 0 or more (S208: YES), the delay amount of the delay unit 25 is increased (S209), Δφ12 is If smaller than 0 (S208: NO), the delay amount of the delay unit 25 is reduced (S231).

If .DELTA..phi.12 and .DELTA..phi.1 and .DELTA..phi.2 fall within the range below the threshold values Pth12, Pth1 and Pth2 due to the increase and decrease of the delay amount of the delay unit 25 (S210: YES), it is determined that the feedback is stable. Then, the MCU 23 calculates the delay amount of the sensor element 11 from the delay amount of the delay of the delay device 25, that is, the set value of the delay, and calculates the adhesion amount of PM from the delay amount of the sensor element 11 (S211). The PM concentration in the exhaust gas is calculated from the time change of the adhesion amount of PM, and is output to the ECU 3.

Thereafter, the MCU 23 determines whether the delay amount of the delay unit 25 exceeds a prescribed value (S212). As a result of the determination, if the delay amount does not exceed the specified value (S212: NO), the process returns to the beginning. On the other hand, if the delay amount exceeds the specified value (S212: YES), the sensor element 11 is heated by the heater 40 to burn PM adhering to the surface of the sensor element 11 (S213) Refresh to the state that you are not doing. Thereafter, the delay amount of the delay unit 25 is reset to 0 (S214), and the process returns to the beginning.

3A to 3D are waveforms showing the relationship between the delay amount and the phase difference and the difference between the phase differences when the delay difference between the sensor element 11 and the reference element 12 is 100 ns, the frequency f1 is 100 MHz, and f2 is 101 MHz. FIG. The horizontal axis is a time axis, but it is a value dependent on the feedback time of control, and the absolute value is not important. FIG. 3A shows the time change of the phase difference Δφ 1 of the output signals of the sensor element 11 and the reference element 12 when the frequency is 100 MHz and the phase difference Δφ 2 when the frequency is 101 MHz. FIG. 3B shows the time change of the difference between Δφ1 and Δφ2. FIG. 3C shows a correction value Δφ12 corrected about the phase of Δφ1 and Δφ2. FIG. 3D shows the change of the delay amount of the delay unit 25.

When the delay amount of the delay device becomes equal to the delay difference 100 ns between the sensor element 11 and the reference element 12, the correction value of the phase difference difference in FIG. 3C becomes zero. Moreover, although the phase difference of FIG. 3A rotates many times more than 360 degrees with the increase of delay amount, the correction value of the difference of the phase difference of FIG. 3C is settled between -180 degrees to 180 degrees. . If the difference of the phase difference in FIG. 3C is positive, the delay amount of the delay is increased. If the difference is negative, the delay amount of the delay is equal to the difference of the phase difference. It becomes stable at the point which becomes 0. Further, since the difference in phase difference is zero, the delay amount of the delay unit is equal to the delay difference between the SAW sensor element and the SAW reference element.
By measuring the difference of the phase difference when the frequency is changed in this way, the delay measurement range can be expanded. Moreover, since the feedback control is performed on the delay device to variably control the delay amount of the delay device each time to calculate the PM adhesion amount, it is possible to prevent the deterioration of the sensitivity.

An example of the circuit configuration of the phase comparator 21 according to the second embodiment is shown in FIG.
The phase comparator 21 mainly includes a comparator 43, a comparator 44, an XOR (exclusive OR gate) 45, and a low pass filter 46.

The operation of the phase comparator 21 will be described. First, the output signal 13 of the sensor element 11 and the output signal 15 of the reference element 12 are converted by the

comparators

43 and 44 into digital signals that oscillate from low level to high level. The comparison reference signal 47 of the comparator is set to the center value of the amplitudes of the input signals 13 and 15. The

signals

48 and 49 converted to digital signals by the

comparators

43 and 44 are input to the XOR 45. The output signal 50 of the XOR 45 outputs a pulse signal having a width proportional to the phase shift of the input signals 48 and 49 of the XOR 45. When this pulse signal is converted to a DC voltage by the low pass filter 46, the ratio of the pulse width to one cycle is converted to a voltage ratio.

The relationship between the phase difference and the output voltage of the output signal 27 of the low pass filter is shown in FIG. The graph of FIG. 5 shows the case where the low level is 0V and the high level is 5V. When the phase shift is 0 degrees, the combination of the XOR 45 input signals 48 and 49 is always low and low or high and high, and the output of XOR 45 is always low. When the phase difference is 180 degrees, the combination of input signals 48 and 49 is always high and low, or low and high, the output of XOR 45 is maximum at high, and when the phase difference is 360 degrees, it is also low level It becomes. In the graph of FIG. 5, it can be seen that the slope of the voltage change with respect to the phase difference decreases near 0 degrees, 180 degrees, and 360 degrees.

This is because the pulse width is shorter than the transition time when the output signal of the XOR 45 transitions from high to low or low to high, and the pulse does not reach the high level completely from the low level, and the response time of the XOR circuit 45 By seeing. If control is performed such that the phase difference is always 0 degree in the phase comparator 21 having such characteristics, the position where the sensitivity of the phase shifter is bad is always used. On the other hand, in order to avoid use of a portion with poor sensitivity of the phase comparator, the phase difference of the convergence point may be set to other than 0 degree. If it is the phase comparator 21 of the characteristic of the graph of FIG. 5, control should be performed so that the phase difference becomes constant at 90 degrees while avoiding 0 degrees and 180 degrees 360 degrees.

FIG. 6 shows the processing operation of the MCU 23.
The MCU 23 first sets the frequency of the oscillator 26 to f1 (Hz) (S601), and measures the phase difference Δφ1 between the sensor element 11 and the reference element 12 (S602). Next, the delay amount of the delay unit 25 is increased until the difference (that is, the absolute value of (.DELTA..phi.1-90.degree.) With respect to 90.degree. Of .DELTA..phi.1 approaches the error Pth1 'or less (S603, S621).

When the MCU 23 determines that the difference with respect to 90 degrees of .DELTA..phi.1 becomes equal to or less than the error Pth1 '(S603: YES), the frequency of the oscillator 26 is set to f2 (S604), and the sensor element 11 and the reference element 12 are positioned. The phase difference Δφ2 is measured (S605). Then, the difference Δφ12 between Δφ1 and Δφ2 is calculated (S606).

In the second embodiment, a delay amount in which Δφ12 only changes to a range of ± 90 degrees is assumed, and Δφ1 is adjusted to 90 degrees and then Δφ2 is measured. Therefore, one of the outputs of Δφ1 and Δφ2 is Since the change from 360 degrees to 0 degrees (around phase) does not occur, the correction of adding or subtracting 360 degrees to Δφ 12 performed in the first embodiment is not performed. Therefore, it is determined whether the absolute value of Δφ12 is smaller than the specified value Pth12 '(S607). As a result of the judgment, when the absolute value of Δφ12 is smaller than the prescribed value Pth12 ′, the delay amount obtained by subtracting the delay amount corresponding to the phase 90 degrees of the frequency f1 from the delay amount of the delay device 25 The amount of deposition of PM is calculated from the difference in delay (S608).

On the other hand, if Δφ12 is larger than the prescribed value Pth12 ′ (S607: NO), if Δφ12 is positive (S622: NO), the delay amount of the delay unit 25 is reduced (S624), and if negative (S622: YES) Is increased (S623). The specified value Pth12 'is a value such that the delay difference between the sensor element 11 and the reference element 12 is equal to or less than one cycle of the frequency f1. Thereafter, the process returns to S602, and adjustment of the delay is repeated until the difference Δφ12 of the phase difference whose frequency is changed becomes smaller than the specified value Pth12 '. Then, when the absolute value of Δφ12 becomes smaller than the prescribed value Pth12 '(S607: YES), the delay amount obtained by subtracting the delay amount for the phase difference 90 degrees of the frequency f1 from the delay amount of the delay unit 25 becomes the sensor element 11 and the reference element Since the delay difference of 12 is obtained, the adhesion amount of PM is calculated from this delay difference (S 608). Delay adjustment amounts dp12 and dm12 when the absolute value of Δφ12 is larger than Pth12 ′ are points shifted by one cycle when adjusting to a phase difference of 90 degrees at the frequency of f1, that is, 90 degrees + 360 degrees or 90 degrees-360 degrees Is a delay amount that can be converged to

Thereafter, the MCU 23 determines whether the delay amount of the delay unit 25 exceeds a prescribed value (S609). As a result of the determination, if the delay amount does not exceed the specified value (S609: NO), the process returns to the beginning. On the other hand, if the delay amount exceeds the specified value (S 609: YES), the sensor element 11 is heated by the heater 40 to burn PM adhering to the surface of the sensor element 11 (S 610). Refresh to the state that you are not doing. Thereafter, the delay amount of the delay unit 25 is reset to 0 (S214), and the process returns to the beginning.

According to the second embodiment, even when the phase comparator 21 has the sensitivity difference due to the phase difference, the change of the delay amount of the SAW sensor is accurately measured by applying feedback so as to obtain the phase difference with good sensitivity. Can. In the second embodiment, a phase comparator using XOR 45 is taken as an example of the phase comparator 21. However, the present invention is not limited to XOR, and can be realized using other phase comparators of different systems.

If the phase difference to be adjusted as a constant value is made closer to 180 degrees, it is possible to expand the measurement range of Δφ12 to a range close to ± 180 degrees and not perform correction about the phase of Δφ12.

FIG. 7 shows a block diagram of the surface acoustic wave sensor measurement device according to the third embodiment.
The third embodiment has a delay reference circuit 51 added to the first embodiment. The delay unit 25 is formed by connecting a plurality of delay elements such as inverters, for example, and the delay reference circuit 51 uses a ring oscillator formed of the same delay elements as the delay elements constituting the delay unit 25. The delay reference circuit 51 outputs a signal 55 which is an oscillation signal, and the output signal 55 is sent to the MCU 23. The MCU 23 corrects the amount of delay of the delay reference circuit 51 when calculating the amount of propagation delay of the SAW sensor from the amount of delay of the delay device 25. That is, the MCU 23 calculates the change in the delay amount of the delay reference circuit 51 by counting the number of oscillations within the fixed time of the delay reference circuit 51, and based on the change in the delay amount, It is possible to correct the change in delay amount. This can reduce the effects of temperature and manufacturing variations. Further, the delay reference circuit 51 only needs to have the same delay change ratio with respect to the temperature of the delay device 25 and manufacturing variations, so the number of delay elements constituting the delay reference circuit 51 can be reduced compared to the delay device 25. The area overhead of the delay reference circuit 51 can be suppressed.

FIG. 8 is a block diagram of a surface acoustic wave sensor measurement device according to a fourth embodiment.
The fourth embodiment has a voltage generation circuit 52 added to the third embodiment. Further, in the fourth embodiment, the delay unit 25 uses a delay element whose delay amount is changed by the output voltage signal 54 of the voltage generation circuit 52. Reference numeral 53 denotes a voltage control signal supplied from the MCU 23 to the voltage generation circuit 52. The delay amount of the delay can be changed by voltage control. Furthermore, it is possible to change the delay amount of the delay by switching the number of stages of the delay element. By using the former and the latter, since the delay amount can be continuously changed by voltage control while the delay amount is switched over a wide range by switching the number of stages of delay elements, fine adjustment is also possible. In addition, the maximum value of the delay amount can also be increased by the smaller number of delay element stages.

In the fifth embodiment, the MCU 23 calculates the delay amount due to the change of the frequency only at the time of startup and immediately after the PM attached to the sensor by the heater 40 is burned. As shown in FIG. 9, in the fifth embodiment, a power on reset circuit 56 and a counter 57 for counting the number of times the phase of the phase shifter has been turned are added to the first embodiment. The power on reset circuit 56 generates a power on reset signal 58 when the sensor control circuit 2 is powered on. The counter 57 functions as storage means for storing how many times the phase difference of the phase comparator 21 has been turned. A signal 60 is a signal for the MCU 23 to set the count number of the counter 57, and a signal 59 is a signal for the counter 59 to read the counter number of the counter 57.

Next, the processing operation of the MCU 23 will be described.
The MCU 23 receives the power on reset signal 58 from the power on reset circuit 56 when the power is turned on. When the MCU 23 receives the power-on reset signal 58 or after burning PM attached to the sensor element 11 by the heater 40 (this state is referred to as state 1), the frequencies of the oscillator 26 are set to f1 and f2 as an initial operation. Change and find the difference of the phase difference in the case of the change. And MCU23 calculates | requires the delay difference of the sensor element 11 and the reference element 12 from the difference of the phase difference, and calculates the delay difference the multiple of the period of f1. The calculated multiple is set in the counter 57 as the count number. For example, if the delay difference is 770 degrees converted to the period of f1, since 770 degrees = 2 × 360 degrees + 50 degrees, the count number is “2”.

After the completion of the initial operation (this time is referred to as state 2), the MCU 23 fixes the frequency to f1 (makes a constant value) and detects the phase difference between the sensor element 11 and the reference element 12. If the phase difference is a position where the sensitivity of the phase comparator 21 is poor, the delay 25 shifts the delay by 90 degrees of the period of f1 so that the range of sensitivity of the phase comparator 21 is used. Every time the phase of the phase comparator 21 rotates 360 degrees, the count number of the counter 57 is reflected. The MCU 23 calculates the PM deposition amount of the sensor element 11 by obtaining the absolute value of the delay difference between the sensor element 11 and the reference element 12 based on the count number of the counter 57 and the phase difference of the phase comparator 21. The MCU 23 can obtain the PM concentration from the time change of the PM adhesion amount of the sensor element 11 and can finally output it to the ECU 3.

Although the power on reset circuit 56 and the counter 57 are added as hardware circuits in the example shown in FIG. 9, these functions can also be realized as functions by execution of a program by the MCU 23.

According to the fifth embodiment, it is possible to improve the response and reduce the control load of the MCU by omitting the control of the frequency change in the normal operation. The reduction in control load of the MCU results in lower power. In addition, when mounting an MCU with a custom IC, it is possible to reduce the area, and when using discrete MCUs, it is possible to select a low-performance low-cost product, resulting in cost reduction.

As shown in FIG. 10, in the sixth embodiment, the nonvolatile memory 61 in which the data is not erased even if the power is shut off is added to the first embodiment as a storage unit. Further, the control signal 31 (Example 1) for changing the frequency of the oscillator 26 is deleted. The non-volatile memory 61 stores the number of times the phase of the phase comparator 21 rotates 360 degrees or more at the start of use or after the combustion of PM attached to the sensor element 11 by the heater 40. The MCU 23 calculates the absolute value of the delay difference between the sensor element 11 and the reference element 12 from the phase difference detected by the phase comparator 21 and the value stored in the non-volatile memory 61. This eliminates the need for control of frequency change, and enables speeding up of the response of the sensor and cost reduction by simplification of the circuit. Moreover, the phase difference immediately after burning PM attached to the sensor element 11 by the heater 40 is recorded, and the combustion of PM by the heater 40 is incomplete by subtracting it as an offset when obtaining the delay difference thereafter. It is possible to prevent an increase in errors due to deposits or deposits after PM combustion.

As described above, according to some preferred embodiments of the present invention, it is possible to perform PM measurement with high sensitivity while extending the delay detection range of the SAW sensor. As a result, the sensor measurement device can be realized with a small scale circuit and at low cost.

1: SAW sensor 2: sensor control circuit 3: ECU
11: SAW sensor element 12: SAW reference element 21: phase comparator 22: ADC
23: MCU
24: input / output circuit 25: delay device 26: oscillator 39: voltage generation circuit 40: heater 41: control signal 42: applied voltage

Claims

A SAW sensor in which the amount of propagation delay of a signal is changed due to a change in physical quantity to be detected;
A phase comparator for detecting a phase difference of an output signal of the SAW sensor with respect to a reference signal;
An oscillator having a variable oscillation frequency that generates an input signal of the SAW sensor and the reference signal;
A delay capable of adjusting a delay difference between an input signal of the SAW sensor and the reference signal;
It controls the oscillation frequency of the oscillator and controls the delay amount of the delay unit so that the phase difference between the output signal of the SAW sensor and the reference signal becomes constant, and the SAW sensor can be determined from the delay amount of the delay unit. A control unit that calculates the amount of propagation delay of the
A sensor measurement device characterized by having.
The SAW sensor has a SAW sensor element whose propagation delay amount of a signal changes according to a change in a physical quantity to be detected, and a SAW reference element having the same characteristics as the SAW sensor element and not detecting a physical quantity to be detected.
The output of the delay is provided to the SAW reference element,
The sensor measurement according to claim 1, wherein an output of said SAW reference element is given to said phase note comparator and is used as said reference signal for detecting a phase difference from an output signal of said SAW sensor element in said phase comparator. apparatus.
The sensor measurement device according to claim 1, wherein the SAW sensor has a SAW sensor element in which an amount of propagation delay of a signal is changed when solid fine particles (PM) contained in gas adhere to a sensing unit.
A heater for burning PM attached to the sensing portion of the SAW sensor element;
It further comprises a voltage generation circuit that generates an applied voltage to the heater,
The control unit heats the heater to burn the PM attached to the sensing unit of the SAW sensor element when the adhesion amount of PM reaches a specified value based on the delay amount of the signal of the SAW sensor element. The sensor measurement device according to claim 3, wherein the voltage generation circuit is controlled.
The sensor measurement device according to claim 1, wherein the control unit performs control such that the phase difference is 0 degree so as to be constant.
The sensor measurement device according to claim 1, wherein the control unit controls the sensitivity of the phase comparator to be constant at a good phase difference when the sensitivity of the phase comparator is not constant due to the phase difference.
A delay reference circuit having different delay units and absolute values of delay amounts and having the same characteristics;
The sensor measurement device according to claim 1, wherein the control unit corrects the amount of delay of the delay reference circuit when calculating the amount of propagation delay of the SAW sensor from the amount of delay of the delay device.
The sensor measurement device according to claim 7, wherein the delay amount of the delay unit can be changed by changing the number of delay stages and the applied voltage, and the delay amount can be continuously changed to enable fine adjustment.
The delay reference circuit is a ring oscillator,
8. The control unit according to claim 7, wherein the control unit counts an absolute value of the delay amount of the delay unit by counting the number of counts within a predetermined time of the ring oscillator, and uses it for calculating the propagation delay amount of the SAW sensor. Sensor measuring device.
A heater for burning PM attached to the SAW sensor;
A power on reset circuit that generates a control signal when the sensor measurement device is powered on;
Storage means for storing the number of times the phase difference of the phase comparator has been turned;
The control unit
At power on or after combustion of PM attached to the SAW sensor by the heater (state 1), the frequency of the oscillator is changed, and the signal propagation delay of the SAW sensor is initialized from the difference in phase difference when the frequency is changed. Calculated as a delay, keeping the frequency constant at other than the state 1 (state 2), the phase difference between the SAW sensor and the reference signal was measured using the phase comparator, and the phase difference was 360 degrees. The number of times is stored in the storage means, and the signal propagation delay of the SAW sensor is calculated from the initial delay, the number of times the phase difference has been 360 degrees, and the current phase difference.
The sensor measurement device according to claim 1, characterized in that:
A heater for burning PM attached to the SAW sensor;
Storage means for storing the number of times the phase difference of the phase comparator has been turned;
The phase difference of the SAW sensor after combustion of PM attached to the SAW sensor by the heater is stored in the storage means as an initial value, and the number of times the phase difference is rotated 360 degrees is stored in the storage means Remember,
The control unit calculates the signal propagation delay of the SAW sensor based on the current phase difference and the initial value stored in the storage means and the number of times the phase difference has been rotated 360 degrees;
The storage means is a storage means that does not lose memory even if power is not supplied.
The sensor measurement device according to claim 1, characterized in that:
A SAW sensor in which the amount of propagation delay of a signal is changed due to a change in physical quantity to be detected;
A phase comparator for detecting a phase difference of an output signal of the SAW sensor with respect to a reference signal;
An oscillator having a variable oscillation frequency that generates an input signal of the SAW sensor and the reference signal;
A delay capable of adjusting a delay difference between an input signal of the SAW sensor and the reference signal;
A control unit that performs feedback control on the delay amount of the delay device such that the phase difference before and after the change of the frequency of the input signal of the SAW sensor becomes a desired value;
A sensor measurement device characterized by having.