JP2017020937A - Sensing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensing system in which a physical quantity calculation error due to a fluctuation of the propagation characteristic of a SAW can be corrected when a SAW sensor of a delay line type is used.SOLUTION: A sensing device 4 outputs a drive signal to a SAW sensor 3 and detects a delay signal delayed via a SAW element 15. A control device 14 calculates a phase angle from the delay signal detected by the sensing device 4 and calculates, on the basis of the phase angle, a physical quantity that has acted on the SAW sensor 3. The sensing device 4 uses drive signals of two or more kinds of different frequencies when detecting the delay signal of the SAW element 15. The control device 14 corrects the sensitivity of the SAW element 15 to the physical quantity using a difference in phase angle of delay signals of the SAW element 15 at the two or more kinds of different frequencies.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sensing system using a surface acoustic wave (SAW) sensor.

  The SAW element is a passive element in which a comb-shaped electrode for generating a surface acoustic wave (SAW) is formed on a piezoelectric substrate. The electrical characteristics of the SAW element change according to changes in physical quantities such as temperature and force. This is because the distance between the comb electrodes that determine the electrical characteristics of the SAW element and the SAW propagation characteristics change in accordance with changes in physical quantities such as temperature and force. A SAW sensing system is a system that calculates a physical quantity to be measured based on detecting the change in electrical characteristics.

  A reflection comprising a transversal SAW delay element having a comb-shaped electrode for input and a comb-shaped electrode for output on a piezoelectric body, and a reflector disposed at a position away from the comb-shaped electrode for input / output and the comb-shaped electrode. A SAW sensor system using a delay line type SAW element such as a type SAW delay element calculates a physical quantity to be measured based on a delay time (passing / reflecting phase) in the SAW delay element and a signal intensity change amount.

Japanese National Patent Publication No. 5-506504

  In general, in order to correctly calculate a physical quantity to be measured by the SAW sensing system, it is necessary to accurately grasp the sensitivity of the electrical characteristics of the SAW element with respect to changes in the physical quantity to be measured. However, this sensitivity varies depending on factors such as deterioration over time. The following example is given as an example. A SAW element having a silicon oxide film laminated on its surface absorbs moisture when exposed to a high-temperature and high-humidity environment for a long time, so that the SAW propagation speed decreases and the sensitivity varies. Such fluctuations in sensitivity due to fluctuations in SAW propagation characteristics cause a large error when the sensor system calculates a change in the physical quantity to be measured, and it is necessary to suppress the influence. As a method for suppressing fluctuations in the propagation characteristics of the SAW, a method of enclosing the SAW element in a hermetically sealed structure is conceivable. As another method, a method of forming a protective film on the surface of the SAW element is conceivable. However, an electrode design in consideration of the influence of the protective film is required, and design restrictions are increased. As a method for correcting the sensitivity fluctuation due to the propagation characteristic fluctuation, a method of detecting the fluctuation of the SAW propagation characteristic by separately measuring the resonance frequency of the SAW element can be considered. However, in a SAW sensor system using a transversal SAW delay element or a reflective SAW delay element, a separate detection circuit is required due to the difference in electrical characteristics to be detected, resulting in an increase in circuit scale.

  An object of the present invention is to provide a sensing system capable of correcting a physical quantity calculation error due to a change in SAW propagation characteristics of a SAW element.

  In order to achieve the above object, according to the first aspect of the present invention, a SAW sensor including a delay line type SAW element, and a delay signal that outputs a drive signal to the SAW sensor and delays the SAW sensor via the SAW element. And a control device that calculates a phase angle of the delayed signal detected by the sensing device and calculates a physical quantity that has acted on the SAW sensor based on the phase angle. When the sensing device detects the delayed signal of the SAW element, two or more kinds of driving signals having different frequencies are used, and the control apparatus uses the phase angle difference of the delayed signal of the SAW element at two or more kinds of different frequencies. The sensitivity to the physical quantity of the SAW element is corrected.

  According to the first aspect of the present invention, the sensing device corrects the sensitivity to the physical quantity of the SAW element using the difference in the phase angle of the delayed signal of the SAW element at two or more different frequencies. It becomes possible to correct a calculation error of a physical quantity due to fluctuations.

The block diagram which shows roughly the electric constitution of the sensor system in 1st Embodiment. The figure which shows the structure of a SAW element typically ((a) is a top view, (b) is sectional drawing) Flow chart for schematically explaining the flow of operation The block diagram which shows roughly the electrical structure of the sensor system in 2nd Embodiment. Plan view schematically showing the structure of a SAW element Flow chart for schematically explaining the flow of operation The block diagram which shows roughly the electrical structure of the sensor system in 3rd Embodiment. Flow chart for schematically explaining the flow of operation Flowchart for schematically explaining the flow of operation in the fourth embodiment A block diagram showing roughly an electric composition of a sensor system in a 5th embodiment. Flow chart for schematically explaining the flow of operation The block diagram which shows schematically the electric constitution of the sensor system in 6th Embodiment Flow chart for schematically explaining the flow of operation

  Hereinafter, some embodiments of the sensing system will be described with reference to the drawings. In each embodiment described below, configurations that perform the same or similar operations are denoted by the same or similar reference numerals, and description thereof is omitted as necessary.

(First embodiment)
1 to 3 are explanatory diagrams of the first embodiment. A sensing system 1 in FIG. 1 includes a SAW sensor 3 as a sensor head that is appropriately arranged according to a physical quantity to be measured, and a sensing device 4 connected to the SAW sensor 3.

  The sensing device 4 includes a signal source 5 that outputs a drive signal, a transmission amplifier 6, a transmission / reception switching switch 7, a reception amplifier 8, mixers 9 and 10, low-pass filters 11 and 12, A phase shifter 13, and a control device 14 is connected to the sensing device 4. The signal source 5 can select two or more types of frequencies (for example, 200 MHz and 201 MHz) in the vicinity of 200 [MHz], for example, and outputs a drive signal having the selected frequency.

  When receiving the drive signal from the signal source 5, the transmission amplifier 6 amplifies the drive signal and outputs it to the switch 7. The switch 7 switches to the transmission side / reception side in accordance with a control signal given from the control device 14. When switched to the transmission amplifier 6 side, the switch 7 outputs an amplified drive signal of the transmission amplifier 6 to the SAW sensor 3.

  The SAW sensor 3 is configured by using one delay line type SAW element 15. The SAW element 15 includes a piezoelectric substrate 17 and a comb-shaped electrode 18 for generating SAW on the piezoelectric substrate 17 as schematically shown in FIG. 2A and FIG. And a reflector 19 disposed apart from the comb electrode. The piezoelectric substrate 17 is made of, for example, lithium niobate. As shown in FIG. 2B, the comb-shaped electrode 18 and the reflector 19 are made of, for example, aluminum, and are disposed at one end and the other end of the piezoelectric substrate 17, respectively.

  As an example, the comb-shaped electrode 18 is configured by a pair of two electrodes having a number of comb teeth of several tens (for example, 20), and these teeth are arranged at a predetermined pitch (for example, 9.6 μm). The comb-shaped electrode 18 of the SAW element 15 is configured by pairing two electrodes 18 a and 18 b, one electrode 18 b of the paired electrodes is grounded, and the other electrode 18 a is connected to the sensing device 4. Has been.

  The reflector 19 is made of, for example, aluminum which is the same material as the comb electrode 18. In the reflector 19, predetermined (for example, 40) electrodes 19a extending in a direction perpendicular to the SAW traveling direction are arranged at a predetermined pitch (for example, 9.6 μm pitch).

  As shown in FIG. 1, when a driving signal having a predetermined frequency is applied to the comb-shaped electrode 18 through the signal source 5, the transmission amplifier 6, and the switch 7, the sensing device 4 applies to the piezoelectric substrate 17 shown in FIG. SAW can be generated. The SAW generated at this time travels from the comb electrode 18 toward the reflector 19. The SAW is reflected by the reflector 19 and returns to the comb electrode 18. In the present embodiment, the distance between the comb electrode 18 and the reflector 19 is set to about several mm (for example, 3 mm).

  As described above, the switch 7 shown in FIG. 1 switches between the transmission side and the reception side according to the control signal given from the control device 14, but in this embodiment, the control device 14 uses the SAW element 15 as a drive signal. While propagating, the switch 7 is switched to the receiving amplifier 8 side. The reflected signal propagated through the SAW element 15 is transmitted to the receiving amplifier 8 as a delayed signal. The receiving amplifier 8 amplifies the transmitted signal and outputs the amplified signal to the first and second mixers 9 and 10.

  A phase shifter 13 is configured between the signal source 5 and the second mixer 10. The phase shifter 13 shifts the phase of the drive signal generated from the signal source 5 by a predetermined angle and outputs it to the second mixer 10. In the present embodiment, the phase shifter 13 shifts the drive signal by 90 degrees, for example, and outputs it to the second mixer 10.

  The first mixer 9 is composed of, for example, a passive mixer, receives a drive signal from the signal source 5, mixes this input signal and the amplified signal of the receiving amplifier 8, and outputs the mixed signal to the control device 14 through the low-pass filter 11. . The second mixer 10 is constituted by, for example, a passive mixer, and receives a drive signal shifted by 90 degrees from the signal source 5 by the phase shifter 13 and mixes this input signal and the amplified signal of the receiving amplifier 8. And output to the control device 14 through the low-pass filter 12.

  The control device 14 can be configured using, for example, a microcomputer. The control device 14 includes a control unit 20 that is a main subject of control, an A / D converter 21, and a storage unit 22. The control unit 20 digitally converts the signal that has passed through the low-pass filter 11 from the first mixer 9 by the A / D converter 21 and stores it in the storage unit 22, and also stores the signal from the second mixer 10 into the low-pass filter 12. The signal that has passed through is digitally converted by the A / D converter 21 and stored in the storage unit 22. The control device 14 calculates the phase angle of the delayed signal of the SAW element 15 based on the A / D conversion data stored in the storage unit 22.

  The SAW sensor 3 is installed so that the phase angle of the delayed signal of the SAW element 15 changes according to the physical quantity to be measured. For example, when measuring the Y-direction distortion given externally as a physical quantity to be measured, the SAW element 15 is installed so as to be deformed according to the distortion. At this time, since the phase angle of the delayed signal of the SAW element 15 changes in proportion to the amount of change in the Y-direction distortion, the distortion can be calculated using the phase angle. However, the amount of change (sensitivity) of the phase angle with respect to the physical quantity to be measured changes due to fluctuations in SAW propagation characteristics (for example, SAW propagation speed) due to deterioration over time of the SAW element.

  Signals having frequencies fa and fb (> fa) within the frequency band in which the SAW element 15 can propagate signals are used as drive signals output from the signal source 5, and L is an effective propagation path length of the SAW element 15, V Assuming that the effective propagation speed of SAW in the SAW element 15 is assumed, the phase rotation angle P [deg] of the SAW element 15 is derived as shown in the following equation (1).

P = L / V × fa × 360
= (Θb−θa) / (fb−fa) × fa (1)
If TCD [ppm / ° C.] is the temperature coefficient of the delay time, the temperature sensitivity G [deg / ° C.] of the phase rotation angle of the SAW element 15 is derived as in the following equation (2).

G≈P [deg] × TCD [ppm / ° C.] ∝ (θb−θa) (2)
Furthermore, when the distortion sensitivity of the phase rotation angle of the SAW element 15 is F [deg], this F [deg] is derived as in the following equation (3).

F≈P [deg] × 1 [ε] ∝ (θb−θa) (3)
That is, by measuring and comparing the difference (θb−θa) of the phase angle of the delay signal with respect to the driving signals of the frequencies fa and fb in the same environment, the propagation characteristics of the SAW element 15 (for example, the propagation speed of SAW) can be changed. Based on this, it is possible to correct variations in sensitivity with respect to the physical quantity to be measured.

  If such a technical idea is taken into consideration, the physical quantity to be measured can be calculated as accurately as possible by the control device 14 performing processing as described below. This will be described below with reference to FIG.

  First, the control unit 20 of the control device 14 detects a delay signal with the frequencies fa and fb of the drive signal by the sensing device 4 (S1). Then, the control unit 20 calculates the phase angle θa based on the delayed signal having the frequency fa (S2), and calculates the phase angle θb based on the delayed signal having the frequency fb (S3). Then, the control unit 20 calculates the phase angle difference (θb−θa) (S4), and corrects the sensitivity of the SAW element 15 to the physical quantity using the phase angle difference (θb−θa) and the proportional coefficient. (S5). This proportionality coefficient is a coefficient calculated in advance by experiments or simulations, and is stored in the storage unit 22 in advance. Therefore, the control unit 20 can correct the sensitivity of the SAW element 15 to the physical quantity using the phase angle difference (θb−θa) and the proportionality coefficient. Then, the control unit 20 calculates a physical quantity using the phase angle θa (or θb) and the corrected sensitivity (S6). In this way, the physical quantity to be measured can be calculated as accurately as possible.

  According to the present embodiment, the sensitivity to the physical quantity of the SAW element 15 is corrected using the phase angle difference (θb−θa) of the delayed signal of the SAW element 15 at two different frequencies fa and fb. As a result, it is possible to suppress as much as possible the influence of deformation due to deterioration of the SAW element over time and fluctuations in SAW propagation characteristics (for example, SAW propagation speed), and the physical quantity to be measured can be calculated as accurately as possible. According to the present embodiment, the sensitivity can be corrected and the physical quantity can be calculated by arithmetic processing, so that it is not necessary to provide a separate circuit, and an increase in circuit scale can be suppressed. In addition, design constraints can be eliminated as much as possible.

(Second Embodiment)
4 to 6 show additional explanatory views of the second embodiment. In the second embodiment, as shown in FIG. 4, the sensing system 101 includes a SAW sensor 103 appropriately arranged according to the first and second physical quantities to be measured, and a sensing connected to the SAW sensor 103. Device 4. The SAW sensor 103 includes a plurality (two) of first and second SAW elements 15 and 16.

  As shown in FIG. 5, the first and second SAW elements 15 and 16 are connected in parallel. Each of the comb-shaped electrodes 18 of the first and second SAW elements 15 and 16 is configured by pairing two electrodes 18a and 18b, and one electrode 18b of the paired electrodes is grounded, The electrode 18 a is connected to the sensing device 4. The first and second SAW elements 15 and 16 are the ratio of the sensitivity of the SAW element 15 to the first physical quantity and the sensitivity to the second physical quantity, and the sensitivity of the SAW element 16 to the first physical quantity and the second physical quantity. The sensitivity ratio is set differently. For example, when assuming the shear strain of a cylinder having a rotation axis in the X direction of the measurement target as the first physical quantity and the detection of temperature as the second physical quantity, the first and second SAW elements 15 and 16 have the strain. They are installed on the XY plane so that the detection directions intersect each other. It is desirable to install the SAW elements 15 and 16 so that the strain detection directions are orthogonal to each other. In other words, it is desirable to install with θ = 45 ° in FIG. The propagation path lengths LA and LB of the SAW elements 15 and 16 are set to different lengths, and the sensing device 4 can receive the delayed signals at different timings. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  As shown in the present embodiment, when the first and second SAW elements 15 and 16 are used, the sensitivity of each of these SAW elements 15 and 16 is calculated by calculating the phase angle difference at the frequencies fa and fb. It is good to correct | amend and the control apparatus 14 can calculate the 1st and 2nd physical quantity used as a measuring object as accurately as possible by processing as shown below. This will be described below with reference to FIG. Note that θa1 is a phase angle [deg] of measurement of the SAW element 15 at the frequency fa, θb1 is a phase angle [deg] of measurement of the SAW element 15 at the frequency fb, and θa2 is a measurement phase of the SAW element 16 at the frequency fa. The phase angle [deg] and θb2 are set as the phase angle [deg] in measurement of the SAW element 16 at the frequency fb.

  As illustrated in FIG. 6, the control unit 20 detects a delay signal at the frequencies fa and fb by the sensing device 4 (T1). Then, the control unit 20 calculates the phase angle θa1 of the first SAW element 15 at the frequency fa (T21), calculates the phase angle θb1 of the first SAW element 15 at the frequency fb (T31), and compares the phase angle difference (θb1− θa1) is calculated (T41), and the sensitivity of the first SAW element 15 to the first and second physical quantities is corrected using the phase angle difference (θb1−θa1) and the proportionality coefficient (T51). The proportionality coefficient is a coefficient calculated in advance by experiment or simulation, and is stored in the storage unit 22 in advance.

  Further, the control unit 20 calculates the phase angle θa2 of the second SAW element 16 at the frequency fa (T22), calculates the phase angle θb2 of the second SAW element 16 at the frequency fb (T32), and the phase difference (θb2−θa2). Is calculated (T42), and the sensitivity of the second SAW element 16 to the first and second physical quantities is corrected using the phase difference (θb2−θa2) and the proportionality coefficient (T52). This proportional coefficient is also a coefficient calculated in advance by experiment or simulation, and is stored in the storage unit 22 in advance. Then, the control unit 20 calculates the first and second physical quantities using the phase angles θa1 and θa2 and the sensitivities corrected in steps T51 and T52 (T6).

According to this embodiment, when the first and second SAW elements 15 and 16 are used, the sensitivity can be corrected using the phase angle differences (θb1−θa1) and (θb2−θa2).
(Third embodiment)
7 and 8 show additional explanatory views of the third embodiment. As in the second embodiment, the third embodiment also includes first and second SAW elements 15 and 16, and another form in which the sensitivity is corrected using each of these SAW elements 15 and 16. Show.

  As shown in FIG. 7, the sensing system 201 includes a SAW sensor 103 appropriately arranged according to the first and second physical quantities to be measured, and a sensing device 204 connected to the SAW sensor 103. A sensing device 204 that replaces the sensing device 4 includes a measurement unit (equivalent to measurement means) 23 that measures a frequency. The measurement unit 23 is composed of a frequency counter and the like, and measures the frequency of the drive signal output from the signal source 5. That is, the sensing device 204 has a function of measuring the frequency of the drive signal output from the signal source 5 by the measurement unit 23 as compared to the sensing devices 4 and 104 of the first or second embodiment.

  The frequencies fa and fb (> fa) within the frequency band in which the SAW elements 15 and 16 can propagate signals are used as drive signals output from the signal source 5, respectively, LA is the effective propagation path length of the SAW element 15, and LB is the SAW. Effective propagation path length of the element 16, VA is an effective SAW propagation speed in the SAW element 15, VB is an effective SAW propagation speed in the SAW element 16, and PA is an effective phase rotation angle of the SAW element 15. , PB is the effective phase rotation angle of the SAW element 16, the phase rotation angles PA and PB can be derived as shown in the following equations (4) and (5).

PA [deg] = LA / VA x fa x 360
= (Θb1−θa1) / (fb−fa) × fa (4)
PB [deg] = LB / VB × fa × 360
= (Θb2−θa2) / (fb−fa) × fa (5)
If TCD [ppm / ° C.] is a temperature coefficient of the delay time, the temperature sensitivity GA and GB [deg / ° C.] of the phase rotation angle of the SAW elements 15 and 16 are expressed by the following equations (6) and (7). Derived.

GA ≒ PA [deg] x TCD [ppm / ° C] (6)
GB≈PB [deg] × TCD [ppm / ° C.] (7)
Further, assuming that the distortion sensitivity of the phase rotation angle of the SAW elements 15 and 16 is FA and FB [deg], the FA and FB [deg] are derived as in the following equations (8) and (9).

FA≈PA [deg] × 1 [ε] (8)
FB≈PB [deg] × 1 [ε] (9)
That is, by measuring and comparing the phase rotation angles PA and PB in the same environment, the first and second physical quantities to be measured based on fluctuations in the propagation characteristics of the SAW element 15 (for example, the SAW propagation speed) are measured. Sensitivity fluctuations can be corrected.

  Considering such a technical idea, the control device 14 performs processing as shown below, whereby the first and second physical quantities to be measured can be calculated as accurately as possible. This will be described below with reference to FIG.

  As shown in FIG. 8, the control unit 20 detects a delay signal at the frequencies fa and fb by the sensing device 4 (T1). Then, the control unit 20 measures the frequency fa of the drive signal output from the signal source 5 by the measurement unit 23 of the sensing device 4 (T21a), and calculates the phase angle θa1 of the first SAW element 15 at the frequency fa (T21b). . Then, the control unit 20 changes the frequency of the signal source 5 to fb, measures the frequency fb of the drive signal output from the signal source 5 by the measurement unit 23 of the sensing device 4 (T31a), and the first SAW element at the frequency fb The phase angle θb1 of 15 is calculated (T31b). Then, the control unit 20 calculates the gradient (θb1−θa1) / (fb−fa) of the phase angle (T41a). The controller 20 corrects the sensitivity of the first SAW element 15 with respect to the first and second physical quantities using the gradient (θb1−θa1) / (fb−fa) of the phase angle (T51a).

  Further, the control unit 20 calculates the phase angle θa2 of the second SAW element 16 at the frequency fa (T22), calculates the phase angle θb2 of the second SAW element 16 at the frequency fb (T32), and the phase angle gradient (θb2−). θa2) / (fb−fa) is calculated (T42a). And the control part 20 correct | amends the sensitivity with respect to the 1st and 2nd physical quantity of the 2nd SAW element 16 using the gradient ((theta) b2- (theta) a2) / (fb-fa) of this phase angle (T52a). Then, the control unit 20 calculates the first and second physical quantities using the phase angles θa1 and θa2 (or the phase angles θb1 and θb2) and the corrected sensitivity (T6a).

  According to the present embodiment, when the first and second SAW elements 15 and 16 are used, phase angle gradients (θb1−θa1) / (fb−fa), (θb2−θa2) / (fb−fa ) Can be used to correct the sensitivity.

  In addition, since the measurement unit 23 measures the frequencies fa and fb of the drive signal of the signal source 5 and corrects the sensitivity using the gradient of the phase angle calculated according to the measurement result, the sensitivity correction The accuracy can be improved, and more accurate first and second physical quantities can be calculated.

(Fourth embodiment)
FIG. 9 shows an additional explanatory diagram of the fourth embodiment. Similarly to the second embodiment, the fourth embodiment also includes first and second SAW elements 15 and 16, and the respective SAW elements 15 and 16 are used for the first and second physical quantities. Another mode for correcting the sensitivity ratio will be described.

  The ratio of sensitivity to the first and second physical quantities can be derived as follows. Here, when the frequencies fa and fb (> fa) within the frequency band in which the SAW elements 15 and 16 can operate are used as drive signals, GB / GA is the first phase between the delayed signals of the SAW elements 15 and 16. The ratio of sensitivity to a physical quantity of 1 (for example, temperature sensitivity ratio), the ratio of FB / FA to the first physical quantity of the phase between the delayed signals of the SAW elements 15 and 16 (for example, distortion sensitivity ratio), and α to the SAW element Assuming that the coefficients represent the mutual effects of 15 and 16 (depending on the relative installation relationship), the phase rotation angles PA and PB, the first physical quantity, as shown in the following equations (10) and (11) The sensitivity ratio GB / GA to the second physical quantity, and the sensitivity ratio FB / FA to the second physical quantity can be derived.

GB / GA≈ (θb2−θa2) / (θb1−θa1) (10)
FB / FA≈ (θb2−θa2) / (θb1−θa1) × α (11)
In consideration of such a technical idea, the control device 14 performs processing as shown below, so that the first and second physical quantities requiring the highest accuracy in the process of calculating the first and second physical quantities are processed. The sensitivity ratio can be corrected, and the first and second physical quantities to be measured can be calculated as accurately as possible. This will be described below with reference to FIG.

  As illustrated in FIG. 9, the control unit 20 detects a delay signal at frequencies fa and fb by the sensing device 4 (T1). Then, the control unit 20 calculates the phase angle θa1 of the first SAW element 15 at the frequency fa (T21), and calculates the phase angle θb1 of the first SAW element 15 at the frequency fb (T31). Further, the control unit 20 calculates the phase angle θa2 of the second SAW element 16 at the frequency fa (T22), and calculates the phase angle θb2 of the second SAW element 16 at the frequency fb (T32). Then, the control unit 20 calculates the phase angle difference ratio (θb2−θa2) / (θb1−θa1) (T4b), and the control unit 20 uses the phase angle difference ratio to calculate the first SAW element. The ratio of the sensitivity to the first and second physical quantities of 15 and the sensitivity of the second SAW element 16 to the first and second physical quantities is corrected (T5b). The control unit 20 calculates the first and second physical quantities using the phase angles θa1 and θa2 and the ratio of the corrected sensitivity (T6b).

According to the present embodiment, when the first and second SAW elements 15 and 16 are used, the sensitivity can be corrected using the phase angle difference ratio (θb2−θa2) / (θb1−θa1).
(Fifth embodiment)
10 and 11 show additional explanatory views of the fifth embodiment. As in the first embodiment, the fifth embodiment includes one delay line type SAW element 15 and a separate sensor 24. Whether the sensor signal of the sensor 24 is within a specified value or not is determined. A feature is provided in that processing is divided depending on the case.

  As shown in FIG. 10, the sensor 24 is connected to the control device 14, and the control unit 20 of the control device 14 is configured to acquire the sensor signal of the sensor 24. The sensor 24 is a sensor that can detect a change in the environment around the SAW element 15 such as a hygrometer and / or a thermometer. For example, the sensor 24 may be provided to perform sensitivity correction processing under substantially the same environment under conditions where the temperature is in the same range.

  As shown in FIG. 11, the control unit 20 receives the sensor signal of the sensor 24, and one type of frequency fa according to whether or not the sensor signal of the simple sensor 24 is within a specified value (S1a, S3a). Whether the delayed signal is detected (S11a) or the delayed signal is detected at two frequencies fa and fb (S12a).

  When the sensitivity correction is not performed, the control unit 20 determines NO in steps S1a and S3a, calculates the phase angle θa of the SAW element 15 at the frequency fa (S21), and uses the phase angle θa and the sensitivity. The physical quantity is calculated (S6).

  Conversely, when correcting the sensitivity, the control unit 20 determines YES in steps S1a and S3a, calculates the phase angles θa and θb of the SAW element 15 at the frequencies fa and fb (S21 and S32), The difference (θb−θa) between the phase angle θb and the phase angle θa is calculated (S42), and the sensitivity to the physical quantity of the SAW element 15 is corrected using the phase angle difference (θb−θa) (S52). Then, the control unit 20 calculates a physical quantity using the corrected sensitivity and the phase angle θa (or θb) (S6).

  According to the present embodiment, since the sensor 24 is provided, the sensing device 4 can control the timing for switching the use frequency, and the control unit 20 can measure the sensitivity correction timing.

(Sixth embodiment)
12 and 13 show additional explanatory views of the sixth embodiment. The sixth embodiment shows a form in which the sensitivity is corrected by switching the use frequency with reference to an externally applied trigger signal. As shown in FIG. 12, a trigger signal is given to the sensing device 4 and the control device 14 from the outside. This trigger signal is a signal corresponding to a timer signal generated with the passage of time or the like, and when the sensing device 4 and the control device 14 are given a trigger signal, the sensitivity is corrected in accordance with the trigger signal. The operation frequency is switched to. Specifically, as described in the first embodiment, the signal source 5 outputs a drive signal that can select two or more types of frequencies (for example, 200 MHz and 201 MHz) near 200 [MHz], for example. 4 and the control device 14 are configured to switch to the frequency fa or fb corresponding to the trigger signal when the trigger signal is received. The timing for correcting the sensitivity is determined according to the trigger signal.

  As shown in FIG. 13, when the trigger signal is set to a value other than a predetermined value (NO at S1b, NO at S31b), the sensing device 4 measures the delay signal at the frequency fa (S11b) and performs control. The unit 20 calculates the phase angle θa of the SAW element 15 at the frequency fa (S21), and calculates a physical quantity using a predetermined sensitivity (S6).

  On the other hand, when the trigger signal is set to a predetermined specified value (YES in S1b, YES in S31b), the sensing device 4 measures the delay signal at both frequencies fa and fb (S12b), and the control unit 20 Calculates these phase angles θa and θb (S12b, S32), corrects the sensitivity to the physical quantity of the SAW element 15 using the phase angle difference (θb−θa) (S52), and uses the phase angle θa and the sensitivity. The physical quantity is calculated (S6).

  In this way, the control unit 20 can measure the sensitivity correction timing while the sensing device 4 controls the timing for switching the use frequency in accordance with the trigger signal given from the outside.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and for example, the following modifications or expansions are possible. The configurations of these embodiments can be applied in appropriate combinations.

  Two SAW elements 15 and 16 are used, but three or more may be used. Although the phase angle difference is calculated using two different frequencies, the phase angle difference may be calculated using more than two types (ie, two or more types) of different frequencies. In this case, when the frequencies fa and fb (<fa) that can drive the SAW sensor 3 and the like are set, and the intermediate frequency fn (fa <fn <fb) is used, the following (1) The formula 1a) may be applied.

P = L / V × fa × 360
= (Θb−θa) / (fb−fa) × fn (1a)
Also in this case, the same correction can be performed as shown in the above embodiment, and the same effect can be obtained.

  In the drawings, 1 is a sensing system, 3 is a SAW sensor, 4 is a sensing device, 14 is a control device, 15 is a SAW element (first SAW element), 16 is a second SAW element, 20 is a control unit, and 21 is an A / D converter. , 22 is a storage unit, 23 is a measurement unit (measurement means), and 24 is a sensor.

Claims (6)

A SAW sensor (3, 103) including a delay line type SAW element (15, 16);
A sensing device (4, 104, 204) for outputting a drive signal to the SAW sensor and detecting a delay signal delayed via the SAW element of the SAW sensor;
A control device (14) that calculates a phase angle from the delayed signal detected by the sensing device and calculates a physical quantity acting on the SAW sensor based on the phase angle;
The sensing device (4, 104, 204) uses two or more types of drive signals having different frequencies when detecting the delayed signal of the SAW element,
The said control apparatus correct | amends the sensitivity with respect to the physical quantity of the said SAW element using the difference of the phase angle of the delay signal of the said SAW element in two or more types of different frequencies. The SAW sensor (103) includes a plurality of delay line type SAW elements (15, 16),
The sensing device (104) uses two or more types of drive signals having different frequencies when detecting delayed signals of the plurality of SAW elements,
The control device corrects the sensitivity of each of the plurality of SAW elements with respect to a physical quantity by using the difference in phase angle of the delayed signal at the two or more different frequencies for each of the plurality of SAW elements. The sensing system according to claim 1. The sensing device (104) includes measuring means (23) for measuring the frequency of the driving signal of the SAW element,
The control device calculates a gradient of the phase angle with respect to the frequency of the driving signal of the SAW element using the measurement result of the measuring means, and corrects the sensitivity to the physical quantity of the SAW element using the gradient of the phase angle. The sensing system according to claim 1 or 2.   The control device corrects the ratio of the sensitivity to the physical quantity of each of the plurality of SAW elements by using the ratio of the phase angle difference of the delayed signals at the two or more different frequencies for each of the plurality of SAW elements. The sensing system according to claim 2, wherein: A sensor (24) for detecting the correction timing of the sensitivity of the SAW sensor;
The sensing device (4) controls timing for switching a use frequency based on a sensor signal of the sensor,
The sensing system according to any one of claims 1 to 4, wherein the control device controls timing for correcting sensitivity with respect to a physical quantity of the SAW element. The sensing device (4) controls the timing of switching the use frequency with reference to a trigger signal given from the outside,
The sensing system according to any one of claims 1 to 4, wherein the control device controls timing for correcting sensitivity with respect to a physical quantity of the SAW element.

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