JP7492121B2 - Physical quantity measuring system and physical quantity measuring device - Google Patents

Description

This relates to a physical quantity measuring system and a physical quantity measuring device equipped with a surface acoustic wave element.

Patent Document 1 discloses a surface acoustic wave sensor. The surface acoustic wave sensor disclosed in Patent Document 1 includes a delay line type surface acoustic wave element, and inputs a burst signal to the surface acoustic wave element using two types of signals with different frequencies, and calculates the phase angle of the output signal that is output after the burst signal is delayed by the surface acoustic wave element. Then, a physical quantity such as temperature is calculated based on the difference in phase angle of the two types of output signals. In this way, by calculating a physical quantity based on the difference in phase angle of two types of output signals with different frequencies, the range of measurable physical quantities can be widened.

Japanese Patent No. 5942656

The technology disclosed in Patent Document 1 artificially reduces the sensitivity of a physical quantity to a phase angle, i.e., the change in the physical quantity relative to a change in the phase angle. This reduction in sensitivity may result in a decrease in the measurement accuracy of the physical quantity.

This disclosure was made based on these circumstances, and its purpose is to provide a physical quantity measurement system and a physical quantity measurement device that can increase the accuracy of physical quantity measurement while widening the range of physical quantity measurement.

The above object is achieved by a combination of features recited in the independent claims, and the subclaims define further advantageous specific examples. The reference characters in parentheses in the claims indicate a correspondence with the specific means described in the embodiments described below as one aspect, and do not limit the disclosed technical scope.

One disclosure relating to a physical quantity measurement system for achieving the above object includes:
a delay line type surface acoustic wave element (20) including a first element portion (20a) and a second element portion (20b) arranged close to each other and having different propagation distances;
a radio section (30a) for transmitting burst signals at two or more frequencies to the surface acoustic wave element and receiving a response wave from the surface acoustic wave element;
a two-frequency phase difference calculation unit (S75) that calculates a phase difference between response waves reflected by the first element unit and the second element unit as a two-element phase difference (Δφ1i) for radio waves of two kinds of frequencies successively transmitted by the radio unit, and further calculates a phase difference between the two-element phase differences calculated for the two kinds of frequencies as a two-frequency phase difference (Δθi);
a physical quantity determining unit (S76) that determines an absolute physical quantity (Ti) based on a preset relationship between the two-frequency phase difference and the physical quantity and the two-frequency phase difference calculated by the two-frequency phase difference calculating unit;
a time phase difference calculation unit (S65) that repeatedly measures the phase of a reply wave in response to a radio wave of one type of frequency successively transmitted by the wireless unit, and continuously calculates the difference between the previously measured phase and the currently measured phase as a time phase difference (Δφt i );
A physical quantity change calculation unit (S94) that calculates a physical quantity change amount (ΔTi) based on the time phase difference;
a determination unit (S50) that repeatedly determines whether or not a reliability evaluated based on the power of the response wave exceeds a preset threshold value for the reliability;
a selection unit which, when a first determination is made by the determination unit that the reliability of the response wave exceeds a threshold, causes the physical quantity determination unit to determine an absolute physical quantity and stores the determined absolute physical quantity in the storage unit, and, when a second determination is made by the determination unit that the reliability of the response wave does not exceed the threshold, does not cause the physical quantity determination unit to determine the absolute physical quantity;
a physical quantity estimation unit (S95) that estimates an absolute physical quantity at the time when the second judgment is obtained based on the absolute physical quantity stored in the storage unit and a physical quantity change amount based on a time phase difference calculated at the time when the second judgment is obtained;
A physical quantity measurement system comprising:

This physical quantity measurement system includes a two-frequency phase difference calculation unit and a physical quantity determination unit. The physical quantity determined from the two-frequency phase difference can be measured over a wide measurement range. However, the absolute physical quantity determined from the two-frequency phase difference artificially reduces the sensitivity, so there is a risk that the required accuracy cannot be ensured.

Therefore, a selection unit is provided, and the physical quantity is determined by a two-frequency phase difference calculation unit and a physical quantity determination unit based on the reliability of the response wave being such that the absolute physical quantity can be determined from the two-frequency phase difference with the required accuracy.

The selection unit also calculates the physical quantity change amount using the time phase difference calculation unit and the physical quantity change amount calculation unit, based on the fact that the reliability of the response wave is not high enough to determine the absolute physical quantity from the two-frequency phase difference with the necessary accuracy. This is because the time phase difference has only one type of frequency and is not low-sensitivity, so a decrease in accuracy can be suppressed.

However, when there is only one type of frequency, the phase difference has a narrow physical quantity measurement range, making it difficult to measure the physical quantity over a wide physical quantity range. Therefore, the time phase difference is calculated, and the physical quantity change amount is calculated from the time phase difference. Then, in the physical quantity estimation unit, an undetermined and unestimated absolute physical quantity is estimated from the physical quantity change amount, which has the determined or estimated absolute physical quantity as either before or after the change, and the absolute physical quantity. In this way, the absolute physical quantity is continuously estimated based on the continuously calculated physical quantity change amounts. By estimating the absolute physical quantity in this way, the absolute physical quantity can be estimated over a wide physical quantity range, and measurement accuracy is easily ensured.

The selection unit may determine that when the power (S) of the response wave is higher than a two-frequency threshold (TH) as a threshold , the reliability of the response wave is the reliability that allows the absolute physical quantity to be determined with the required accuracy from the two-frequency phase difference.

If the power of the response wave is high, it is easier to ensure the required signal-to-noise ratio. And if the signal-to-noise ratio is high, the accuracy of measuring physical quantities can be improved.

The surface acoustic wave element is attached to a moving body (40),
The time phase difference calculation section repeatedly calculates the two-element phase difference , and can calculate the phase difference between the previously calculated two-element phase difference and the currently calculated two-element phase difference as the time phase difference.

When attached to a moving object, the distance between the wireless unit and the surface acoustic wave element changes successively. In that case, it is not possible to determine whether a phase change is due to a change in distance or a change in physical quantity with only one element unit. However, in this physical quantity measurement system, the surface acoustic wave element is provided with a first element unit and a second element unit that are arranged close to each other and have different propagation distances. Since the first element unit and the second element unit are arranged close to each other, the physical quantity can be considered to be the same. In addition, the distance between the first element unit and the second element unit does not change. Therefore, if the phase difference over time of the two-element phase difference is calculated as the time phase difference, and the phase difference over frequency of the two-element phase difference is calculated as the two-frequency phase difference, the phase change due to the successive change in the distance between the wireless unit and the surface acoustic wave element can be offset and the physical quantity can be measured.

In the above physical quantity measurement system, the first element section and the second element section may both be of a reflective delay line type and may share a comb electrode.

One example of a mode in which the first element portion and the second element portion are arranged close to each other is a mode in which they share a comb-shaped electrode like this.

When the selection unit selects to determine the physical quantity using the two-frequency phase difference calculation unit and the physical quantity determination unit, the radio unit may transmit radio waves of two different frequencies, and when the selection unit selects to estimate the physical quantity using the time phase difference calculation unit, the physical quantity change calculation unit, and the physical quantity estimation unit, the radio unit may transmit radio waves of one different frequency.

In this way, the number of frequencies transmitted by the radio unit can be switched depending on the number of frequencies selected by the selection unit.

the physical quantity change calculation unit calculates a physical quantity change amount by averaging the time phase differences for the first number of times;
the physical quantity determination unit determines the physical quantity by averaging the two-frequency phase differences for the second number of times;
The first number may be greater than the second number.

In this way, when the radio unit transmits radio waves at one frequency, the number of averaging operations is increased compared to when the radio unit transmits radio waves at two frequencies.

If there is one type of radio wave to be transmitted, it is possible to transmit radio waves of one type of frequency more times per unit time than when there are two types of radio waves to be transmitted. Therefore, when the radio unit transmits radio waves of one type of frequency, the number of averaging is increased compared to when the radio unit transmits radio waves of two types of frequencies. Increasing the number of averaging reduces noise. As a result, by doing this, it is possible to further improve the accuracy of the time phase difference and the amount of change in physical quantity and absolute physical quantity calculated from that time phase difference.

The radio section is
Transmitting burst signals at three frequencies included in one permitted transmission frequency band defined by a spectrum mask;
When there is one type of frequency of radio waves to be transmitted, the frequency of the three types of frequencies that is closest to the center frequency of the permitted transmission frequency band shall be the frequency of the radio waves to be transmitted, and when there are two types of frequencies of radio waves to be transmitted, the remaining two frequencies of the three types of frequencies shall be the frequencies of the radio waves to be transmitted, and
The transmission power when the radio waves to be transmitted have one frequency may be higher than the transmission power when the radio waves to be transmitted have two frequencies.

Regardless of the frequency of the radio waves being transmitted, the power must be below the upper limit set by law for that frequency. This upper limit power is called the spectrum mask. Consider the case where there are two types of transmission frequencies contained in one permitted transmission frequency band defined by the spectrum mask. If there are two types of frequencies, one of the frequencies will be used as the frequency for calculating the time phase difference and the frequency for calculating the two-frequency phase difference.

In this case, neither of the two frequencies can be set to the frequency that allows the highest transmission power in the permitted transmission frequency band. This is because the other frequency is far from the frequency that allows the highest transmission power relatively, and as a result, the transmission power of the other frequency cannot be increased. When calculating the two-frequency phase difference, the transmission power of the radio waves of the two frequencies must be the same. Therefore, when considering calculating the two-frequency phase difference, neither of the two frequencies can be set to the frequency that allows the highest transmission power in the permitted transmission frequency band.

Therefore, the burst signal is transmitted at three different frequencies as described above. In this way, if the radio unit transmits radio waves at one frequency, the frequency of the three frequencies that is closest to the center frequency of the spectrum mask can be used as the frequency of the radio waves to be transmitted.

This makes it possible to increase the transmission power when only one type of radio frequency is transmitted without exceeding the spectrum mask, even for burst signals that have the characteristic of having a wide frequency band.

The radio unit sequentially transmits two or more types of frequencies regardless of the selection result of the selection unit,
The selection section is
determining the reliability of each of the response waves based on the response power, which is the power (S) of the response waves of two or more frequencies; and determining an absolute physical quantity by a two-frequency phase difference calculation unit and a physical quantity determination unit based on the reliability of the response waves of two or more frequencies exceeding a threshold value ;
When there is one or less type of response wave whose reliability exceeds the threshold, the time phase difference may be calculated using the single response wave with the highest reliability.

By using highly reliable response waves, the accuracy of estimating physical quantities can be improved.

One disclosure relating to a physical quantity measuring device for achieving the above object is a physical quantity measuring device included in the physical quantity measuring system. The physical quantity measuring device includes:
a radio section (30a) that transmits burst signals at two or more frequencies to a delay line type surface acoustic wave element (20) including a first element section (20a) and a second element section (20b) that are arranged close to each other and have different propagation distances, and receives a response wave from the surface acoustic wave element;
a two-frequency phase difference calculation unit (S75) that calculates a phase difference between response waves reflected by the first element unit and the second element unit as a two-element phase difference (Δφ1i) for radio waves of two kinds of frequencies successively transmitted by the radio unit, and further calculates a phase difference between the two-element phase differences calculated for the two kinds of frequencies as a two-frequency phase difference (Δθi);
a physical quantity determining unit (S76) that determines an absolute physical quantity (Ti) based on a preset relationship between the two-frequency phase difference and the physical quantity and the two-frequency phase difference calculated by the two-frequency phase difference calculating unit;
a time phase difference calculation unit (S65) that repeatedly measures the phase of a reply wave in response to a radio wave of one type of frequency successively transmitted by the wireless unit, and continuously calculates the difference between the previously measured phase and the currently measured phase as a time phase difference (Δφt i );
A physical quantity change calculation unit (S94) that calculates a physical quantity change amount (ΔTi) based on the time phase difference;
a determination unit (S50) that repeatedly determines whether or not a reliability evaluated based on the power of the response wave exceeds a preset threshold value for the reliability;
a selection unit which, when a first determination is made by the determination unit that the reliability of the response wave exceeds a threshold, causes the physical quantity determination unit to determine an absolute physical quantity and stores the determined absolute physical quantity in the storage unit, and, when a second determination is made by the determination unit that the reliability of the response wave does not exceed the threshold, does not cause the physical quantity determination unit to determine the absolute physical quantity;
and a physical quantity estimation unit (S95) that estimates the absolute physical quantity at the time when the second judgment is obtained, based on the absolute physical quantity stored in the memory unit and the physical quantity change amount based on the time phase difference calculated at the time when the second judgment is obtained.

1A and 1B are diagrams illustrating a state in which the temperature measurement system 10 of the first embodiment is used. FIG. 2 is a diagram showing the configuration of a surface acoustic wave element 20. FIG. 2 is a diagram showing the configuration of a temperature measuring device 30. 5 is a diagram showing a process executed by a calculation unit 30b in the first embodiment. FIG. FIG. 5 is a diagram showing detailed processing of S60 in FIG. 4; FIG. 5 is a diagram showing detailed processing of S70 in FIG. 4; FIG. 5 is a diagram showing detailed processing of S90 in FIG. 4; FIG. 13 is a diagram for explaining the process of S95, and is a diagram before S95 is applied. FIG. 13 is a diagram for explaining the process of S95, and is a diagram after S95 has been applied. FIG. 4 is a diagram showing transmission timing of a burst signal. 13 is a diagram showing a burst signal of a third frequency f3, with the horizontal axis representing frequency. 2 is a diagram showing a burst signal of a first frequency f1, with the horizontal axis representing frequency. 4 is a diagram showing a burst signal of a second frequency f2, with the horizontal axis representing frequency. FIG. 10 is a diagram showing a process executed in place of FIG. 4 in the third embodiment;

The following describes the embodiments with reference to the drawings. In the embodiments, temperature is measured as a physical quantity. That is, the physical quantity measurement system of the first embodiment is a temperature measurement system 10. FIG. 1 is a diagram for explaining the use state of the temperature measurement system 10 of the first embodiment. The temperature measurement system 10 includes a surface acoustic wave element 20, a temperature measurement device 30, and an operation terminal 50. The surface acoustic wave element 20 is attached to a measurement object 40 whose temperature is to be measured. The measurement object 40 moves in the direction of the arrow shown in FIG. 1 by a belt 41. That is, the measurement object 40 is a moving body. The measurement object 40 is transported by the belt 41 and introduced into a furnace 42. The measurement object 40 is brazed or the like in the furnace 42.

The temperature measuring device 30, which is a physical quantity measuring device, is fixed to the center of the furnace 42 in the longitudinal direction. The temperature measuring device 30 transmits a burst signal to the surface acoustic wave element 20 and receives a response wave R. The surface acoustic wave element 20 measures the temperature of the surface acoustic wave element 20 based on the phase φ of this response wave R. This temperature can be considered as the temperature of the measurement object 40. The operation terminal 50 is a terminal operated by the user to operate the temperature measuring device 30, and is connected to the temperature measuring device 30. The operation terminal 50 includes an operation unit 51 equipped with switches operated by the user, and a display unit 52 on which the measurement results by the temperature measuring device 30 are displayed.

[Configuration of the surface acoustic wave element 20]
2 shows the configuration of a surface acoustic wave element 20. The surface acoustic wave element 20 includes a piezoelectric substrate 21, a comb-shaped electrode 22 that generates a surface acoustic wave (hereinafter, SAW) in response to an input of a burst signal, and two reflectors 23 and 24 that reflect the SAW. The element also includes an antenna 25 that receives the burst signal and inputs it to the comb-shaped electrode 22. The comb-shaped electrode 22 is configured with two comb-shaped electrodes in a pair, one of which is grounded and the other connected to the antenna 25.

The reflectors 23 and 24 are made of the same material as the comb electrode 22, and are configured with multiple electrodes extending in a direction perpendicular to the direction of travel of the SAW, arranged at a specified pitch. When a burst signal is input to the comb electrode 22, a transverse SAW is generated in the piezoelectric substrate 21, and travels from the comb electrode 22 toward the reflectors 23 and 24. The SAW is then reflected by the reflectors 23 and 24 and returns to the comb electrode 22, causing a response wave R to be transmitted from the antenna 25.

Reflectors 23 and 24 are arranged at different distances from comb electrode 22. The distance between comb electrode 22 and reflector 23 and the distance between comb electrode 22 and reflector 24 are designed so that the time when the SAW reaches comb electrode 22 from reflectors 23 and 24 do not overlap. Even when considering temperature changes, it is preferable to make the distance from reflector 23 and reflector 24 to comb electrode 22 as short as possible while preventing the time when the SAW reaches comb electrode 22 from reflectors 23 and 24 from overlapping. This is because if the distance is long, it becomes difficult to consider the temperatures of reflector 23 and reflector 24 to be the same.

The propagation distance of the SAW that travels from the comb electrode 22 to the comb electrode 22 after being reflected by the reflectors 23 and 24 is twice the length from the effective SAW generation position in the comb electrode 22 to the effective SAW reflection position in the reflectors 23 and 24. The antenna 25 has an electrical length that allows it to receive radio waves of frequency f transmitted by the temperature measuring device 30.

With this configuration, the surface acoustic wave element 20 receives one burst signal and transmits two response waves R with different transmission times. Therefore, the surface acoustic wave element 20 can be seen as having a configuration including a first element portion 20a and a second element portion 20b arranged close to each other. The first element portion 20a and the second element portion 20b share the comb-shaped electrode 22 and the antenna 25, but as non-shared members, the first element portion 20a includes a reflector 23, and the second element portion 20b includes a reflector 24.

[Configuration of temperature measuring device 30]
3 shows the configuration of the temperature measuring device 30. The temperature measuring device 30 includes a wireless unit 30a and a calculation unit 30b. The temperature measuring device 30 is the same as a general tag reader except for the content of the calculation performed by the calculation unit 30b. The wireless unit 30a includes an antenna 31, a transmitter 32, a coupler 33, an antenna duplexer 34, a quadrature demodulator 35, bandpass filters 36i and 36q, and AD converters 37i and 37q.

The antenna 31 transmits a burst signal as radio waves to the surface acoustic wave element 20 and receives a response wave R from the surface acoustic wave element 20. In this embodiment, the frequency f of the radio waves transmitted and received by the antenna 31 is of two types: a first frequency f1 and a second frequency f2. The first frequency f1 is 916.8 MHz, and the second frequency f2 is 923.4 MHz. These frequencies f are widely used in wireless tags.

The transmitter 32 generates and outputs a burst signal to be transmitted to the surface acoustic wave element 20. The transmitter 32 is equipped with an oscillator circuit, which generates signals of the two types of frequency f. The burst signal is a signal with a short duration. As an example, the duration of the burst signal is 500 ns. One reason for making the signal transmitted to the surface acoustic wave element 20 a signal with a short duration is to improve the accuracy of calculating the phase φ. Another reason is to prevent the time when the SAW from the reflector 23 reaches the comb electrode 22 from overlapping with the time when the SAW from the reflector 24 reaches the comb electrode 22.

The burst signal is branched by the coupler 33 and directed to the antenna duplexer 34 and the quadrature demodulator 35. The antenna duplexer 34 outputs the signal from the transmitter 32 to the antenna 31, and outputs a signal representing the received wave received by the antenna 31 to the quadrature demodulator 35. The antenna 31 radiates the burst signal into the air and receives the response wave R from the surface acoustic wave element 20.

The response wave R received by the antenna 31 is input to the quadrature demodulator 35 as an electrical signal (hereinafter, the response signal). The quadrature demodulator 35 includes a phase shifter 351 and two mixers 352i and 352q. The burst signal branched by the coupler 33 is input to the phase shifter 351. The response signal and the burst signal are input to one of the mixers, 352i. When the response signal and the burst signal are mixed in the mixer 352i, an I signal, which is an in-phase component of the baseband signal, is obtained. The response signal and a signal in which the phase φ of the burst signal has been shifted by 90 degrees by the phase shifter 351, are input to the other mixer 352q. A Q signal, which is an orthogonal component of the baseband signal, is obtained from this mixer 352q.

The signal obtained by mixer 352i is input to calculation unit 30b via bandpass filter 36i and AD converter 37i, and the signal obtained by mixer 352q is input to calculation unit 30b via bandpass filter 36q and AD converter 37q.

The calculation unit 30b is a computer equipped with a CPU, ROM, RAM, etc., and the CPU executes a program stored in a recording medium such as ROM while utilizing the temporary storage function of the RAM, thereby executing the processes shown in the flowcharts in FIG. 4 and subsequent figures. Executing the processes shown in FIG. 4 and subsequent figures means that a method corresponding to the program is executed. Note that some or all of the functional blocks provided in the calculation unit 30b may be realized using one or more ICs, etc. (in other words, as hardware). Also, some or all of the functions provided in the calculation unit 30b may be realized by a combination of software execution by the CPU and hardware components.

[Processing of Calculation Unit 30b]
The calculation unit 30b executes the process shown in Fig. 4 in order to measure the temperature of the surface acoustic wave element 20. The process shown in Fig. 4 is started by a measurement start operation by a user. The measurement start operation may be an operation on the operation unit 51, or may be turning on the power of the temperature measuring device 30.

In step (hereinafter, step will be omitted) S10, the phase φ of the response wave R is measured n times at the first frequency f1. The phase φ of the response wave R is calculated from Equation 1. In Equation 1, A _Q is the amplitude of the Q signal, and A _I is the amplitude of the I signal. In this embodiment, the phase φ is calculated as a value between -180 degrees and 180 degrees.

(Equation 1) φ=tan ₋₁ (A _Q /A _I )
The phase φ is described without specifying the frequency f. When the phase φ is the phase of the reply wave R transmitted at the first frequency f1, it is described as the phase φ(f1), and when the phase φ is the phase of the reply wave R transmitted at the second frequency f2, it is described as the phase φ(f2).

There are two types of response waves R: response wave R1 from reflector 23 and response wave R2 from reflector 24. The phase φ of response wave R1 of the burst signal transmitted at the first frequency f1 is phase φ(f1R1), and the phase φ of response wave R2 of the burst signal transmitted at the first frequency f1 is phase φ(f1R2).

In S10, the phase φ (f1R1) and the phase φ (f1R2) are calculated n times. To calculate this phase φ, a burst signal is transmitted n times at the first frequency f1.

In S20, i = 0. In S30, the n measurement data measured in S10, i.e., the n phases φ(f1R1) and φ(f1R2), are averaged by frequency.

In S40, the two-element phase difference Δφ1i and the response power S1i (dBm) are calculated. The two-element phase difference Δφ1i is the difference between the i-th phase φ(f1R1) and phase φ(f1R2). The response power S1i is the received power of the i-th response wave R. The received power is calculated using Equation 2.

S1=√(A _Q ² +A _I ² ) (Equation 2)
S50 corresponds to a selection unit. In S50, it is determined whether the latest response power S1 is greater than the two-frequency threshold TH. The two-frequency threshold TH is a threshold for determining whether the temperature determination accuracy is not significantly reduced even if the phase difference Δθ due to the two frequencies f is used. The specific value of the two-frequency threshold TH is determined based on an experiment or the like.

If the determination result in S50 is YES, the process proceeds to S60. In S60, the time phase difference Δφti is calculated. The process of S60 is shown in FIG. 5. In S61, the same process as in S10 is executed. That is, the phase φ(f1R1) and the phase φ(f1R2) are calculated n times. In S62, 1 is added to i. In S63, the n measurement data measured in S61, that is, the n phases φ(f1R1) and phases φ(f1R2), are averaged by frequency.

S64 is the same process as S40, and calculates the two-element phase difference Δφ1i and the response power S1i. S65 corresponds to the time phase difference calculation unit. In S65, the time phase difference Δφti of the two-element phase difference Δφ1i is calculated and stored in a predetermined memory unit. The memory unit uses, for example, the RAM in the calculation unit 30b. The time phase difference Δφti of the two-element phase difference Δφ1i is calculated by subtracting the two-element phase difference Δφ1(i-1) calculated in the previous S64 from the two-element phase difference Δφ1i calculated in the current S64. The process of S60 is executed repeatedly (in other words, continuously) before the temperature measurement end button is pressed and the judgment result of S50 is NO. Therefore, the time phase difference Δφti is calculated continuously before the temperature measurement end button is pressed and the judgment result of S50 is NO.

Referring back to FIG. 4 for the explanation, after S60 has been executed, the process proceeds to S80. In S80, it is determined whether the temperature measurement end button has been pressed. If the determination result in S80 is NO, the process returns to S50. As shown in FIG. 1, the temperature measuring device 30 is disposed in the center of the furnace 42 in the direction of movement of the surface acoustic wave element 20 by the belt 41. Therefore, if the surface acoustic wave element 20 is located in the position shown in FIG. 1, the surface acoustic wave element 20 gradually approaches the temperature measuring device 30. If the surface acoustic wave element 20 approaches the temperature measuring device 30, the determination result in S50 becomes YES. If the determination result in S50 becomes YES, the process proceeds to S70.

In S70, absolute temperature determination processing is executed. The absolute temperature determination processing is shown in detail in FIG. 6. In FIG. 6, in S71, the phase φ of the response wave R is measured n/2 times at each of the first frequency f1 and the second frequency f2. At each frequency f, there is a phase φ of the response wave R1 and a phase φ of the response wave R2. Therefore, in S71, four types of phases φ(f1R1), φ(f1R2), φ(f2R1), and phase φ(f2R2) are measured.

In S72, i is incremented by 1. In S73, the n/2 pieces of measurement data measured for each frequency in S71 are averaged. In S74, the two-element phase difference Δφ1i and response power S1i for the first frequency f1, and the two-element phase difference Δφ2i and response power S2i for the second frequency f2 are calculated. The two-element phase difference Δφ1i and response power S1i for the first frequency f1 are calculated using the same process as in S64. The two-element phase difference Δφ2i for the second frequency f2 is calculated using φ(f2R1) - φ(f2R2).

S75 corresponds to a two-frequency phase difference calculation unit. In S75, the phase difference Δθi between the two two-element phase differences Δφ1i and Δφ2i calculated for the two frequencies f in S74 (hereinafter, the two-frequency phase difference) is calculated by Δφ1i-Δφ2i. This two-frequency phase difference Δθi is the same as that described in Patent Document 1. The relationship between the two-frequency phase difference Δθi and the absolute temperature Ti is preset and stored.

S76 corresponds to a physical quantity determination unit. In S76, the absolute temperature Ti is determined from a preset relationship between the two-frequency phase difference Δθi and the absolute temperature Ti and the two-frequency phase difference Δθi calculated in S75. The absolute temperature Ti is an example of an absolute physical quantity.

In S77, the time phase difference Δφti of the two-element phase difference Δφ1i is calculated by subtracting the two-element phase difference Δφ1(i-1) calculated in the previous S74 from the two-element phase difference Δφ1i calculated in this S74. In S77, this time phase difference Δφti and the absolute temperature Ti determined in S76 are further stored.

Referring back to FIG. 4 for the explanation, even if S70 is executed, the process proceeds to S80. If the determination result of S80 is YES, the process proceeds to S90. In S90, an estimated temperature calculation process is executed. The estimated temperature calculation process is shown in detail in FIG. 7.

In S91, the maximum value of the response power Si, i.e., the maximum response power Sm, is determined. Note that if there are multiple maximum response powers Si, the one with the smallest i is set as the maximum response power Sm.

In S92, it is determined whether the maximum response power Sm determined in S91 is greater than the two-frequency threshold TH. If the determination result in S92 is NO, the process proceeds to S93. In S93, the measurement failure is displayed on the display unit 52.

S94 corresponds to a physical quantity change calculation unit. In S94, the temperature change amount ΔTi for i without absolute temperature Ti is calculated. The temperature change amount ΔTi is calculated using Equation 3. In Equation 3, 1/UT is a coefficient that converts the time phase difference Δφti into the temperature change amount ΔTi, and means the change in temperature per unit time phase difference. This coefficient is preset based on experiments. 1/UT is, for example, 20°C.

(Equation 3) ΔTi=Δφti/UT
S95 corresponds to a physical quantity estimation unit. In S95, absolute temperatures Ti for i without absolute temperatures Ti are estimated. Then, they are displayed on the display unit 52 together with the absolute temperatures Ti determined in S76. The estimation method is to sequentially estimate from the i without absolute temperatures Ti that is closest to the i with absolute temperatures Ti. The i closest to the i with absolute temperatures Ti is the i that is closer to the maximum response power Sm determined in S91 than the i without absolute temperatures Ti.

The closest i to the i with absolute temperature Ti is the absolute temperature Ti before or after the temperature change ΔTi. Since ΔTi = Ti - T(i - 1), the absolute temperature Ti can be estimated.

The process of S95 will be described in detail with reference to Figures 8 and 9. Figure 8 shows the absolute temperature Ti obtained before executing S95. Figure 8 also shows the temperature change amount ΔTi along with the absolute temperature Ti.

In the example shown in Figure 8, absolute temperatures Ti have been obtained for i=4, 5, 6, 7, and 8, but not for i=0 to 3 and 9 to 11. In the example shown in Figure 8, among the i's without absolute temperatures Ti, the i's closest to the i's with absolute temperatures Ti are i=3 and 9. For i=3, it is known that the absolute temperature T4 after the temperature change is 56°C, so absolute temperature T3 is estimated to be 44°C by subtracting 12°C, which is the temperature change ΔT4 when reaching absolute temperature T4, from 56°C, which is the absolute temperature T4 after the temperature change. Absolute temperatures T2, T1, and T0 are estimated in the same way.

For i=9, since the referenceable absolute temperature T8 is the temperature before the temperature change, the absolute temperature T9 is estimated to be 86°C by adding the temperature change amount ΔT9 of i, which is the same as the estimated absolute temperature T9, -4°C to the absolute temperature T8, which is 90°C. Figure 9 shows the absolute temperature Ti estimated in this way. In Figure 9, the absolute temperature Ti estimated in S95 is shown with an underlined number.

Summary of the First Embodiment
In the embodiment described above, the absolute temperature determination process S70 is executed. In the absolute temperature determination process S70, a two-frequency phase difference Δθi, which is the phase difference between each of the response waves R to the radio waves of the two frequencies f1 and f2, is calculated (S75).

As explained in Patent Document 1, the two-frequency phase difference Δθi can measure temperature over a wide measurement range. However, the absolute temperature Ti determined from the two-frequency phase difference Δθi artificially reduces the sensitivity, so there is a risk that the required signal-to-noise ratio cannot be ensured.

Therefore, in this embodiment, the absolute temperature Ti is determined from the two-frequency phase difference Δθi based on the fact that the response power Si is higher than the two-frequency threshold TH (S76). This is because if the power of the response wave R is high, it is easier to ensure the required S/N ratio.

If the response power S1 is equal to or less than the two-frequency threshold TH (S50: NO), the temperature change amount ΔTi is calculated from the time phase difference Δφti (S60, S94). Since the time phase difference Δφti has only one type of frequency f and is not low-sensitivity, it is easy to ensure the required S/N ratio even if the power of the response wave R is low. And if the required S/N ratio can be ensured, the temperature measurement accuracy can be improved.

However, if there is only one type of frequency f, the phase difference has a narrow temperature measurement range, making it difficult to measure temperature over a wide temperature range. Therefore, the time phase difference Δφti is calculated (S65), and the temperature change amount ΔTi is calculated from the time phase difference Δφti (S94). Then, an undetermined and unestimated absolute temperature Ti is estimated from the temperature change amount ΔTi, which is either before or after the change and the absolute temperature Ti, with the determined or estimated absolute temperature Ti being used (S95). In this way, the absolute temperature Ti is continuously estimated based on the continuously calculated temperature change amount ΔTi. By estimating the absolute temperature Ti in this way, it is possible to estimate the absolute temperature Ti over a wide temperature range, and it is also easy to ensure a high signal-to-noise ratio.

The surface acoustic wave element 20 of this embodiment includes a first element portion 20a and a second element portion 20b that are arranged close to each other and have different propagation distances. The temperatures of the first element portion 20a and the second element portion 20b can be considered to be the same. Furthermore, the propagation distance of both the first element portion 20a and the second element portion 20b does not change.

In this embodiment, the time phase difference Δφti of the two-element phase difference Δφ is calculated as the time phase difference Δφti (S65), and the phase difference due to the frequency f of the two-element phase difference Δφ is calculated as the two-frequency phase difference Δθi (S75). Therefore, the change in phase φ caused by the successive changes in the distance between the wireless unit 30a and the surface acoustic wave element 20 can be offset to measure the temperature.

In addition, in this embodiment, when S50 is YES and the absolute temperature determination process S70 is executed, the frequency f of the radio waves transmitted by the wireless unit 30a is two types. On the other hand, when S50 is NO and the time phase difference calculation process S60 is executed, the frequency f of the radio waves transmitted by the wireless unit 30a is one type.

By transmitting only one type of frequency f, when S60 is executed, the number of times radio waves are transmitted for one frequency f can be greater within the same measurement time than when S50 is executed. Specifically, in S60, radio waves of frequency f1 are transmitted n times, whereas in S50, radio waves of frequency f1 are transmitted n/2 times. If n times is the first number of times and n/2 times is the second number of times, the first number of times is twice the second number of times.

Due to the difference in the number of measurement data, S60 can average twice as many measurement data as S50. Increasing the number of data to be averaged reduces noise. Therefore, it is possible to further improve the signal-to-noise ratio of the time phase difference Δφti and the temperature change ΔTi and absolute temperature Ti calculated from the time phase difference Δφti.

S60 is executed when the response power S is equal to or less than the two-frequency threshold TH, i.e., when the response power S is low. When the response power S is low, there is a lot of noise. In such a situation, the number of measurement data can be increased to improve the S/N ratio, so that it becomes possible to estimate the absolute temperature Ti that satisfies the S/N ratio criteria even when the surface acoustic wave element 20 is located far from the temperature measuring device 30.

Second Embodiment
Next, a second embodiment will be described. In the following description of the second embodiment, elements having the same reference numbers as those used in the previous embodiments are the same as those having the same reference numbers in the previous embodiments, unless otherwise specified. Furthermore, when only a part of the configuration is described, the previously described embodiment can be applied to the other parts of the configuration.

In the second embodiment, the number of types of frequencies f transmitted by the wireless unit 30a differs from that of the first embodiment. In the second embodiment, the wireless unit 30a transmits radio waves of three types of frequencies f. Specifically, the wireless unit 30a of the second embodiment transmits radio waves of a third frequency f3 in addition to the first frequency f1 and second frequency f2 as in the first embodiment.

In the second embodiment, the calculation unit 30b also executes the processes shown in Figures 4 to 7. The absolute temperature determination process S70 uses the first frequency f1 and the second frequency f2, which are the same as in the first embodiment. On the other hand, the time phase difference calculation process S60 in the second embodiment uses the third frequency f3 instead of the first frequency f1. The third frequency f3 is a frequency f between the first frequency f1 and the second frequency f2. When the first frequency f1 is 916.8 MHz and the second frequency f2 is 923.4 MHz, the third frequency f3 is, for example, 922.2 MHz. Note that all frequencies f refer to the center frequency.

Figure 10 shows the timing of the burst signal transmitted in S61 in the second embodiment. Note that the timing of the burst signal transmitted in S61 in the first embodiment is the same as in S61 in the first embodiment, except for the frequency f.

In the example shown in FIG. 10, the burst signal is pulsed, with a pulse width of 500 ns and a transmission interval of 500 μs. FIG. 11 is a diagram showing a burst signal of the third frequency f3, with the horizontal axis representing frequency. Since the burst signal has a narrow time width, the frequency band is wide. Also, the power is highest at the center frequency, and gradually decreases as the frequency deviates from the center frequency.

Figure 11 also shows a spectrum mask. The spectrum mask indicates the upper limit power for frequency f set by regulations. As shown in Figure 11, the upper limit power differs depending on frequency f. Frequency bands with higher upper limit power are called permitted transmission frequency bands.

The third frequency f3 is a frequency f near the center of the permitted transmission frequency band. As shown in FIG. 11, the power of the burst signal decreases in accordance with the decrease in transmission power defined by the spectrum mask. Therefore, when the radio unit 30a transmits radio waves at one frequency f, the frequency f can have a higher transmission power than the first frequency f1 or the second frequency f2.

Figure 12 is a diagram showing a burst signal of the first frequency f1, with the horizontal axis representing frequency. Figure 13 is a diagram showing a burst signal of the second frequency f2, with the horizontal axis representing frequency. Comparing Figures 11, 12, and 13, it can be seen that the third frequency f3 allows the highest transmission power. Figure 11, which shows the third frequency f3, has a transmission power of -10.5 dBm, while Figure 12, which shows the first frequency f1, and Figure 13, which shows the second frequency f2, have a transmission power of -19.5 dBm.

Summary of the Second Embodiment
In the second embodiment, the radio unit 30a can transmit burst signals at three different frequencies f1, f2, and f3 included in one permitted transmission frequency band.

As in the first embodiment, when there are two types of frequencies f to be transmitted, a first frequency f1 and a second frequency f2, one of the frequencies f is set as the frequency f for calculating the time phase difference Δφti and the frequency f for calculating the two-frequency phase difference Δθi.

In addition, it is necessary to increase the power of the radio waves of both the first frequency f1 and the second frequency f2 while ensuring that the other frequency f for calculating the two-frequency phase difference Δθi is also within the same permitted transmission frequency band. Therefore, it is not possible to set either one of the frequencies f as the frequency at which the transmission power can be maximized in the permitted transmission frequency band.

As a result, the transmission power of the first frequency f1 and the second frequency f2 cannot be made as high as that of the third frequency f3. Therefore, in this second embodiment, when the frequency f transmitted by the wireless unit 30a is one type, the third frequency f3, which is closer to the center frequency of the permitted transmission frequency band than the first frequency f1 and the second frequency f2, is set as the frequency f of the transmitted radio waves. This makes it possible to increase the transmission power when the frequency f of the transmitted radio waves is one type while preventing the spectrum mask from being exceeded, even for burst signals that have a wide frequency band characteristic.

Third Embodiment
Next, a third embodiment will be described. In the third embodiment, similarly to the first embodiment, the wireless unit 30a transmits two types of radio waves, a first frequency f1 and a second frequency f2. In the third embodiment, the calculation unit 30b executes the process shown in FIG. 14 instead of the process shown in FIG. 4. In FIG. 14, i=0 in S110. S120 is the same as S71, and measures the phase φ of the response wave R n/2 times at each of the first frequency f1 and the second frequency f2. In S130, the measurement data for n/2 times measured by frequency in S120 is averaged.

In S140, the reliability is determined for each frequency based on the values averaged in S130. In this embodiment, there are five levels of reliability. Of course, instead, there may be six or more levels of reliability, or two to four levels. The reliability can be determined from the magnitude of the response power Si. The higher the response power Si, the higher the reliability. The higher the response power Si, the more the S/N ratio can be improved. As a result, the accuracy of determining the absolute temperature Ti can be increased, in other words, a reliable absolute temperature Ti can be determined.

In addition to the response power Si, the reliability may be determined from the RSSI. This is because, although the RSSI is a relative index, it indicates the magnitude of power, just like the response power Si. The reliability may also be determined based on the standard deviation or variance of the response power Si or RSSI at each i. The smaller the standard deviation or variance, the higher the reliability.

S150 is also a process that functions as a selection unit. In S150, it is determined whether the reliability determined in S140 is high for both frequencies f. If it is equal to or greater than a preset threshold value for reliability (e.g., 3), the reliability is deemed high. This threshold value is used to determine whether the reliability of the response waves R1 and R2 of the two frequencies f1 and f2 is high enough to determine the absolute temperature Ti from the two-frequency phase difference Δθi with the required accuracy. If the determination result in S150 is NO, the process proceeds to S160.

In S160, a time phase difference calculation process is executed. In the time phase difference calculation process executed in S160, the one having the relatively higher reliability of the two frequencies f1 and f2 is used, and S64 and S65 shown in FIG. 5 are executed.

If the determination result in S150 is NO, proceed to S170. In S170, absolute temperature determination processing is executed. The absolute temperature determination processing executed in S170 executes S74 to S77 shown in FIG. 6.

After executing S160 or S170, the process proceeds to S180. In S180, it is determined whether the temperature measurement end button has been pressed. If the determination result in S180 is NO, the process returns to S120. If the determination result in S180 is YES, the process proceeds to S190. In S190, an estimated temperature calculation process is executed. This S190 is the same as S90.

[Effects of the third embodiment]
In the third embodiment described above, the wireless unit 30a sequentially transmits two frequencies f1 and f2 regardless of the result of the determination in S150 (S120). Then, the reliabilities of the response waves R1 and R2 of the two frequencies f1 and f2 are determined (S140). If it is determined that both reliabilities are high (S150: YES), the absolute temperature determination process S170 is executed to determine the absolute temperature Ti. On the other hand, if at least one of the two reliabilities is lower than the threshold, the time phase difference Δφti is calculated using the response wave R with the highest reliability.

In this way, by selecting the response wave R used to calculate the time phase difference Δφti based on the reliability, the accuracy of the absolute temperature Ti estimated from the time phase difference Δφti can be improved.

Although the embodiments have been described above, the disclosed technology is not limited to the above-mentioned embodiments, and the following modifications are also included within the scope of the disclosure. Furthermore, various modifications other than those described below can be made without departing from the spirit of the invention.

<Modification 1>
In the first and second embodiments, RSSI may be used instead of the response power Si.

<Modification 2>
In the embodiment, the temperature measuring device 30 and the operation terminal 50 are separate entities. However, the temperature measuring device 30 and the operation terminal 50 may be integrated into one body.

<Modification 3>
In the third embodiment, steps S160 and S170 may be executed after the temperature measurement end button is pressed. In this case, the reliability can also be determined as follows. The temperature change amount ΔTi for each i is determined for each frequency, and an approximation curve showing the change in the temperature change amount ΔTi is determined based on the temperature change amount ΔTi. The deviation between the temperature change amount ΔTi for each i determined from this approximation curve and the actually measured temperature change amount ΔTi is calculated. The smaller this deviation, the higher the reliability.

<Modification 4>
In the embodiment, the phase φ is averaged, and then the time phase difference Δφt i is calculated using the averaged phase φ, and the temperature change amount ΔT i is calculated from the time phase difference Δφt i. However, the time phase difference Δφt i may be averaged after being calculated, or the temperature change amount ΔT i may be averaged after being calculated.

<Modification 5>
In the embodiment, the temperature is exemplified as the physical quantity, but a physical quantity other than the temperature, such as pressure, may be measured.

10: Temperature measurement system 20: Surface acoustic wave element 20a: First element section 20b: Second element section 21: Piezoelectric substrate 22: Comb-shaped electrode 23: Reflector 24: Reflector 25: Antenna 30: Temperature measurement device 30a: Wireless section 30b: Calculation section 40: Measurement object (moving body) 41: Belt 42: Furnace 50: Operation terminal 51: Operation section 52: Display section R: Response wave S: Response power Ti: Absolute temperature (absolute physical quantity) TH: Dual frequency threshold ΔTi: Temperature change amount (physical quantity change amount) Δθ: Frequency phase difference Δφ: Dual element phase difference Δφti: Time phase difference S50: Selection section S65: Time phase difference calculation section S75: Dual frequency phase difference calculation section S76: Physical quantity determination section S94: Physical quantity change amount calculation section S95: Physical quantity estimation section S150: Selection section

Claims (9)

a delay line type surface acoustic wave element (20) including a first element portion (20a) and a second element portion (20b) arranged close to each other and having different propagation distances;
a radio section (30a) for transmitting burst signals at two or more frequencies to the surface acoustic wave element and receiving a response wave from the surface acoustic wave element;
a two-frequency phase difference calculation unit (S75) that calculates a phase difference between the response waves reflected by the first element unit and the second element unit as a two-element phase difference (Δφ1i) for radio waves of two kinds of frequencies successively transmitted by the wireless unit, and further calculates the phase differences of the two-element phase differences calculated for the two kinds of frequencies as a two-frequency phase difference (Δθi);
a physical quantity determining unit (S76) that determines an absolute physical quantity (Ti) based on a preset relationship between the two-frequency phase difference and a physical quantity and the two-frequency phase difference calculated by the two-frequency phase difference calculating unit;
a time phase difference calculation unit (S65) that repeatedly measures the phase of the reply wave in response to the radio wave of one type of frequency sequentially transmitted by the radio unit, and continuously calculates the difference between the previously measured phase and the currently measured phase as a time phase difference (Δφt i );
A physical quantity change calculation unit (S94) that calculates a physical quantity change amount (ΔTi) based on the time phase difference;
A determination unit (S50) that repeatedly determines whether or not the reliability evaluated based on the power of the response wave exceeds a preset threshold value for the reliability;
a selection unit that, when a first determination is made by the determination unit that the reliability of the response wave exceeds the threshold, causes the physical quantity determination unit to determine the absolute physical quantity and stores the determined absolute physical quantity in a storage unit, and, when a second determination is made by the determination unit that the reliability of the response wave does not exceed the threshold, does not cause the physical quantity determination unit to determine the absolute physical quantity;
a physical quantity estimation unit (S95) that estimates the absolute physical quantity at the time when the second determination is obtained based on the absolute physical quantity stored in the storage unit and the physical quantity change amount based on the time phase difference calculated at the time when the second determination is obtained;
A physical quantity measurement system comprising: 2. The physical quantity measuring system according to claim 1,
A physical quantity measurement system in which, when the power (S) of the response wave is higher than a two-frequency threshold (TH) as the threshold , the selection unit determines that the reliability of the response wave is the reliability that allows the absolute physical quantity to be determined with the required accuracy from the two -frequency phase difference. 3. A physical quantity measuring system according to claim 1,
The surface acoustic wave element is attached to a moving body (40),
The time phase difference calculation unit repeatedly calculates the two-element phase difference, and calculates, as the time phase difference, a phase difference between the two-element phase difference previously calculated and the two-element phase difference currently calculated . The physical quantity measuring system according to any one of claims 1 to 3,
A physical quantity measuring system, wherein the first element section and the second element section are both of a reflective delay line type and share a comb electrode. The physical quantity measuring system according to any one of claims 1 to 4,
a physical quantity determination unit that determines whether the physical quantity is determined by the physical quantity determination unit and the time phase difference calculation unit, and a physical quantity change amount calculation unit that determines whether the physical quantity is determined by the physical quantity determination unit and the time phase difference calculation unit, and a physical quantity change amount calculation unit that determines whether the physical quantity is determined by the physical quantity determination unit and the time phase difference calculation unit, and a physical quantity change amount calculation unit that determines whether the physical quantity is determined by the physical quantity determination unit and the time phase difference calculation unit, and a physical quantity change amount calculation unit. 6. The physical quantity measuring system according to claim 5,
the physical quantity change calculation unit calculates the physical quantity change by averaging the time phase differences for a first number of times;
the physical quantity determination unit determines the physical quantity by averaging the two-frequency phase differences a second number of times,
The first number of times is greater than the second number of times. 7. A physical quantity measuring system according to claim 5,
The wireless unit includes:
Transmitting the burst signal at three frequencies included in one transmission permitted frequency band defined by a spectrum mask;
When the frequency of the radio wave to be transmitted is one type, the frequency of the three types of frequencies that is closest to the center frequency of the permitted transmission frequency band is set as the frequency of the radio wave to be transmitted, and when the frequency of the radio wave to be transmitted is two types, the remaining two frequencies of the three types of frequencies are set as the frequencies of the radio wave to be transmitted, and
A physical quantity measurement system that transmits radio waves at one frequency and has a higher transmission power than a physical quantity measurement system that transmits radio waves at two frequencies. The physical quantity measuring system according to any one of claims 1 to 4,
the radio unit sequentially transmits two or more types of frequencies regardless of the selection result of the selection unit;
The selection unit is
determining the reliability of the response waves based on response powers, which are powers (S) of the response waves of two or more frequencies, and determining the absolute physical quantity by the two-frequency phase difference calculation unit and the physical quantity determination unit based on the reliability of the response waves of two or more frequencies exceeding the threshold ;
A physical quantity measurement system, wherein when there is one or less type of response wave whose reliability exceeds the threshold, the time phase difference is calculated using one of the response waves having the highest reliability. a radio section (30a) that transmits burst signals at two or more frequencies to a delay line type surface acoustic wave element (20) including a first element section (20a) and a second element section (20b) that are arranged close to each other and have different propagation distances, and receives a response wave from the surface acoustic wave element;
a two-frequency phase difference calculation unit (S75) that calculates a phase difference between the response waves reflected by the first element unit and the second element unit as a two-element phase difference (Δφ1i) for radio waves of two kinds of frequencies successively transmitted by the wireless unit, and further calculates the phase differences of the two-element phase differences calculated for the two kinds of frequencies as a two-frequency phase difference (Δθi);
a physical quantity determining unit (S76) that determines an absolute physical quantity (Ti) based on a preset relationship between the two-frequency phase difference and a physical quantity and the two-frequency phase difference calculated by the two-frequency phase difference calculating unit;
a time phase difference calculation unit (S65) that repeatedly measures the phase of the reply wave in response to the radio wave of one type of frequency sequentially transmitted by the radio unit, and continuously calculates the difference between the previously measured phase and the currently measured phase as a time phase difference (Δφt i );
A physical quantity change calculation unit (S94) that calculates a physical quantity change amount (ΔTi) based on the time phase difference;
A determination unit (S50) that repeatedly determines whether or not the reliability evaluated based on the power of the response wave exceeds a preset threshold value for the reliability;
a selection unit that, when a first determination is made by the determination unit that the reliability of the response wave exceeds the threshold, causes the physical quantity determination unit to determine the absolute physical quantity and stores the determined absolute physical quantity in a storage unit, and, when a second determination is made by the determination unit that the reliability of the response wave does not exceed the threshold, does not cause the physical quantity determination unit to determine the absolute physical quantity;
a physical quantity estimation unit (S95) that estimates the absolute physical quantity at the time when the second determination is obtained based on the absolute physical quantity stored in the storage unit and the physical quantity change amount based on the time phase difference calculated at the time when the second determination is obtained;
A physical quantity measuring device comprising:

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