JP7485921B2 - Passive sensor reading device and physical quantity measuring system - Google Patents

Description

This relates to a passive sensor reading device that reads signals from a passive sensor, and a physical quantity measurement system that includes the device.

Patent Document 1 discloses a surface acoustic wave sensor. The surface acoustic wave sensor disclosed in Patent Document 1 transmits a burst signal wirelessly from a sensing device to a surface acoustic wave element. The surface acoustic wave element receives the burst signal and wirelessly transmits a response wave to the sensing device.

The surface acoustic wave sensor described in Patent Document 1 includes a delay line type surface acoustic wave element, and two types of burst signals with different frequencies are input to the surface acoustic wave element, and the phase angle of the output signal that is output after the burst signal is delayed by the surface acoustic wave element is calculated. A physical quantity such as temperature is then 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

In Patent Document 1, the element can be said to be a passive sensor that operates with a burst signal. If the passive sensor is wirelessly connected to a reader that reads the physical quantity detected by the passive sensor, the flexibility of the installation of the passive sensor and the reader can be improved. For example, it becomes easy to use the passive sensor to measure the temperature of parts that are heated in a high-temperature furnace.

The furnace is made of metal. Therefore, if a passive sensor is installed inside the furnace, the passive sensor will be placed inside a housing that reflects radio waves.

When a passive sensor is surrounded by a material that reflects radio waves, forming a closed space or a space close to it, and the time between when the reader transmits a transmission wave and when the passive sensor transmits a reply wave is short, reverberation of the transmission wave becomes a problem. If the reverberation of the transmission wave remains at a large signal level even at the time when the reply wave is transmitted, the detection accuracy of the reply wave decreases.

The present disclosure has been made based on this situation, and its purpose is to provide a passive sensor reader and a physical quantity measurement system that can detect response waves from a passive sensor while reducing the effects of reverberation.

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.

To achieve the above object, one disclosure of a passive sensor reader includes:
A passive sensor reader including a transmitting unit (30c) for transmitting a transmission wave (TW) toward a passive sensor for operating the passive sensor, and a receiving unit (30d) for receiving a response wave (R) transmitted by the passive sensor in response to the transmission wave,
a reverberation intensity determination unit (S22, S42, S52) that determines whether or not the signal intensity of the reverberation wave received together with the reply wave is within an allowable range based on the signal intensity of the reception signal received by the receiving unit;
The device further includes a characteristic changing unit (S35, S31-1, S31-2) that changes preset transmission unit characteristics capable of reducing reverberation waves in the transmission unit based on the reverberation intensity determining unit determining that the signal strength of the reverberation waves exceeds an allowable range.

This passive sensor reading device is equipped with a reverberation intensity determination unit and can determine whether the signal strength of the reverberation wave is within an acceptable range. If the signal strength of the reverberation wave exceeds the acceptable range, the transmission unit changes the pre-set transmission unit characteristics that can reduce the reverberation wave. By changing the transmission unit characteristics, the effect of the reverberation wave can be reduced and the response wave from the passive sensor can be detected.

The transmitter characteristic includes a frequency. In other words, the characteristic change unit can be configured to change the frequency at which the transmitter transmits.

Transmitter characteristics include antenna characteristics. In other words, the characteristics of the antenna equipped in the transmitter may be changed.

In addition, both the frequency and the antenna characteristics may be changed. That is, the characteristic change unit may change the frequency of the radio waves transmitted by the transmission unit and the characteristics of the antenna (31) equipped in the transmission unit.

One of the characteristics of an antenna is the electrical length of the antenna. Therefore, the antenna characteristic that the characteristic change unit changes can be the electrical length of the antenna.

Another characteristic of an antenna is the position of the antenna. In order to change the position of the antenna, multiple antennas may be provided, and the characteristic change unit may change the antenna that transmits the transmission wave.

Another characteristic of an antenna is the power of the radio waves transmitted by the antenna. That is, the characteristic change unit may reduce the transmission power of the radio waves transmitted by the transmission unit.

One disclosure relating to a physical quantity measurement system for achieving the above object includes:
A physical quantity measurement system including the passive sensor reader in which the characteristic change unit changes the frequency and a passive sensor,
The passive sensor is a delay type surface acoustic wave element (20) having a first element portion (20a) and a second element portion (20b) arranged close to each other and having different propagation distances, the delay type surface acoustic wave element (20) is attached to a moving body (40),
the transmitting section sequentially transmits burst signals at a first frequency (f1) and a second frequency (f2) higher than the first frequency to the surface acoustic wave element;
a two-frequency phase difference calculation unit (S13, S14) that calculates a two-frequency phase difference (Δθ) that is a phase difference between each reply wave to radio waves of two different frequencies successively transmitted by the transmission unit;
a physical quantity determining unit (S15) that determines an absolute physical quantity (T) based on a preset relationship between a two-frequency phase difference and a physical quantity and the two-frequency phase difference calculated by the two-frequency phase difference calculating unit,
the two-frequency phase difference calculation unit calculates a two-element phase difference (Δφ) which is a phase difference between a phase of a response wave from the first element unit and a phase of a response wave from the second element unit for radio waves of two different frequencies, and calculates a phase difference due to the frequency of the two two-element phase differences as a two-frequency phase difference;
the reverberation intensity determination unit determines whether or not an influence of reverberation waves is within an allowable range based on the signal strength of a received signal when a burst signal is transmitted at the first frequency and the signal strength of a received signal when a burst signal is transmitted at the second frequency;
The characteristic modification unit changes the first frequency and the second frequency to a higher frequency based on the reverberation intensity determination unit determining that the signal strength of the reverberation wave at the first frequency exceeds the allowable range, and changes the first frequency and the second frequency to a lower frequency based on the reverberation intensity determination unit determining that the signal strength of the reverberation wave at the second frequency exceeds the allowable range.

In this physical quantity measurement system, a surface acoustic wave element is attached to a moving object. Since the physical quantity of the moving object is to be measured, the surface acoustic wave element has a first element portion and a second element portion with different propagation distances to offset the phase change caused by the change in distance. Then, the phase difference between the two elements is calculated.

In addition, to measure temperature over a wide range, burst signals are transmitted at two frequencies and the two-element phase difference is calculated for the two frequencies. The absolute physical quantity is then determined from the phase difference due to the frequency of these two-element phase differences.

Furthermore, by utilizing the configuration required to measure the absolute physical quantities of a moving object over a wide range, the first and second frequencies are quickly changed to frequencies that can reduce the effects of reverberation waves.

That is, by utilizing the need to transmit burst signals at the first and second frequencies, the first and second frequencies are changed to higher frequencies based on the determination that the signal strength of the reverberation waves at the first frequency has exceeded the allowable range. On the other hand, the first and second frequencies are changed to lower frequencies based on the determination that the signal strength of the reverberation waves at the second frequency has exceeded the allowable range. In this way, it is possible to determine whether to change the first and second frequencies to higher frequencies or lower frequencies, so that the first and second frequencies can be quickly changed to frequencies at which the magnitude of the reverberation waves falls within the allowable range.

The physical quantity measurement system can be configured as follows:

the transmitting unit is capable of transmitting a burst signal by continuously changing a frequency within a settable frequency band in which the first frequency and the second frequency can be set;
a frequency search processing unit (S2, S32) that executes a frequency search process for detecting a signal strength of a reverberation wave by making a transmitter transmit a burst signal while changing the frequency over the entire range of a settable frequency band;
The apparatus further includes an initial frequency determination unit (S3, S33) which determines, based on the signal strength of the reverberation waves obtained in the frequency search processing unit, the widest frequency band among the frequency bands in which the strength of the consecutive reverberation waves falls within the allowable range as the band to be used, and determines the first frequency and the second frequency so that the frequency band between the first frequency and the second frequency is at the center of the band to be used.

By doing this, it is possible to lengthen the time until the signal strength of the reverberation waves at the first and second frequencies exceeds the acceptable range.

1A and 1B are diagrams illustrating a state in which the temperature measurement system 10 of the first embodiment is used. FIG. 4 is a diagram showing a state in which a plurality of measurement objects 40 are separated by partition plates 43. 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. FIG. 4 is a diagram showing a main process executed by a calculation unit 30b. 1 is a conceptual diagram of a transmitted wave TW and a response wave R when there is no influence of a reverberation wave REV. FIG. 13 is a diagram showing the variation of reverberation level in a settable frequency band. 6 is a diagram showing detailed processing of acquiring sensor information in S7 of FIG. 5; 6 is a diagram showing detailed processing of sensor information acquisition determination in S8 of FIG. 5; 11A and 11B are diagrams for explaining the influence of a reverberation wave REV. FIG. 10 is a diagram showing detailed processing of the frequency control in FIG. 9 . FIG. 13 is a diagram showing the relationship between frequency f and the magnitude of a reverberation wave REV. FIG. 11 is a diagram showing a sensor information acquisition determination process executed in the second embodiment. FIG. 4 is a diagram for explaining the signal strength of a received signal at times tb and tc. FIG. 13 is a diagram showing a sensor information acquisition determination process executed in the third embodiment. 13A to 13C are diagrams for explaining a method for estimating the signal strength of a reply wave R in the third embodiment. FIG. 13 is a diagram showing a sensor information acquisition determination process executed in the fourth embodiment. FIG. 13 is a diagram showing an antenna 31 provided in a temperature measuring device 30 according to a fifth embodiment. FIG. 13 is a diagram showing frequency control executed in the fifth embodiment. FIG. 4 is a diagram showing the signal intensity of a response wave R that varies periodically.

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 moving speed of the belt 41 is, for example, several cm/s, which is sufficiently longer than one measurement interval. The measurement interval is the transmission interval of the transmission wave TW, which is, for example, several μs.

The temperature measuring device 30, which is a passive sensor reader, 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 to be 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.

Although not shown in FIG. 1, as shown in FIG. 2, multiple partition plates 43 are fixed to the belt 41. Because the inside of the furnace 42 becomes very hot, the belt 41 and the partition plates 43 are made of metal. The outer wall of the furnace 42 is also made of metal.

The partition plates 43 are of the same shape and are arranged at equal intervals. The partition plates 43 are flat members that stand vertically from the belt 41 and have the same length in the width direction as the belt 41.

As shown in FIG. 2, a measurement object 40 is placed between each pair of partition plates 43, and a surface acoustic wave element 20 is placed on each measurement object 40.

[Configuration of the surface acoustic wave element 20]
3 shows the configuration of the 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, referred to as 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 as a pair of two comb-shaped electrodes, 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]
4 shows the configuration of the temperature measuring device 30. The temperature measuring device 30 includes a radio unit 30a and a calculation unit 30b. The radio unit 30a includes an antenna 31, a transmission circuit 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. An example of the first frequency f1 is 916.8 MHz, and an example of the second frequency f2 is 923.4 MHz. These frequencies f are frequencies f that are widely used in wireless tags. However, in this embodiment, the first frequency f1 and the second frequency f2 can be changed successively.

The transmission circuit 32 generates and outputs a burst signal to be transmitted to the surface acoustic wave element 20. 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 transmission circuit 32 includes an oscillator circuit that generates signals at a predetermined frequency pitch over the entire range of the settable frequency band. The settable frequency band is a frequency band in which the first frequency f1 and the second frequency f2 can be set. The settable frequency band is a frequency band in which the transmission and reception of radio waves is permitted by law. The settable frequency band is also a frequency band that can be received by the antenna 25 included in the surface acoustic wave element 20.

The burst signal is branched by coupler 33 and directed to antenna duplexer 34 and quadrature demodulator 35. Antenna duplexer 34 outputs the signal from transmission circuit 32 to antenna 31, and outputs a signal representing the received wave received by antenna 31 to quadrature demodulator 35. Antenna 31 radiates the burst signal into the air and receives a response wave R from the surface acoustic wave element 20. The configuration from transmission circuit 32 to antenna 31 is transmission section 30c related to transmission in wireless section 30a, and the remaining configuration is reception section 30d. Note that antenna 31 is a configuration common to transmission section 30c and reception section 30d.

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. 5 and subsequent figures. Executing the processes shown in FIG. 5 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. 5 in order to measure the temperature of the surface acoustic wave element 20. The process shown in Fig. 5 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 (hereafter, step will be omitted) S1, it is determined whether the initial frequency has been determined. The initial frequency is the first frequency f of the first frequency f1 and the second frequency f2. Here, the first means before the intensity of the reverberation wave REV is determined.

If the result of the determination in S1 is NO, that is, if the initial frequency has not been determined, the process proceeds to S2. S2 corresponds to a frequency search processing unit. In S2, a frequency search process is executed. In the frequency search process, the transmitter 30c transmits a burst signal while changing the frequency f at a preset frequency interval across the entire settable frequency band. Then, the level of the reverberation wave REV is measured based on the received signal. In this embodiment, the signal strength V at time tb shown in FIG. 6 is the level of the reverberation wave REV. Time tb is the time after the transmission of the transmission wave TW is completed and before the response wave R is detected. Note that time ta is the time when the peak of the transmission wave TW is detected.

Time tb can be set in advance based on the time when the transmission wave TW is transmitted. In S3, an initial frequency determination process is executed. S3 corresponds to the initial frequency determination unit. Specifically, the process of S3 is a process of executing S4 to S6.

In S4, the usable band UAB is determined. The usable band UAB is a frequency band in which the reverberation level determined in S2 is equal to or lower than a preset threshold value THn. Figure 7 shows an example of the usable band UAB. In the example of Figure 7, three usable bands UAB1, UBD2, and UBD3 have been determined.

In S5, the widest frequency band among the usable bands UAB determined in S4 is determined as the frequency band (hereinafter, the usable band UB) for actually transmitting the transmission wave TW. In the example of FIG. 7, the usable band UAB2 is determined as the usable band UB.

In S6, the frequencies f1 and f2 to be used for temperature measurement are determined. The method for determining the frequencies f1 and f2 is to determine the frequency band between the frequencies f1 and f2 so that it is at the center of the band UB to be used determined in S5. The frequencies f1 and f2 determined in this manner are also shown in FIG. 7.

In S7, the sensor information acquisition process is executed. The sensor information acquisition process is shown in FIG. 8. The sensor information acquisition process is a process for measuring the temperature by receiving a response wave R from the surface acoustic wave element 20.

In FIG. 8, in S11, 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. To calculate this phase φ, a burst signal is transmitted n/2 times at each of the first frequency f1 and the second frequency f2.

n is determined based on experiments, etc., to ensure the required S/N ratio. To increase the S/N ratio, it is better to have a larger n, but the larger n is, the longer it takes to measure. Since the temperature is measured periodically, there is an upper limit to the time that can be spent on one temperature measurement.

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 S71, four types of phases φ(f1R1), φ(f1R2), φ(f2R1), and phase φ(f2R2) are measured.

In S12, the n/2 pieces of measurement data measured for each frequency in S11 are averaged for each frequency. S13 and S14 correspond to a two-frequency phase difference calculation unit. In S13, the two-element phase difference Δφ1 for the first frequency f1 and the two-element phase difference Δφ2 for the second frequency f2 are calculated. The two-element phase difference Δφ1 for the first frequency f1 is the difference between the phase φ(f1R1) and the phase φ(f1R2). The two-element phase difference Δφ2 for the second frequency f2 is the difference between the phase φ(f2R1) and the phase φ(f2R2).

In S14, the phase difference Δθ between the two two-element phase differences Δφ1 and Δφ2 calculated for the two frequencies f in S13 (hereinafter, the two-frequency phase difference) is calculated by Δφ1-Δφ2. This two-frequency phase difference Δθ is the same as that described in Patent Document 1. The relationship between the two-frequency phase difference Δθ and the absolute temperature T is preset and stored.

S15 corresponds to a physical quantity determination unit. In S15, the absolute temperature T is determined from a preset relationship between the two-frequency phase difference Δθ and the absolute temperature T, and the two-frequency phase difference Δθ calculated in S14. Note that the absolute temperature T is an example of an absolute physical quantity.

Referring back to FIG. 5 for the explanation, when the sensor information acquisition process (S7) has been executed, the process of FIG. 5 ends. When the process of FIG. 5 ends, the process of FIG. 5 starts again after a preset temperature measurement period has elapsed. When S1 is executed next, the determination result of S1 becomes YES. When the determination result of S1 becomes YES, proceed to S8.

In S8, a sensor information acquisition determination process is executed. The sensor information acquisition determination process is shown in FIG. 9. In FIG. 9, a received signal is acquired in S21. In this embodiment, transmission waves TW1 and TW2 are transmitted at a first frequency f1 and a second frequency f2, respectively, and a received signal is acquired. The reason for acquiring a received signal at two frequencies f is that it is necessary for frequency control, which will be described later.

S22 corresponds to a reverberation intensity judgment unit. In S22, it is judged whether the signal strength V at time tb shown in FIG. 6 is equal to or greater than a threshold value TH1. Time tb is a time when neither the transmitted wave TW nor the response wave R is present. Therefore, it can be assumed that the signal that can be detected at this time tb is the reverberation wave REV. The threshold value TH1 is a threshold value that judges whether the influence of the reverberation wave REV is large. If the signal strength V at time tb is smaller than the threshold value TH1, it is determined that the signal strength V of the reverberation wave REV is within the allowable range. The magnitude of the threshold value TH1 is determined based on an experiment, etc.

Figure 10 shows an example in which the signal strength V at time tb exceeds the threshold value TH1. In such an example, the reply wave R cannot be detected with a sufficient signal-to-noise ratio. If the signal strength V at time tb is equal to or greater than the threshold value TH1 for either the received signal of the first frequency f1 or the received signal of the second frequency f2, the result of the determination in S22 is YES. If the result of the determination in S22 is YES, proceed to S23. In S23, it is determined that reading is not possible.

In the next step S24, a frequency control process is executed. The frequency control process is shown in FIG. 11. In FIG. 11, in S31, it is determined whether the reverberation level of the first frequency f1 and the reverberation level of the second frequency f2 are both greater than the threshold value THn. Note that while in S22 in FIG. 9 it is determined whether the signal strength V at time tb is greater than or equal to the threshold value TH1, in this S31, the reverberation level that overlaps with the response wave R is determined. Both are the same in that they determine the magnitude of the reverberation wave REV. Note that the determination criterion for this S31 may be the same as that for S22. Conversely, the determination criterion for S22 may be the same as that for S31.

If the determination result in S31 is YES, proceed to S32. In S32, the same process as S2 is executed. Therefore, S32 also corresponds to a frequency search processing unit. In S33, the same process as S3 is executed. Therefore, S33 also corresponds to an initial frequency determination unit. By executing S32 and S33, the first frequency f1 and the second frequency f2 are reset. In the following S34, a sensor information acquisition process is executed. This S34 is the same as the sensor information acquisition process shown in FIG. 8, and determines the absolute temperature T.

If the result of the determination in S31 is NO, proceed to S35. The result of the determination in S31 is NO when either the reverberation level of the first frequency f1 or the reverberation level of the second frequency f2 is smaller than the threshold value THn.

The process of S35 is specifically a process of executing S36 to S38. S35 corresponds to a characteristic change unit. In S36, it is determined whether the frequency f exceeding the threshold value THn is the first frequency f1 or the second frequency f2. If the determination result in S36 is the first frequency f1, the process proceeds to S37. In S37, the first frequency f1 and the second frequency f2 are each shifted to the high frequency side by a preset frequency change amount Δf.

On the other hand, if the result of the determination in S36 is the second frequency f2, the process proceeds to S38. In S38, the first frequency f1 and the second frequency f2 are each shifted to the lower frequency side by the frequency change amount Δf.

The reason for processing from S36 to S38 will be explained. Figure 12 shows the relationship between frequency f and the magnitude of the reverberation wave REV at signal acquisition times t1 and t2. The signal acquisition time t is the time that arrives for each temperature measurement period.

In the example shown in FIG. 12, it can be seen that the reverberation wave REV has shifted to the lower frequency side. In this embodiment, the partition plates 43 are arranged at equal intervals, so that each measurement object 40 is located in one closed space partitioned by the partition plates 43. This closed space then moves relative to the temperature measuring device 30. As a result, the magnitude of the reverberation wave REV fluctuates periodically. For this reason, a time change occurs in the magnitude of the reverberation wave REV relative to the frequency f.

This change over time is not random but periodic. As shown in FIG. 12, when the reverberation wave REV is shifted to the lower frequency side, the reverberation wave REV at the second frequency f2 becomes large before the reverberation wave REV at the first frequency f1. In this case, if the first frequency f1 and the second frequency f2 are also shifted to the lower frequency side, the reverberation level at the first frequency f1 and the reverberation level at the second frequency f2 can again be made below the threshold value THn. For this reason, S38 is executed.

Conversely, if the reverberation waves REV are shifted to the higher frequency side, the reverberation waves REV at the first frequency f1 will increase before the reverberation waves REV at the second frequency f2. In this case, if the first frequency f1 and the second frequency f2 are also shifted to the higher frequency side, the reverberation levels at the first frequency f1 and the second frequency f2 can again be made below the threshold value THn. For this reason, S37 is executed.

In this way, by changing the frequency f transmitted by the transmitter 30c, the level of the reverberation waves REV can be reduced. Therefore, the frequency f transmitted by the transmitter 30c is one of the transmitter characteristics that can reduce the reverberation waves REV.

After executing S37 or S38, proceed to S39. In S39, the sensor information acquisition process is executed. This sensor information acquisition process is the same as FIG. 8 except for the number of measurements. The number of measurements at each frequency f is m1/2, where m1>n. In other words, the number of measurements is greater in S39 than in S34.

The reason that the number of measurements can be increased is that S37 and S38 do not perform a full search for frequency f, so that the changed frequency f can be determined quickly. m1 can be increased beyond n by the number of measurements that can be made in a time that shortens the time it takes to change frequency f. After S39 and S34 are executed, the process returns to FIG. 5. When the process returns to FIG. 5, the initial value has already been set, so the process proceeds to S8.

Referring back to FIG. 9 for the explanation, if the result of the determination in S22 is NO, proceed to S26. In S26, it is determined whether the signal strength V at time tc is equal to or greater than the threshold value TH2 shown in FIG. 6. Time tc is the time at which the response wave R is predicted to be detected.

The time tc is determined as follows. The time at which the response wave R is detected, based on the time at which the transmission wave TW is transmitted, depends on the distance from the antenna 31 to the surface acoustic wave element 20 and the temperature of the surface acoustic wave element 20. In this embodiment, the latter is measured sequentially, and even before the start of temperature measurement, the temperature of the surface acoustic wave element 20 can be approximated to room temperature. By measuring or estimating the temperature in this manner, the delay time due to temperature can be calculated.

And before the measurement object 40 enters the furnace 42, the effect of reverberation is small. At that time, the peak of the response wave R, i.e., the time tc, can be confirmed.

If the peak can be confirmed, the distance from the antenna 31 to the surface acoustic wave element 20 can be estimated based on the time difference between transmitting the transmission wave TW and detecting the peak of the response wave R, and the speed of the radio waves. Once the distance can be estimated, the moving speed of the belt 41 is known, so the distance from the antenna 31 to the surface acoustic wave element 20 can be estimated thereafter. Therefore, once the distance can be estimated, the time tc can be determined successively thereafter.

Alternatively, a camera may be provided to detect the position of the surface acoustic wave element 20 and estimate the time tc based on the detected position. For each frequency, the transmission wave TW may be transmitted multiple times to calculate the average reverberation level.

Threshold TH2 is a value greater than threshold TH1. This is because threshold TH1 is a threshold for determining the noise level, whereas threshold TH2 is a threshold for determining the signal level.

If the determination result in S26 is YES, proceed to S27. In S27, a sensor information acquisition process is executed. The sensor information acquisition process in S27 is the same as that in FIG. 8 except for the number of measurements. The number of measurements at each frequency f is m2/2 times, where m2>n. In other words, the number of measurements is greater in S27 than in S34. This is because the time required for frequency search can be omitted. Note that m1 and m2 may be the same or different.

Summary of the First Embodiment
In the present embodiment described above, it is determined whether the signal strength V of the reverberation wave REV is within an allowable range. If the signal strength V of the reverberation wave REV is equal to or greater than the threshold value TH1, the frequency f transmitted by the transmitting unit 30c is changed (S35). By changing the frequency f, the effect of the reverberation wave REV can be reduced and the response wave R from the surface acoustic wave element 20 can be detected.

In addition, in this embodiment, the surface acoustic wave element 20 is installed on a moving measurement target 40. When measuring the temperature of a moving object, the surface acoustic wave element 20 has a first element portion 20a and a second element portion 20b to offset the phase change caused by the change in distance. Then, the two-element phase difference Δφ is calculated (S13).

In addition, to measure absolute temperature T over a wide range, burst signals are transmitted at two frequencies, f1 and f2, and two-element phase differences Δφ1 and Δφ2 are calculated for the two frequencies, f1 and f2 (S13). Then, the absolute temperature T is determined from the phase difference Δθ due to the frequency f of these two-element phase differences Δφ (S14, S15).

Furthermore, in this embodiment, by utilizing the configuration required to measure the absolute temperature T of a moving object over a wide range, the frequency f can be quickly changed to one that can reduce the effects of reverberation waves REV.

That is, by utilizing the need to transmit burst signals at the first frequency f1 and the second frequency f2, the reverberation level of the first frequency f1 and the reverberation level of the second frequency f2 are determined. Then, if the first frequency f1 exceeds the threshold THn, the first frequency f1 and the second frequency f2 are shifted to the higher frequency side (S37), and if the second frequency f2 exceeds the threshold THn, the first frequency f1 and the second frequency f2 are shifted to the lower frequency side (S38). In this way, the first frequency f1 and the second frequency f2 can be quickly changed to a frequency f at which the magnitude of the reverberation wave REV falls within the allowable range, rather than searching the entire settable frequency band.

Furthermore, since the frequency f can be changed quickly, the number of measurements can be increased in the subsequent sensor information acquisition process (S39). And, if the number of measurements is increased, the noise after averaging (S12) can be reduced, improving the signal-to-noise ratio and thus the accuracy of the absolute temperature T.

In addition, in this embodiment, when the first frequency f1 and the second frequency f2 are set by performing a full search of the settable frequency bands, the widest frequency band among the usable bands UAB is determined as the usable band UB (S5). The first frequency f1 and the second frequency f2 are determined so that the band between the first frequency f1 and the second frequency f2 is the center of the usable band UB. In this way, the time until the reverberation levels of the first frequency f1 and the second frequency f2 exceed the threshold value THn can be extended.

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, instead of the sensor information acquisition determination process shown in FIG. 9, the sensor information acquisition determination process shown in FIG. 13 is executed.

S41 is the same as S21, and transmits transmission waves TW1 and TW2 at the first frequency f1 and the second frequency f2, respectively, and acquires a received signal.

S42 corresponds to the reverberation intensity determination unit in the second embodiment. In S42, it is determined whether the value obtained by subtracting the signal strength Vb at time tb from the signal strength Vc at time tc is greater than a threshold value THv. Figure 14 shows examples of signal strengths Vc and Vb.

Vc-Vb is a value that correlates with the S/N ratio. The threshold value THv is determined in advance based on the required S/N ratio. Therefore, the judgment in S42 is to determine whether the S/N ratio is within an acceptable range, in other words, whether the signal strength V of the reverberation wave REV is within an acceptable range.

If Vc-Vb is equal to or less than THv in either the received signal of the first frequency f1 or the received signal of the second frequency f2, the result of the determination in S42 is NO. If the result of the determination in S42 is NO, the process proceeds to S43. In S43, it is determined that reading is not possible. The following S44 is the same as S24, and the frequency control shown in FIG. 11 is executed. If the result of the determination in S42 is YES, the process proceeds to S45. S45 is the same as S27, and the sensor information acquisition process is executed.

As in this second embodiment, it is also possible to determine whether the signal strength V of the reverberation wave REV is within an acceptable range based on the magnitude of Vc-Vb.

Third Embodiment
Next, a third embodiment will be described. In the third embodiment, a sensor information acquisition determination process shown in FIG. 15 is executed instead of the sensor information acquisition determination process shown in FIG.

S51 is the same as S21, and transmits transmission waves TW1 and TW2 at the first frequency f1 and the second frequency f2, respectively, and acquires a received signal.

S52 is specifically a process that executes S53 to S55. S52 corresponds to a reverberation intensity determination unit. S53 estimates the noise intensity at time tc. In this embodiment, the noise intensity at time tc is estimated from the signal intensity V at times t before and after time tc, which are times t before and after the time t at which the response wave R is estimated to be detected. Figure 16 shows times tb, td, and te as times t at which the noise intensity at time tc is estimated. Vb, Vd, and Ve are the received signal intensities at those times t. These times t are determined in advance.

A variety of estimation methods can be used, including estimation from the slope of the received signal, Kalman filters, particle filters, the least squares method, and sparse estimation.

In the next step S54, the intensity of the response wave R is estimated by subtracting the intensity of the noise estimated in S53 from Vc, which is the peak intensity of the response wave R. In step S55, it is determined whether the signal-to-noise ratio, which is the ratio of the intensity of the response wave R estimated in S54 to the intensity of the noise estimated in S53, is greater than a preset threshold value THsn.

If the determination result in S55 is NO, proceed to S56. In S56, it is determined that reading is not possible. The following S57 is the same as S24, and executes the frequency control shown in FIG. 11. If the determination result in S55 is YES, proceed to S58. S58 is the same as S27, and executes the sensor information acquisition process.

As in the third embodiment, it is also possible to determine whether the signal strength V of the reverberation wave REV is within an acceptable range based on the S/N ratio.

Fourth Embodiment
Next, a fourth embodiment will be described. In the fourth embodiment, instead of the frequency control shown in Fig. 11, a frequency control shown in Fig. 17 is executed. In Fig. 17, if the determination result in S31 is YES, S31-1 is executed. S31-1 is also a process performed by the characteristic change unit.

In S31-1, the characteristics of the antenna 31 are changed. Specifically, the electrical length of the antenna 31 is changed. A variable impedance circuit is connected to the antenna 31, and the electrical length of the antenna 31 is changed by changing the impedance of the circuit. For example, the electrical length is changed in constant increments so that the antenna 31 moves back and forth within a preset variable electrical length range. After executing S31-1, proceed to S32.

Changing the electrical length of the antenna 31 also changes the effect of the reverberation wave REV on the response wave R. Therefore, even in the fourth embodiment, the effect of the reverberation wave REV can be reduced and the response wave R can be detected.

Fifth Embodiment
18 shows an antenna 31 provided in a temperature measuring device 30 in the fifth embodiment. In the fifth embodiment, a plurality of antennas 31, specifically, three antennas 31, are provided. Note that three is just an example, and two, four or more antennas 31 may be provided.

In the fifth embodiment, instead of the frequency control shown in FIG. 17, the frequency control shown in FIG. 19 is executed. In FIG. 19, S31-2 is executed after S31-1. S31-2 is also a process performed by the characteristic change unit.

In S31-2, the antenna 31 used for transmission and reception is changed to a different antenna 31 from the previous one. The order in which the antennas 31 are changed is determined in advance. By changing the antenna 31 used for transmission and reception, the position of the antenna 31 used for transmission and reception is changed. If the position of the antenna 31 is changed, the resonance conditions change, and therefore the effect of the reverberation wave REV also changes. After executing S31-2, proceed to S32.

Changing the position of the transmitting and receiving antenna 31 also changes the effect of the reverberation wave REV on the response wave R. Therefore, even in the fifth embodiment, the effect of the reverberation wave REV can be reduced and the response wave R can be detected.

In addition, in the fifth embodiment, multiple antennas 31 are provided, and the reverberation waves REV are received even by antennas 31 that are not used for transmission or reception, so that the reverberation waves REV decay faster than when there is only one antenna 31.

Sixth Embodiment
In the sixth embodiment, even if the initial frequency has been determined, steps S2 and S3 in Fig. 5 may be executed. Since the belt 41 on which the partition plates 43 are arranged at regular intervals moves at a constant speed, the radio wave shielding state in the furnace 42 changes periodically.

Since the radio wave blocking state changes periodically, even if a transmission wave TW is transmitted at a constant period with the same transmission power, the signal strength V of the reply wave R increases and decreases periodically, as conceptually shown in FIG. 20. In time periods when the signal strength V of the reply wave R is low, it is often difficult to ensure a sufficient S/N ratio. Therefore, in this embodiment, the time period when the signal strength V of the reply wave R is at its lowest within the range of periodic fluctuations is estimated. The time period when the signal strength V is at its lowest is set to a certain time before and after the minimum value of the signal strength V.

The time period when the signal strength V is at its lowest is estimated, for example, from the period of the peak of the response wave R. Conversely, the time period when the signal strength V is at its lowest may be estimated from the time period when the response wave R cannot be detected. In addition, if position information of the partition plate 43 can be obtained from the control device that controls the furnace 42, the time period when the signal strength V is at its lowest may be estimated based on that position information.

After estimating the time period when signal strength V is at its lowest, the frequency search process (S2) and the initial frequency determination process (S3) are executed even during the time period when signal strength V is at its lowest.

By performing these processes, the first frequency f1 and the second frequency f2 can be reset to the center of the widest available frequency band. This allows the sensor information acquisition process (S27) to be performed more frequently, which can increase the signal-to-noise ratio.

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 addition to the characteristics described in the embodiment, the characteristic of the antenna 31 that is changed by the characteristic change unit includes the transmission power of the antenna 31. Therefore, the characteristic change unit may reduce the transmission power of the radio waves transmitted by the transmission unit 30c as a process. The degree of reduction may be a preset constant value or a constant rate. Furthermore, the greater the reverberation wave REV, the greater the amount or rate of reduction may be. Reducing the transmission power can reduce the reverberation wave REV.

<Modification 2>
In S36 and S37 of the first embodiment, the first frequency f1 and the second frequency f2 are shifted by the frequency change amount Δf. However, it is also possible to determine only whether the range in which the frequency f is searched is the high frequency side or the low frequency side, and to search for the frequency f on the determined side. Even in this way, the first frequency f1 and the second frequency f2 can be quickly changed to a frequency f at which the magnitude of the reverberation wave REV falls within the allowable range, rather than searching the entire settable frequency band.

<Modification 3>
In the embodiment, the transmitter characteristics to be changed are the frequency f or the frequency f and the antenna characteristics, but it is also possible to change only the antenna characteristics.

<Modification 4>
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 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 (passive sensor) 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: Radio section 30b: Calculation section 30c: Transmitter section 30d: Receiver section 31: Antenna 32: Transmission circuit 33: Coupler 34: Antenna duplexer 35: Quadrature demodulator 36i: Bandpass filter 36q: Bandpass filter 37i: AD converter 37q: AD converter 40: Measurement object (moving object) 41: Belt 42: Furnace 43: Partition plate 50: Operation terminal 51: Operation section 52: Display section 351: Phase shifter 352i: Mixer 352q: Mixer f1: First frequency f2: Second frequency R: Response wave REV: Reverberation wave T: Absolute temperature (absolute physical quantity) TW: Transmission wave UAB: Usable band UB: Used band V: Signal strength Δφ: Two-element phase difference S22, S42, S52: Reverberation strength determination unit S35, S31-1, S31-2: Characteristics change unit S13, S14: Two-frequency phase difference calculation unit S15: Physical quantity determination unit S2, S32: Frequency search processing unit S3, S33: Initial frequency determination unit

Claims (9)

A passive sensor reader including a transmitting unit (30c) that transmits a transmission wave (TW) toward a passive sensor for operating the passive sensor, and a receiving unit (30d) that receives a response wave (R) transmitted by the passive sensor in response to the transmission wave,
a reverberation intensity determination unit (S22, S42, S52) for determining whether or not a signal intensity of a reverberation wave received together with the reply wave is within a tolerable range based on a signal intensity of a received signal received by the receiving unit;
A passive sensor reading device comprising: a characteristic changing unit (S35, S31-1, S31-2) that changes a preset transmission unit characteristic capable of reducing the reverberation wave in the transmission unit based on the reverberation intensity judgment unit determining that the signal strength of the reverberation wave exceeds an allowable range. 2. A passive sensor reader as claimed in claim 1,
The characteristic change unit changes the frequency at which the transmission unit transmits. 2. A passive sensor reader as claimed in claim 1,
The characteristic change unit changes the characteristics of an antenna (31) provided in the transmission unit. 3. A passive sensor reader as claimed in claim 2, comprising:
The characteristic change unit changes the frequency of the radio waves transmitted by the transmission unit and the characteristics of an antenna (31) provided in the transmission unit. 5. A passive sensor reader as claimed in claim 3 or 4, comprising:
A passive sensor reader, wherein the antenna characteristic changed by the characteristic change unit is the electrical length of the antenna. 5. A passive sensor reader as claimed in claim 3 or 4, comprising:
A plurality of the antennas are provided,
The characteristic change unit changes the antenna that transmits the transmission wave to another antenna. 5. A passive sensor reader as claimed in claim 3 or 4, comprising:
The characteristic change unit reduces the transmission power of the radio waves transmitted by the transmission unit. A physical quantity measurement system comprising the passive sensor reader according to claim 2 or 4 and the passive sensor,
The passive sensor is a delay type surface acoustic wave element (20) having a first element portion (20a) and a second element portion (20b) arranged close to each other and having different propagation distances, the element being attached to a moving body (40);
the transmitting section sequentially transmits burst signals at a first frequency (f1) and a second frequency (f2) higher than the first frequency toward the surface acoustic wave element;
a two-frequency phase difference calculation unit (S13, S14) that calculates a two-frequency phase difference (Δθ) that is a phase difference between each of the reply waves and the radio waves of the two kinds of frequencies sequentially transmitted by the transmission unit;
a physical quantity determining unit (S15) that determines an absolute physical quantity (T) 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,
the two-frequency phase difference calculation unit calculates a two-element phase difference (Δφ) which is a phase difference between a phase of the response wave from the first element unit and a phase of the response wave from the second element unit for radio waves of two different frequencies, and calculates a phase difference due to a frequency of the two two-element phase differences as the two-frequency phase difference;
the reverberation intensity determination unit determines whether or not an influence of the reverberation wave is within a tolerable range based on a signal strength of the received signal when the burst signal is transmitted at the first frequency and a signal strength of the received signal when the burst signal is transmitted at the second frequency,
the characteristic modification unit changes the first frequency and the second frequency to a higher frequency based on a determination by the reverberation intensity determination unit that the signal strength of the reverberation wave at the first frequency has exceeded a tolerable range, and changes the first frequency and the second frequency to a lower frequency based on a determination by the reverberation intensity determination unit that the signal strength of the reverberation wave at the second frequency has exceeded a tolerable range. 9. The physical quantity measuring system according to claim 8,
the transmitting unit is capable of transmitting the burst signal by continuously changing a frequency within a settable frequency band in which the first frequency and the second frequency can be set;
a frequency search processing unit (S2, S32) that causes the transmitting unit to transmit the burst signal while changing the frequency over the entire range of the settable frequency band, and executes a frequency search process to detect the signal strength of the reverberation wave;
a first frequency determining unit that determines, based on the signal strength of the reverberation waves obtained in the frequency search processing unit, the widest frequency band among the frequency bands in which the intensities of the reverberation waves are continuously within the allowable range as a usage band, and determines the first frequency and the second frequency such that the frequency band between the first frequency and the second frequency is at the center of the usage band .

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