Waveform shaping device and gas concentration measuring device

Abstract

To accurately measure a concentration of gas.SOLUTION: A waveform shaping device comprises: a receiving unit 16 that receives ultrasonic waves having a frequency according to a frequency control value, and outputs a received signal; and an analysis unit 18 that generates a shaped received signal obtained by combining an adjusted signal obtained by delaying the received signal and adjusting its level with the received signal. The analysis unit 18 obtains an evaluation value obtained by combining and integrating a delayed signal obtained by delaying the received signal by a delay time according to the frequency control value and the received signal, and searches for the frequency control value when the evaluation value is minimal. The analysis unit 18 generates the adjusted signal based on the delay signal corresponding to the frequency control value when the evaluation value is minimal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a waveform shaping device and a gas concentration measuring device, and particularly to signal waveform shaping.

Background Art

[0002] Regarding fuel cell vehicles that run on electric power supplied from fuel cells, extensive research and development have been carried out. A fuel cell generates electric power by a chemical reaction between hydrogen and oxygen. Generally, hydrogen is supplied as fuel to the fuel cell, and oxygen is taken into the fuel cell from the surrounding air. A fuel cell vehicle is equipped with a hydrogen tank, and hydrogen is supplied from the hydrogen tank to the fuel cell. When the hydrogen in the hydrogen tank decreases, hydrogen is supplied from a hydrogen supply device installed at a service station to the hydrogen tank of the fuel cell vehicle.

[0003] Since hydrogen is a flammable gas, it is necessary to monitor for hydrogen leakage from fuel cell vehicles and hydrogen supply devices. Therefore, a hydrogen concentration measuring device is widely used together with fuel cell vehicles and hydrogen supply devices. The hydrogen concentration measuring device has a function of measuring the concentration of hydrogen contained in the air and issuing an alarm when the hydrogen concentration exceeds a predetermined value.

[0004] The following Patent Document 1 describes a device for measuring the concentration of a specific gas. This device measures the concentration of a specific gas based on the propagation speed of ultrasonic waves in the air to be measured. The propagation time from when ultrasonic waves are transmitted from a transmission unit until the ultrasonic waves that have propagated through a measurement section in a concentration measurement space are received by a reception unit is measured, the propagation speed is measured from this propagation time, and further, the concentration of the gas is measured.

[0005] Patent Document 2 describes a gas concentration sensor that transmits ultrasonic waves into a measurement chamber, receives the reflected waves reflected by the wall surface of the measurement chamber, determines the propagation time of the ultrasonic waves through the measurement chamber, and further determines the propagation speed to detect the concentration of the gas to be measured. It is described that the propagation time is determined from the difference between the time when the first reflected wave first received by the ultrasonic element is received and the time when the second reflected wave later received by the ultrasonic element is received.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] As described in Patent Document 2, when determining the time for ultrasonic waves to propagate through the measurement chamber from the difference between the time when the first ultrasonic wave first received by the ultrasonic element is received and the time when the second ultrasonic wave later received by the ultrasonic element is received, the following problems may occur. That is, when the propagation distance in the measurement chamber is short or the propagation speed is high, the first ultrasonic wave and the second ultrasonic wave may overlap on the time axis, resulting in an error in the measurement of the propagation time.

[0008] An object of the present invention is to accurately measure the concentration of a gas.

Means for Solving the Problems

[0009] The present invention includes a receiving unit that receives ultrasonic waves of a frequency according to a frequency control value and outputs a received signal, an analysis unit that generates a shaped received signal obtained by synthesizing an adjustment signal obtained by delaying and adjusting the level of the received signal and the received signal, the analysis unit obtaining an evaluation value obtained by synthesizing and integrating a delay signal obtained by delaying the received signal by a delay time corresponding to the frequency control value and the received signal, searching for the frequency control value when the evaluation value becomes minimum, and generating the adjustment signal based on the delay signal corresponding to the frequency control value when the evaluation value becomes minimum.

[0010] Desirably, the analysis unit obtains a level evaluation value obtained by synthesizing and integrating a level-adjusted delay signal obtained by multiplying the delay signal corresponding to the frequency control value when the evaluation value becomes minimum by a level adjustment coefficient and the received signal, searches for the level adjustment coefficient when the level evaluation value becomes minimum, and generates the adjustment signal based on the level-adjusted delay signal corresponding to the level adjustment coefficient when the level evaluation value becomes minimum.

[0011] Further, the present invention includes a concentration measurement space for measuring a gas concentration, a transmission unit that transmits ultrasonic waves to the concentration measurement space according to a transmission pulse signal, a reception unit that receives ultrasonic waves propagated through the concentration measurement space and outputs a received signal, and an analysis unit that obtains a space propagation time during which ultrasonic waves propagate through the concentration measurement space based on a timing at which a plurality of pulses of the received signal are output from the reception unit, and obtains the concentration of the gas to be measured based on the space propagation time, the analysis unit generating a shaped received signal by synthesizing an adjustment signal obtained by delaying and adjusting the level of the received signal and the received signal, and obtaining the space propagation time based on the shaped received signal.

[0012] Desirably, the analysis unit obtains the space propagation time based on a difference between a first reception timing at which a pulse of the received signal is first output from the reception unit after the transmission pulse signal is input to the transmission unit and a second reception timing at which a pulse of the received signal is output from the reception unit for the second time after the transmission pulse signal is input to the transmission unit.

[0013] Preferably, the transmitting unit transmits ultrasonic waves having a frequency according to a frequency control value. Separately from the process of obtaining the concentration of the gas, the analyzing unit obtains an evaluation value obtained by synthesizing, integrating, and delaying the received signal by a delay time corresponding to the frequency control value with the received signal, searches for the frequency control value when the evaluation value becomes minimum, and in the process of obtaining the concentration of the gas, generates the delay signal corresponding to the frequency control value when the evaluation value becomes minimum, and generates the adjustment signal based on the delay signal.

[0014] Preferably, separately from the process of obtaining the concentration of the gas to be measured, the analyzing unit obtains a level evaluation value obtained by synthesizing, integrating, and multiplying a level adjustment coefficient by the delay signal corresponding to the frequency control value when the evaluation value becomes minimum with the received signal, searches for the level adjustment coefficient when the level evaluation value becomes minimum, and in the process of obtaining the concentration of the gas, generates the level adjustment delay signal corresponding to the level adjustment coefficient when the level evaluation value becomes minimum, and generates the adjustment signal based on the level adjustment delay signal.

Advantages of the Invention

[0015] According to the present invention, the concentration of a gas can be accurately measured.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0017] Embodiments of the present invention will be described with reference to the respective drawings. The same components shown in a plurality of drawings are denoted by the same reference numerals to simplify the description.

[0018] FIG. 1 shows the configuration of a gas concentration measuring apparatus 100 according to an embodiment of the present invention. The gas concentration measuring apparatus 100 includes a housing 10, a transmitting unit 14, a receiving unit 16, and an analyzing unit 18. The housing 10 forms an analysis unit accommodation space 20 and a concentration measurement space 22. The concentration measurement space 22 is a cylindrical space with both ends closed. The transmitting unit 14 is disposed at one end of the concentration measurement space 22, and the receiving unit 16 is disposed at the other end.

[0019] The analysis unit 18 is accommodated in the analysis unit accommodation space 20. The analysis unit 18 is constituted by an electronic circuit, and the electronic circuit may be fixed in the analysis unit accommodation space 20 in a state of being fixed to a substrate.

[0020] Each of the transmitting unit 14 and the receiving unit 16 includes an ultrasonic vibrator. The transmitting unit 14 and the receiving unit 16 are connected to the analyzing unit 18. The transmitting unit 14 transmits ultrasonic waves to the concentration measurement space 22 according to the control of the analyzing unit 18. That is, the analyzing unit 18 outputs a transmission pulse signal, which is an electrical signal, to the transmitting unit 14. The transmitting unit 14 converts the transmission pulse signal into ultrasonic waves and transmits them. The receiving unit 16 receives the ultrasonic waves propagated through the concentration measurement space 22. The receiving unit 16 converts the received ultrasonic waves into a received signal, which is an electrical signal, and outputs it to the analyzing unit 18.

[0021] Based on the timing at which a plurality of pulses of the received signal are output from the receiving unit 16, the analysis unit 18 obtains the spatial propagation time for the ultrasonic wave to propagate through the concentration measurement space 22, and obtains the concentration of the gas to be measured based on the spatial propagation time.

[0022] The analysis unit 18 measures the spatial propagation time required for the ultrasonic wave to propagate from one end to the other end of the concentration measurement space 22 by the process described below. After outputting a transmission pulse signal to the transmission unit 14, the analysis unit 18 determines the spatial propagation time based on the difference (time difference) between the first reception timing at which a pulse of the received signal (received pulse) is first output from the receiving unit 16 and the second reception timing at which the received pulse is output from the receiving unit 16 for the second time.

[0023] The first received pulse output from the receiving unit 16 corresponds to the direct ultrasonic wave first received by the receiving unit 16. The direct ultrasonic wave is the ultrasonic wave transmitted from the transmitting unit 14, propagating through the concentration measurement space 22 from one end to the other end, and received by the receiving unit 16. The second received pulse output from the receiving unit 16 for the second time corresponds to the reflected ultrasonic wave that propagates through the concentration measurement space 22 for one and a half round trips after being transmitted from the transmitting unit 14 and is received by the receiving unit 16. The reflected ultrasonic wave is the ultrasonic wave transmitted from the transmitting unit 14, propagating through the concentration measurement space 22 from one end to the other end, reflected at the other end, propagating through the concentration measurement space 22 from the other end to one end, and further reflected at one end and propagating through the concentration measurement space 22 to be received by the receiving unit 16.

[0024] FIG. 2 schematically shows the time waveform of the received pulse output from the receiving unit 16. A transmission pulse signal is output from the analysis unit 18 to the transmission unit 14 at time t = 0. The received signal output from the receiving unit 16 to the analysis unit 18 includes a received pulse having a time waveform of a sine wave amplitude-modulated in a pulse shape. The first received pulse (direct wave received pulse 24) output from the receiving unit 16 has the absolute value of the wave peak value maximized at time t = t1. The second received pulse (reflected wave received pulse 26) output from the receiving unit 16 for the second time has the absolute value of the wave peak value maximized at time t = t2, which is later than time t = t1.

[0025] FIG. 2 schematically shows an ideal time waveform of the received pulse output from the receiving unit 16. The actual received pulse has a time waveform (oscillation waveform) of free oscillation with a tail trailing behind the received pulse. FIG. 3 shows a time waveform obtained by simulation of the received signal. In this time waveform, the oscillation waveform of the direct wave received pulse 24 and the waveform of the reflected wave received pulse 26 overlap, and it is difficult for the device to recognize the waveform of the reflected wave received pulse 26.

[0026] Therefore, in the gas concentration measuring device 100 according to the embodiment of the present invention, the analysis unit 18 performs waveform shaping processing on the received signal to generate a shaped received signal with the oscillation waveform suppressed, and based on the direct wave received pulse and the reflected wave received pulse included in the shaped received signal, obtains the space propagation time for the ultrasonic wave to propagate through the concentration measurement space 22. Here, the waveform shaping processing is a process of generating an adjustment signal obtained by delaying the received signal and adjusting the level, and synthesizing the adjustment signal and the received signal to generate a shaped received signal.

[0027] FIG. 4 shows a specific configuration of the gas concentration measuring device 100. The gas concentration measuring device 100 includes a transmitting ultrasonic oscillator 42 included in the transmitting unit 14, a receiving ultrasonic oscillator 44 included in the receiving unit 16, and an analysis unit 18. The analysis unit 18 includes a transmission circuit 40, a reception circuit 46, a waveform shaping unit 48, and a gas concentration measurement unit 50. The waveform shaping unit 48 and the gas concentration measurement unit 50 may be configured by a processor that executes a program stored in advance.

[0028] The gas concentration measurement unit 50 controls the transmission circuit 40 to cause the transmission circuit 40 to output a transmission pulse signal. The transmission circuit 40 outputs the transmission pulse signal to the transmitting ultrasonic oscillator 42 in response to the control of the gas concentration measurement unit 50. At this time, the transmission circuit 40 sets the frequency of the transmission pulse signal according to the frequency control value determined by the waveform shaping unit 48. The transmitting ultrasonic oscillator 42 transmits ultrasonic waves having a frequency according to the frequency control value in response to the transmission pulse signal.

[0029] The credit ultrasonic vibrator 44 converts the ultrasonic wave that has propagated through the concentration measurement space 22 into a received signal that is an electrical signal, and outputs it to the receiving circuit 46. The receiving circuit 46 converts the received signal into a digital signal and outputs it to the waveform shaping unit 48. The waveform shaping unit 48 performs waveform shaping processing on the received signal to generate a shaped received signal, and outputs it to the gas concentration measurement unit 50.

[0030] Based on the direct wave reception pulse and the reflected wave reception pulse included in the shaped reception signal, the gas concentration measurement unit 50 may detect the first reception timing and the second reception timing, and subtract the time indicating the first reception timing from the time indicating the second reception timing to obtain the spatial propagation time.

[0031] The gas concentration measurement unit 50 may store the direct wave reception pulse and the reflected wave reception pulse included in the shaped reception signal, and execute the following processing to obtain the spatial propagation time. That is, the gas concentration measurement unit 50 obtains the correlation value between the shifted pulse obtained by advancing the reflected wave reception pulse by the shift time τ and the direct wave reception pulse. The gas concentration measurement unit 50 obtains the shift time τ when the correlation value is maximized as the spatial propagation time.

[0032] Note that when obtaining the spatial propagation time, the Euclidean distance may be used instead of the correlation value. The Euclidean distance is defined as the square root of the value obtained by integrating the squares of the differences between two signals. When obtaining the Euclidean distance, for example, the magnitudes of one or both signals may be adjusted so that the maximum values of the two signals are the same. The smaller the Euclidean distance, the greater the degree of approximation between the two signals.

[0033] A concentration calculation formula (Equation 1) representing the relationship between the propagation speed of ultrasonic waves and the concentration of a specific gas contained in the gas through which the ultrasonic waves propagate is widely known. The analysis unit 18 obtains the gas concentration from the spatial propagation time T and the length L of the concentration measurement space 22 using the concentration calculation formula (Equation 1) or a mathematical formula having the same meaning as it.

[0034]

Equation

[0035] Here, k is the specific heat ratio of the gas, R is the gas constant, and T mp is the temperature of the concentration measurement space 22. M h is the molecular weight of the gas to be measured, and M a is the molecular weight of the air that does not contain the gas to be measured. Assuming that the composition of the air is only 80% nitrogen and 20% oxygen, the specific heat ratio k can be set to 1.4. Also, the gas constant R is 8.31, and the molecular weight M a of the air is 28.8. When the gas to be measured is hydrogen, the molecular weight M h is 2.0. L / T in (Equation 1) represents the propagation speed of the ultrasonic wave.

[0036] FIG. 5 shows the specific configuration of the waveform shaping unit 48. The waveform shaping unit 48, together with the receiving unit 16 and the receiving circuit 46, constitutes a waveform shaping device, and performs waveform shaping processing on the received signal to generate a shaped received signal. The waveform shaping unit 48 includes a first memory 60, a second memory 62, and an arithmetic processing unit 64. The arithmetic processing unit 64 includes a delay unit 66, a level adjuster 68, an adder 70, an integrator 72, a delay time determiner 74, and a level determiner 76.

[0037] The waveform shaping unit 48 operates in either a calibration mode or a waveform shaping mode. The calibration mode is an operation mode for determining control variables for generating a shaped received signal. The waveform shaping mode is an operation mode for generating a shaped received signal using the control variables determined in the calibration mode. The control variables include a frequency control value for determining the frequency of the ultrasonic wave transmitted by the transmitting unit 14, and a level adjustment coefficient applied to the received signal.

[0038] The operation in the waveform shaping mode will be described. The operation in the waveform shaping mode is executed after the control variables are obtained by the operation in the calibration mode. That is, the operation in the waveform shaping mode is executed when the gas concentration measurement unit 50 measures the gas concentration. As described above, the transmission ultrasonic vibrator 42 transmits ultrasonic waves to the concentration measurement space 22, and the reception ultrasonic vibrator 44 receives ultrasonic waves from the concentration measurement space 22. Based on the transmission and reception of ultrasonic waves, the received signals are stored in the first memory 60 and the second memory 62.

[0039] The delay unit 66 reads the received signal from the first memory 60 and outputs a delayed signal obtained by delaying the received signal by the delay time determined by the delay time determination unit 74 to the level adjuster 68. The level adjuster 68 multiplies the delayed signal by the level adjustment coefficient determined by the level determination unit 76 to generate an adjustment signal (level-adjusted delayed signal) and outputs it to the adder 70. The adder 70 outputs a shaped received signal obtained by adding the adjustment signal and the received signal read from the second memory 62.

[0040] FIG. 6 shows the time waveform of the shaped received signal obtained by simulation. Compared with the time waveform of the received signal shown in FIG. 3, the vibration waveform between the direct wave reception pulse 24 and the reflected wave reception pulse 26 is suppressed, and the peak of the direct wave reception pulse 24 and the peak of the reflected wave reception pulse 26 are prominently shown.

[0041] Next, the calibration mode will be described. The operation in the calibration mode is executed separately from the measurement of the gas concentration. Ultrasonic waves are transmitted and received to and from the concentration measurement space 22 by the same process as when measuring the gas concentration. Based on the transmission and reception of ultrasonic waves, the received signals are stored in the first memory 60 and the second memory 62.

[0042] While the control variable is determined by the calibration mode, the transmission circuit 40 outputs a transmission pulse signal having a frequency according to a provisional frequency control value (frequency candidate value) output by the delay time determiner 74 to the transmission ultrasonic vibrator 42. Also, while the control variable is determined by the calibration mode, the delay unit 66, the level adjuster 68, the adder 70, and the integrator 72 execute the following processes to obtain an evaluation value. The evaluation value is a value obtained by synthesizing and integrating a delayed signal obtained by delaying the received signal by a delay time corresponding to the frequency control value and the received signal.

[0043] The delay unit 66 reads the received signal from the first memory 60 and outputs a delayed signal obtained by delaying the received signal by a delay time (provisional delay time) provisionally determined by the delay time determiner 74 to the level adjuster 68. The level adjuster 68 multiplies the delayed signal by a level adjustment coefficient (provisional level adjustment coefficient) provisionally determined by the level determiner 76 and outputs it to the adder 70. The adder 70 outputs a composite signal obtained by adding the delayed signal (provisional level adjustment delayed signal) multiplied by the provisional level adjustment coefficient and the received signal read from the second memory 62 to the integrator 72. The integrator 72 obtains, as an evaluation value, a cumulative value obtained by integrating the square of the composite signal over a predetermined time, and outputs it to the delay time determiner 74 and the level determiner 76.

[0044] The delay time determiner 74 determines the delay time based on the evaluation value thus obtained. While the delay time determiner 74 determines the delay time, the level determiner 76 fixes the level adjustment coefficient output to the level adjuster 68 to 1.

[0045] Here, there is a deviation between the frequency of the transmission pulse signal and the frequency of the received signal due to the inherent characteristics of the transmission ultrasonic transducer 42 and the reception ultrasonic transducer 44. As a result, the frequency control value for performing appropriate waveform shaping becomes unknown. When determining the delay time, it is necessary to determine an appropriate frequency control value and determine the delay time based on that frequency control value. Therefore, the delay time determiner 74 determines the frequency control value by the following search process, and determines the delay time by multiplying the reciprocal (period control value) of the frequency control value by N. Here, N is a predetermined positive number, for example, N = 2.5.

[0046] In FIG. 7, the relationship between the frequency candidate value (temporary frequency control value) and the evaluation value is shown by a curve 80. The horizontal axis represents the frequency candidate value and the vertical axis represents the evaluation value. In this figure, the evaluation value when the level of the delay signal is assumed to be 0, that is, the cumulative value obtained by integrating the square of the received signal over a predetermined time is shown by a straight line 82.

[0047] The evaluation value indicated by the vertical axis is the evaluation value when N times the reciprocal of the frequency candidate value is used as the temporary delay time. As shown in FIG. 7, the evaluation value repeats increases and decreases with an increase in the frequency candidate value. In this embodiment, N = 2.5, and among the minimum-frequency candidate values at which the evaluation value becomes minimum, the minimum-frequency candidate value at which the evaluation value is the smallest, that is, the second minimum-frequency candidate value from the left is the frequency candidate value (frequency control value) to be obtained. By determining N times the reciprocal of this frequency control value as the delay time, a well-shaped received signal can be obtained.

[0048] Therefore, the delay time determiner 74 changes the frequency candidate value, obtains the evaluation value from the integrator 72 while changing the temporary delay time obtained as N times the reciprocal of the frequency candidate value, and searches for the minimum-frequency candidate value at which the evaluation value is the smallest. The delay time determiner 74 obtains the searched minimum-frequency candidate value as the frequency control value. The delay time determiner 74 determines the delay time by multiplying the reciprocal (period control value) of the frequency control value by N.

[0049] The process of the delay time determiner 74 searching for the minimum frequency candidate value with the smallest evaluation value may be performed as follows. In the first step, the delay time determiner 74 obtains evaluation values E1, E1p, and E1m for frequency candidate values F1, F1 + Δ1, and F1 - Δ1, respectively. However, the frequency candidate value F1 and the deviation width Δ1 are set such that the frequency candidate value F1 - Δ1 exceeds the lower limit value of the range in which the frequency candidate value changes, and the frequency candidate value F1 + Δ1 is less than the upper limit value of the range in which the frequency candidate value changes. Also, the range in which the frequency candidate value changes is the range between two maximum frequency candidate values sandwiching the minimum frequency candidate value with the smallest evaluation value. Here, the maximum frequency candidate value refers to the frequency candidate value when the evaluation value becomes the maximum value.

[0050] The delay time determiner 74 determines the frequency candidate value corresponding to the smallest of the evaluation values E1, E1p, and E1m as the second step center value F2. That is, when the evaluation value E1m is the smallest, the delay time determiner 74 determines the frequency candidate value F1 - ΔF1 as the second step center value F2. Also, when the evaluation value E1 is the smallest, the delay time determiner 74 determines the frequency candidate value F1 as the second step center value F2, and when the evaluation value E1p is the smallest, the frequency candidate value F1 + Δ1 is determined as the second step center value F2.

[0051] In the second step, the delay time determiner 74 obtains evaluation values E2, E2p, and E2m for frequency candidate values F2 (the second step center value), F2 + Δ2, and F2 - Δ2, respectively. However, the deviation width Δ2 is a value smaller than the deviation width Δ1. The delay time determiner 74 determines the frequency candidate value corresponding to the smallest of the evaluation values E2, E2p, and E2m as the third step center value F3.

[0052] In the third step, the delay time determiner 74 obtains evaluation values E3, E3p, and E3m for frequency candidate values F3 (the center value of the third step), F3 + Δ3, and F3 - Δ3, respectively. Here, the deviation width Δ3 is a value smaller than the deviation width Δ2. The delay time determiner 74 determines the frequency candidate value corresponding to the smallest of the evaluation values E3, E3p, and E3m as the center value F4 of the fourth step.

[0053] Thus, in the j-th step, the delay time determiner 74 obtains evaluation values Ej, Ejp, and Ejm for frequency candidate values Fj, Fj + Δj, and Fj - Δj, respectively. Here, the deviation width Δj is a value smaller than the deviation width Δj - 1. The delay time determiner 74 determines the frequency candidate value corresponding to the smallest of the evaluation values Ej, Ejp, and Ejm as the center value Fj+1 of the (j + 1)-th step. Here, j is an integer of 2 or more.

[0054] The delay time determiner 74 determines the center value FM of the M-th step obtained in the (M - 1)-th step as the minimum frequency candidate value with the smallest evaluation value, that is, the final frequency control value. Here, M is an integer of 2 or more such that the deviation width ΔM - 1 becomes sufficiently small.

[0055] Next, the process by which the level determiner 76 obtains the level adjustment coefficient will be described. While the level determiner 76 determines the level adjustment coefficient, the delay time determiner 74 fixes the delay time output to the delay device 66 to the finally obtained delay time. The level determiner 76 obtains an evaluation value (level evaluation value) from the integrator 72 while changing a provisional level adjustment coefficient, and determines the provisional level adjustment coefficient when the level evaluation value becomes minimum as the final level adjustment coefficient.

[0056] In the operation of the waveform shaping mode, the delay time determiner 74 outputs the delay time determined by the operation of the calibration mode to the delay device 66, and the level determiner 76 outputs the level adjustment coefficient determined by the operation of the calibration mode to the level adjuster 68.

[0057] According to such processing, even when there is a deviation between the frequency of the transmission pulse signal and the frequency of the reception signal, an appropriate delay time for generating the adjustment signal is determined, and the adjustment signal is adjusted to an appropriate level. As a result, the vibration waveform is suppressed, and a shaped reception signal in which the peak of the direct wave reception pulse and the peak of the reflected wave reception pulse are prominently represented is generated by the waveform shaping unit 48. Therefore, the accuracy of the gas concentration required by the gas concentration measurement unit 50 is improved.

[0058] FIG. 8 shows an example of the process of gas concentration measurement. In gas concentration measurement, the measurement process is repeated at a predetermined measurement period. One measurement process includes operations in the calibration mode, transmission and reception of ultrasonic waves for gas concentration measurement, waveform shaping of the reception signal (operation in the waveform shaping mode), and gas concentration measurement.

[0059] In the operation of the calibration mode in one measurement process, ultrasonic waves are transmitted and received four times. That is, the first to fourth transmissions and receptions are performed. By the first transmission and reception, the second transmission and reception, and the third transmission and reception, the delay time determination unit 74 acquires evaluation values Ejm, Ej, and Ejp, respectively. The delay time determination unit 74 sets the smallest of the evaluation values Ejm, Ej, and Ejp as the center value Fj+1 of the (j + 1)-th step.

[0060] In the operation of the calibration mode in the next measurement process, the delay time determination unit 74 acquires evaluation values E(j+1)m, E(j+1), and E(j+1)p by the same process. The delay time determination unit 74 sets the frequency candidate value corresponding to the smallest of the evaluation values E(j+1)m, E(j+1), and E(j+1)p as the center value Fj+2 of the (j + 2)-th step.

[0061] When the delay time determination unit 74 obtains the center value FM of the M-th step by repeating the measurement process, the delay time determination unit 74 determines the center value FM of the M-th step as a new frequency control value and updates the frequency control value.

[0062] Until the frequency control value is updated by the measurement process repeated M times, in the fourth transmission / reception, the process is executed using the previously determined frequency control value. The level determiner 76 determines and updates the level adjustment coefficient based on the received signal obtained by the fourth transmission / reception.

[0063] For the transmission / reception of ultrasonic waves for gas concentration measurement, waveform shaping of the received signal, and gas concentration measurement in one measurement process, they are executed using the frequency control value and the level adjustment coefficient that were last updated in the measurement process executed in the past.

[0064] Note that the process of determining the frequency candidate value corresponding to the smallest one among the evaluation values Ejm, Ej, and Ejp as the center value Fj+1 in the (j + 1)-th step may be performed by acquiring the set of the evaluation values Ejm, Ej, and Ejp a plurality of times. In this case, the delay time determiner 74 acquires the set of the evaluation values Ejm, Ej, and Ejp for the same j in a plurality of continuously executed measurement processes. The delay time determiner 74 determines the frequency candidate value corresponding to the one with the largest number of times of being the smallest among these three values among the evaluation values Ejm, Ej, and Ejp as the center value Fj+1 in the (j + 1)-th step.

[0065] For example, after acquiring the set of the evaluation values E1m, E1, and E1p three times, the center value F2 in the second step is determined. After acquiring the set of the evaluation values E2m, E2, and E2p three times, the center value F3 in the third step is determined. Further, after acquiring the set of the evaluation values E3m, E3, and E3p three times, the center value F4 in the fourth step is determined, and when the center value F4 in the fourth step is determined as the frequency control value, the frequency control value is determined by nine measurement processes. That is, every time the measurement process is executed nine times, the frequency control value is updated.

Explanation of Signs

[0066] 10 housing, 14 transmission unit, 16 reception unit, 18 analysis unit, 20 analysis unit accommodation space, 22 concentration measurement space, 24 direct wave reception pulse, 26 reflected wave reception pulse, 40 transmission circuit, 42 ultrasonic transducer for transmission, 44 ultrasonic transducer for reception, 46 reception circuit, 48 waveform shaping unit, 50 gas concentration measurement unit, 60 first memory, 62 second memory, 64 arithmetic processing unit, 66 delay unit, 68 level adjuster, 70 adder, 72 integrator, 74 delay time determiner, 76 level determiner, 80 curve showing the relationship between the frequency candidate value and the evaluation value, 82 straight line showing the cumulative value obtained by integrating the square of the reception signal over a predetermined time.

Claims

1. A receiving unit that receives ultrasonic waves of a frequency according to a frequency control value and outputs a received signal; An analysis unit that generates a shaped received signal obtained by synthesizing an adjustment signal obtained by delaying and adjusting the level of the received signal and the received signal; The analysis unit is: Obtain an evaluation value obtained by synthesizing and integrating a delay signal obtained by delaying the received signal by a delay time corresponding to the frequency control value and the received signal, and search for the frequency control value when the evaluation value becomes minimum, A waveform shaping device characterized by generating the adjustment signal based on the delay signal corresponding to the frequency control value when the evaluation value becomes minimum.

2. In the waveform shaping device according to claim 1, The analysis unit is: Obtain a level evaluation value obtained by synthesizing and integrating a level adjustment delay signal obtained by multiplying the delay signal corresponding to the frequency control value when the evaluation value becomes minimum by a level adjustment coefficient and the received signal, and search for the level adjustment coefficient when the level evaluation value becomes minimum, A waveform shaping device characterized by generating the adjustment signal based on the level adjustment delay signal corresponding to the level adjustment coefficient when the level evaluation value becomes minimum.

3. A concentration measurement space for measuring gas concentration; A transmission unit that transmits ultrasonic waves to the concentration measurement space according to a transmission pulse signal; A receiving unit that receives ultrasonic waves propagated through the concentration measurement space and outputs a received signal; An analysis unit that obtains a space propagation time for ultrasonic waves to propagate through the concentration measurement space based on the timing at which a plurality of pulses of the received signal are output from the receiving unit, and obtains the concentration of the gas to be measured based on the space propagation time; The analysis unit is: Generate a shaped received signal by synthesizing an adjustment signal obtained by delaying and adjusting the level of the received signal and the received signal, A gas concentration measurement device characterized by obtaining the space propagation time based on the shaped received signal.

4. In the concentration measurement device according to claim 3, The analysis unit is: Based on the difference between a first reception timing at which a pulse of the received signal is first output from the receiving unit after the transmission pulse signal is input to the transmission unit and a second reception timing at which a pulse of the received signal is output from the receiving unit for the second time after the transmission pulse signal is input to the transmission unit, obtain the space propagation time. A gas concentration measurement device characterized by this.

5. In the gas concentration measurement device according to claim 3 or claim 4, The transmitting unit transmits ultrasonic waves at a frequency according to a frequency control value. Separate from the process of obtaining the concentration of the gas, the analysis unit obtains an evaluation value obtained by synthesizing and integrating a delayed signal obtained by delaying the received signal by a delay time corresponding to the frequency control value and the received signal, searches for the frequency control value when the evaluation value becomes minimum, In the process of obtaining the concentration of the gas, a gas concentration measuring device is characterized in that a delayed signal corresponding to the frequency control value when the evaluation value becomes minimum is generated, and an adjustment signal is generated based on the delayed signal.

6. In the gas concentration measuring device according to claim 5, Separate from the process of obtaining the concentration of the gas to be measured, the analysis unit obtains a level evaluation value obtained by synthesizing and integrating a level-adjusted delayed signal obtained by multiplying the delayed signal corresponding to the frequency control value when the evaluation value becomes minimum by a level adjustment coefficient and the received signal, searches for the level adjustment coefficient when the level evaluation value becomes minimum, In the process of obtaining the concentration of the gas, a gas concentration measuring device is characterized in that a level-adjusted delayed signal corresponding to the level adjustment coefficient when the level evaluation value becomes minimum is generated, and an adjustment signal is generated based on the level-adjusted delayed signal.

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