Gas concentration measuring device

Abstract

To accurately measure concentration of a gas.SOLUTION: A gas concentration measuring device 100 includes: a transmission part 14 for transmitting ultrasonic waves to a concentration measurement space 22; a reception part 16 for receiving ultrasonic waves propagated through the concentration measurement space 22 and outputting reception signals; and a concentration measurement part 48 for obtaining spacial propagation time in which ultrasonic waves are propagated through the concentration measurement space 22 and obtaining concentration of a gas on the basis of the spacial propagation time. The concentration measurement part 48 includes: a first memory 60 and a second memory 62; and a time shift filter 64 for performing time shift processing to a reception signal stored in the first memory 60. A concentration measurement part 18 obtains a degree of approximation between a reception signal read from the second memory 62 and a time shift signal read from the first memory 60 and subjected to time shift processing, obtains a time difference of pulses of reception signals that are adjacent on a time axis on the basis of minute shift time and a degree of approximation in time shift processing, and obtains spacial propagation time on the basis of the time difference.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a gas concentration measuring device, and more particularly to measuring the propagation time of ultrasonic waves. [Background technology]

[0002] Research and development is being conducted extensively on fuel cell vehicles, which run on electricity supplied from fuel cells. Fuel cells generate electricity through a chemical reaction between hydrogen and oxygen. Generally, hydrogen is supplied to the fuel cell as fuel, and oxygen is taken in from the surrounding air. Fuel cell vehicles are equipped with hydrogen tanks, which supply hydrogen to the fuel cell. When the hydrogen in the hydrogen tank runs low, hydrogen is supplied to the fuel cell vehicle's hydrogen tank from a hydrogen supply device installed at a service station.

[0003] Because hydrogen is a flammable gas, it is necessary to monitor hydrogen leaks from fuel cell vehicles and hydrogen supply systems. Therefore, hydrogen concentration measuring devices are widely used along with fuel cell vehicles and hydrogen supply systems. Hydrogen concentration measuring devices have the function of measuring the concentration of hydrogen in the air and sounding an alarm when the hydrogen concentration exceeds a predetermined value.

[0004] Patent Document 1 below 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 being measured. The device measures the propagation time from when ultrasonic waves are transmitted from a transmitter until the ultrasonic waves propagate through a measurement section in a concentration measurement space and are received by a receiver, and the propagation speed is calculated from this propagation time, which in turn determines the concentration of the gas.

[0005] Patent Document 2 describes a gas concentration sensor that detects the concentration of a gas to be measured by transmitting ultrasonic waves into a measurement chamber, receiving the waves reflected by the wall of the measurement chamber, calculating the propagation time for the ultrasonic waves to propagate through the measurement chamber, and further calculating the propagation velocity. It describes that the propagation time is calculated from the difference between the time when a first reflected wave, which is received first by an ultrasonic element, is received and the time when a second reflected wave, which is received later by the ultrasonic element, is received. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-100916 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-249691 Summary of the Invention [Problem to be solved by the invention]

[0007] When determining the time it takes for an ultrasonic wave to propagate through a measurement chamber based on the time (timing) at which the ultrasonic wave is received by an ultrasonic element, the following problem may occur: When the received signal output from the ultrasonic element is digitally sampled, it becomes difficult to determine the propagation time in a time shorter than the sampling period, and sufficient measurement accuracy for the gas concentration may not be obtained.

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

[0009] The present invention Gas concentration measuring device relating toa transmitting unit that transmits ultrasonic waves into the concentration measurement space in response to a transmission pulse signal; a receiving unit that receives the ultrasonic waves that have propagated through the concentration measurement space and outputs a reception signal; and an analyzing unit that calculates a spatial propagation time for the ultrasonic waves to propagate through the concentration measurement space based on timings at which a plurality of pulses of the reception signal are output from the receiving unit, and calculates the concentration of the gas to be measured based on the spatial propagation time, wherein the analyzing unit includes a first memory and a second memory that store the reception signal, a time shift filter that performs time shift processing on the reception signal stored in the first memory, and a control and calculation unit that calculates the spatial propagation time, and calculates a degree of approximation between the reception signal read from the second memory and the time shifted signal that has been read from the first memory and has been subjected to the time shift processing, and calculates a time difference between pulses of the reception signal that are adjacent on the time axis based on the minute shift time in the time shift processing and the degree of approximation. The analysis unit further includes a sampling period shift unit that performs sampling period shift processing on the received signal read from the second memory, in which the sampling period shift processing shifts the signal on the time axis in sampling period units, and calculates a degree of approximation between the received signal that has been subjected to the sampling period shift processing and the time-shifted signal, and a minute shift time in the time shift processing is shorter than the sampling period. It is characterized by:

[0012] Preferably, the calculation unit searches for the minute shift time when the degree of approximation indicated by the degree of approximation is greatest, and calculates the time difference based on the minute shift time when the degree of approximation indicated by the degree of approximation is greatest.

[0013] Preferably, the degree of approximation is a Euclidean distance between the received signal read from the second memory and the time-shifted signal.

[0014] Preferably, the degree of approximation is a correlation value between the received signal read from the second memory and the time-shifted signal.

[0015] Preferably, the time shift filter is an FIR filter. [Effects of the Invention]

[0016] According to the present invention, the concentration of a gas can be measured accurately. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing a configuration of a gas concentration measuring device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram schematically showing a time waveform of a received pulse. [Figure 3] FIG. 1 is a diagram showing a specific configuration of a gas concentration measuring device. [Figure 4] FIG. 2 is a diagram showing a specific configuration of a gas concentration measuring unit. DETAILED DESCRIPTION OF THE INVENTION

[0018] The embodiments of the present invention will be described with reference to the drawings. The same components shown in multiple drawings will be denoted by the same reference numerals to simplify the description.

[0019] 1 shows the configuration of a gas concentration measuring device 100 according to an embodiment of the present invention. The gas concentration measuring device 100 comprises a housing 10, a transmitter 14, a receiver 16, and an analyzer 18. The housing 10 forms an analyzer housing space 20 and a concentration measurement space 22. The concentration measurement space 22 is a cylindrical space with both ends closed. The transmitter 14 is disposed at one end of the concentration measurement space 22, and the receiver 16 is disposed at the other end.

[0020] The analysis unit accommodating space 20 accommodates an analysis unit 18. The analysis unit 18 is configured by an electronic circuit, and the electronic circuit may be fixed to the analysis unit accommodating space 20 in a state where it is fixed to a substrate.

[0021] The transmitting unit 14 and the receiving unit 16 each include 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 under 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 that have propagated through the concentration measurement space 22. The receiving unit 16 converts the received ultrasonic waves into a reception signal, which is an electrical signal, and outputs it to the analyzing unit 18.

[0022] The analysis unit 18 calculates the spatial propagation time that the ultrasonic waves take to propagate through the concentration measurement space 22 based on the timing at which multiple pulses of the received signal are output from the receiving unit 16, and calculates the concentration of the gas to be measured based on the spatial propagation time.

[0023] The analysis unit 18 measures the spatial propagation time required for an 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 calculates the time difference between pulses of the reception signal that are adjacent on the time axis, and calculates the spatial propagation time based on this time difference. In other words, the analysis unit 18 calculates the spatial propagation time based on the difference (time difference) between the first reception timing at which the reception signal pulse (reception pulse) is first output from the reception unit 16, and the second reception timing at which the reception pulse is secondly output from the reception unit 16.

[0024] The first received pulse output from the receiving unit 16 corresponds to the direct ultrasonic wave that is first received by the receiving unit 16. The direct ultrasonic wave is an ultrasonic wave that is transmitted from the transmitting unit 14, propagates through the concentration measurement space 22 from one end to the other, and is received by the receiving unit 16. The second received pulse output from the receiving unit 16 corresponds to the reflected ultrasonic wave that is transmitted from the transmitting unit 14, propagates through the concentration measurement space 22 for one and a half round trips, and is received by the receiving unit 16. The reflected ultrasonic wave is an ultrasonic wave that is transmitted from the transmitting unit 14, propagates through the concentration measurement space 22 from one end to the other, is reflected at the other end, propagates through the concentration measurement space 22 from the other end to the one end, is further reflected at one end, propagates through the concentration measurement space 22, and is received by the receiving unit 16.

[0025] FIG. 2 shows a schematic diagram of the time waveform of the received pulse output from the receiving unit 16. At time t=0, the analyzing unit 18 outputs a transmitted pulse signal to the transmitting unit 14. The received signal output from the receiving unit 16 to the analyzing unit 18 includes a received pulse having a sinusoidal time waveform that has been amplitude-modulated into a pulse shape. The first received pulse (direct wave received pulse 24) output from the receiving unit 16 reaches a maximum absolute value of its peak value at time t=t1. The second received pulse (reflected wave received pulse 26) output from the receiving unit 16 reaches a maximum absolute value of its peak value at time t=t2, which is later than time t=t1. The analyzing unit 18, using the configuration and processing described below, calculates the time difference equivalent to the time obtained by subtracting time t1 from time t2, and calculates the concentration of the gas to be measured based on this time difference.

[0026] 3 shows a specific configuration of gas concentration measuring device 100. Gas concentration measuring device 100 includes transmitting ultrasonic vibrator 42 included in transmitting unit 14, receiving ultrasonic vibrator 44 included in receiving unit 16, and analyzing unit 18. Analyzing unit 18 includes transmitting circuit 40, receiving circuit 46, and gas concentration measuring unit 48.

[0027] The gas concentration measurement unit 48 controls the transmission circuit 40 to cause it to output a transmission pulse signal. The transmission circuit 40 outputs the transmission pulse signal to the transmitting ultrasonic vibrator 42 in accordance with the control of the gas concentration measurement unit 48. The receiving ultrasonic vibrator 44 converts the ultrasonic waves propagating through the concentration measurement space 22 into a reception signal, which is an electrical signal, and outputs it to the reception circuit 46. The reception circuit 46 discretizes the reception signal at a predetermined sampling period, converts it into a digital signal, and outputs it to the gas concentration measurement unit 48.

[0028] The gas concentration measurement unit 48 stores the received signal and performs the following process to determine the spatial propagation time. That is, the gas concentration measurement unit 48 determines the degree of approximation between a pulse obtained by temporarily advancing the reflected wave received pulse by the shift time τ and a direct wave received pulse. Here, the degree of approximation is a value indicating the degree of approximation between two signals, such as the Euclidean distance between the two signals. The Euclidean distance is defined as the square root of the value obtained by time-integrating the square of the difference between the two signals. When determining the Euclidean distance, for example, the magnitude of one or both signals may be adjusted so that the maximum values ​​of the two signals are the same. The gas concentration measurement unit 48 determines the shift time τ when the degree of approximation indicated by the degree of approximation is greatest as the spatial propagation time.

[0029] A concentration calculation formula (Equation 1) that expresses 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 uses the concentration calculation formula (Equation 1) or an equation having the same meaning to calculate the gas concentration from the spatial propagation time T and the length L of the concentration measurement space 22.

[0030]

number

[0031] where 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. h is the molecular weight of the gas to be measured, and M a is the molecular weight of air that does not contain the gas to be measured. If we assume that the composition of air is 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 of air is a When the gas to be measured is hydrogen, the molecular weight M h is 2.0. In (Equation 1), L / T represents the propagation speed of ultrasonic waves.

[0032] 4 shows a specific configuration of the gas concentration measurement unit 48. The gas concentration measurement unit 48 includes a first memory 60, a second memory 62, a time shift filter 64, a sampling period shift unit 66, a level correction value determination unit 68, a level correction unit 70, an approximation calculation unit 72, and a control and calculation unit 74. The gas concentration measurement unit 48 may be configured by a processor. The processor configures each component (the time shift filter 64, the sampling period shift unit 66, the level correction value determination unit 68, the level correction unit 70, the approximation calculation unit 72, and the control and calculation unit 74) by executing a program.

[0033] The first memory 60 and the second memory 62 may be configured by separate pieces of hardware or by a single piece of hardware. When the first memory 60 and the second memory 62 are configured by a single piece of hardware, the first memory 60 and the second memory 62 may be configured by storing or erasing information in the same storage area in a time-division manner.

[0034] An overview of the operation of the gas concentration measurement unit 48 will now be described. The same received signal is stored in the first memory 60 and the second memory 62. The sampling period shift unit 66 reads the received signal from the second memory 62. The sampling period shift unit 66 performs sampling period shift processing on the received signal read from the second memory 62. The sampling period shift processing is processing that shifts the signal on the time axis in sampling period units.

[0035] That is, the sampling period shift unit 66 reads the received signal from the second memory 62, shifts the received signal on the time axis by the sampling period shift time set by the control and calculation unit 74, and outputs the shifted signal to the level correction unit 70. The sampling period shift time is a time unit where one unit is the sampling period of the received signal and is expressed as an integer multiple of the sampling period. The process of shifting the received signal on the time axis may be performed by shifting the address of the received signal stored in the second memory 62 and reading the received signal. In this case, the second memory 62 stores each discrete value of the received signal in association with an address such that the value increases in chronological order. The sampling period shift unit 66 increases or decreases the value of the address specified when reading the received signal by a value corresponding to the sampling period shift time, thereby performing a process equivalent to shifting the received signal on the time axis.

[0036] The time shift filter 64 may be configured with a digital filter such as an FIR filter (Finite Impulse Response Filter) whose characteristics are determined by a plurality of tap coefficients (tap coefficient group). The time shift filter 64 reads the received signal from the first memory 60, performs time shift processing on the received signal in accordance with the tap coefficient group set by the control and calculation unit 74, generates a time shifted signal, and outputs the time shifted signal to the level correction unit 70. The time shift processing is processing in which the signal to be processed is shifted on the time axis by an infinitesimal shift time determined by the tap coefficient group. In this embodiment, the infinitesimal shift time is shorter than the sampling period.

[0037] The level correction unit 70 adjusts the levels of the received signal (time shift signal) output from the time shift filter 64 and the received signal output from the sampling period shift unit 66 using the correction coefficient output from the level correction value determination unit 68. The process by which the level correction value determination unit 68 determines the correction coefficient will be described later.

[0038] The approximation calculation unit 72 calculates the degree of approximation indicating the degree of similarity between the received signal (level-corrected time-shifted signal) output from the time shift filter 64 and whose level has been corrected by the level correction unit 70, and the received signal output from the sampling period shift unit 66 and whose level has been corrected by the level correction unit 70. The control and calculation unit 74 obtains the degree of approximation while changing the sampling period shift time in the sampling period shift unit 66 and the minute shift time in the time shift filter 64. The control and calculation unit 74 calculates the time difference between the first reception timing and the second reception timing as the spatial propagation time based on the sampling period shift time and minute shift time when the degree of approximation indicated by the degree of approximation is greatest. The control and calculation unit 74 calculates the gas concentration using the spatial propagation time according to Equation 1.

[0039] Next, the configuration and processing by which the gas concentration measurement unit 48 calculates the spatial propagation time will be described in detail. The level correction value determination unit 68 reads the received signal stored in the first memory 60 and calculates a direct wave level correction value that normalizes the peak value of the absolute value of the direct wave received pulse. The direct wave level correction value is a value by which the direct wave received pulse is multiplied so that the direct wave received pulse fluctuates within a predetermined range. The level correction value determination unit 68 also calculates a reflected wave level correction value for the reflected wave received pulse. The reflected wave level correction value is a value by which the reflected wave received pulse is multiplied so that the reflected wave received pulse fluctuates within the same range as the level-corrected direct wave received pulse.

[0040] Next, basic shift processing is performed. In the basic shift processing, a tap coefficient group is set for the time shift filter 64 so that the minute shift time in the time shift filter 64 is 0. The direct wave reception pulse included in the reception signal is read from the first memory 60 into the time shift filter 64. The time shift filter 64 performs time shift processing on the direct wave reception pulse with a minute shift time of 0, and outputs the result to the level correction unit 70. The level correction unit 70 multiplies the direct wave reception pulse (time shift signal) by the direct wave level correction value, and outputs the result to the approximation calculation unit 72.

[0041] The reflected wave reception pulse contained in the reception signal is read from the second memory 62 into the sampling period shift unit 66. The sampling period shift unit 66 shifts the reflected wave pulse on the time axis by the sampling period shift time set by the control calculation unit 74, and outputs the result to the level correction unit 70. The level correction unit 70 multiplies the reflected wave reception pulse by the reflected wave level correction value, and outputs the result to the approximation calculation unit 72.

[0042] The approximation calculation unit 72 calculates the Euclidean distance between the direct wave reception pulse and the reflected wave reception pulse as the approximation. That is, the approximation calculation unit 72 calculates the Euclidean distance, which is the square root of the value obtained by time-integrating the square of the value obtained by subtracting the reflected wave reception pulse from the direct wave reception pulse. The smaller the Euclidean distance, the greater the degree of approximation between the direct wave reception pulse and the reflected wave reception pulse.

[0043] The control calculation unit 74 obtains the Euclidean distance from the approximation calculation unit 72 while changing the sampling period shift time, and searches for the sampling period shift time when the Euclidean distance is minimum. The control calculation unit 74 determines the sampling period shift time when the Euclidean distance is minimum as the coarse space propagation time.

[0044] After the coarse spatial propagation time is calculated, a fine adjustment shift process is executed. In the fine adjustment shift process, the sampling period shift time in the sampling period shift unit 66 is fixed to the coarse spatial propagation time. The direct wave reception pulse included in the reception signal is read from the first memory 60 into the time shift filter 64. The time shift filter 64 performs time shift processing on the direct wave reception pulse in accordance with the fine shift time determined by the tap coefficient group provided by the control calculation unit 74, and outputs the result to the level correction unit 70. The level correction unit 70 multiplies the direct wave reception pulse by a direct wave level correction value and outputs the result to the approximation calculation unit 72.

[0045] The reflected wave reception pulse contained in the reception signal is read from the second memory 62 into the sampling period shifter 66. The sampling period shifter 66 shifts the reflected wave pulse on the time axis by the course space propagation time and outputs the result to the level corrector 70. The level corrector 70 multiplies the reflected wave reception pulse by a reflected wave level correction value and outputs the result to the approximation calculator 72. The approximation calculator 72 calculates the Euclidean distance between the direct wave reception pulse and the reflected wave reception pulse.

[0046] The control calculation unit 74 acquires the Euclidean distance from the approximation calculation unit 72 while changing the minute shift time by changing the tap coefficient filter group, and searches for the minute shift time when the Euclidean distance is minimum. The control calculation unit 74 calculates the final space propagation time by adding the minute shift time when the Euclidean distance is minimum (adjusted minute shift time) and the course space propagation time.

[0047] With this configuration and processing, the spatial propagation time can be determined with a resolution higher than the sampling period, thereby improving the accuracy of measuring the gas concentration.

[0048] In the above, an embodiment has been described in which the Euclidean distance is used as the degree of approximation between two signals. The degree of approximation may also be determined by using a correlation value between the two signals. The correlation value is defined as the time integral of the product of the two signals. When the correlation value is used as the degree of approximation, the condition that the degree of approximation is greatest is that the correlation value is maximum. Furthermore, the condition that the Euclidean distance is minimum in the above can be replaced by the condition that the correlation value is maximum. When the correlation value is used as the degree of approximation, level correction by the level correction unit 70 does not need to be performed. [Explanation of symbols]

[0049] 10 housing, 14 transmitting unit, 16 receiving unit, 18 analyzing unit, 20 analyzing unit accommodating space, 22 concentration measurement space, 24 direct wave receiving pulse, 26 reflected wave receiving pulse, 40 transmitting circuit, 42 transmitting ultrasonic vibrator, 44 receiving ultrasonic vibrator, 46 receiving circuit, 48 gas concentration measuring unit, 60 first memory, 62 second memory, 64 time shift filter, 66 sampling period shift unit, 68 level correction value determining unit, 70 level correction unit, 72 approximation calculation unit, 74 control calculation unit.

Claims

1. a concentration measurement space for measuring a gas concentration; a transmitting unit that transmits ultrasonic waves into the concentration measurement space in response 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 calculates a spatial propagation time for an ultrasonic wave to propagate through the concentration measurement space based on the timing at which the plurality of pulses of the received signal are output from the receiving unit, and calculates the concentration of the gas to be measured based on the spatial propagation time; The analysis unit a first memory and a second memory for storing the received signal; a time shift filter that performs time shift processing on the received signal stored in the first memory; a control and calculation unit that calculates the spatial propagation time, determining a degree of approximation between the received signal read from the second memory and the time-shifted signal read from the first memory and subjected to the time-shift processing; calculating a time difference between pulses of the received signals that are adjacent on a time axis based on the minute shift time in the time shift processing and the degree of approximation, and calculating the spatial propagation time based on the time difference; The analysis unit further a sampling period shift unit that performs sampling period shift processing on the received signal read from the second memory, the sampling period shift processing shifting the signal on a time axis by a sampling period; determining a degree of approximation between the received signal that has been subjected to the sampling period shift processing and the time-shifted signal; A gas concentration measuring device, wherein the minute shift time in the time shift processing is shorter than a sampling period.

2. 2. The gas concentration measuring device according to claim 1, The control calculation unit searching for the minute shift time when the degree of approximation indicated by the degree of approximation is greatest; A gas concentration measuring apparatus, characterized in that the time difference is calculated based on the minute shift time when the degree of approximation indicated by the degree of approximation is greatest.

3. 3. The gas concentration measuring device according to claim 1, The gas concentration measuring apparatus, wherein the degree of approximation is a Euclidean distance between the received signal read from the second memory and the time-shifted signal.

4. The gas concentration measuring device according to any one of claims 1 to 3, The gas concentration measuring apparatus is characterized in that the degree of approximation is a correlation value between the received signal read from the second memory and the time-shifted signal.

5. The gas concentration measuring device according to any one of claims 1 to 4, The time shift filter is A gas concentration measuring device characterized by being an FIR filter.

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