JP2015158403A - Gas concentration measuring method and gas concentration measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas concentration measuring method capable of instantaneously identifying the type and concentration of gas.SOLUTION: A gas concentration measuring method for measuring a gas concentration and a temperature in a measuring environment by an ultrasonic wave, comprises: gas concentration measuring means identifying the gas temperature by measuring propagation time of the ultrasonic wave transmitted in the measuring environment with respect to a preset first distance; and temperature measuring means identifying the temperature by measuring propagation time of the ultrasonic wave transmitted in the measuring environment with respect to a preset second distance. The measuring target gas is hydrogen, and the ultrasonic wave for measuring the gas concentration and the ultrasonic wave for measuring the temperature are assumed to be emitted from ultrasonic generators synchronized during transmission or from an identical ultrasonic generator.

Description

  The present invention relates to a gas concentration measurement technique using ultrasonic waves. Specifically, the present invention relates to a technique for measuring the propagation time of ultrasonic waves in a gas, detecting the speed of ultrasonic waves in the gas, and at the same time correcting the speed of sound according to the temperature of the environment to identify the concentration of the gas. .

  In recent years, the popularization of hydrogen-utilizing society as clean energy has begun to be said, and along with research and development and commercialization of automobiles and household fuel cells, practical research and development of hydrogen-related technologies has been promoted. Hydrogen is known to explode in air at concentrations of over 4%. Hydrogen sensors are indispensable for realizing a hydrogen-using society, and various hydrogen sensors are being researched and put into practical use.

  Conventional hydrogen sensors employ various detection methods such as semiconductor and catalytic combustion methods, but response time is slow, and hydrogen detection is often due to adsorption, and it takes time to remove hydrogen after detection. However, there was a limit to instantaneous hydrogen detection.

  As these improved techniques, a hydrogen measurement technique using ultrasonic waves is disclosed in Patent Document 2 and Non-Patent Documents 1 and 2.

  This technology uses the fact that the propagation speed of sound waves changes depending on the type of gas and also the concentration of gas, and transmits ultrasonic waves within a predetermined distance until the ultrasonic waves are transmitted and received. By measuring the time and calculating the speed of sound, the type and concentration of the gas in the atmosphere through which the ultrasonic wave has propagated are measured.

However, the sound speed of gas is very sensitive to temperature, and it is impossible to measure the sound speed of gas accurately without grasping the temperature of gas instantaneously and correcting the sound speed of gas due to that temperature. In addition, the gas concentration cannot be measured accurately.
In particular, by measuring the ambient temperature instantaneously and correcting the sound velocity of the ultrasonic wave using the measured ambient temperature, the technology for measuring the precise gas type and gas concentration is inexpensive and simple. It was necessary to realize.

Application for Japanese Patent Application No. 2013-244628 JP 2000-304732 A

"Hydrogen sensor using ultrasonic waves" Mr. Yoshifumi Kato and Mr. Hideo Fujita Ultrasonic TECHNO 2012.10.2 Page 85-89 "Hydrogen sensor using ultrasonic waves" Mr. Yoshifumi Kato et al. Fukuoka Hydrogen Energy Strategy Conference 2010 Second Research Subcommittee August 10, 2010 www.f-suiso.jp/bunkakai/H22bunnkakai/22_2_1_Kato.pdf

In view of the problems described in the prior art, the present invention measures the environmental temperature instantaneously using ultrasonic waves, and corrects the sound velocity of the ultrasonic waves using the measured environmental temperature, thereby providing a highly accurate gas. It is an object to realize a technique for measuring the kind of gas and the concentration of gas at low cost and simply.

  A first invention of the present invention is a gas concentration measurement method for measuring the gas concentration and temperature of a measurement environment by using ultrasonic waves, and the ultrasonic wave transmitted in the measurement environment with respect to a predetermined first distance. The gas concentration measuring means for specifying the gas concentration by measuring the propagation time and the temperature by measuring the propagation time of the ultrasonic wave transmitted in the measurement environment with respect to a predetermined second distance are specified. And a temperature measuring means.

  According to a second aspect of the present invention, in addition to the first aspect, the gas is hydrogen, and the gas concentration is specified by comparing the measured propagation time with a propagation time for a predetermined hydrogen concentration. This is a gas concentration measurement method to be specified.

  According to a third aspect of the present invention, in addition to the first and second aspects, the ultrasonic waves for gas concentration measurement and the ultrasonic waves for temperature measurement are synchronized at the time of transmission or / and the same. It is a gas concentration measuring method which is an ultrasonic transmitter.

  According to a fourth aspect of the present invention, there is provided a gas concentration measuring apparatus for measuring a gas concentration and a temperature of a measurement environment by using an ultrasonic wave, wherein the ultrasonic wave transmitted in the measurement environment is measured with respect to a predetermined first distance. The gas concentration measuring means for specifying the gas concentration by measuring the propagation time and the temperature by measuring the propagation time of the ultrasonic wave transmitted in the measurement environment with respect to a predetermined second distance are specified. A gas concentration measuring device having temperature measuring means.

  According to a fifth aspect of the present invention, in addition to the fourth aspect, the gas is hydrogen, and the gas concentration is specified by comparing the measured propagation time with a propagation time for a predetermined hydrogen concentration. This is a gas concentration measuring device to be specified.

  According to a sixth aspect of the present invention, in addition to the fourth to fifth aspects of the present invention, the ultrasonic waves for gas concentration measurement and the ultrasonic waves for temperature measurement are synchronized at the time of transmission or / and the same ultrasonic wave. It is a gas concentration measuring device which is a sound wave transmitting device.

  According to the present invention, it is possible to instantaneously identify the type and concentration of gas by measuring the propagation time of the first predetermined distance by ultrasonic waves.

  Also, by measuring the propagation time of the second predetermined distance by the ultrasonic wave, the measurement environment, that is, the temperature of the gas can be instantaneously measured.

  In addition, since the propagation times of the first and second predetermined distances are measured by ultrasonic waves, the measurement can be performed without using a heat source. Therefore, it is not necessary to use an explosion-proof measuring instrument as an inexpensive device. realizable.

  In addition, the ultrasonic waves for gas concentration measurement and the ultrasonic waves for temperature measurement are synchronized at the time of transmission / or by using the same ultrasonic transmission device, gas concentration measurement and gas temperature measurement can be performed. Since it can be realized instantaneously and can be measured without a time lag, the accuracy of gas concentration measurement can be improved.

  In addition, since it is a gas concentration measurement and temperature measurement using ultrasonic waves, post-processing such as gas removal after measurement is unnecessary, and it can be repeatedly used as it is, so that it is a measurement method and measurement apparatus suitable for continuous monitoring.

  In addition, since the first distance and the second distance for measuring the ultrasonic propagation time can be used with very small values, the probe in the measurement atmosphere can be reduced in size, and can also be used for measurements in narrow spaces. Is possible.

  Furthermore, although the embodiment of the present invention has been described based on hydrogen, since the temperature and the concentration can be measured at the same time, it can also be used for measurement of gases having similar propagation velocities.

It is a figure which shows one Example of the apparatus structure of the gas concentration measuring apparatus of this invention. It is a figure which shows typically the behavior about reflection and permeation | transmission of the ultrasonic wave used for this invention. It is a figure which shows attenuation | damping of the signal with respect to the propagation distance (distance between ultrasonic transducers) of the ultrasonic transducer | vibrator of this invention. It is a figure which shows the thickness of the vibrator | oscillator which determines the frequency of the ultrasonic wave of the ultrasonic vibrator of this invention, and the attenuation factor of a signal. FIG. 3 is a diagram showing an example of the configuration of an ultrasonic transducer for gas concentration measurement and temperature measurement according to the present invention. It is a figure which shows the apparatus structure of the ultrasonic transducer | vibrator for gas concentration measurement of Example 1 of this invention. It is a figure which shows the precision verification result of the actual hydrogen concentration by Example 1 of this invention, and the measurement hydrogen concentration by an ultrasonic wave. It is a figure which shows the verification result of the precision of the sound speed of an ultrasonic wave when the environmental temperature by Example 2 of this invention is changed, and a detected hydrogen concentration.

  The present invention relates to a gas concentration measuring means for specifying the gas concentration by measuring a propagation time of an ultrasonic wave transmitted in a measurement environment with respect to a predetermined first distance, and an ultrasonic wave transmitted in the measurement environment. A gas concentration measuring method and a gas concentration measuring apparatus for measuring a gas concentration in a measurement environment by means of a temperature measuring means for specifying the temperature by measuring a propagation time with respect to a predetermined second distance.

The gas to be measured may be any gas as long as it contains a hydrogen component, but is preferably a gas containing hydrogen alone or a molecular component of hydrogen alone.
However, by limiting the measurement gas in the measurement target environment, that is, limiting the presence of gas that hinders the measurement of the concentration of the measurement target gas, it can also be used for the measurement of other gas concentrations, including helium. Can do.

  The gas concentration measuring means determines the concentration of the specific gas by comparing the measured propagation time of the ultrasonic wave in the specific gas with the propagation time of the ultrasonic wave in the gas concentration predetermined for the specific gas. Specific examples will be described in the examples described later.

  The temperature measuring means measures the environmental temperature using ultrasonic waves for measuring the gas concentration in the specific gas or other ultrasonic waves that are transmitted in synchronization with the ultrasonic waves. Based on the measurement result, temperature correction of the measured propagation time in the specific gas is performed. This technique uses the technique of 2013-244628 already filed by the present inventors.

FIG. 1 shows an outline of a gas concentration measuring apparatus according to the present invention.
In the following description, the gas concentration measuring device is abbreviated as a measuring device, and the control program / storage device is abbreviated as a control PRG.

  The measuring apparatus 1 is largely composed of a control apparatus 2 that controls all of the control related to measurement of gas concentration and temperature, and an ultrasonic sensor 3 that transmits and receives ultrasonic waves to and from the measurement environment.

  The control device 2 controls each device connected in the measuring device 1 and based on the information of the control PRG 2e, the ultrasonic transmission control means 2e1, the ultrasonic reception control means 2e2, the gas temperature analysis means 2e3, the gas concentration analysis means. Based on information from the control unit 2a that activates and controls each means of 2e4, the I / O port 2b that mediates and controls signals with the ultrasonic sensor 3 regarding transmission and reception of ultrasonic waves, and the information from the I / O port 2b The transmitting circuit 2 c transmits an ultrasonic signal to the ultrasonic sensor 3 and the receiving circuit 2 d receives an ultrasonic signal from the ultrasonic sensor 3. An input unit 2f for operation of the control unit and a display unit 2g are connected to the control unit 2a, and a display unit 2g for confirming an instruction to the control unit 2a by a measurer and a measurement result in the control unit 2a is provided. It is connected.

  The control PRG 2e incorporates control programs such as ultrasonic transmission control means 2e1, ultrasonic reception control means 2e2, gas temperature analysis means 2e3, and gas concentration analysis means 2e4. Note that the ultrasonic transmission control means 2e1, the ultrasonic reception control means 2e2, and the gas concentration analysis means 2e4 are commonly disclosed techniques including Patent Documents 1 and 2, Non-Patent Documents 1 and 2, Since these techniques are used as appropriate, they are not described in detail in the present invention.

  The ultrasonic sensor 3 transmits ultrasonic waves into the gas in the measurement environment and receives ultrasonic waves reflected from the measurement environment.

  The ultrasonic sensor 3 includes a gas concentration measuring ultrasonic transducer 5 and a gas temperature measuring ultrasonic transducer 4.

  In general, it is known that the reflection and transmission of ultrasonic waves behave as shown in FIG. When the acoustic impedance is relatively similar at the boundary between the ultrasonic medium materials, a numerical value with a high ultrasonic transmittance can be obtained, but from a material with a high acoustic impedance to a material with a low acoustic impedance. When transmitting ultrasonic waves, when transmitting ultrasonic waves from a so-called solid to a gas, the transmittance is only a few percent, making it difficult to use for measurement. Incidentally, the transmittance of the ultrasonic wave from the iron bar to the air is less than several percent, and the ultrasonic wave is not practically propagated. Therefore, it is indispensable to devise a method for efficiently transmitting ultrasonic waves to the gas via a medium having a low acoustic impedance between the ultrasonic transducer and the gas so that the gas is ultrasonically vibrated.

  Therefore, for temperature measurement, the technique of 2013-244628 developed by the present inventors is used as a temperature measurement method using a solid that has less influence on temperature than gas, and temperature measurement is performed. An ultrasonic transducer 4 was obtained.

Further, the transmitting ultrasonic transducer 5 for gas concentration measurement and the receiving ultrasonic transducer 5c are arranged on the opposite side, and a medium with low acoustic impedance is efficiently interposed between the ultrasonic transducer and the gas. The idea of propagating ultrasonic waves to the gas was made, and the gas was ultrasonically vibrated.
However, as an alternative to the receiving ultrasonic transducer 5c, an ultrasonic reflecting member 5d is arranged to reflect the transmitted ultrasonic wave, and the reflected ultrasonic wave is received by the transmitting ultrasonic transducer 5. You can also. In this case, the reflecting member 5d may be a solid having a smooth surface that reflects ultrasonic waves, but is preferably a metal such as stainless steel.

  The ultrasonic wave propagating from the temperature measuring ultrasonic transducer 4 to the temperature measuring metal rod 4b is 4a, the ultrasonic wave propagating in the gas from the gas concentration measuring ultrasonic transducer 5 is converted to a unidirectional straight wave 5a, An ultrasonic wave reflected by the sound wave reflecting member 5d is shown as 5b. When receiving the unidirectionally traveling wave 5a, the ultrasonic reflecting member 5d uses the same ultrasonic transducer as the gas concentration measuring ultrasonic transducer 5 as 5c.

Here, the temperature measurement ultrasonic transducer 4, the gas concentration measurement ultrasonic transducer 5, and the gas concentration measurement ultrasonic transducer 5c will be described.
Although it is desirable that the ultrasonic transducer be small, factors such as attenuation due to the distance of the ultrasonic wave and the thickness and attenuation of the transducer with respect to the frequency are greatly involved.

  FIG. 3 shows the result of the experiment on attenuation due to the distance of the ultrasonic signal.

FIG. 3 shows test data representing signal attenuation with respect to propagation distance (distance between ultrasonic transducers). The ultrasonic signal is plotted in units of a propagation distance of 0.05 m.
From this experimental result, it can be seen that the attenuation increases as the frequency increases.

The solid line represents the magnitude of the signal by plotting the following approximate expression (1).
S = S (0.05) exp (−αL) (1)
Here, S (0.05): the magnitude of the signal at a propagation distance of 0.05 m (the intensity of the initial ultrasonic signal is expressed as 1), α: attenuation factor, and L: propagation distance.

FIG. 4 shows the results of an experiment regarding the thickness and attenuation of the vibrator with respect to the ultrasonic frequency.
FIG. 4 is a diagram summarizing the thickness of the transducer that determines the frequency of the ultrasound and the attenuation rate of the previous operation. The thickness of the vibrator indicated by the solid line is the frequency constant N of the vibrator (the product of the vibrator thickness and the resonance frequency. In the case of the 1-3 composite vibrator used in the test, about 1.34 × 10 ⁶ [mm・ Hz]), the following relational expression (2) was obtained.
y = N / f (2)
Here, y is the thickness (mm) of the ultrasonic transducer, N is the frequency constant of the ultrasonic transducer, and f is the transmission frequency (Hz).
The broken line in FIG. 4 is obtained by inserting the above-described attenuation rate curve by an approximate expression.
From this relationship, it is possible to select the size and frequency of the ultrasonic transducer according to the application.

Thus, as is generally said, the lower the transmission frequency, the thicker the vibrator, and the diameter of the vibrator is generally at least three times the thickness.
In that case, the ultrasonic transducer diameter is about 20 mm (6.7 × 3) at a transmission frequency of 200 kHz, and about 5 mm (1.7 × 3) at 800 kHz, and the ultrasonic transducer becomes larger as the frequency is lower.

For example, when measuring a gas concentration in a wide space, a low-frequency ultrasonic transducer with a low attenuation factor is effective, although the ultrasonic moving element becomes large.
Also, if a large ultrasonic transducer cannot be used due to space constraints, it is not suitable for long propagation distance conditions, but the size of the ultrasonic transducer is reduced using a high-frequency ultrasonic transducer. Is effective.

  Next, a typical example of the ultrasonic sensor 3 according to the present invention will be described with reference to FIG.

  FIG. 5a) shows an ultrasonic transducer for gas concentration measurement and temperature measurement composed of an integrated type 4, 5, and the ultrasonic wave 4a transmitted from the portion 4 is propagated to the temperature measuring metal rod 4b. The reflected wave 4a is received by the portion 4. The ultrasonic wave 5a transmitted in the portion 5 is propagated in the gas and received by the ultrasonic transducer 5c on the opposite side.

  FIG. 5B) shows a configuration in which the gas concentration measurement ultrasonic transducer 5 and the temperature measurement ultrasonic transducer 4 are arranged independently by synchronizing the transmission control or the like with the configuration shown in FIG. 5A). It is shown.

  In FIG. 5c), the ultrasonic transducer 5 for measuring gas concentration and the ultrasonic transducer 4 for measuring temperature are arranged independently by synchronizing the transmission control and the like, and the ultrasonic transducer 5 for measuring gas concentration is used. The transmitted ultrasonic wave 5b is reflected by an ultrasonic wave reflecting member 5d installed on the opposite side, and is received by the ultrasonic transducer 5 for gas concentration measurement.

This configuration is a particularly effective method when there is a flow in the measurement gas. When the measurement gas flow affects the ultrasonic propagation velocity, cancel the difference between the ultrasonic “forward” propagation velocity (propagation time) and the “reverse” ultrasonic propagation velocity (propagation time). Therefore, the influence of the gas flow can be eliminated by setting the total time t _L of the ultrasonic reciprocation.

Here, the relationship between the ultrasonic signals is schematically shown in FIG. In the case of the first predetermined distance (FIG. 5c), L is the first predetermined distance, and 2l represents the second predetermined distance.
Further, time t _L to propagate a first predetermined distance L, and the time t _l to propagate a second predetermined distance 2l. In this figure, (I) is a pulse signal of an outgoing ultrasonic wave, (II) is an ultrasonic reception pulse signal for temperature measurement, and (III) is an ultrasonic reception pulse signal for gas concentration measurement.
[Example]

  As Example 1 of the present invention, using the ultrasonic transducer 5 for gas concentration measurement in FIG. 5b), the ultrasonic transducer 5c on the opposite side, and the ultrasonic wave 5a therebetween, the apparatus of FIGS. 6a) and b) is used. The actual hydrogen concentration and the measured hydrogen concentration by ultrasonic waves were verified.

Here, FIG. 6a) is a diagram of an experimental apparatus in which the gas concentration measuring ultrasonic transducer 5 of FIG. 6b) and the gas concentration measuring ultrasonic transducer 5c on the opposite side are arranged. Although the ultrasonic transducer 4 for temperature measurement is not shown in FIG. 6 a), temperature measurement using a thermocouple is used in this embodiment.
The ultrasonic transducer 5 for gas concentration measurement is constituted by about 200 kHz, applied voltage about 100 V (pulse), L = 50 mm, the measurement temperature is about 20 ° C., and the measurement environment gas is a mixture of nitrogen gas and hydrogen gas. Gas was used.
The verification result is shown in FIG.

  From this result, it was confirmed that the hydrogen concentration in the atmosphere and the hydrogen concentration measured by ultrasonic waves can be highly correlated, and the hydrogen concentration can be measured with good accuracy.

As Example 2 of the present invention, the sound velocity of ultrasonic waves and the detected hydrogen concentration when the environmental temperature was changed under the same conditions as in Example 1 were verified. The verification result is shown in FIG.
From FIG. 8a), for each hydrogen concentration, for example, every 1%, 2%, 3% of hydrogen concentration, the environmental temperature and the sound velocity of the ultrasonic wave are very correlated, and if the hydrogen concentration increases, It was confirmed that the sound velocity of sound waves also increased.
From this, it was proved that the hydrogen concentration can be accurately measured from the environmental temperature and the sound velocity of the ultrasonic waves.
Further, FIG. 8b) is an enlarged view of the part of FIG. 8a), and shows a state in which the measured hydrogen concentration is calculated from the intersection of the environmental temperature and the ultrasonic sound velocity.

  When the ambient temperature is 106 ° C. and the ultrasonic sound velocity is 402 m / s, the intersection of the graph is between the hydrogen concentration 2% and the hydrogen concentration 3%. The intersection is O, and the hydrogen concentration through O is 2%. A perpendicular line is drawn to an approximate line with a hydrogen concentration of 3%, and the intersecting points are defined as X and Y. When the distance from the point O to the points X and Y is a and b, the hydrogen concentration at the point O can be expressed as 2% + a / (a + b)%. In this example, it is represented by an approximate line in increments of 1%, but it is possible to measure the hydrogen concentration with higher accuracy by creating in advance a fine approximate line in increments of 1% → 0.1%.

  The gas concentration analysis means 2e4 is a program that incorporates the processing contents of the second embodiment and is incorporated in the system.

  Next, concentration measurement of other gases will be described.

  Table 1 shows the rate of change of sound speed with respect to the speed of sound and temperature of other gases. The hydrogen gas described in this example has a high sound speed and a large rate of change of sound speed. It can be said that the gas is suitable for measurement.

  However, for other gases, the gas concentration measurement method according to the present invention for a specific gas can be used by controlling the gas coexisting in the measurement environment, by excluding gases other than the so-called measurement target gas, etc. Is possible. For example, when it is desired to measure the ethylene concentration, consideration should be given to an environment in which gases such as ethane and methanol having similar sound speeds are not mixed.

By the ultrasonic gas concentration measuring method and apparatus described above, it is possible to realize gas concentration measurement that is small, inexpensive, highly accurate, and rapid.
Furthermore, since both the gas concentration measurement and the gas temperature measurement are performed by detecting a change in the sound velocity of the ultrasonic wave, it is possible to obtain a quick analysis result and facilitate the compactization. Therefore, for example, it can be easily used for automobiles and household fuel cells. Furthermore, since these automobiles and household fuel cells usually incorporate a PC, a microcomputer or the like as a control device, it is easy to incorporate the function of the control device 2 of the present invention into the PC, the microcomputer or the like.

1 ... Gas concentration measuring device (measuring device)
2 ... Control device 2a ... Control unit 2b ... I / O port 2c ... Transmission circuit 2d ... Reception circuit 2e ... Control PRG (control program / storage device)
2f ... Input unit 2g ... Display unit 3 ... Ultrasonic sensor 4 ... Temperature measurement ultrasonic transducer 4a ... Temperature measurement reflected wave 4b ... Temperature measurement metal rod 5 ... Gas concentration measurement ultrasonic transducer 5a ... One direction Straight wave 5b ... Gas concentration measurement reflected wave 5c ... Gas concentration measurement ultrasonic transducer 5d ... Ultrasonic reflection member L ... First predetermined distance l, lm ... Second predetermined distance

Claims (6)

A gas concentration measurement method for measuring the gas concentration and temperature of a measurement environment by ultrasonic waves,
A gas concentration measuring means for determining the gas concentration by measuring a propagation time of a ultrasonic wave transmitted in a measurement environment with respect to a predetermined first distance;
Temperature measuring means for specifying the temperature by measuring a propagation time of the ultrasonic wave transmitted in the measurement environment with respect to a predetermined second distance;
A gas concentration measuring method comprising: The gas is hydrogen, and the gas concentration is identified by comparing the measured propagation time with a propagation time for a predetermined hydrogen concentration,
The gas concentration measuring method according to claim 1. 3. The gas concentration according to claim 1, wherein the ultrasonic waves for gas concentration measurement and the ultrasonic waves for temperature measurement are synchronized at the time of transmission and / or are the same ultrasonic transmission device. Measuring method. A gas concentration measuring device that measures the gas concentration and temperature of a measurement environment by ultrasonic waves,
A gas concentration measuring means for determining the gas concentration by measuring a propagation time of a ultrasonic wave transmitted in a measurement environment with respect to a predetermined first distance;
Temperature measuring means for specifying the temperature by measuring a propagation time of the ultrasonic wave transmitted in the measurement environment with respect to a predetermined second distance;
A gas concentration measuring device comprising: The gas is hydrogen, and the gas concentration is identified by comparing the measured propagation time with a propagation time for a predetermined hydrogen concentration,
The gas concentration measuring apparatus according to claim 4. 6. The gas concentration according to claim 4, wherein the ultrasonic wave for measuring the gas concentration and the ultrasonic wave for measuring the temperature are synchronized at the time of transmission and / or are the same ultrasonic wave transmitting device. measuring device.