JP2007093507A - Gas detection method, gas detector and gas detection piping - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably detect a target gas over a long time in an extremely simple manner without frequently performing the adjustment of a zero point even when the concentration of the gas to be detected is extremely low while simply confirming the blow-off and blow-out of the gas. <P>SOLUTION: A discharge pipe having a bent part at its almost central part is connected to a detection pipe for allowing the detection target gas, which discharged from a predetermined environment, to flow. Subsequently, a sonic wave is discharged toward the detection pipe in the absence of the detection target gas in the detection pipe and the sonic speed at this time is measured as a first sonic speed. Next, the sonic wave is discharged toward the detection pipe in the presence of the detection target gas in the detection pipe and the sonic speed at this time is measured and a second sonic speed. Then, the difference between the first and second sonic speeds is obtained to detect the presence of the detection target gas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas detection method and a gas detector that can be suitably used for detection of gas leaks in fields that require gas detection continuously for a long period of time, particularly in mining and manufacturing, petrochemical, and high-pressure gas production facilities. And gas detection piping.

  Conventionally, methods for detecting gases existing in the atmosphere include those using chemical reactions such as galvanic cell type and constant potential electrolysis type, and those using the difference in thermal conductivity of gas. Thus, the target gas can be detected with high sensitivity and high accuracy.

  However, since the conventional gas detection method described above uses chemical reaction or heat conduction, there is a problem that the sensor itself used is basically consumed. For this reason, in the gas detector using the above-described method, the sensor must be periodically replaced, which is not suitable for long-term and continuous use. Moreover, in the detection method using heat conduction, it is necessary to adjust the zero point of the detector as appropriate before and during use, and there is a problem in stability.

  On the other hand, when detecting leak gas from a predetermined device or the like, if the leak gas is released into an unrestricted space such as the atmosphere, the concentration of the leak gas becomes too small and the leak gas is detected with high accuracy. There was a problem that could not. As a result, there has been a problem that it cannot be accurately confirmed whether or not the gas in question is actually leaking from the apparatus or the like.

  In addition, there is a problem that it is difficult to confirm the blowout and stop of the detection gas regardless of the concentration of the leak gas.

  In the present invention, even when the concentration of the gas to be detected is extremely low, the target gas can be detected very easily and stably for a long time without frequently performing zero point adjustment and the like. The purpose is to easily check the blowout and the blowout.

In order to achieve the above object, the present invention provides:
Preparing a detection tube for circulating a detection gas released from a predetermined environment;
Connecting a discharge tube having a bent portion at substantially the center to the detection tube;
A step of emitting a sound wave toward the detection tube in the absence of the detection gas in the detection tube, and measuring a sound speed at this time as a first sound speed;
In the state where the detection gas is present in the detection tube, emitting the sound wave toward the detection tube, and measuring the sound speed at this time as a second sound speed;
Detecting the presence of the detection gas by obtaining a difference between the first sound speed and the second sound speed;
It is related with the gas detection method characterized by comprising.

The present invention also provides:
A sound wave source for generating a predetermined sound wave;
Sound wave emitting means for emitting the sound wave;
A sound wave receiving means for receiving the sound wave;
A detection tube for circulating a detection gas released from a predetermined environment;
A discharge tube connected to the detection tube and having a bent portion at substantially the center;
The first sound velocity of the sound wave when the predetermined detection gas is not present in the detection tube and the second sound velocity when the detection gas is present in the detection tube are compared and detected, and the difference Measuring means to obtain
It is related with the gas detector characterized by comprising.

Furthermore, the present invention provides
A first sound velocity obtained by emitting a sound wave in an atmosphere in which no detection gas exists, and a second sound velocity obtained by emitting the sound wave in an atmosphere in which a detection gas exists, A detection pipe used for gas detection for detecting the presence of the detection gas by obtaining a difference between the sound speed of 1 and the second sound speed,
The detection pipe includes a detection pipe for flowing the detection gas, and a discharge pipe having a bent portion at a substantially center connected to the detection pipe.

  According to the present invention, since the target detection gas is introduced into the predetermined detection tube and flows through the detection tube, the detection gas can be prevented from diffusing into the unrestricted space. Therefore, even when the detection gas is very small, for example, a leak gas leaking from the apparatus, the detection gas can be prevented from diffusing into an unrestricted space, so that the leak gas is kept at a high concentration to some extent. become able to.

  In addition, a discharge tube having a bent portion in the approximate center with respect to the detection tube is provided. Therefore, the detection gas is suppressed from being blown out to some extent by the bent portion of the discharge tube. As a result, the degree of stagnation of the detection gas in the detection tube can be increased regardless of the specific gravity of the detection gas, and the synergistic effect with the holding effect by the detection tube allows the detection gas to stay in the detection tube. The leak gas can be maintained at a high concentration.

  Further, since the discharge tube is connected to the detection tube, it is possible to easily detect the blowing and stopping of the detection gas such as the leak gas at the discharge port of the discharge tube.

  Also, the present invention utilizes the fact that the propagation speed (sound speed) of sound waves when the detection gas is not present in the detection tube is different from the propagation speed (sound speed) of sound waves when the detection gas is present. Then, the presence of the detection gas is detected by detecting the difference between the sound speeds. Therefore, the target gas can be detected stably for a long time without exchanging the sensor that has occurred due to the use of chemical reaction or heat conduction.

  Furthermore, if the zero point adjustment is performed as an initial setting by configuring the generation source for generating the sound wave from a source that can generate a sound wave signal extremely stably, such as a crystal oscillator, the zero point adjustment is performed thereafter. Need not be performed frequently. Therefore, the gas detection operation can be simplified.

  In a preferred aspect of the present invention, the bent portion of the discharge pipe is bent so that the pipe line of the discharge pipe faces upward. Further, the discharge port of the discharge pipe is opened downward. As a result, the discharge pipe suppresses the direct ejection of the detection gas to the outside regardless of the specific gravity of the detection gas in a state in which the detection gas is blown out and stopped at the discharge port. The detection gas can be retained more effectively in the detection tube regardless of its specific gravity, and the concentration of the detection gas in the detection tube can be increased.

  In another preferred aspect of the present invention, a pair of openings are formed in a direction substantially perpendicular to the length direction of the detection tube, and the sound wave emitting means and the sound wave receiving means are provided at the openings. They are provided so as to face each other, and are unitized together with a terminal box containing electrical wiring for the sound wave emitting means and the sound wave receiving means. As a result, the number of parts can be reduced and the handling of the gas detector itself can be simplified. Therefore, in the detection of leak gas or the like, the gas detector can be detachably attached to various devices via, for example, a flange, and the leak gas can be easily detected.

  In addition, since transmission / reception of sound waves described in detail below is performed through the opening, transmission / reception of the sound waves is not hindered by the wall surface of the detection tube. Further, the sound wave emitting means, the sound wave receiving means and the detection tube can be unitized without using other complicated jigs.

  In this case, the terminal box can be provided on the outer peripheral surface of the detection tube. As a result, the configuration of the entire detection tube unitized with the terminal box or the like can be further simplified, and the size can be reduced. Therefore, the configuration of the entire gas detector can be further simplified and the handling thereof can be further simplified.

  Furthermore, in another preferable aspect of the present invention, a difference between the first sound speed and the second sound speed is obtained in a predetermined feedback circuit. In this case, the first sound speed and the second sound speed are converted into an input electric signal such as a pulse train signal, and noise and the like are removed under various controls. Can be obtained easily and with high accuracy. Furthermore, while the detection gas is present, the difference can always be calculated and an electric signal resulting from the difference can be output. Therefore, even the remaining state of the detection gas can be detected.

  According to still another preferred aspect of the present invention, the feedback circuit constitutes a phase locked loop (PLL). In this case, in the feedback circuit, a predetermined electrical signal is applied in such a manner that the phase is synchronized (locked) with respect to the first input electrical signal related to the first sound velocity in the state where the detection gas is not present. In the presence of the detection gas, the second input electrical signal relating to the second sound velocity is introduced into the feedback circuit, thereby releasing synchronization (lock) in the circuit. Therefore, the presence of the detection gas can be easily detected by detecting the differential electric signal generated in the phase difference at that time.

  In the gas detection method described above, for example, an alarm setter can be driven by the detected differential electric signal, and a voice or a buzzer can be emitted to notify the operator of the presence of the detected gas.

  The present invention can be used for any detection gas that is not limited to the magnitude of the gas amount or the concentration level, in addition to the extremely small amount and low concentration gas such as the leak gas described above. .

  As described above, according to the present invention, even when the concentration of the gas to be detected is extremely low, the target gas can be detected very easily and stably for a long time without frequent zero adjustment. In addition, it is possible to easily check the blowing and stopping of the gas.

  Hereinafter, other features and advantages of the present invention will be described based on the best mode for carrying out the invention.

  FIG. 1 is a block diagram showing an example of the gas detector of the present invention, and FIGS. 2 and 3 are diagrams showing in detail the configuration in the vicinity of the detection tube of the gas detector shown in FIG. FIG. 5 is a diagram showing in detail the configuration of the discharge tube used in this example. FIG. 4 is a side view of the discharge tube, and FIG. 5 is a front view of the discharge tube.

  The gas detector 10 shown in FIG. 1 is arranged as a reference signal generator 11 as a sound wave generation source composed of a crystal oscillator and the like, and a sound wave emission means for emitting sound waves from the generator. The ultrasonic speaker 13 and an ultrasonic microphone 14 as a sound wave receiving means for receiving the sound wave are provided. A detection tube 17 for circulating a predetermined detection gas is provided between the ultrasonic speaker 13 and the ultrasonic microphone 14.

  The detection tube 17 is provided with an opening 17A for emitting and detecting an ultrasonic wave to the detection gas flowing through the detection tube 17. As shown below, the detection gas is detected by the ultrasonic wave. If it is sufficiently detectable, there is no need to provide it. The detection tube 17 is connected to a discharge tube 37 having a bent portion 37B at the approximate center on the side opposite to the device connection side.

  A speaker driving amplifier 12 is provided between the reference signal generator 11 and the ultrasonic speaker 13 to drive the speaker 13 and amplify the sound wave. The received sound wave is behind the ultrasonic microphone 14. A preamplifier 15 for amplification and a waveform shaper 16 for shaping the waveform of the received sound wave are provided.

  Behind the waveform shaper 16, a feedback circuit 20 constituting a PLL is provided. In the feedback circuit 20, a phase comparator 21, a low-pass filter 22 and a voltage frequency oscillator 23 are provided. Further, an alarm setting device 31 is provided behind the feedback circuit 20.

  As shown in FIG. 2, the ultrasonic speaker 13 and the ultrasonic microphone 14 are connected so as to face each other at the opening 17 </ b> A of the detection tube 17, and a support plate 19 provided on the outer peripheral surface of the detection tube 17. The terminal box 18 is supported by these, and these are unitized and configured as an integral unit. The terminal box 18 is configured so that lead wires, connectors, cables, and the like for the ultrasonic speaker 13 and the ultrasonic microphone 14 can be accommodated together. The detection tube 17 is configured to be connected to a predetermined device or the like via a flange 41 as shown in FIG.

  According to the unitized detection piping configuration as shown in FIG. 2, it is possible to detect leak gas from the device only by connecting this unit to a predetermined device via the flange 41. The operability with respect to can be improved.

  As shown in FIG. 3, in this example, a discharge pipe 37 is connected to the detection pipe 17 via a flange 42. As shown in FIGS. 4 and 5, in this example, the discharge pipe 37 is composed of a single bent pipe, which is bent upward from the flange 42 side and directed toward the discharge port 37A. Thus, it is configured to bend downward and to form an upwardly bent portion 37B in the approximate center. According to such a configuration, as described in detail below, the detection gas is blown out and stopped in the discharge port 37A, and the detection gas is discharged to the outside regardless of the specific gravity of the detection gas. The detection gas can be effectively retained in the detection tube 17 regardless of its specific gravity, and as a result, the concentration of the detection gas in the detection tube 17 can be increased. It becomes like this.

  Next, a gas detection method using the gas detector shown in FIG. 1 will be described. 6 and 7 are diagrams for explaining the gas detection method.

  First, a predetermined electrical signal is emitted from the reference signal generator 11, this electrical signal is amplified through the speaker drive amplifier 12, and then emitted from the ultrasonic speaker 13 toward the detection tube 17 as an ultrasonic wave. . Next, the ultrasonic wave is received by the ultrasonic microphone 14, converted into an electric signal, amplified by the preamplifier 15, and then subjected to waveform shaping by the waveform shaper 16. Thereafter, the electrical signal is introduced into the feedback circuit 20.

  Since the feedback circuit 20 constitutes a PLL, in the feedback circuit 20, as shown in FIG. 6, with respect to the received waveform of the input electric signal of the received pulse train when no detection gas is present in the detection tube 17, An electric signal (VCO electric signal) of a predetermined pulse train that is phase-synchronized from the voltage frequency oscillator 23 is applied and locked. That is, the feedback circuit 20 locks the input electric signal when the detection gas is not present. At this time, a pulse train signal at the time of locking is output from the phase comparator 21, and a reference voltage at the time of locking obtained by integrating this pulse signal can be obtained from the low-pass filter 22.

  However, in this example, as shown in FIG. 6, since the output from the phase comparator 21 is zero, the output from the low-pass filter 22 is also zero.

  On the other hand, when the detection gas is present in the detection tube 17, the propagation speed of the ultrasonic wave emitted from the ultrasonic speaker 13 in the space becomes different. Therefore, as shown in FIG. The ultrasonic input electrical signal is out of phase with the input electrical signal in the absence of the detection gas, that is, the VCO electrical signal synchronized with the input electrical signal. As a result, the phase comparator 21 generates a predetermined electrical signal corresponding to the phase difference (difference) between the input electrical signal and the VCO electrical signal, and outputs the electrical signal via the low-pass filter 22.

  The differential electric signal obtained in this way is introduced into the alarm setting device 31, and the presence of a detection gas such as an operator is recognized by a method such as voice or buzzer.

  Further, the phase difference between the input electric signal and the VCO electric signal is always compared by the phase comparator 21 by the feedback mechanism of the feedback circuit 20, and this comparison operation is performed until the phase difference disappears and synchronizes (locks) again. Become so. That is, the comparison operation is automatically performed until no detection gas exists in the space. When the detection gas is present and the phase difference is present, a predetermined differential electric signal is always output, and the alarm setting device It is comprised so that an operator may recognize through 31. Therefore, even the remaining state of the detection gas can be detected.

  In the gas detection method, since the detection gas is caused to flow in the detection tube 17, the detection gas can be prevented from diffusing into the unrestricted space. Therefore, even when the detection gas is very small, for example, a leak gas leaking from the apparatus, the detection gas can be prevented from diffusing into an unrestricted space, so that the leak gas is kept at a high concentration to some extent. become able to.

  Further, the detection tube 17 is provided with a discharge tube 37 having a bent portion 37B substantially at the center as shown in FIGS. Accordingly, the detection gas is prevented from being blown out to some extent by the bent portion 37B of the discharge pipe 37. As a result, the degree of retention of the detection gas in the detection tube 17 can be increased regardless of the specific gravity of the detection gas. The leak gas can be kept at a high concentration.

  It should be noted that it is possible to easily detect the detection gas blowing and stopping in the discharge port 37A of the discharge pipe 37.

  As described above, the present invention has been described in detail based on the embodiments of the invention with specific examples. However, the present invention is not limited to the above-described contents, and various modifications are possible without departing from the scope of the present invention. And changes are possible.

  8 and 9 are diagrams showing another embodiment of the discharge tube. FIG. 8 is a side view of the discharge tube, and FIG. 9 is a front view of the discharge tube. In the above specific example, the discharge pipe 37 is constituted by a single bent pipe. However, in the examples shown in FIGS. 8 and 9, a plurality of straight pipes 371 and a plurality of curved pipes 372 are connected to a plurality of socket joints. 373 is configured to be connected to each other. Even in such a configuration, the upward bent portion 37B can be formed substantially at the center, and the effects as described in the specific example are obtained.

  10 and 11 are diagrams showing another aspect of the discharge tube. FIG. 10 is a side view of the discharge tube, and FIG. 11 is a front view of the discharge tube. In this example, the discharge pipe 37 is connected to each other by a plurality of straight pipes 371 and a plurality of elbows 374. Even in such a configuration, the upward bent portion 37B can be formed substantially at the center, and the effects as described in the above specific example can be obtained. In this case, the curvature portion of the discharge pipe 37 is constituted by an elbow 374.

  12 is a diagram showing a modification of the configuration in the vicinity of the detection tube shown in FIG. In the configuration shown in FIG. 3, the discharge port 37 </ b> A of the discharge pipe 37 is open, but in this example, an additional pipe 38 is connected to the discharge port 37 </ b> A of the discharge pipe 37 via the flange 43. ing. In this case, the detection gas that has passed through the discharge pipe 37 can be sent to a predetermined location by passing through the pipe 38.

  In the above specific example, the ultrasonic speaker 13 and the ultrasonic microphone 14 are arranged so as to face each other, and the detection gas is allowed to flow between them, but the ultrasonic wave emitted from the ultrasonic speaker 13 is used. If it is comprised so that may be introduce | transduced into the ultrasonic microphone 14, the specific structure will not be limited. For example, if the ultrasonic wave emitted from the ultrasonic speaker 13 is reflected by a wall surface (not shown) and introduced into the ultrasonic microphone 14 across the detection tube 17, the ultrasonic speaker 13 and the ultrasonic microphone 14. Can also be placed back to back in reverse.

  Furthermore, in the above specific example, the ultrasonic speaker 13 and the ultrasonic microphone 14 are prepared and the gas is detected using the ultrasonic wave. However, depending on the type of gas to be detected, other arbitrary It is also possible to use sound waves such as sound waves in the audible band.

  Further, in the above specific example, a PLL feedback circuit is used. However, even if such a feedback circuit is not used, it is used as long as a difference in sound wave propagation speed due to the presence or absence of a detection gas, that is, a sound speed difference can be measured. The type of electric circuit is not limited. Further, the sound speed difference may be directly measured without using an electric circuit.

  Furthermore, in the above specific example, a rectangular wave is used as the pulse signal, but a waveform signal such as a sine wave or a triangular wave may be used.

It is a block diagram which shows an example of the gas detector of this invention. It is a figure which expands and shows the detection piping structure of the detection pipe vicinity of the gas detector shown in FIG. Similarly, it is a figure which expands and shows the detection piping structure of the detection pipe vicinity of the gas detector shown in FIG. It is a side view which shows the structure of an example of the discharge tube used with the said gas detector. It is a front view of the discharge pipe shown in FIG. It is a figure for demonstrating the detection method at the time of using the gas detector shown in FIG. Similarly, it is a figure for demonstrating the detection method at the time of using the gas detector shown in FIG. It is a side view which shows the other structure of the discharge tube used with the said gas detector. It is a front view of the discharge pipe shown in FIG. It is a side view which shows the other structure of the discharge tube used with the said gas detector. It is a front view of the discharge tube shown in FIG. It is a figure which shows the modification in the structure of the detection-tube vicinity shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Gas detector 11 Reference signal generator 12 Speaker drive amplifier 13 Ultrasonic speaker 14 Ultrasonic microphone 15 Preamplifier 16 Waveform shaper 17 Detector tube 18 Terminal box 19 Support plate 20 Feedback circuit 21 Phase comparator 22 Low-pass filter 23 Voltage Frequency oscillator 31 Alarm setter 37 Release pipe 41, 42, 43 Flange

Claims (34)

Preparing a detection tube for circulating a detection gas released from a predetermined environment;
Connecting a discharge tube having a bent portion at substantially the center to the detection tube;
A step of emitting a sound wave toward the detection tube in the absence of the detection gas in the detection tube, and measuring a sound speed at this time as a first sound speed;
In the state where the detection gas is present in the detection tube, emitting the sound wave toward the detection tube, and measuring the sound speed at this time as a second sound speed;
Detecting the presence of the detection gas by obtaining a difference between the first sound speed and the second sound speed;
A gas detection method comprising:   2. The gas detection method according to claim 1, wherein the bent portion of the discharge pipe is formed by bending a pipe line of the discharge pipe upward.   The gas detection method according to claim 2, wherein the discharge port of the discharge pipe is opened downward.   The discharge tube suppresses direct blowing of the detection gas to the outside regardless of the specific gravity of the detection gas, causes the detection gas to stay in the detection tube, and reduces the concentration of the detection gas in the detection tube. It increases, The gas detection method as described in any one of Claims 1-3 characterized by the above-mentioned.   A pair of openings are formed in a direction substantially perpendicular to the length direction of the detection tube, and the sound wave emitting means and the sound wave receiving means are provided so as to face each other in the opening, and the sound wave emitting means The gas detection method according to claim 1, wherein the gas detection method is unitized together with a terminal box that houses electrical wiring for the sound wave receiving means.   The gas detection method according to claim 5, wherein the terminal box is provided on an outer peripheral surface of the detection tube to achieve the unitization.   The gas detection method according to any one of claims 1 to 6, wherein the first sound speed and the second sound speed are measured as electrical signals.   The gas detection method according to claim 7, wherein the electrical signal is a pulse train signal.   The gas detection method according to claim 1, wherein the difference between the first sound speed and the second sound speed is obtained in a predetermined feedback circuit.   The gas detection method according to claim 9, wherein the feedback circuit constitutes a phase-locked loop.   The gas detection method according to claim 10, wherein the phase locked loop is synchronized with a phase of a first input electrical signal related to the first sound velocity.   In the phase-locked loop, the difference between the first sound speed and the second sound speed is the phase of the second input electrical signal related to the second sound speed and the first sound speed related to the first sound speed. The gas detection method according to claim 11, wherein the gas detection method is obtained as a differential electric signal generated according to a difference between the input electric signal and the phase.   The feedback circuit is configured such that the phase of the first input electrical signal related to the first sound speed and the phase of the second input electrical signal related to the second sound speed are the same. The gas detection method according to claim 12, wherein a comparison operation between the phase of the first input electrical signal and the phase of the second input electrical signal is performed.   The gas detection method according to claim 12 or 13, wherein the differential electric signal is output as a detection signal of the detection gas. A sound wave source for generating a predetermined sound wave;
Sound wave emitting means for emitting the sound wave;
A sound wave receiving means for receiving the sound wave;
A detection tube for circulating a detection gas released from a predetermined environment;
A discharge tube connected to the detection tube and having a bent portion at substantially the center;
The first sound velocity of the sound wave when the predetermined detection gas is not present in the detection tube and the second sound velocity when the detection gas is present in the detection tube are compared and detected, and the difference Measuring means to obtain
A gas detector, comprising:   The gas detector according to claim 15, wherein the bent portion of the discharge pipe is formed by bending a pipe line of the discharge pipe upward.   The gas detector according to claim 16, wherein the discharge port of the discharge pipe opens downward.   The discharge tube suppresses direct blowing of the detection gas to the outside regardless of the specific gravity of the detection gas, causes the detection gas to stay in the detection tube, and reduces the concentration of the detection gas in the detection tube. It increases, The gas detector as described in any one of Claims 15-17 characterized by the above-mentioned.   A pair of openings are formed in a direction substantially perpendicular to the length direction of the detection tube, and the sound wave emitting means and the sound wave receiving means are provided so as to face each other in the opening, and the sound wave emitting means The gas detector according to any one of claims 15 to 18, wherein the gas detector is unitized together with a terminal box containing electrical wiring for the sound wave receiving means.   The gas detector according to claim 19, wherein the terminal box is provided on an outer peripheral surface of the detection tube to achieve the unitization.   The gas detector according to any one of claims 15 to 20, wherein the first sound speed and the second sound speed are measured as electrical signals.   The gas detector according to claim 21, wherein the electrical signal is a pulse train signal.   The gas detector according to any one of claims 15 to 22, wherein the difference between the first sound speed and the second sound speed is obtained in a predetermined feedback circuit.   The gas detector according to claim 23, wherein the feedback circuit forms a phase-locked loop.   The gas detector according to claim 24, wherein the phase locked loop is synchronized with a phase of a first input electric signal related to the first sound velocity.   In the phase-locked loop, the difference between the first sound speed and the second sound speed is the phase of the second input electrical signal related to the second sound speed and the first sound speed related to the first sound speed. The gas detector according to claim 25, wherein the gas detector is obtained as a differential electric signal generated according to a difference between the input electric signal and the phase.   The feedback circuit is configured such that the phase of the first input electrical signal related to the first sound speed and the phase of the second input electrical signal related to the second sound speed are the same. 27. The gas detector according to claim 26, wherein a comparison operation is performed between the phase of one input electrical signal and the phase of the second input electrical signal.   28. The gas detection method according to claim 26, wherein the differential electric signal is output as a detection signal of the detection gas. A first sound velocity obtained by emitting a sound wave in an atmosphere in which no detection gas exists, and a second sound velocity obtained by emitting the sound wave in an atmosphere in which a detection gas exists, A detection pipe used for gas detection for detecting the presence of the detection gas by obtaining a difference between the sound speed of 1 and the second sound speed,
The detection pipe includes a detection pipe for flowing the detection gas, and a discharge pipe having a bent portion at a substantially center connected to the detection pipe.   30. The gas detection pipe according to claim 29, wherein the bent portion of the discharge pipe is formed by bending a pipe line of the discharge pipe upward.   The gas detection pipe according to claim 30, wherein the discharge port of the discharge pipe opens downward.   The discharge tube suppresses direct blowing of the detection gas to the outside regardless of the specific gravity of the detection gas, causes the detection gas to stay in the detection tube, and reduces the concentration of the detection gas in the detection tube. The gas detection pipe according to any one of claims 29 to 31, wherein the gas detection pipe is increased.   A pair of openings are formed in a direction substantially perpendicular to the length direction of the detection tube, and the sound wave emitting means and the sound wave receiving means are provided so as to face each other in the opening, and the sound wave emitting means The gas detection pipe according to any one of claims 29 to 32, wherein the gas detection pipe is unitized together with a terminal box containing electrical wiring for the sound wave receiving means.   34. The gas detection pipe according to claim 33, wherein the terminal box is provided on an outer peripheral surface of the detection tube to achieve the unitization.

Images