JPH02143134A - Leak detector - Google Patents

Abstract

PURPOSE:To securely detect an ultrasonic wave from a gas leak hole and to securely and accurately search for the gas leak hole by setting ultrasonic wave sensors in different directions. CONSTITUTION:The detection outputs of a main ultrasonic sensor 1 and a subordinate ultrasonic sensor 2 are inputted to a differential amplifier 3 to obtain their output difference, which is inputted to an integrator 6 through an active filter 4 and a full-wave rectifier 5. The sensors 1 and 2 are fitted at 180 deg. so as to have opposite directivity; and the leak noise detection ability of the sensor 1 when the sensor 1 is directed to the gas leak hole is set much larger than that of the sensor 2.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for maintaining gas-filled communication cables.
By detecting ultrasonic waves generated from gas leak holes at communication cable connections such as at the gas supply end, inside the sinus, and inside the large hole,
Among the detectors for detecting gas leak holes and accurately searching for their positions, the present invention particularly relates to a handy type leak detector.

[Prior Art] It is known that when a gas leak hole occurs in a gas-filled communication cable, ultrasonic waves are generated due to leakage of the filled gas from the gas leak hole. For example, internal pressure 0.5 kg/c
If there is a gas leak hole with a diameter of 2 mm in the gas-filled communication cable of ffl, and the sound is measured at a point 1 m away from the gas leak hole, as shown in Figure 4, the sound will be heard at the measurement point (basement). While the sound pressure level of the background noise hole drops rapidly in the ultrasonic range, the sound pressure level of the leakage sound A generated from the gas leak hole shows a high value in the ultrasonic range.

A leak detector is known that uses an ultrasonic sensor to detect a gas leak hole in a gas-filled communication cable by using ultrasonic waves generated from the gas leak hole.

A conventional leak detector using this ultrasonic sensor is equipped with one ultrasonic sensor that detects ultrasonic waves of a constant frequency generated by gas leakage from a gas leak hole, and the output level of this one ultrasonic sensor is If the value exceeds a predetermined value, it is determined that a gas leak hole has been detected.

[Problem to be solved by the invention]

In this way, since the leakage sound generated from the gas leakage hole contains ultrasonic waves with a high sound pressure level compared to the general background noise hole, it is theoretically possible to detect the gas leakage hole using an ultrasonic sensor. However, actual gas leakage hole search work is often carried out near roads with heavy traffic.
Background noise detected by the ultrasonic sensor Noise containing ultrasonic waves, such as the sound of a car running, a horn, or the sound of a public relations car, enters the background noise detected by the ultrasonic sensor, causing the ultrasonic sensor to output a detection signal. It was not possible to distinguish whether the obtained detection signal of the ultrasonic sensor was due to leakage sound from the gas leak hole or ultrasonic waves in the background noise hole.
It was often impossible to search for gas leak holes.

For this reason, leak detectors using conventional ultrasonic sensors are currently rarely used.

The cause of this problem in the prior art is that it is not possible to select only the ultrasonic waves generated from the gas leak hole from among the ultrasonic waves detected by the ultrasonic sensor.

Therefore, the present invention was devised to solve the above-mentioned problems in the prior art. We use two ultrasonic sensors to determine the level of ultrasonic waves in the background noise within the gas leak hole search location, and based on this level, we can determine that the ultrasonic sensor has directivity and that the ultrasonic waves from the gas leak hole are Being directional;
The ultrasonic waves coming from the gas leak hole are selected by taking advantage of the fact that the level of the ultrasonic waves increases as they get closer to the gas leak hole. The purpose is to reliably and accurately detect gas leakage holes by reliably detecting sound waves.

Another object is to facilitate handling of a leak detector using an ultrasonic sensor.

[Means for solving the problem]':□...The means of the present invention to achieve the above object is to have at least two ultrasonic sensors, a main ultrasonic sensor and a sub ultrasonic sensor, both ultrasonic sensors. a differential amplifier that outputs the difference between the outputs of the two ultrasonic sensors, an active filter that has a bandpass characteristic that passes only the output corresponding to the ultrasonic wave of a specific frequency from among the outputs of the two ultrasonic sensors, and comprising an integrator that inputs the difference between the band-pass processed outputs, and a display function section that is connected to the output terminal of the integrator and displays the magnitude of the detected output; The present invention is characterized in that it has a series circuit of an on/off switch and a zero set inserted and connected between them to form a feedback circuit, and that both ultrasonic sensors are directed in different directions.

It is preferable that the difference between the bandpass-processed outputs of both ultrasonic sensors is subjected to full-wave rectification through a full-wave rectifier connected to the input terminal of the integrator and then input to the integrator.

Both ultrasonic sensors are aligned from 90° to 180°.
It is best to assemble and fix them integrally to a single frame with a shift of up to 1°.

[Effect]

When the leak detector according to the present invention is brought to a gas leak hole search location and operated with both ultrasonic sensors pointing in arbitrary directions, both ultrasonic sensors detect approximately equal amounts of ultrasonic waves in the background noise of the atmosphere at the search location. do. The detection outputs of both ultrasonic sensors are subjected to subtraction processing by a differential amplifier, bandpass processing by an active filter, and inputted to an integrator as an output difference signal. By applying human power to this integrator, the difference between the outputs of both ultrasonic sensors is smoothed and output to the display function section as a nearly constant value.In this state, the integrator's feed bank circuit switch is When you turn on and activate the zero set, the integrator changes the reference value of the comparator to the difference between the input outputs, so
Its output becomes zero, and the display of the display function section becomes zero. That is, the above operations complete the zero cent setting of the display function section of the leak detector according to the present invention.

Once the zero setting of the display function section is completed, direct only the main ultrasonic sensor to the location where you want to search for a gas leak hole, and approach that location.

If there is a gas leak hole at the target location, the detection output of the main ultrasonic sensor will be larger than the detection output of the sub ultrasonic sensor because the ultrasonic waves generated from the gas leak hole are directional. Since the difference between the outputs input to the integrator becomes large, the output from the integrator is output as a search signal to the display function section and displayed on the display function section.

On the other hand, if there is no gas leak hole at the target location, the detection output of the main ultrasonic sensor will not increase and will remain the same as the output of the sub ultrasonic sensor, so the output of the integrator will remain zero. Yes, the display function section does not display the detection of gas leak holes.

If the gas leak hole search location changes due to movement and the atmosphere at the search location changes, turn on the integrator feedback circuit again to perform a new zero cent, and then carry out the gas leak hole search work. .

In this way, the leak detector of the present invention inputs the output value of the main ultrasonic sensor and the output value of the auxiliary ultrasonic sensor to the differential amplifier and performs subtraction processing. The output due to noise is almost completely removed, and the only difference between the outputs output from the differential amplifier is the ultrasonic detection signal from the gas leak hole detected by the main ultrasonic sensor.

Furthermore, by specifying the frequency of the ultrasonic waves to be detected using the active filter, gas leak holes can be searched for with higher sensitivity. In other words, as shown in Fig. 4, the leak from the gas leak hole contains ultrasonic waves with a high sound pressure level, but the ultrasonic waves with a high sound pressure level that reaches the level of background noise are also detected. Since sound waves are included, when searching for gas leak holes, select the frequency band that has the largest difference between the sound pressure level of the ultrasonic waves in the leak table and the sound pressure level of the ultrasonic waves in the background noise hole. Therefore, it is advantageous to specify the

The difference between the outputs of both ultrasonic sensors is input manually to the integrator and then output to the display function section, so even if the difference in output includes incorrect outputs due to extremely short collisions or horns, etc. Even if the incorrect output is smoothed by the integrator, it is output to the display function section only for a short time, and the display function section returns to stable display operation immediately after the pointer oscillates for a very short time. to return to.

In other words, if the sound pressure level of the leakage sound A near both ultrasonic sensors due to the ultrasonic waves generated from the gas leak hole is Po, and the sound pressure level of the background noise port around the search location is Pl, then the detection of the main ultrasonic sensor The output E1 and the detection output E2 of the sub-ultrasonic sensor are: EI = +Po + 2P +
... (1) 4Pl to K2"K3PO+
... (2) However, K2, K2, K1, K4
is a sensitivity coefficient that takes into account the directivity of both ultrasonic sensors.

Therefore, the output v0 of the differential amplifier is ν. -EI K2 = (K+ Kz) Po+ (Kz Kg) P
I... (3) becomes.

The first item in this equation (3) is the output generated by the leak table A generated from the gas leak hole, and the second item is the output generated by the background noise port.

The search for gas leak holes is carried out inside the tunnel and inside the large hole, and in this case, the sensitivity coefficient of both ultrasonic sensors for the leak table A is:
Since the main ultrasonic sensor is directed toward the gas leak hole, K
+ ) K*, and in the case of a background noise hole, the noise source is relatively far from the gas leak hole, and the sound waves propagate within the tunnel and the large hole due to the diffraction phenomenon, so K2! = i is 4, so equation (3) becomes v0ζKIPO---(4), and the influence of the background noise port is almost eliminated.

In addition, even if Kz>K4 or Kz<K4, the output voltage of the integrator is set to zero by zero setting before the gas leak hole search operation, so the main ultrasonic sensor and the sub-ultrasonic sensor for the background noise hole are The difference in sensitivity coefficient with the ultrasonic sensor will be completely eliminated, and only the detection output obtained by directing the main ultrasonic sensor toward the gas leak hole, that is, the leak point A will be detected and displayed.

Full-wave rectification of the difference between the outputs of both ultrasonic sensors input to the integrator ensures reliable operation of the integrator, thereby ensuring reliable and stable display operation of the display function section.

By integrally mounting the main ultrasonic sensor and the sub ultrasonic sensor on one frame, both ultrasonic sensors can be placed in the same atmospheric environment, which makes gas leak hole search operations more accurate. At the same time, handling becomes extremely easy.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment that is considered to be the simplest embodiment of the present invention. The embodiment shown in FIG. The configuration is such that the output difference is input to an amplifier 3 to obtain an output difference, and this output difference is input to an integrator 6 through an active filter 4 and a full-wave rectifier 5.

Both ultrasonic sensors I and 2 are installed 180 degrees apart so that their directivity is opposite, and the main ultrasonic sensor 1
Main ultrasonic sensor 1 when pointing to the gas leak hole
The leakage sound detection capability of the sub-ultrasonic sensor 2 is made to be much larger than the leakage sound detection capability of the sub-ultrasonic sensor 2.

The active filter 4 is for making it easier to separate the leakage table A by specifying the frequency of the detection signal, so as is clear from the characteristics of the leakage table A and the background noise port shown in FIG. , it is advantageous to set the center frequency of the bandpass characteristic to 40 KHz in terms of S/N.

Note that the resistor inserted and connected between the integrator 6 and the full-wave rectifier 5 is a resistor for input protection, and also inserted and connected in series with the input terminal of the integrator 6 in the feedback circuit of the integrator 6. The resistor is a protection resistor that also serves as an amplification level setting.

FIG. 2 shows another embodiment of the present invention.
In the illustrated embodiment, the detection outputs of both ultrasonic sensors 1 and 2 are individually passed through an amplifier 10, an active filter 4, and a full-wave rectifier 5, and then input to a differential amplifier 3. The difference between the outputs of the two outputs is input to the integrator 6.

In this way, since the outputs of both ultrasonic sensors I and 2 are individually amplified, bandpass processed, and full-wave rectified,
The signals subjected to each process maintain a relatively large value, which makes it easy to carry out each process. Further, since the subtraction processing by the differential amplifier 3 is a DC subtraction processing, the accuracy of the processing result can be improved.

FIG. 3 shows an embodiment of the probe in which both ultrasonic sensors 1.2 are integrally attached to one frame 11. The main ultrasonic sensor 1 is attached to one end of the cylindrical frame 11. At the same time, the auxiliary ultrasonic sensor 2 is attached to the other end, and due to this configuration, the direction of direction of both ultrasonic sensors 1 and 2 is opposite to each other.

Note that the number of main ultrasonic sensors 1 and sub-ultrasonic sensors 2 to be installed is not limited; for example, a plurality of main ultrasonic sensors 1 may be provided and each main ultrasonic sensor 1 may be scanned by a multiplexer or the like. This makes it possible to expand the search range for gas leak holes.

[Effects of the Invention] Since the present invention has the above-described configuration, it has the following effects.

Since the leak sound can be searched for while the influence of background noise at the gas leak hole search location is eliminated by subtraction processing and zero set processing, the leak sound search can be performed reliably and accurately.

Searching for gas leak holes is extremely easy, as all you have to do is turn on the leak detector, turn on the switch, set the display function to zero, and then point the main ultrasonic sensor in the appropriate direction. It is.

Zero set processing requires simply turning on the switch, so even if the location of the gas leak hole to be searched for changes, or in other words, even if the background noise environment changes, it can easily adapt to this changed environment. The effects of background noise can be eliminated.

Background noise is detected simultaneously by the main ultrasonic sensor and the sub-ultrasonic sensor, and the background noise detected by the recurrent acoustic sensor is always canceled out, so even if a sudden background noise occurs, this sudden Background noise does not enter the search signal, and accurate and reliable leakage sound detection can be achieved and maintained at all times.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the simplest electric circuit configuration of a leak detector according to the present invention. FIG. 2 is an electrical circuit configuration diagram showing another embodiment of the present invention configured to obtain higher sensitivity. FIG. 3 is an overall perspective view showing a configuration example of a probe as a sensor microphone. FIG. 4 is a known frequency sound pressure level characteristic diagram of leakage sound and background noise. Explanation of symbols 1: Main ultrasonic sensor, 2: Sub-ultrasonic sensor, 3: Differential amplifier, 4: Active filter, 5: Full-wave rectifier, 6: Integrator, 7: Display function section, 8: Zero sector, 9 Switch, 10; Amplifier, Engineering l: Frame, A; Leakage sound, Mouth; Background noise. Zoom gong Boo 2γ defense + -4 super sound burst ze〉bu 4-,, -active 11 shift 2---$11! 1 sound fzu 5-11; & Hiruuki 3-4t * anzu e -4 divider 7-Display Usha review 8--Z

Claims (3)

[Claims] (1) A main ultrasonic sensor (1), a sub-ultrasonic sensor (2), a differential amplifier (3) that outputs the difference between the outputs of both the sensors (1) and (2), and both the sensors ( an active filter (4) having a bandpass characteristic that allows only the output corresponding to an ultrasonic wave of a specific frequency to pass from among the outputs of 1) and (2); and a bandpass of both the sensors (1) and (2). an integrator (6) inputting the difference of the processed output; a switch (9) and a zero set (8) inserted and connected between the input terminal and the output terminal of the integrator (6) to form a feedback circuit; ), and a display function section (7) connected to the output terminal of the integrator (6), and both the sensors (1) and (2) are directed in different directions. leak detector. (2) A full-wave rectifier (5) is provided at the input terminal of the integrator (6), and the difference between the band-pass processed outputs of both sensors (1) and (2) is full-wave rectified, and then the integrator (6) The leak detector according to claim 1, wherein the leak detector is inputted to (6). (3) The leak detector according to claim 1, wherein both the sensors (1) and (2) are integrally attached to one frame (11) with their pointing directions mutually shifted in the range of 90° to 180°. .