JP2009276309A - Leak detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a waiting time due to fatigue of a gas sensor. <P>SOLUTION: In a leak detector, specimen gas and background gas are alternately supplied to first and second gas sensors, and the gas flow rates of the specimen gas and the background gas are set to be constant and to be equal to each other. When gas leakage is detected from an output of the gas sensor contacting with the specimen gas, and the output of the gas sensor is equal to or exceeds a threshold for a prescribed time or longer continuously, flow passages of the specimen gas and the background gas are switched. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a leak detector using a gas sensor, and more particularly to a leak detector that eliminates the waiting time due to fatigue of the gas sensor.

  It is known that hydrogen is sealed in a product or facility that is inspected for leaks, and the leaked hydrogen is detected by a gas sensor. By the way, the gas sensor may get tired when touched with high-concentration gas or the like, and the output may not easily return to the level in clean air. When waiting for the output of the gas sensor to return to the level in the clean air in the inspection of the leak, a waiting time occurs every time a high-concentration gas is touched, which is inefficient. The leak detector that detects other gases such as chlorofluorocarbon also detects that the gas sensor is fatigued by touching a high-concentration gas and cannot be detected until the sensor output recovers to a level in clean air.

As for related prior art, Patent Document 1: JP1999-264809A discloses that a gas is detected from a transient characteristic when an atmosphere supplied to a gas sensor is switched between a reference gas and a sample gas. is doing.
JP1999-264809A

  An object of the present invention is to eliminate waiting time due to fatigue of a gas sensor.

The leak detector of the present invention comprises a sample gas suction hole, a background gas suction hole,
First and second at least two gas sensors;
The flow path is between a state in which the sample gas is supplied to the first gas sensor and the background gas is supplied to the second gas sensor, and a state in which the sample gas is supplied to the second gas sensor and the background gas is supplied to the first gas sensor. A switching valve,
Flow rate control means for making the flow rates of the sample gas and the background gas constant and equal to each other;
Leak detection means for detecting a gas leak from the output of the gas sensor supplied with the sample gas among the first and second gas sensors;
And a flow path switching means for switching the flow path through the valve when the output of the sensor to which the sample gas is supplied increases to satisfy a predetermined condition.

The gas sensors are of the same type, and when three or more gas sensors are provided, three or more flow paths are also provided, and the flow paths are switched according to sensor switching.
Preferably, the flow path switching unit switches the flow path when the output of the sensor supplied with the sample gas does not decrease below the second threshold value within a predetermined time after the output increases above the first threshold value. Switch.
More preferably, the leak detection means has two modes, a leak detection mode and a gas concentration measurement mode,
In the leak detection mode, the gas leak is detected from the time derivative of the gas sensor output, and at the time when a predetermined time elapses after the output of the sensor supplied with the sample gas exceeds the first threshold value, When the second threshold is exceeded, the flow path is switched,
In the gas concentration measurement mode, the gas concentration is measured from the stable value after the output of the sensor to which the sample gas is supplied is increased, and the flow path is switched when the stable value is acquired.

  In the present invention, when one gas sensor touches the sample gas and the output increases and satisfies the condition of low, the flow is switched and detection is started by the other gas sensor. Since the other gas sensor was in contact with the background gas having the same flow rate, the environment in which the sensor is placed is the same even when the flow path is switched, and detection can be started immediately after detection is started. For this reason, there is no waiting time due to fatigue of the gas sensor.

Here, the flow path switching unit switches the flow path when the output of the sensor to which the sample gas is supplied does not decrease below the second threshold value within a predetermined time after the output from the sensor increases. When the sensor output does not decrease to the original level, the flow path can be switched.
If two modes, a leak detection mode and a gas concentration measurement mode, are provided, two types of detection can be performed: a check for the presence of a leak and a measurement of the gas concentration. In the leak detection mode, the gas leak is detected from the time derivative of the gas sensor output, and at the time when a predetermined time elapses after the output of the sensor supplied with the sample gas increases to the first threshold value or more. When the second threshold value is exceeded, the flow path is switched. On the other hand, in the gas concentration measurement mode, if the gas concentration is measured from the stable value after the output of the sensor to which the sample gas is supplied increases, and the flow path is switched when the stable value is acquired, the gas concentration is stabilized. After the value can be measured, the flow path can be switched.

  In the following, an optimum embodiment for carrying out the present invention will be shown.

  1 to 4 show a leak detector according to the embodiment. In each figure, 2 and 4 are gas sensors, for example, metal oxide semiconductor hydrogen sensors, and the gas sensors 2 and 4 are, for example, two gas sensors of the same lot with the same model number. 6 and 8 are three-way valves, and these may be combined into a single four-way valve, etc. 10 and 12 are needle valves, and any valve that can adjust the flow rate, and 14 and 16 are flow meters. is there. Reference numeral 18 denotes a suction pump, and separate pumps may be provided for the needle valves 10 and 12, respectively. 20 and 21 are dust filters, excluding dust in the gas, and 22 and 23 are gas filters, which are filters such as activated carbon and zeolite. The dust filters 20 and 21 are the same type of filter, and the gas filters 22 and 23 are the same type of gas filter so that the flow rate does not fluctuate even when the flow path is switched. A gas suction hole 25 is provided at the tip of a probe (not shown) and connected to the dust filter 20 via the tube 27. Reference numeral 26 denotes a background gas suction hole which is provided in a main body case of the leak detector.

  The switching signals for the three-way valves 6, 8 are (S, R), the output signals from the gas sensors 2, 4 are S1, S2, and the output signals from the flow meters 14, 16 are F1, F2. The control signals for the needle valves 10 and 12 are Q1 and Q2. A control unit 24 includes an AD converter, a microcomputer, and an LCD display. The sensor signals S1 and S2 and the flow rate signals F1 and F2 are input, and the three-way valve 6.8 is switched by the signals S and R. The needle valves 10 and 12 are controlled by Q2.

  FIG. 2 shows the control unit 24 of the leak detector. Sensor signals S1 and S2 and flow rate signals F1 and F2 are input to the AD converter 30, and the flow rate control unit 40 controls the needle valves 10 and 12 so that these flow rates are constant and equal. Instead of providing the flow control unit 40, the needle valves 10 and 12 may be manually controlled, and the control method of the valves 10 and 12 may be displayed on the display unit 35. The leak detector 31 time-differentiates the output of the gas sensor that is in contact with the sample gas, and detects the presence or absence of hydrogen leak.

  Similarly, when the gas sensor signal in contact with the sample gas increases and reaches a stable value, the hydrogen concentration measuring unit 32 detects the hydrogen concentration from the stable value. Instead of waiting for the sensor signal to actually reach the stable value, the hydrogen value may be obtained by predicting the stable value from the waveform of the sensor signal or the like. The presence or absence of hydrogen leak and the hydrogen concentration are detected from the signal of the gas sensor that is in contact with the sample gas, and the detection results are displayed on the display unit 35. The channel switching unit 33 outputs channel switching signals S and R based on the gas sensor signal that is in contact with the sample gas. Reference numeral 34 denotes a timer attached to the flow path switching unit 33. The storage unit 36 stores the average value or steady value of the gas sensor signal that is in contact with the background gas, switches the flow path, and when this sensor is used for measurement, the stored average value or steady value is stored in the background. A reference signal indicating the level is used. The mode selection unit 37 is a manual switch that switches between a leak detection mode and a hydrogen concentration measurement mode.

  FIG. 3 shows a flow path switching algorithm in the leak detection mode. Here, it is assumed that the sensor A is in contact with the sample gas, the presence or absence of leakage is obtained from the time differentiation of the sensor signal, and the detection result is displayed on the display unit. When the output of the sensor A exceeds the first detection threshold, a timer is started, and the flow path is switched if the sensor output has not decreased below the second detection threshold before time-out. In this way, after the gas sensor signal increases, the flow path is switched when the return to the background level is slow. Further, for example, the flow path is switched at regular intervals such as 1 minute or 2 minutes. Here, the detection threshold 2 is set to be equal to or less than the detection threshold 1, but these may be the same value. Further, the flow path may be switched when the gas sensor signal exceeds the detection threshold 1 without providing a timer. In this case, it is preferable to set the first detection threshold value to a value larger than that of the embodiment so as not to prevent detection of leak by differentiation.

  FIG. 4 shows a flow path switching algorithm in the hydrogen concentration measurement mode. For example, the detection threshold 1 and the detection threshold 2 are the same as those in FIG. 3, and the flow path is switched when the sensor output reaches a stable value or when the stable value can be predicted, not when the timer 34 times out. . That is, in 1) of FIG. 4, a stable value is measured or predicted from the waveform of the sensor output, and when the timer 34 has timed out at this time, the flow path is switched. In the hydrogen concentration measurement mode, since the demand for the detection tact time is not high, it is not necessary to switch the flow path after touching the high concentration gas. In addition, the sensor output is calibrated, and the difference between the gas concentration obtained from the stable value in the sample gas and the gas concentration corresponding to the sensor output in the background is output as the hydrogen concentration.

In the embodiment, an example of detecting hydrogen leakage by a metal oxide semiconductor gas sensor has been described. However, the detection target gas may be any other fluorocarbon, and the gas sensor may be a contact combustion gas sensor, a solid electrolyte gas sensor, an electrochemical gas sensor, or the like.

The figure which shows the gas flow path of the leak detector of an Example Block diagram of the control unit in the embodiment FIG. 5 is a diagram showing a flow path switching algorithm in the leak detection mode, where 1) shows the output waveform of the gas sensor, 2) shows the timer operation, and 3) shows the flow path switching. FIG. 4 is a diagram showing a flow path switching algorithm in the hydrogen concentration measurement mode, where 1) shows the output waveform of the gas sensor, 2) shows the timer operation, and 3) shows the flow path switching.

Explanation of symbols

2,4 Gas sensor 6,8 Three-way valve 10,12 Needle valve 14,16 Flow meter 18 Pump 20,21 Dust filter 22,23 Gas filter 24 Control unit 25 Sample gas suction hole 26 Background gas suction hole 27 Tube 30 AD converter 31 Leak Detection Unit 32 Hydrogen Concentration Measurement Unit 33 Channel Switching Unit 34 Timer 35 Display Unit 36 Storage Unit 37 Mode Selection Unit 40 Flow Rate Control Unit

Claims (3)

Sample gas suction holes, background gas suction holes,
First and second at least two gas sensors;
The flow path is between a state in which the sample gas is supplied to the first gas sensor and the background gas is supplied to the second gas sensor, and a state in which the sample gas is supplied to the second gas sensor and the background gas is supplied to the first gas sensor. A switching valve,
Flow rate control means for making the flow rates of the sample gas and the background gas constant and equal to each other;
Leak detection means for detecting a gas leak from the output of the gas sensor supplied with the sample gas among the first and second gas sensors;
A leak detector comprising: a flow path switching means for switching the flow path via the valve when an output of the sensor supplied with the sample gas increases to satisfy a predetermined condition. The flow path switching means switches the flow path when the output of the sensor to which the sample gas is supplied does not decrease below the second threshold value within a predetermined time after the output of the sensor increases above the first threshold value. The leak detector of claim 1, characterized in that The leak detection means has two modes, a leak detection mode and a gas concentration measurement mode,
In the leak detection mode, the gas leak is detected from the time derivative of the gas sensor output, and at the time when a predetermined time elapses after the output of the sensor supplied with the sample gas exceeds the first threshold value, When the second threshold is exceeded, the flow path is switched,
In the gas concentration measurement mode, the gas concentration is measured from the stable value after the output of the sensor to which the sample gas is supplied is increased, and the flow path is switched when the stable value is acquired. The leak detector according to claim 2.

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