JPH09250979A - Gas detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect cracked gas present in inactive gas with high sensitivity by charging a sensor vessel with standard gas and sample gas alternately, detecting concentration of the cracked gas contained in the sample gas based an characteristic change of a vibrator, and providing the sensor vessel with a means which brings the standard gas and the sample gas into contact with a gas sensor under the condition of the same pressure and temperature. SOLUTION: A vacuum pump 49 starts exhaust operation, and an electromagnetic valve 45 is opened, to exhaust a sensor chamber 25 and a piping system. After completion, an electromagnetic valve 35a is opened to fill a sensor vessel 25 with standard gas of a standard gas tank 37 so as to be specified pressure, and then the valve 35a is closed, and a cap 61 is lowered to finish filling. Then, the pump 49 starts exhaust operation for evacuating the vessel 25, etc. Then, an electromagnetic valve 35b is opened, and the vessel 25 is so filled with sample gas of a sample gas tank 39 as to be specified pressure, and then the valve 35b is closed to finish filling. Then an electric current is sent to a gas sensor 23 with a heater driving circuit 55 while a chamber A is closed, to raise temperature of the element. After heat radiation, generated frequency change of the sensor 23 is measured with a frequency measurement device 29.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detection device capable of detecting decomposition gas existing in an inert gas.

[0002]

2. Description of the Related Art Conventionally, as a gas sensor for detecting a reducing gas in the atmosphere, a semiconductor gas sensor using a sintered body of a metal oxide such as tin oxide (SnO ₂ ) or zinc oxide (ZnO) is generally used. Are known. This sensor utilizes the phenomenon that when the metal oxide comes into contact with a reducing gas, its electrical resistance decreases.

This phenomenon is caused by the generation of a reducing gas, whereby the oxygen adsorbed by the negative ions on the surface of the metal oxide undergoes an oxidation reaction, and the electrons captured by the adsorbed oxygen move to the metal oxide. This is a phenomenon that occurs when the electron concentration of the metal oxide increases.

However, since the above semiconductor type gas sensor is effective in detecting reducing gas in the atmosphere because of the above-described detection principle, it is effective in detecting flame retardant gas or in oxygen-free atmosphere. Not suitable for use.

Sulfurous acid gas (SO ₂ ) which is a flame retardant gas,
A low potential electrolytic gas sensor is known as a gas sensor for detecting hydrogen chloride (HCl), hydrogen fluoride (HF), and the like. This sensor is a method of measuring the electrolytic current generated by electrolyzing a gas while keeping the interface between the electrode and the electrolyte at a specific potential. This type of sensor has high sensitivity to both reducing gas and flame-retardant gas, but has the drawback of short life because it uses an electrolyte. Moreover, the gas that can be detected by this type of sensor is limited.
SOF ₂ , which is a decomposition gas of F ₆ , cannot be detected.

On the other hand, in recent years, a crystal oscillator type gas sensor has been attracting attention as a gas sensor having high sensitivity and capable of operating at room temperature. This sensor has a structure in which an organic material or the like is formed as a gas adsorption film on an electrode of a crystal oscillator plate. For example, as shown in the following equation (1), the gas adsorbed on the gas adsorption film is The weight change ΔW is detected as the resonance frequency change Δf of the crystal unit.

[0007]

## EQU1 ## Δf = −2.3 × 10 ⁶ × f ² × ΔW / A (1) where f is the resonance frequency of the crystal unit, and A is the electrode area of the crystal unit.

Further, this crystal oscillator type gas sensor can detect the amount of adsorbed gas as a change in impedance or inductance.

As described above, since the above-described crystal oscillator type gas sensor operates on the above-described detection principle, it exhibits high sensitivity to both reducing gas and flame retardant gas, and p
A gas of pb order can be detected, and further, JP-A-55-42054 and JP-A-1-229935.
As disclosed in Japanese Unexamined Patent Application Publication No. 2005-242242, a quartz oscillator gas sensor has been widely developed as a sensor for odorous gas, etc. that operates at room temperature.

However, in reality, not all gases can be detected at room temperature. For example, regarding the decomposition gas of SF ₆ , SO ₂ cannot be detected by the gas sensor disclosed in JP-A-55-42054. On the other hand, JP-A-1-
The gas sensor disclosed in Japanese Patent No. 229935 can detect HF but cannot detect SOF ₂ .

Therefore, in order to solve such a problem, the present inventors proposed a gas sensor capable of repeatedly detecting SOF ₂ with high sensitivity in the invention of the patent application of Japanese Patent Application No. 6-5511.

The gas sensor proposed here uses a metal oxide as the above-mentioned gas adsorption film, and has a structure as described below, for example.

FIG. 14 is a sectional view showing the structure of a crystal oscillator type gas sensor proposed in Japanese Patent Application No. 6-5511 of the present inventors.

In FIG. 14, the gas sensor 23 is
A 50 MHz AT-cut crystal oscillator plate is used as the crystal oscillator plate 1. On both sides of the crystal oscillator plate 1, electrodes 3 having a gold (Au) layer formed on the surface of a chromium (Cr) underlayer are formed.
a and 3b are provided. Gas adsorption films 5a and 5b made of tin oxide or copper oxide are provided on the upper surfaces of the electrodes 3a and 3b, and lead wires 9a and 9b are adhered to the electrodes 3a and 3b by a highly heat-resistant conductive paste 7a and 7b. ing.

On the other hand, the lead wire 9 is attached to the lead pins 13a, 13b, 13c and 13d fixed to the insulating support 11.
By connecting a and 9b, elements such as the crystal oscillator plate 1 are held. Also, the lead pins 13c and 13d
Flat ceramic heaters 17a and 17b, which are installed so as to face the respective surfaces of the crystal resonator plate 1, are attached to the supporting lead frame 15 connected to.
Further, a cap 21 provided with a protection net 19 made of stainless steel is covered on the support base 11 to protect the above elements and the like.

FIG. 15 is a plan view of an element such as the crystal oscillator plate 1 described above. As shown in FIG. 15, the crystal oscillator plate 1
Has a disk shape, and the electrode 3a formed thereon has a substantially circular shape and has a pad portion. Furthermore, the electrode 3a
The gas adsorption film 5a is formed on the upper portion, and the conductive paste 7a is applied to the pad portion of the electrode 3a. The back side has the same structure.

The sensitivity characteristic evaluation using the above gas sensor will be described. FIG. 16 is a diagram showing a configuration of a gas detection device using the gas sensor.

[0018]

[Outside 1] A gas sensor 23 is attached to the sensor container 25, the gas sensor 23 is driven by an oscillation circuit 27 outside the sensor container 25, and a frequency measuring instrument 29 is connected so that the resonance frequency can be monitored.

Next, the measurement operation of this apparatus is shown in FIG.
This will be described with reference to FIGS.

First, the inside of the sensor container 25 is evacuated to vacuum, then SF ₆ which is an inert gas is filled from the gas cylinder 31, the pressure is set to 1 atmospheric pressure, and the sensor container 25 is left standing for a certain period of time.

Next, the heaters 17a and 17b are energized to raise the temperature of the heater for 30 seconds to reach the temperature of the gas sensor 23 up to about 400 ° C., the energization of the heater is stopped, and the temperature of the gas sensor 23 is lowered. To start.

Next, a predetermined volume of the test gas (SOF ₂ ) is injected from the syringe 33 so that the inside of the sensor container 25 has a predetermined concentration, and the frequency measuring device 29 measures the oscillation frequency change due to the temperature decrease of the gas sensor 23. To measure. For example, in FIG. 17, the test gas (SF ₆ + SOF ₂ ) concentration is 0 ppm.
It is a figure which shows the evaluation result of the change of the oscillation frequency in the case of and 20 ppm.

Finally, from FIG. 17, the decrease rate of the frequency when the test gas is not injected (SOF ₂ concentration is 0 ppm) and the decrease rate of the frequency when the test gas is injected (SOF ₂ concentration is 20 ppm). The concentration of the test gas can be detected by obtaining the difference between

As described above, by using the gas sensor and the gas detector using the gas sensor proposed in Japanese Patent Application No. 6-5511 of the present inventors, SF ₆
SOF ₂ , which is a decomposition gas of SF ₆ , can be repeatedly detected with high sensitivity and in the long term.

The usage of this gas sensor is, for example,
The gas generated inside the gas insulated circuit breaker (hereinafter, referred to as “GIS”) can be taken out of the device for detection, and the gas sensor and the gas detection device proposed by the present inventors can detect the 20 ppm level. It is possible.

However, in gas-insulated electric equipment, the generation of decomposed gas itself indicates insulation abnormality. Therefore, it is necessary to detect a minimum amount of decomposed gas as early as possible, and therefore, with even higher sensitivity. Although a highly accurate gas sensor is desired, the above gas sensor can detect the decomposition gas of the inert gas repeatedly and with good reproducibility, but in order to monitor the insulation function of the gas-insulated electrical equipment, from the viewpoint of sensitivity. Was not enough.

Therefore, as a method of increasing the sensitivity of the gas sensor, from the above formula (1), a method of increasing the oscillation frequency of the crystal resonator and a method of thickening the gas adsorption film can be considered. However, in order to increase the oscillation frequency, the thickness of the quartz crystal diaphragm must be made thinner, but if it is made thinner, the mechanical strength of the resonator itself will decrease, causing damage to the resonator and lowering its reliability. Will end up. On the other hand, in the method of thickening the gas adsorption film, the oscillation of the gas sensor becomes unstable, or even if it oscillates stably, it oscillates only in the temperature range lower than the normal operating temperature, and the measurement is repeated. The gas adsorption film sometimes cracked or peeled off. Therefore, the characteristics of the gas sensor are unstable and poor in reproducibility, and it is difficult to secure the detection accuracy for a long period of time.

By the way, as described above, an application of the gas sensor is to detect a gas generated inside the device. However, when the gas is taken out from the device and detected, the flow of the device is usually simple. The through method is used.

FIG. 18 is a diagram showing the structure of a gas detection device for switching gases by a flow-through method. In addition,
The same parts as those in FIG. 16 are designated by the same reference numerals.

In FIG. 18, this gas detecting apparatus is provided with the gas sensor 23 shown in FIG. 14 in the sensor container 25, the standard gas tank 37 and the test gas tank 39 are switched by the electromagnetic valves 35a and 35b, and the particulates are filtered by the filters 41a and 41b. After the removal, the gas pressure is made constant by the pressure regulator 43 and alternately flowed in the sensor container 25, and the difference in oscillation frequency change of the gas sensor 23 between the standard gas and the test gas is detected by the oscillation circuit 27 and the frequency measuring instrument 29. It is an apparatus which measures as a signal and detects the concentration of the decomposition gas contained in the test gas from the magnitude of the gradient of the change curve of the detection signal.

Next, the measuring operation of this gas detector will be described with reference to FIGS. 14 and 18.

First, the temperature of the gas sensor 23 is raised to about 400 ° C. while flowing the standard gas into the sensor container 25, and the gas adsorbed on the gas adsorption films 5a and 5b is desorbed.

Next, the temperature rise is stopped, the temperature of the gas sensor 23 is started to be lowered, and after a certain period of time, the frequency change (reference change) is measured while the temperature is being lowered.

Next, the temperature of the gas sensor 23 is set to about 4 again.
The temperature is raised to 00 ° C. to desorb the gas adsorbed on the gas adsorption films 5a and 5b.

Next, the temperature rise is stopped and the temperature of the gas sensor 23 is started to be lowered. After a certain period of time, the electromagnetic valve 33 is switched to the electromagnetic valve 35 to flow the test gas, and the frequency is changed while the temperature is lowered (response). Change).

Finally, a response curve to the test gas is obtained from the difference in frequency change between the standard gas and the test gas thus obtained, and the slope of the response curve is obtained as a detection signal for the concentration of the test gas.

FIG. 19 is a diagram showing changes in the oscillation frequency when the standard gas and the test gas are flowed. Here, tin oxide is used as the gas adsorption film of the gas sensor and SF is used as the standard gas.
₆ , when SOF ₂ (10 ppm) was used as the test gas. As is clear from FIG. 19, the fluctuations decrease with the passage of time, but the frequencies fluctuate irregularly, and the difference between these frequencies is accurately determined, and the slope is read from the obtained response curve. It turns out to be practically difficult (see FIG. 20). This is also the case with high-concentration gas, and the slope of the response curve rises faster as the concentration increases, so if the frequency fluctuates when the gas is switched as shown in FIG. 19, the slope of the response curve will increase. Can not be read accurately.

The reason why the frequency fluctuates is considered to be the influence of temperature and mechanical strain. The above m (1) expression is an expression that holds when the temperature is constant and no external force is applied. In the conventional crystal oscillator gas sensor, a commercially available product that is manufactured so as to have a small change due to temperature in the room temperature range is used. Since it is used, even if the gas is made to flow, the frequency fluctuation is small and can be ignored. However, in the gas sensor proposed by the present inventors, since the crystal resonator is operated in a temperature range considerably higher than room temperature, the resonance frequency actually greatly changes according to the following equation (2).

[0039]

[Number 2] _{(f T -f To) / f} To = A (T-T 0) + B (T-T 0) 2 + C (T-T 0) 3 ... (2) where, T ₀ is a reference temperature , T is an arbitrary temperature, f _T0 is T ₀
Resonance frequency in ° C, f _T is the resonance frequency in T ° C, A is the first-order temperature coefficient determined by the crystal orientation of the crystal unit,
B is a second-order temperature coefficient, and C is a third-order temperature coefficient.

On the other hand, regarding the influence of the mechanical strain, the change of the resonance frequency due to the change of the gas pressure of the crystal resonator itself is relatively small, but as shown in FIGS. 14 and 15, the crystal diaphragm 1 has only two points. Since it is supported, it is considered that when a pressure is applied vertically to the crystal diaphragm 1, the crystal diaphragm 1 is distorted and the resonance frequency changes depending on the pressure as shown in the following formula (3).

[0041]

Δf = Kf · F · f ² · η / (n · D) (3) where Kf is the stress sensitivity coefficient, n is the overtone order, D is the diameter of the crystal oscillator, and f is the resonance. The frequency, Δf is the amount of change in the resonance frequency, F is the pressing force, and η is a coefficient.

That is, the crystal oscillator type gas sensor is a sensor for detecting the change in weight of the adsorbed gas with extremely high sensitivity, but at the same time, it is also highly sensitive to temperature and mechanical strain. Therefore, when the measurement is performed while the gas is flowing, the detection signal fluctuates irregularly, so that the correction accuracy by the reference signal is lowered, and it is impossible to accurately read the transient frequency change due to the adsorption of the gas. Moreover, since the gas replacement time is long, a large amount of sample gas and a large amount of reference gas are required, which makes it difficult to realize a small portable detection device.

[0043]

As described above,
The gas sensor shown in FIG. 14 can repeatedly detect the decomposition gas of the inert gas with good reproducibility, but its sensitivity is not sufficient to monitor the insulating function of the gas-insulated electrical equipment.

Further, in the gas sensor for improving the above problems, in the method of reducing the thickness of the crystal diaphragm to increase the oscillation frequency, the reliability is deteriorated as the strength of the crystal resonator is decreased, and the gas adsorption is reduced. In the method of thickening the film, the characteristics of the gas sensor were not stable and the detection accuracy could not be kept constant.

On the other hand, in the flow-through type gas detector using the gas sensor shown in FIG. 14, the oscillation frequency of the gas sensor fluctuates irregularly due to temperature and pressure changes due to the gas flow,
The decomposition gas concentration could not be detected accurately. Further, since it takes a long time to replace the gas, a large amount of gas is required.

Therefore, the present invention has been made in view of the above, and an object of the present invention is to detect a low-concentration decomposed gas existing in an inert gas with high sensitivity and high accuracy. To provide a device.

[0047]

In order to achieve the above object, the invention according to claim 1 is a gas detection device for detecting a decomposition gas of an inert gas present in the inert gas. A gas sensor for detecting the decomposition gas by changing the characteristics of the oscillator formed, and the gas sensor is stored, the standard gas is an inert gas containing no decomposition gas and the test gas is an inert gas containing decomposition gas. It has a sensor container filled alternately and a control means for detecting the decomposition gas concentration contained in the test gas by the characteristic change of the oscillator, the sensor container is the same standard gas and the test gas It is characterized by comprising means for contacting the gas sensor with pressure and temperature.

According to a second aspect of the present invention, in the gas detection device for detecting the decomposition gas of the inert gas existing in the inert gas, the decomposition gas is detected by the characteristic change of the vibrator having the gas adsorption film. Gas sensor, a sensor container that stores the gas sensor and is alternately filled with a standard gas that is an inert gas that does not include a decomposition gas and a test gas that is an inert gas that includes a decomposition gas, and the standard gas is filled. The above-mentioned sensor container is further provided with a means for filling the test gas and a control means for detecting the decomposition gas concentration contained in the test gas based on the characteristic change of the oscillator.

According to the configuration of the invention described in claim 1 or 2, by eliminating the irregular frequency fluctuation of the gas sensor due to the pressure difference of the gas, it is possible to detect only the frequency change due to the adsorption of the decomposed gas.

Here, the film thickness of the gas adsorption film is from 0.01 to
Particularly good characteristics can be obtained when the thickness is about 1 μm.

As the vibrator, a crystal vibrator, a tuning fork vibrator, a ceramic piezoelectric vibrator, a vibrator made of a combination of single crystal silicon or other crystal silicon and a piezoelectric thin film can be used.

The metal oxide used as the gas adsorption film is not particularly limited as long as it exhibits high temperature stability, and tin oxide, copper oxide, tungsten oxide, aluminum oxide,
Zinc oxide, magnesium oxide, cobalt oxide, nickel oxide or the like is used.

It is important that the surface shape of the gas adsorption film is formed so that the mechanical properties of the film do not affect the oscillator and the gas adsorption amount is maximized. Any shape can be used as long as it is uneven, but if the width of the recess is wide, the amount of film decreases and the sensitivity decreases, and if the width of the projection is narrow and the film thickness of the recess becomes zero, the film peels off. Or the test gas may corrode the oscillator, so the lower limit of the width of the recess should be so large that the end faces of the film do not come into contact with each other due to thermal expansion, while the thickness of the recess depends on the oscillator used. Although it is possible to make it zero depending on the resonance frequency and the width of the convex portion, generally, a good characteristic is to set it to 0.05 to 0.2 μm, which does not adversely affect the oscillator due to its mechanical properties. It is necessary to get it.

The change in the amount of gas adsorbed is detected as a change in the oscillation frequency of the vibrator, but in addition to this, it is also possible to detect it as a change in impedance and inductance using, for example, the network analyzer method.

[0055]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a diagram showing a configuration of a gas detection device according to a first embodiment of the present invention. This gas detection device uses a gas sensor shown in FIG. GIS) is used to detect the decomposed gas generated off-line. The same parts as those in the conventional example are designated by the same reference numerals, and the gas tank 29 to be detected corresponds to the GIS here.

In FIG. 1 (a), this gas detecting device is provided with a solenoid valve 45 at a gas inlet of a sensor container 25 (for example, an internal volume of about 40 cc), and a standard gas is supplied via a pressure regulator 43 and filters 41a and 41b. Alternatively, it is connected so that the test gas can be introduced into the sensor container 25. Further, an electromagnetic valve 47 is provided at the gas outlet of the sensor container 25,
The vacuum pump 49 is connected so that the inside of the sensor container 25 can be evacuated.

Further, the input terminal of the detection control circuit 51 is
The output of the frequency measuring device 29 is connected so that the output of the oscillation circuit 27 can be monitored. Further, the detection control circuit 51 is connected to a drive circuit 53 for the solenoid valve and the pump, a heater drive circuit 55, a recording device 57, and a display device 59.

The detection control circuit 51 controls the frequency measuring device 29, the solenoid valve and pump drive circuit 53, and the heater drive circuit 55 according to the timing of the reference clock based on the procedure recorded in advance in the non-volatile memory (ROM). The data of the frequency measuring device 29 is recorded in the recording device 57, and the processing result of the recorded data is output to the display device 59.

FIG. 1B is a diagram showing an outline of the inside of the sensor container 25. In FIG. 1B, the gas sensor 23 is arranged in the sensor chamber A inside the sensor container 25, and the sensor chamber A can be opened and closed by the upper and lower sides of the lid 61.

Next, a method for extracting and detecting the gas inside the GIS using this detection device will be described with reference to FIGS. 1 and 14.

First, when the detection control circuit 51 outputs a control signal to the drive circuit 53 for the solenoid valve and the pump, the vacuum pump 49 first starts the evacuation operation, then the solenoid valve 45 opens, and the piping system and the sensor container 25. Start exhausting. At this time, the sensor chamber A is opened.

When the piping system and the sensor container 25 are exhausted for a predetermined time, the electromagnetic valve 45 is closed, and the vacuum pump 49 is stopped, the exhaust operation is completed.

Next, the solenoid valve 35a is opened, the standard gas (SF ₆ ) in the standard gas tank 37 is filled into the sensor container 25 until a predetermined pressure is reached, and then the solenoid valve 35a is closed to complete the filling.

Next, when the lid 61 is lowered to close the sensor chamber A, the heater drive circuit 55 starts energizing the heaters 17a and 17b of the gas sensor 23, and the temperature of the element such as the crystal oscillator plate 1 rises.

Next, when the temperature reaches a predetermined temperature, the energization is stopped and the element is allowed to cool for a predetermined time. After that, the measurement of the oscillation frequency change of the gas sensor 23 is started by the frequency measuring device 29, then the lid 61 is lifted to open the sensor chamber A, and the oscillation frequency (reference change) is measured for a certain period of time. At this time, since the sensor chamber A and the space other than the sensor chamber A have the same pressure, the irregular frequency change of the gas sensor due to the pressure difference of the gas can be eliminated, and only the frequency change in the reference gas atmosphere can be eliminated. Can be detected.

Next, the vacuum pump 49 starts the evacuation operation,
Then, the solenoid valve 45 is opened to start exhausting the piping system and the sensor container 25. At this time, the sensor room A is opened.

When the piping system and the sensor container 25 are exhausted for a predetermined time, the electromagnetic valve 45 is closed, and the vacuum pump 49 is stopped, the exhaust operation is completed.

Next, the solenoid valve 35a is opened, the standard gas (SF ₆ ) in the standard gas tank 37 is filled into the sensor container 25 until a predetermined pressure is reached, and then the solenoid valve 35a is closed and the lid 61 is lowered. To complete the filling.

Next, the vacuum pump 49 starts the evacuation operation,
Then, the solenoid valve 45 is opened to start exhausting the piping system and the sensor container 25. At this time, the sensor chamber A is closed.

When the piping system and the sensor container 25 are exhausted for a predetermined time, the electromagnetic valve 45 is closed, and the vacuum pump 49 is stopped, the exhaust operation is completed.

Next, the solenoid valve 35b is opened, and the test gas (SF ₆ and SOF ₂ ) in the test gas tank 39 is transferred to the sensor container 2.
5 is filled up to a predetermined pressure, and then the solenoid valve 35b
Closes and the filling is completed.

Next, with the sensor chamber A kept closed, the heater driving circuit 55 drives the heater 17a of the gas sensor 23,
Energization of 17b starts and the temperature of the element rises.

Next, when a predetermined temperature is reached, the power supply is stopped and the element is left to cool for a predetermined time. After that, the measurement of the oscillation frequency change of the gas sensor 23 is started by the frequency measuring device 29, then the lid 61 is lifted to open the sensor chamber A, and the oscillation frequency (response change) is measured for a certain period of time. At this time, since the sensor chamber A and the space other than the sensor chamber A have the same pressure, the irregular frequency change of the gas sensor due to the gas pressure difference can be eliminated, and the test gas atmosphere (reference gas and Only the frequency change in SOF ₂ ) can be detected.

Finally, the frequency data recorded in the recording device 57 is taken into the detection control circuit 51, and the difference between the frequency data when the standard gas and the test gas are brought into contact with each other is calculated. The slope of the response curve is obtained as a detection signal, compared with basic data (calibration curve data) measured in advance, converted into a concentration, and displayed on the display device 59. The above detection operation is repeated as necessary.

With the above operation, the SO in the GIS
Electric discharge was performed so that the concentration of F ₂ became a desired concentration, and SF ₆
Was repeatedly measured.

FIG. 2 is a diagram showing changes in the oscillation frequency when the standard gas and the test gas were flown, which were evaluated by the gas detection device. As is clear from FIG. 2, SF ₆ ,
Both the decomposition gas of SF ₆ shows a straight change without the fluctuation of the frequency as shown in FIG. 22 of the related art, and the difference between these frequencies can be accurately obtained, and the slope can be read from the obtained response curve. It turns out to be easy (see FIG. 3).

FIG. 4 is a diagram showing the result of examining the relationship between the decomposed gas concentration and the detection signal. From 1 to 20 ppm,
It can be seen that the relationship is almost proportional.

FIG. 5 is a diagram showing the result of repeating the measurement by discharging so that the concentration of SOF ₂ becomes 10 ppm. Although the concentration is slightly lower at the beginning, it is almost constant in 100 measurements. It can be seen that it indicates the concentration of.

Next, a second embodiment of the present invention will be described. FIG. 6 is a diagram showing a configuration of the gas detection device according to the second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals.

In FIG. 6, this gas detecting device is arranged such that the standard gas is supplied to the gas inlet of the sensor container 25 through the filter 41a, the pressure regulator 63 and the solenoid valve 47a, and the filter 41b, the pressure regulator 65 and the solenoid valve 47b. The test gas is connected to each of the test gases via the. Also,
An electromagnetic valve 45 is provided at the gas outlet of the sensor container 25, and is connected so that the inside of the sensor container 25 can be evacuated by a vacuum pump 49.

The input terminal of the detection control circuit 51 is
The output of the frequency measuring device 29 is connected so that the output of the oscillation circuit 27 can be monitored. Further, the detection control circuit 51 is connected to a drive circuit 53 for the solenoid valve and the pump, a heater drive circuit 55, a recording device 57, and a display device 59.

The detection control circuit 51 controls the frequency measuring device 29, the solenoid valve and pump drive circuit 53, and the heater drive circuit 55 according to the timing of the reference clock based on the procedure recorded in advance in the non-volatile memory (ROM). The data of the frequency measuring device 29 is recorded in the recording device 57, and the processing result of the recorded data is output to the display device 59.

Next, a method of extracting and detecting the gas inside the GIS using this detection device will be described with reference to FIGS. 6 and 14.

First, when the detection control circuit 51 outputs a control signal to the solenoid valve and pump drive circuit 53, the vacuum pump 49 first starts the evacuation operation, and then the solenoid valves 45, 47a,
47b and 36 are opened, and exhaust of the piping system and the sensor container 25 is started.

When the piping system and the sensor container 25 are evacuated for a predetermined time, the solenoid valves 45 and 47b are closed, and the vacuum pump 49 is stopped, the evacuation operation is completed.

Next, the solenoid valve 35a is opened, and the standard gas (SF ₆ ) in the standard gas tank 37 is filled into the pipes between the sensor container 25 and the solenoid valves 35a, 36, 47b until the respective pressures reach predetermined pressures. , Solenoid valves 35a, 36, 47a
Closes and the filling is completed.

Next, the heater drive circuit 55 starts energizing the heaters 17a and 17b of the gas sensor 23, and the temperature of the element such as the crystal oscillator plate 1 rises.

Next, when the temperature reaches the predetermined temperature, the power supply is stopped and the element is allowed to cool for a predetermined time. After that, the measurement of the oscillation frequency change of the gas sensor 23 is started by the frequency measuring device 29, then the solenoid valves 35a, 36, 47b are opened, and the standard gas (SF ₆ ) is again supplied to the sensor container 25 at a pressure higher than the standard gas. Fill and measure the oscillation frequency (reference change) for a certain period of time. At this time, since the sensor container 25 filled with the standard gas is filled with the higher-pressure standard gas, a pressure change occurs in the atmosphere, but since the change is a short time, it is possible to effectively perform the irregular frequency fluctuation of the sensor. It is possible to detect only the frequency change when the standard gas is filled. When the measurement is completed, the solenoid valve 47
b, 36, 35a are closed.

Next, the vacuum pump 49 starts the evacuation operation,
Subsequently, the solenoid valves 45 and 47b are opened, and the exhaust of the piping system and the sensor container 25 is started again.

When the piping system and the sensor container 25 are exhausted for a predetermined time, the electromagnetic valves 45 and 47b are closed, and the vacuum pump 49 is stopped, the exhaust operation is completed.

Next, the solenoid valves 35a and 47a are opened, and the standard gas (SF ₆ ) in the standard gas tank 37 is transferred to the sensor container 25.
Is charged to a predetermined pressure and then the solenoid valve 35
a and 47a are closed to complete the filling.

Next, the heater driving circuit 55 starts energizing the heaters 17a and 17b of the gas sensor 23, and the temperature of the element rises.

Next, when the temperature reaches the predetermined temperature, the power supply is stopped and the element is allowed to cool for a predetermined time. Thereafter, the measurement of the oscillation frequency change of the gas sensor 23 is started by the frequency measuring device 29, 35b and 47b are subsequently opened, and the test gas (SF ₆ + SOF ₂ ) is filled with a pressure higher than the standard gas,
Measure the oscillation frequency (response change) for a certain period of time. This time,
Since the sensor container 25 filled with the standard gas is filled with the higher-pressure standard gas, the atmosphere can be switched promptly, and the irregular frequency fluctuation of the sensor can be effectively eliminated, and the test object Only the frequency change when the gas is filled can be detected. 35 when the measurement is completed
Close b and 47b.

Finally, the frequency data recorded in the recording device 57 is taken into the detection control circuit 51, and the difference between the frequency data when the standard gas and the test gas are brought into contact with each other is calculated. The slope of the response curve is obtained as a detection signal, compared with basic data (calibration curve data) measured in advance, converted into a concentration, and displayed on the display device 59. The above detection operation is repeated as necessary.

Next, a third embodiment of the present invention will be described. FIG. 7A is a diagram showing the configuration of the gas adsorption film of the gas sensor according to the third embodiment of the present invention, FIG.
(B) is a figure which shows the structure of the gas adsorption film of the conventional gas sensor, and the characteristic of this invention is that the lattice-shaped unevenness | corrugation was provided in the gas adsorption film.

In FIG. 7A, the gas adsorption film of the gas sensor according to the present embodiment uses tin oxide and tungsten oxide as film materials, and the film thickness is formed on the entire surface of the crystal resonator plate 1 excluding the protruding portions of the electrodes 3. There is a gas adsorption film 5 of 0.1 μm, and the gas adsorption film 5 is further formed on the electrode 3 with a grid-like groove having a recess width of about 100 μm and a recess depth of about 0.4 μm. There is. The film thickness of the gas adsorption film of the conventional gas sensor shown in FIG. 7B is about 0.4 μm.

The method of forming the gas adsorption film shown in FIG. 7A will be described below. Here, there is also a method in which the gas adsorption film is deposited by a CVD method, a sputtering method, a vapor deposition method, a coating method, or the like, and the shape is determined by a mask or etching, but in this embodiment, a relatively fine pattern can be easily formed. An example using the laser heating method, which is simple in process, will be described.

In the above laser heating method, the first step of applying an organic compound containing a metal to form a metal oxide film and the step of selectively heating the applied organic compound to form a metal or metal oxide. A second step of forming a thin film made of, a third step of removing an unheated portion of the organic compound, and a step of performing heat treatment after the third step. As a raw material for tin oxide, tin ethylhexanoate,
Tungsten resinate was used as a raw material of tungsten oxide. Since the film thickness is different between the first layer and the second layer, the film thickness when forming tin oxide and tungsten oxide is 0.1
Each raw material solution is diluted with butanol so that the second layer has a thickness of 0.4 μm.

First, an appropriate amount of the raw material solution for the first layer is applied on the entire surface of the crystal resonator plate 1 on which the electrodes 3 are formed by the drop method, and preliminarily dried for about 20 minutes in the atmosphere, and then 120
Dry at ℃ for about 20 minutes.

Next, a CO ₂ gas laser beam (beam diameter 50 μm) was formed on the entire surface of the crystal resonator plate 1 excluding the protruding portions of the electrodes 3.
mΦ, output 3 W / sec, scan speed 5 cm / se
It is irradiated with c) to change into a thin film in which tin and tin oxide or tungsten and tungsten oxide are mixed.

Next, the quartz crystal diaphragm 1 is washed with acetone to remove the raw material in the non-irradiated portion, and then baked at 500 ° C. for 30 minutes in the air atmosphere.

Next, an appropriate amount of the raw material solution for the second layer is applied on the electrode 3 by the drop method, preliminarily dried in the atmosphere for about 20 minutes, and then dried at 120 ° C. for about 20 minutes.

Next, a CO ₂ gas laser beam is irradiated onto the electrode while avoiding the groove portion shown in FIG. 7A to change it into a thin film in which tin and tin oxide or tungsten and tungsten oxide are mixed. When forming the gas adsorption film shown in FIG. 7B, a laser beam is applied to the entire surface of the crystal unit 1.

Finally, the quartz crystal diaphragm 1 was washed with acetone to remove the raw material in the non-irradiated area, and then the atmosphere was kept at 500 ° C. in the atmosphere.
Bake for 30 minutes.

A gas sensor is manufactured by forming lead wires on the quartz resonator plate 1 on which the gas adsorption film 5 is formed as described above according to a usual procedure, and welding and mounting the lead wire together with the heater on the system.

FIG. 8 is a diagram showing an oscillation frequency change-temperature characteristic of the gas sensor manufactured by the above method.
This is the result of measuring the frequency immediately before the oscillation was stopped by gradually raising the heater voltage while oscillating in F ₆ .
As is clear from FIG. 8, the gas sensor having no groove in tin oxide stopped oscillating when the voltage exceeded 6.2 V, but the gas sensor having the groove oscillated stably up to about 7 V although the gas adsorption film was thick. did.

On the other hand, in the case of tungsten oxide, the gas sensor provided with the groove oscillated stably up to 6.5 V, but the gas sensor without the groove oscillated after 5.5 V.

FIG. 9 shows the results of evaluating the sensitivity by using the gas sensor having a groove in the gas adsorption film (tin oxide film) and the gas sensor not having the groove in the gas detecting apparatus of FIG. 16 shown in the conventional example. It is a figure, SOF by a syringe injection method
It is the change of the detection signal when measuring ₂ gases 1 to ₂₀ ppm five times each.

As is apparent from FIG. 9, the gas sensor without the groove shows a change at 5 to 20 ppm, but 10 ppm
Below, there are large variations in the data. On the other hand, the gas sensor provided with the groove has high sensitivity and small variation in data.
This is a characteristic that enables identification of ppm or less.

Since the results shown in FIGS. 8 and 9 are obtained by detecting SOF ₂ in a state where the surrounding environment is constant, the results obtained by actually detecting the decomposition gas of SF ₆ are also shown below. explain. Here, as the gas sensor, a gas sensor having a tin oxide film having the shape shown in FIG. 7A is used.

FIG. 10 is a cross-sectional view showing the arrangement of the gas sensor. The gas sensor 23 is installed in a vacuum container 67 having a structure in which a gas sensor storage chamber is provided in a part of the pipe, and the periphery of the gas sensor 23 is cooled and heated. Peltier element 6 as an element
9, a thermocouple 71 is mounted near the heater as a temperature sensor.

FIG. 11 shows, for example, a gas insulation circuit breaker (GI) using the gas sensor arranged as shown in FIG.
It is a figure which shows one structural example of the gas apparatus apparatus which detects the off-line of the decomposition gas generate | occur | produced in S). In FIG. 11, this gas detection device guides SF ₆ of the standard gas to the gas introduction port side of the vacuum container 67, and therefore has a filter 75 a and a solenoid valve 8
7a, a pressure regulator 77a, and a solenoid valve 82a, and a route for bypassing and filling the solenoid valve 76, the pressure regulator 77b, and the solenoid valve 82b after the filter 75a and the solenoid valve 87a. On the other hand, in order to guide the gas of GIS101 to the gas inlet side of the vacuum container 67, the filter 75
b, a solenoid valve 87b, a pressure regulator 77b, and a solenoid valve 82b are provided to provide a filling path. An electromagnetic valve 81, an adsorbent 83, and a vacuum pump 85 are provided on the exhaust side of the vacuum container 67.

The oscillation circuit 89 converts a change in the resonance frequency of the crystal oscillator plate of the gas sensor 23 into an electric signal. The heaters 17a and 17b, the thermocouple 71, and the Peltier element 69 of the gas sensor 23 are connected to the heater and Peltier element driving circuit 90, and drive the heater and the Peltier element by the signal of the detection control circuit 93. The drive circuit 91 uses the signals of the detection control circuit 93 to control the solenoid valves 76, 81, 82.
a, 82b, 87a, 87b and the vacuum pump 85 are driven. The detection control circuit 93 controls the oscillation circuit 89 and the drive circuit 91. The display device 95 and the recording device 97 are connected to the detection control circuit 93. Power is supplied from the power supply 99 to the detection control circuit 93. On the other hand, gas insulated circuit breaker (GI
An on-off valve 103 is provided at the gas sampling port of S) 101. Then, the gas inlet of the vacuum container 67 and the GIS 10
The gas sampling port 1 is connected from the quick joint 105.

The detection control circuit 93 outputs a control signal to the drive circuit 91 in accordance with the timing of the reference clock based on the procedure recorded in advance in the non-volatile memory (ROM), and the drive circuit 91 drives each device. Detection control circuit 93
Is configured to compare the output from the oscillating circuit 89 with the detection data of the standard sample which is measured in advance and recorded in the ROM, converts it into a density signal and outputs it to the display device 95 and the recording device 97. Has a function that can be updated by measuring a standard sample.

Using such a gas detector, SOF
FIG. 12 shows the results obtained by repeatedly detecting the gas decomposed by discharge under the condition that the amount of ₂ produced was approximately 5 ppm. FIG.
When the ambient temperature is 10 ° C. and 40 ° C., the temperature reached by the sensor is 400 ° C. when the temperature is raised, and the temperature of the cooling element 19 when the temperature is lowered is
It is a figure which shows the change of the density | concentration display value of the said gas detection device when a detection is repeated as ° C. As is clear from FIG. 12, even if the detection is performed 100 times, the sensitivity is almost constant, which shows that the gas sensor according to the present embodiment is also effective in the actual detection of decomposed gas.

In this embodiment, the shape of the gas adsorbing film has the lattice-shaped grooves shown in FIG. 7A, but the spiral grooves shown in FIG. 13A are shown. 13A, the cross-shaped groove shown in FIG. 13B, the groove dividing the concentric circle shown in FIG. 13C into crosses, and the groove shown in FIG. 13D. The same effect can be obtained even if the center of the electrode surface is recessed.

[0117]

As described above, according to the present invention,
The decomposed gas existing in the inert gas can be detected with high sensitivity and high accuracy.

[Brief description of drawings]

1A is a diagram showing a configuration of a gas detection device according to a first embodiment of the present invention, and FIG. 1B is a diagram showing an outline of an inside of a sensor container 25 shown in FIG. 1A. .

FIG. 2 is a diagram showing a change in oscillation frequency when a standard gas and a test gas are flown evaluated by the gas detection device of FIG.

FIG. 3 is a diagram showing a difference in oscillation frequency when a standard gas and a test gas in FIG. 2 are flown.

FIG. 4 is a diagram showing a result of examining a relationship between a decomposition gas concentration and a detection signal.

FIG. 5 is a diagram showing a result of repeating measurement by discharging the decomposition gas (SOF ₂ ) to a concentration of 10 ppm.

FIG. 6 is a diagram showing a configuration of a gas detection device according to a second embodiment of the present invention.

7A is a diagram showing a configuration of a gas adsorption film of a gas sensor according to a third embodiment of the present invention, and FIG. 7B is a diagram showing a configuration of a gas adsorption film of a conventional gas sensor. .

8 is a diagram showing the relationship between the oscillation frequency and temperature of the gas sensor of FIG. 7 (a).

9 is a diagram showing the results of evaluating the sensitivities of the gas sensor of FIG. 7 (a) and the gas sensor of FIG. 7 (b).

FIG. 10 is a diagram for explaining the gas sensor of FIG. 7 (a).

FIG. 11 is a diagram showing an example of the configuration of a gas detection device that uses the gas sensor of FIG. 7A to detect decomposed gas generated in, for example, a gas insulated circuit breaker (GIS) offline.

FIG. 12 is a gas detection device of FIG. 11 when detection is repeated when the ambient temperature is 10 ° C. and 40 ° C., when the temperature reached by the sensor is 400 ° C. and the temperature of the cooling element 19 during temperature decrease is 20 ° C. FIG. 6 is a diagram showing changes in the density display value of FIG.

FIG. 13 is a diagram showing another example of the shape of the gas adsorption film of FIG.

FIG. 14 Japanese Patent Application No. 6-5511 relating to the invention of the present inventors.
2 is a cross-sectional view showing the configuration of a crystal resonator type gas sensor proposed in No.

15 is a plan view of an element such as the crystal resonator plate 1 of FIG.

16 is a diagram showing a configuration of a gas detection device using the gas sensor of FIG.

FIG. 17: Decomposition gas (SOF ₂ ) concentration is 0 ppm and 2
It is a figure which shows the evaluation result of the change of the oscillation frequency in the case of 0 ppm.

FIG. 18 is a diagram showing a configuration of a gas detection device that switches gases by a flow-through method.

FIG. 19 is a diagram showing changes in oscillation frequency when a standard gas and a test gas are flown.

20 is a diagram showing a difference in oscillation frequency when the standard gas and the test gas in FIG. 19 are flown.

[Explanation of symbols]

1 Crystal oscillator plate 3, 3a, 3b Electrode 5, 5a, 5b Gas adsorption film 7a, 7b Conductive paste 9a, 9b Lead wire 11 Support stand 13a, 13b, 13c, 13d Lead pin 15 Support lead frame 17a, 17b Ceramic Heater 19 Protective net 21 Cap 23 Gas sensor 25 Sensor container 27, 89 Oscillation circuit 29 Frequency measuring instrument 31 Gas cylinder 33 Syringe 35a, 35b, 45, 47, 76, 81, 87a, 8
7b, 82a, 82b Solenoid valve 37, 79 Standard gas tank 39 Test gas tank 41, 75 Filter 43, 63, 65, 77 Pressure regulator 49, 85 Vacuum pump 51, 93 Detection control circuit 53, 91 Solenoid valve and pump drive Circuit 55 Heater drive circuit 57, 97 Recording circuit 59, 95 Display circuit 61 Lid 67, 73 Vacuum container 69 Peltier element 71 Thermocouple 83 Adsorbent 90 Heater and Peltier element drive circuit 99 Power supply 101 Gas insulation breaker (GIS) 103 Open / close valve 105 quick joint

Claims (2)

[Claims] 1. A gas detection device for detecting a decomposition gas of an inert gas existing in an inert gas, comprising: a gas sensor for detecting the decomposition gas by a characteristic change of a vibrator having a gas adsorption film; and the gas sensor. And a sensor container that is alternately filled with a standard gas that is an inert gas that does not include a decomposition gas and a test gas that is an inert gas that includes a decomposition gas; And a control means for detecting the concentration of decomposed gas contained therein, wherein the sensor container comprises means for bringing the standard gas and the test gas into contact with the gas sensor at the same pressure and temperature. apparatus. 2. A gas detection device for detecting a decomposition gas of the inert gas existing in the inert gas, the gas sensor detecting the decomposition gas by a characteristic change of a vibrator having a gas adsorption film, and the gas sensor. And a sensor container in which a standard gas that is an inert gas that does not include a decomposition gas and a test gas that is an inert gas that includes a decomposition gas are alternately filled, and the sensor container that is filled with the standard gas In addition, the gas detection device further comprises means for filling the test gas, and control means for detecting the concentration of the decomposed gas contained in the test gas by changing the characteristic of the oscillator.