JPS6264938A - Apparatus for detecting gas - Google Patents

Abstract

PURPOSE:To detect gas with high reliability over a long period of time, in an apparatus for detecting reducible gas, by detecting the generation and distinction of the oscillation of an output signal and resetting a detection level corresponding to the operation temp. at that time. CONSTITUTION:The heater part 3 of a gas sensor 1 is brought to operative temp. by controlling a heater control part 5 at every definite time by a timer part 6 and the output of the sensor 1 is detected by a signal detection part 7. Further, the presence of the oscillation of the output signal of the sensor 1, when the operative temp. of the heater part 3 was changed, is detected by an oscillation detecting part 8. Next, the heater current signal determining the operative temp. of the heater part 3 at the time of the distinction of oscillation is inputted to a detection level circuit 9 to alter a detection level. Then, the detection signal is compared with the detection level by a comparing part 10 to perform the alarm of gas leakage by an alarm. At this time, the sensor 1 is changed from low temp. to high temp. and the deterioration of the capacity of the sensor 1 is detected on the basis of the temp. distincting oscillation and the detection level is corrected corresponding thereto. Because correction is performed corresponding to the deterioration of the sensor, gas can be detected with high accuracy.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a gas detection device for detecting a reducing gas, and particularly relates to a gas detection device suitable for highly reliable detection over a long period of time. .

[Background of the invention]

Various proposals have been made for gas detection devices for combustible gases1, but there are problems in that malfunctions and false alarms are likely to occur due to miscellaneous gases other than the detected gas, such as alcohol. This is because the specific resistance value of the gas sensor decreases during this period.

If you continue to use the alarm at the predetermined alarm level,
Gradually, alarms began to be issued even at gas concentrations lower than the set value, and this appeared to be equivalent to a gas sensor becoming more sensitive, posing problems in terms of long-term stability and reliability.

As a solution to these problems, there are measures to use filters for oxidizing miscellaneous gases, as disclosed in Japanese Patent Publication No. 58-7940 and Japanese Patent Publication No. 58-47663, and methods to use filters for oxidizing miscellaneous gas, as disclosed in Japanese Patent Publication No. 57-53531. As described above, strategies have been used to offset changes in gas sensors over time by using multiple gas sensors. However, although the initial characteristics have been improved by putting these measures into practical use, it is still not sufficient. There is a need for a highly reliable gas detection device that can detect (deterioration) and self-correct.

[Purpose of the invention]

An object of the present invention is to provide a gas detection device that can perform highly reliable and highly accurate detection over a long period of time, regardless of changes in the characteristics of the gas sensor itself.

[Summary of the invention]

As a result of various studies on changes in gas sensor performance over time, the present inventors have newly discovered that when a gas sensor's performance deteriorates, an oscillation phenomenon occurs in the output signal of the gas sensor.

This was done by taking advantage of this phenomenon. This phenomenon will be explained in detail below.

If the performance of the gas sensor deteriorates significantly due to long-term use, the output signal of the gas sensor in an air atmosphere without reducing gas will oscillate at the rated operating temperature. We have newly discovered that this oscillation phenomenon of the output signal of the gas sensor changes depending on the operating temperature of the gas sensor, and disappears when the operating temperature is made higher than the rated operating temperature. Furthermore, the operating temperature at which the oscillation phenomenon of the output signal of this gas sensor occurs is related to the degree of performance deterioration due to changes in gas sensor performance over time.In gas sensors with little performance deterioration, oscillation occurs at low operating temperatures; It disappears during the process of increasing the temperature. In other words, it has been newly discovered that there is a correlation between the degree of deterioration of a gas sensor over time and the operating temperature at which the oscillation phenomenon of the gas sensor in an air atmosphere disappears.

In order to take advantage of the above phenomenon, the present invention includes means for changing the operating temperature of the heater section and means for detecting the presence or absence of oscillation of the output signal of the gas sensor. The detection level is reset to one of predetermined values depending on the operating temperature when the occurrence or disappearance of oscillation of the output signal is detected.

In particular, by configuring the operating temperature of the heater section to change stepwise to a predetermined temperature at predetermined intervals, it is possible to self-compensate for sensor performance deterioration, ensuring high reliability and long-term performance. This is designed to ensure accuracy.

[Embodiments of the invention]

An embodiment of the gas detection device according to the present invention will be described below.

This will be explained with reference to FIGS. 1 to 3. FIG. 1 is a block diagram showing the configuration of the apparatus of this embodiment. FIG. 2 is a characteristic diagram showing an example of the performance characteristics of the gas sensor used in the device of the present invention. Moreover, FIG. 3 is a time chart showing the operation of the apparatus of this embodiment.

In FIG. 1, 1 is a semiconductor type gas sensor, 2 is a gas sensing part of the gas sensor 1 for detecting a reducing gas, 3 is a heater part for heating the gas sensing part 2, and 4 is a sensing part of the gas sensor 1. An output resistor 5 controls the operating temperature of the heater section 3 of the gas sensor 1, and 6 controls the heater every time a certain period of time elapses after the gas sensor 1 is used. A timer section for sending a control signal to change the operating temperature of the heater section 3 to a predetermined temperature by the section 5; a signal detection section 7 for detecting the output signal of the gas sensor 1 in the rated operating temperature state; 8 is an oscillation detection unit for detecting the presence or absence of oscillation of the output signal of the gas sensor 1 when the operating temperature of the heater unit 3 is changed; 9 is a heater that determines the operating temperature of the heater unit 3 when the oscillation of the gas sensor 1 is stopped; A detection level control unit inputs a current or heater voltage signal and changes the detection level of the reducing gas to a predetermined level according to the signal; 10 is a signal of the output signal of the signal detection unit 7; A comparison section 11 compares the detection level with the detection level newly set by the detection level control section 9 and outputs a signal when the signal level exceeds the detection level. Show leaks or
This is a control unit for controlling other equipment, such as issuing alarms or closing the main valve of gas piping.

Figure 2 shows the rate of change in resistance of a semiconductor gas sensor over time (shown as a relative value with the initial value before deterioration in a reducing gas atmosphere of a constant concentration as lOO) and the output signal of the gas sensor in an air atmosphere. This is an example of a characteristic line showing the relationship between the operating temperature (expressed as the reciprocal of the absolute temperature) when the oscillation disappears, and this relationship is a newly discovered phenomenon. In general, changes over time in the gas-sensing performance (changes in performance) of an n-type semiconductor gas sensor appear as a decrease in the resistance value of the gas sensor in an atmosphere with a constant concentration of reducing gas to be detected. This is apparently the same as the gas detection level shifting to the lower concentration side of the detected gas, and the control unit will operate as a gas leak even if the gas concentration is lower than the preset detection level. This change in gas sensor resistance over time (change in gas sensing performance over time), which is undesirable as it may result in malfunction, is caused by extremely low frequencies ( 10-
"~10-" Hz) is correlated with the oscillation phenomenon.

FIG. 2 shows that when the operating temperature is changed from low to high temperature, there is a correlation with the reciprocal of the operating temperature (expressed in absolute temperature) at which the oscillation phenomenon of the output signal of the gas sensor disappears. In other words, by changing the operating temperature of a gas sensor in an air atmosphere from low to high temperature and determining the operating temperature at which the oscillation phenomenon of the output signal of the gas sensor disappears, it is possible to determine the degree of change in the gas sensor over time. It turns out it can be done. Therefore, by determining the degree of change over time of the gas sensor during actual use from the operating temperature at which the oscillation phenomenon of the output signal of the gas sensor disappears, it is possible to self-correct the change over time (performance deterioration) of the gas sensor. Various methods can be used to self-correct the changes in the gas sensor over time using the characteristics shown in FIG. 2, but in this embodiment whose configuration is shown in FIG. This figure shows an example using a method of automatically correcting the detection level of.

Hereinafter, the operation of the gas detection device according to the present invention shown in FIG. 1 will be explained with reference to the time chart shown in FIG. 3. First, the heater control section 5 operates the heater section 3 of the gas sensor 1 at the rated operating temperature T, (K). Further, the detection level of the reducing gas is set in advance to the detection level L1 by the detection level control unit 9 with respect to the gas concentration of the reducing gas to be detected. At this time, if a reducing gas leaks at a concentration lower than that to be detected and the reducing gas detection signal output v1 occurs, since -V h < L-, the comparator 10 does not output a signal. In the 0th order, the control unit 11 also does not output any signals, and therefore no display or alarm operations occur.
When the usage time of the gas sensor 1 reaches the time 11 (for example, several tens to hundreds of hours) set in advance in the timer section 6, control is sent from the timer section 6 to the heater control section 5 and the oscillation detection section 8, respectively. A signal is sent every time t2 (for example, several minutes), and the heater control unit 5 sends a signal every 1 hour t.
The operating temperature of the heater section 3 is T, -→T2→T3→T, →T
.

(However, T, <T, <T, <T4<Ts), and at the same time, the oscillation detection unit 8 detects the presence or absence of oscillation of the output signal of the gas sensor 1 at intervals of 1 s.

Now, oscillation is detected at the operating temperature T1.

From now on, assuming that no oscillation is detected, gas sensor 1
It is determined that the characteristic deterioration of is small, and the reducing gas detection level remains at Ll and is not changed.Next, when reducing gas leaks at a concentration higher than that which should be detected, and reducing gas detection signal output v2 is generated. , v8≧L8, the comparison unit 10 and the control unit 11 output a signal and notify the abnormality by display or alarm. Subsequently, when the elapsed time reaches time t0, control signals are sent from the timer section 6 to the heater control section 5 and the oscillation detection section 8, respectively, in the same manner as described above.
The operating temperature of the heater section 3 changes from T to T at every time t3. At this time, if oscillation is detected at the operating temperatures T0 and T2 in response to characteristic deterioration of the gas sensor 1, and no oscillation is detected at the operating temperature T or later, the detection level control unit 9 adjusts the reducing gas detection level. , the detection level is changed to a preset detection level L, (L,>LX) depending on the degree of characteristic deterioration (decrease in resistance value) of the gas sensor 1. It is assumed that a gas leakage below the detected concentration occurs after that, and a reducing gas detection signal output V is generated. Also, this V
Assume that, due to a decrease in resistance value due to deterioration of the gas sensor 1, the output was equivalent to the gas detection signal output v2 when a gas leaked at a concentration higher than the detection concentration described above, despite the gas leakage at a concentration lower than the detection concentration. .

However, in this case, the detection level is reset from Ll to (L□>L, ) according to the degree of characteristic deterioration of the gas sensor 1, and since V ) < Lz, the comparison unit 10 No signal is output, and the control unit 11 also does not output a signal, which means that detection errors due to changes over time have been corrected. Next, when a detection signal output v4 larger than the reset detection level L2 occurs due to gas leakage exceeding the detection concentration, the control section 11 outputs a signal via the comparison section 10, and indicates an abnormality by displaying, alarming, etc. Inform.

Next, if the characteristic deterioration of the gas sensor 1 further progresses due to long-term use and oscillation is detected at the operating temperature T~T4, but no oscillation is detected at the operating temperature T, the reducing gas detection level should be changed. Furthermore, (L.

>L2) and continue reducing gas detection.

In addition, if the oscillation does not disappear even at T4 when the operating temperature of the heater part is close to the rated operating temperature, it is assumed that this gas sensor has reached the end of its life, and a signal for replacing the gas sensor is output.
A display or a warning may be issued.

Further, in the above embodiment, the operating temperature of the heater section by the heater control section is changed from the low temperature side to the high temperature side (T-work→T2→T, →T
4→'r s ) We have explained the method of detecting the extinction of the oscillation of the output signal of the gas sensor by changing it every time t2, but conversely, the operating temperature of the heater section can be changed from a high temperature side close to the rated operating temperature to a low temperature side. (T,→T4→T3→T8→”r
x) It is clear that deterioration in the characteristics of the gas sensor can be automatically corrected in the same manner as in the above embodiment even by using a method of detecting the occurrence of oscillation of the output signal of the gas sensor by changing it every time t2.

〔Effect of the invention〕

According to the present invention, in the gas detection V device, performance deterioration of the gas sensor can be self-checked at arbitrary fixed time intervals while in actual use, and correction can be automatically performed according to the degree of characteristic deterioration. Therefore, it is possible to realize a gas detection device that has high reliability and high accuracy over a long period of time and does not cause malfunctions.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of one embodiment of the gas detection device according to the present invention, FIG. 2 is a characteristic diagram showing an example of the performance characteristics of the gas sensor used in the device of the present invention, and FIG.
3 is a time chart showing the operation of the device shown in the figure. Explanation of symbols 1...Gas sensor 2...Gas sensing part 3...
Heater section 4... Output resistor 5... Heater control section 6... Timer section 7... Signal detection section
8... Oscillation detection section 9... Detection level control section 10
... Comparison section 11 ... Control section

Claims (4)

[Claims] (1) A semiconductor gas sensor that has a gas sensing section and a heater section that heats the gas sensing section, a signal detection section that detects the output signal of the gas sensor, and a detection signal set from the signal detection section. Compare with the level and the result will be
A gas detection device for a reducing gas, comprising a comparison section that outputs a signal to a control section for displaying, issuing alarms, or controlling other equipment, the device comprising means for changing the operating temperature of the heater section; , a means for detecting the presence or absence of oscillation of the output signal of the gas sensor, and changing the operating temperature of the heater section and depending on the operating temperature when detecting the occurrence or disappearance of the oscillation of the output signal of the gas sensor, A gas detection device characterized in that the detection level is reset to one of predetermined values. (2) In the gas detection device according to claim 1, the means for changing the operating temperature of the heater portion changes the predetermined operating temperature in stages at predetermined intervals. A gas detection device characterized by: (3) In the gas detection device according to claim 1 or 2, the operating temperature of the heater section is changed from the rated operating temperature at the time of detecting the reducing gas to a lower temperature side, and A gas detection device characterized by detecting occurrence of oscillation of an output signal. (4) In the gas detection device according to claim 1 or 2, the operating temperature of the heater section is changed from a low temperature side to a high temperature side, and the oscillation of the output signal of the gas sensor is stopped. A gas detection device characterized by detecting gas.