JPS5926040A - Apparatus for detecting gas selectivity - Google Patents

Abstract

PURPOSE:To detect an aimed gas (CH4) with high accuracy, by adding two series resistance and compensating resistance to a bridge circuit connected so that the outputs of both sensors may become differential by two kinds of gas sensors and two resistors. CONSTITUTION:Resistors pi5, pi6 are connected in parallel with the first gas sensor pi1 and a resistor pi2 which are connected in series and a compensating resistor pi0 is inserted between a connecting point (c) of the gas sensor pi1 and the resistor pi2 and a connecting point (b) of the resistors pi5, pi6. An output V is generated between a connecting point (a) of the second gas sensor pi3 with a resistor pi4 and the connecting point (b). Resistance values of the resistors pi5, pi6 are selected so as to satisfy the following equation pi5/pi6=pi1/pi2 (=pi3/pi4) in the air. When either CH4 or H2 is mixed in the air, electric potential of the connecting points c and b, is displaced but the variation rate of the connecting point (b) is lowered by the resistor pi0. Then, the sensor pi1 desired to cancell for one gas (H2) is made accorded with the sensor pi3 by selecting suitably the value of the resistor pi0, and the aimed gas (CH4) is detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas selectivity detection device that is capable of selectively detecting one type of gas from two types of gas with high sensitivity. .

Various gas sensors have been put into practical use. For example, there are catalytic combustion type gas sensors, gas heat conduction type gas sensors, and solid heat conduction type gas sensors.
Although it has the advantage of being able to detect toxic gases, it does not have selectivity for certain gases. For this reason, selectivity is achieved by changing the catalyst, changing the semiconductor material, changing the operating temperature, etc.

Here, taking a solid heat conduction type waste sensor as an example, it is easy to obtain the characteristics shown in FIGS. 1 and 2, for example. That is, Figure 41.

In FIG. 2, the horizontal axis represents the gas concentration, and the vertical axis represents the output of the gas sensor. In the waste sensor with the characteristics shown in Figure 1, CH
4. Both outputs for H2 gas are large. Further, a gas sensor having the characteristics shown in FIG. 2 has an output of H2, but almost no output of CH4. In the gas sensor shown in Figure 1, CH4, H
Although both have large outputs, they cannot be detected separately.

Further, the waste sensor shown in FIG. 2 is good for obtaining only the output of H2, but is not suitable for detecting only CH4. Therefore, it can be seen that only CH4 can be detected with high sensitivity by differentially combining gas sensors having the characteristics shown in FIGS. 1 and 2.

FIG. 3 is an example of a circuit in which two types of gas sensors are differentially connected, and rI+r3 is a circuit example in which two types of gas sensors are differentially connected. JJ2's gas sensor 9 r2+r4 is a resistor, E
indicates the DC power supply, and ■ indicates the output. Note that in this specification, rl+r2, etc. also indicate resistance values.

Next, the operation will be explained.

in the air r3　r.

4 r2 Adjust each side so that At this time, V=o.

If H2 is mixed in, the output of gas sensor rI+r3 will be the same as both gas sensors rIlr3'7)
This will be the difference output.

FIG. 4 shows the output characteristics of the circuit shown in FIG. 3 above.

Comparing Figure 4 with Figure 1, the output of CH4 is almost unchanged from that shown in Figure 1, and the output of H2 is much lower, indicating that CH71 can be selectively detected. has been done.

However, since this circuit still has an output of H2, there is a drawback that this amount appears as an error.

This invention was developed in consideration of the above points, and makes it possible to detect only the target gas by reducing unnecessary output to almost zero. This invention will be explained below.

FIG. 5 shows an embodiment of the present invention. In this figure, r5 and r6 are resistors, the series body of which is connected in parallel to the series body of the first gas sensor r1 and resistor r2. In addition, ro is a compensation resistor, and the first gas sensor r1
is inserted between the connection point of resistor r2 and the connection point of resistor rS r r6.

Then, the output V appears between the connection point a between the second gas sensor r3 and the resistor r4 and the connection point between the resistors Br5 and r6.

Next, the operation will be explained.

The resistance value of the resistor rs+r6 is selected to satisfy the following in air. As a result, the output ■ between a and b is zero.

Next, if CH4 or H2 mixes into the air, the potential at the connection point S changes at the same time as the potential at the connection point C between the first gas sensor r1 and the resistor r2, but since there is a compensation resistor ro, the connection The rate of change of the point is reduced. Resistor r5, r
6 is larger than the resistance value of the first gas sensor rl + resistor r2, the fluctuation in the potential of the connection point S when rO=0 is almost the same as in the conventional circuit shown in FIG.

FIG. 6 shows the correlation between the value of the compensation resistor r0 and the reduction rate.

An example is shown in which the horizontal axis represents 1 and the vertical axis represents the normalized output.

As we will see, the reduction ratio can be changed by appropriately selecting the value of the compensation resistor ro, so the first . The outputs of the second gas sensor rl+r3 can be matched. Therefore, a cass selectivity detection device having the characteristics shown in FIG. 7 can be obtained.

Note that this invention is not limited to the embodiment shown in FIG. 5 above,
The first gas sensor r1 and resistor r2 may be replaced, the second gas sensor r3 and resistor r4 may be replaced, or a compensation resistor r may be placed on the side of the second gas sensor r3 and resistor r4. , a resistor rs r r6 may be provided. Further, the compensation resistor rO may be inserted and variable type resistors may be used.

As explained in detail above, the present invention has a first gas sensor that outputs an output for one type of gas, a second gas sensor that outputs an output for two types of gas, and two resistors to control the output of both gas sensors. Since we added a series body consisting of two resistors connected in series and a compensating resistor to the bridge circuit connected in a differential manner, the unnecessary output of the second gas sensor is reduced to almost zero by the first gas sensor. This has the advantage that the target gas can be detected with high precision.

[Brief explanation of drawings]

Figures 1 and 2 are output characteristic diagrams of conventional gas sensors, Figure 3 is a circuit diagram when two types of gas sensors having the characteristics shown in Figures 1 and 2 are differentially connected, and Figure 4 is a diagram of the output characteristics of a conventional gas sensor. The figure is an output characteristic diagram of the circuit in Figure 3, Figure 5 is a circuit diagram showing an embodiment of the present invention, and Figure 6 is a characteristic diagram showing an example of the correlation between the value of the compensation resistor and the reduction rate in Figure 5. 7 is an output characteristic diagram of the circuit shown in FIG. 5. In the figure, rl is the first gas sensor, r2 + "1
+r5. r6 is the resistor, r3 is the second gas sensor, ro
is a compensation resistor, E is a DC power supply, and ■ is an output. Procedural amendment (sealed) October 25, 1980 Mr. Commissioner of the Japan Patent Office 1, Indication of the case, Patent Application 1982-134 He No. 2, Invention
Name Relationship between the gas selectivity detection device 3 and the person making the correction Patent applicant address 2-5-4 Mitsuya Naka, Yodogawa-ku, Osaka-shi, Osaka Name Shin-Cosmos Electric Co., Ltd. Representative Riichi Sujihara 4. Agent: 5th floor, 6th floor, Okunomatsu Building, 31-16 Sakuragaoka-cho, Shibuya-ku, Tokyo 150, Japan.
The correction drawing 6 and the contents of the correction drawing 6 will be corrected as shown in the attached sheet. J2

Claims (1)

[Claims] A bridge circuit is configured by a first gas sensor that outputs for one type of gas, a second gas sensor that outputs for two types of gas, and two resistors, and a bridge circuit is configured between the first gas sensor and the resistor. The connection point and the connection point between the second gas sensor and the resistor are respectively output terminals, and two terminals are provided in at least one of the series series body of the first gas sensor and resistor or the series series body of the second gas sensor and resistor. series-connected resistors are connected in parallel, and a compensation resistor is inserted between the connection point of these two resistors and the connection point of the two series bodies, and the two series-connected resistors are connected in parallel. A gas selectivity detection device characterized in that the connection point of the resistor is one of the output terminals.