JP2001188056A - Gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detector by which a drop in the detecting sensitivity of a gas sensor module with reference to a change in an ambient temperature can be compensated. SOLUTION: A first amplification means 4 which amplifies sensor output data from the gas sensor module 3 to which an operating voltage is supplied from a power supply 1 is provided. A current detection means Rcs which is connected across the power supply 1 and the gas sensor module 3 and which detects a current value flowing in the gas sensor module 3 so as to generate current data is provided. A second amplification means 5 which voltage-amlifies the current data from the current detection means Rcs is provided. A compensation means 6 to which the sensor output data from the first amplification means 4 is input, to which the current data from the second amplification means 5 is input and by which the drop in the sensitivity of the gas sensor module generated due to the change in the ambient temperature is compensated on the basis of the current data to be input is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detector for detecting the presence of a gas in a state where the gas is grounded in a gas atmosphere, and more particularly, to a catalytic combustion for detecting a combustible gas and detecting the concentration of the gas. The present invention relates to a gas detection device of the type.

[0002]

2. Description of the Related Art Conventionally, as a gas detector of this kind,
For example, Japanese Patent Application Laid-Open No. Hei 7-198652 proposed earlier by the application.
And JP-A-10-38833. As an example, FIG. 2 shows a block diagram of a gas detection device disclosed in JP-A-10-38833.

In FIG. 2, a gas detection device 10 detects the presence of a gas while being grounded in a gas atmosphere, detects the concentration of the gas, and generates sensor output data; A constant voltage source 20 for generating a predetermined voltage for operating the module 12, and electrically connected between the constant voltage source 20 and the gas sensor module 12 to detect a current value input to the gas sensor module 12 A current detecting means 14 for generating current data, and a temperature compensating means 15 for generating gas concentration data by performing temperature compensation on sensor output data based on the current data.

[0004] The gas sensor module 12 is a sensor element 1 for detecting a gas concentration when installed in a gas atmosphere.
22 and a reference element 124 for performing temperature compensation of the sensor element 122.

[0005] Specifically, the sensor element 122 is a catalytic combustion type gas detecting means. As the contact combustion type gas detection means, a flammable gas detection element is used.

[0006] The detecting element for flammable gas is, for example, 20
A platinum resistance wire having a wire diameter of 50 μm to 50 μm is wound to form a coil shape, a catalyst such as palladium = alumina is applied around the coil, and then baked.
It is formed with a double mesh wire mesh.

The electric resistance Rs of the sensor element 122 is determined by the diameter and length of the wound platinum resistance wire.

The reference element 124 has the same structure as the sensor element 122, and is subjected to a desensitization process so as to be insensitive to gas. More specifically, the blind processing can be performed by covering the entire reference element 124 with a seal cap.

The electric resistance Rr of the reference element 124 is determined by the diameter and length of the wound platinum resistance wire, similarly to the sensor element 122.

The constant voltage source 20 includes the gas sensor module 1
2 for generating a predetermined voltage 20a for operating the power supply 2.

A resistance element 14, a sensor element 122, and a reference element 124 are connected in series to the constant voltage source 20, and the electric resistance of the sensor element 122 is Rs, and the reference element 1
24 has an electric resistance of Rr, and the electric resistance of the resistance element 14 has an electric resistance of Rc.
s, the current value of the current Is input to the gas sensor module 12 is Is = (predetermined voltage 20a) /
(Rcs + Rs + Rr).

The sensor element 122 and the reference element 124
Since the current Is flows in each case, the built-in platinum resistance wire is heated and the temperature rises. In this state, if a combustible (specifically, reducing) gas is present in the atmosphere, the combustible gas comes into contact with the sensor element 122 and burns (ie, oxidizes). The resistance value Rs of the sensor element 122 due to the temperature rise due to the heat of reaction
Changes by ΔRs.

The sensor output data 12a is output as a voltage change corresponding to the resistance value change ΔRs.

On the other hand, as described above, since the referential element 124 has been subjected to the insensitive treatment (specifically, the treatment for covering the seal cap), the combustible gas does not react, and the combustion as described above occurs. Does not wake up.

The sensor element 122 and the reference element 12
Since No. 4 is exposed to the same gas atmosphere, a resistance change occurs according to the temperature of this atmosphere.

Such a change in resistance due to the temperature of the atmosphere is caused by a malfunction in detection of the presence of gas (that is, sensor output data 1 indicating that gas is detected even though no gas is present).
2a) or a concentration error of the detected gas concentration.

The reference element 124 is a compensating means for generally compensating for a malfunction or a density error in the sensor element 122 due to the ambient temperature. It is intended to cancel the resistance change of the sensor element 122 caused by the temperature of the atmosphere by the resistance change of the reference element 124 placed in the same atmosphere.

However, it is difficult for the reference element 124 and the sensor element 122 to completely match their resistance temperature coefficients due to variations in materials and structures.

Therefore, as the current detecting means 14, a resistor Rcs is provided between the constant voltage source 20 and the gas sensor module 12.
And the current value I flowing through the gas sensor module 12
s is detected. The detected current value Is is a voltage value (= I
s × Rcs) to generate current data 14a.

The current data 14a is data according to a change in ambient temperature, as described later,
Even when the temperature coefficient of resistance of the sensor element 122 and the temperature coefficient of resistance of the sensor element 122 do not match, it is useful to perform temperature compensation more precisely.

That is, the resistance values of the sensor element 122 and the reference element 124 of the gas sensor module 12 installed in the gas atmosphere change according to the change of the ambient temperature, and the current value Is flowing through the gas sensor module 12 is changed.
Changes. Therefore, if the current value Is flowing through the sensor module 12 is monitored by the current detecting means 14, a change in the ambient temperature can be detected.

The current data from the current detecting means 14 is supplied to the temperature compensating means 15. The temperature compensating means 15 has a temperature data generating circuit 16 and a gas concentration data generating circuit 18.

The temperature data generation circuit 16 is configured to generate temperature compensation data 16a relating to the ambient temperature of the gas sensor module 12 based on the current data 14a from the current detection means 14.

The gas concentration data generation circuit 18 is configured to perform temperature compensation on the sensor output data 12a based on the temperature compensation data 16a from the temperature data generation circuit 16 to generate gas concentration data 18a. The temperature compensating means 15 obtains in advance a correlation between the current value Is generated as described above, the ambient temperature of the gas sensor module 12, and the sensor output data 12a of the gas sensor module 12, and based on the correlation, obtains a lookup table or the like. Reference means is generated in advance.

When receiving the current data 14a, the temperature data generation circuit 16 determines the ambient temperature of the gas sensor module 12 by referring to the above-mentioned reference means for the sensor output data 12a of the gas sensor module 12 and the current value Is. To generate the temperature compensation data 16a.

The gas concentration data generation circuit 18 performs temperature compensation on the sensor output data 12a based on the temperature compensation data 16a to generate gas concentration data 18a.

As described above, even when the temperature coefficient of resistance value of the reference element 124 and the temperature coefficient of resistance of the sensor element 122 do not completely match, the current data 14a from the current detecting means 14 is used to adjust the gas concentration of, for example, about 100 ppm. However, high-precision temperature compensation that can achieve high detection accuracy can be performed.

On the other hand, a gas sensor module is generally installed and used in atmospheres having different temperatures, and the sensor element in the gas sensor module has a gas sensitivity that changes according to a change in the ambient temperature. It has the property of doing. Some of the sensor elements have an ambient temperature of 25 ° C. to 225 ° C., for example.
It has a sensitivity of 1000 ppm / ° C. at ℃, but has a sensitivity of about 750 ppm / ° C. when the ambient temperature is 225 ° C., and the sensitivity may be reduced by about 25%.

[0029]

The above-described gas detection device performs high-precision temperature compensation using current data obtained by detecting a current flowing through the sensor element by current detection means. No countermeasures are taken against the sensitivity drop.

Accordingly, an object of the present invention is to provide a gas detection device capable of compensating for a decrease in gas sensitivity with respect to a change in ambient temperature in view of the above-mentioned problems.

[0031]

DISCLOSURE OF THE INVENTION In view of the above-mentioned object, a gas detection device according to the first aspect of the present invention is a gas detection device for detecting the presence of a gas when installed in a gas atmosphere, A gas sensor module that detects the presence of a gas in a state where the gas sensor module is installed and detects the concentration of the gas to generate a sensor output, a power supply for operating the gas sensor module, and a power supply from the gas sensor module. First amplifying means for amplifying sensor output data; current detecting means connected between the power supply and the gas sensor module for detecting a current value flowing through the gas sensor module to generate current data; and the current detecting means Amplify the current data from the second
Amplifying means, the sensor output data from the first amplifying means, and the current data from the second amplifying means are inputted, and based on the inputted current data,
And compensating means for compensating for a decrease in sensitivity of the gas sensor module caused by a change in ambient temperature.

In the first aspect of the present invention, the gas sensor module detects the presence of a gas in a state where the gas sensor module is installed in a gas atmosphere, and detects the concentration of the gas to generate a sensor output. The first amplifying unit amplifies sensor output data from the gas sensor module. Current detection means connected between the power supply and the gas sensor module detects a current value flowing through the gas sensor module to generate current data. The second amplifier amplifies the voltage of the current data from the current detector. The compensating means receives the sensor output data from the first amplifying means and the current data from the second amplifying means, and generates a gas sensor module generated by a change in ambient temperature based on the inputted current data. To compensate for the sensitivity drop.

According to a second aspect of the present invention, the gas detecting device is characterized in that the compensation means is a microcomputer.

According to the second aspect of the present invention, the microcomputer as compensation means compensates for a decrease in sensitivity of the gas sensor module caused by a change in ambient temperature based on the input current data.

[0035]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a gas detection device according to the present invention.

First, the configuration of the gas detection device will be described.

In FIG. 1, the gas detection device includes a constant voltage source 1, a current detection resistor Rcs as current detection means, a bridge circuit 2, an operational amplifier circuit 4 as first amplification means, and a second amplification circuit. An operational amplifier circuit 5 as a means;
And a microcomputer 6 as compensation means.

The bridge circuit 2 includes a gas sensor module 3 and resistors R1 and R2.
The operating voltage is supplied to the gas sensor module 3 via the current detection resistor Rcs.

The gas sensor module 3 is provided with a sensor element Rs for detecting a gas concentration when installed in a gas atmosphere.
ns and a reference element Rref for performing temperature compensation of the sensor element Rsns.

The sensor element Rsns is specifically a contact combustion type gas detecting means, and is a sensor element 12 shown in FIG.
It is the same as 2. Similarly, the reference element Rref is the same as the reference element 124 shown in FIG.

The operational amplifier circuit 4 comprises an operational amplifier A1 and resistors R3 and R4. The inverting input terminal of the operational amplifier A1 is connected to a connection point between the reference element Rref and the sensor element Rsns of the gas sensor module 3 via the resistor R3, and the non-inverting input terminal is connected to a connection point between the resistor R1 and the resistor R2. . The output of the operational amplifier A1 is connected to the output terminal 7. The resistor R4 is connected to the inverting input terminal and the output terminal of the operational amplifier A1.

The operational amplifier circuit 5 comprises an operational amplifier A2 and resistors R5, R6, R7, R8. An inverting input terminal of the operational amplifier A2 is connected to a connection point between the current detection resistor Rcs and the gas sensor module 3 via a resistor R7, and a non-inverting input terminal is a connection between a resistor R5 and a resistor R6 connected in series to the constant voltage source 1. Connected to a point. The resistor R8 is connected to the inverting input terminal and the output terminal of the operational amplifier A1.

The microcomputer 6 has an ADC input port (that is, a port having an analog / digital converter), an output voltage from the operational amplifier circuit 5 is input to a port i1, and an operational amplifier is input to a port i2. The output voltage from the circuit 4 is input.

Next, the basic operation of the gas detecting device having the above configuration will be described.

First, before the gas sensor module 3 is installed in a gas atmosphere, when the bridge circuit 2 to which a constant voltage is applied from the constant voltage source 1 is in a balanced state, the inverting input terminal of the operational amplifier A1 of the operational amplifier circuit 4 There is no potential difference between the non-inverting input terminals, and the output supplied from the operational amplifier A1 to the ADC port i2 of the microcomputer is at the "zero" level.

Next, when the gas sensor module 3 is installed in a gas atmosphere, the sensor element Rsns and the reference
In ref, a current flows from the constant voltage source 1, so that the built-in platinum resistance wire is heated and the temperature rises. In this state, if a combustible (specifically, reducing) gas is present in the atmosphere, the combustible gas comes into contact with the sensor element Rsns and burns (that is, oxidizes). The resistance value of the sensor element Rsns changes due to the temperature rise due to the heat of reaction.

On the other hand, since the reference element Rref has been subjected to the insensitive processing, it does not oxidize because combustion by the combustible gas does not occur, and its resistance value does not change.

Therefore, when a combustible gas is present in the atmosphere, only the resistance value of the sensor element Rsns changes, so that the balance of the bridge circuit 2 is lost and the sensor element Rsn
A sensor output corresponding to the amount of the flammable gas oxidized in s is generated, and a potential difference corresponding thereto is generated between the inverting inverting terminal and the non-inverting input terminal of the operational amplifier A1. Sensor output voltage Vc according to amount
o is supplied to the ADC port i2 of the microcomputer 6.

Since the gas detection device operating as described above is used in atmospheres having different temperatures, as described above, when the ambient temperature of the gas sensor module 3 rises, the sensor element Rsns and the reference The temperature coefficient of both resistance values of the element Rref, that is, the sensitivity is reduced. In such a case, the ambient temperature changes
The output voltage Vco supplied from the operational amplifier A1 to the ADC port i2 of the microcomputer 6 fluctuates.
That is, from the operational amplifier A1 to the microcomputer 6
The output voltage Vco supplied to the ADC port i2 has a lower voltage value when the ambient temperature is higher than a voltage value when the ambient temperature is low.

Ideally, even when the ambient temperature changes, the output voltage Vco supplied from the operational amplifier A1 to the ADC port i2 of the microcomputer 6 should be constant without change. Fluctuates as described above.

Therefore, in the present invention, the current detection resistor Rcs
By compensating for such fluctuations using the operational amplifier circuit 5 and the microcomputer 6, the sensitivity of the sensor element Rsns of the gas sensor module 3 is kept constant regardless of changes in the ambient temperature.

The current detection resistor Rcs is connected between the constant voltage source 1 and the gas sensor module 3, and detects a current value Is flowing through the gas sensor module 3. The detected current value Is is converted into a voltage value (= Is × Rcs) to generate current data.

This current data is data according to the change of the ambient temperature, as will be described later, and is a sensor element Rsns.
Helps to compensate for the drop in sensitivity.

That is, the resistance values of the sensor element Rsns and the reference element Rref of the gas sensor module 3 installed in the gas atmosphere change according to the change of the ambient temperature, and the current value Is flowing through the gas sensor module 3
Changes. Therefore, if the current value Is flowing through the gas sensor module 3 is monitored by the current detecting means Rcs, a change in the ambient temperature can be detected.

The current data from the current detection resistor Rcs is
The voltage is supplied to the operational amplifier circuit 5 and amplified. The voltage-amplified current data is supplied to the ADC port i1 of the microcomputer 6 as the current detection voltage Vcs.

The microcomputer 6 compares the current value Is generated as described above with the gas sensor module 1.
A correlation between the ambient temperature and the sensor output data of the gas sensor module 12 is obtained in advance, and a reference means such as a look-up table is generated in advance based on the correlation and stored in an internal memory (not shown).

When the microcomputer 6 receives the current data from the operational amplifier circuit 5, that is, the current detection voltage Vcs at the ADC port i1, the microcomputer 6 operates as follows.
Sensor output data received at ADC port i2 from
That is, regarding the sensor output voltage Vco and the current value Is, referring to the above-mentioned reference means, the gas sensor module 3
Of the sensor output data (voltage) at the ambient temperature, and corrects the sensor output data (voltage) to a value irrespective of the change in the ambient temperature.

Thus, the gas sensor module 3
Element Rsns when the ambient temperature of the sensor changes
Of the gas sensitivity can be compensated, and the gas sensitivity can be kept constant regardless of the ambient temperature.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications and applications are possible.

For example, the power supply for supplying the operating voltage to the gas sensor module 3 may be a constant current source. But,
As in the embodiment, the use of the constant voltage source 1 is generally preferable in terms of cost because it can be configured at a lower cost than the constant current source.

[0061]

According to the first aspect of the present invention, the decrease in sensitivity of the gas sensor module caused by a change in the ambient temperature can be compensated for by using the current data obtained by the current detecting means. Even higher detection accuracy can be realized.

According to the second aspect of the present invention, based on the current data input from the current detecting means, the microcomputer is capable of controlling the decrease in the sensor output voltage from the gas sensor module caused by the change in the ambient temperature. By performing the compensation by the arithmetic processing, the sensitivity of the gas sensor module can be kept constant.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a gas detection device according to the present invention.

FIG. 2 is a block diagram illustrating an example of a conventional gas detection device.

[Explanation of symbols]

 Reference Signs List 1 constant voltage source (power supply) 2 bridge circuit 3 gas sensor module 4 operational amplifier circuit (first amplifying means) 5 operational amplifier circuit (second amplifying means) 6 microcomputer (compensation means) Rcs current detection resistor

Claims (2)

[Claims] 1. A gas detection device for detecting the presence of a gas when installed in a gas atmosphere, wherein the gas detection device detects the presence of the gas when installed in a gas atmosphere and detects the concentration of the gas. A gas sensor module that generates a sensor output, a power supply for operating the gas sensor module, first amplifying means for amplifying sensor output data from the gas sensor module, and a connection between the power supply and the gas sensor module. And
Current detection means for detecting a current value flowing through the gas sensor module to generate current data; second amplification means for voltage-amplifying the current data from the current detection means; and Sensor output data and the current data from the second amplifying means are input,
A compensating means for compensating a decrease in sensitivity of the gas sensor module caused by a change in ambient temperature based on the input current data. 2. The gas detection device according to claim 1, wherein said compensation means is a microcomputer.