JP2001091487A - Gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detector capable of detecting a plurality of types of gases by a single sensor device. SOLUTION: This gas detector is provided with a catalytic combustion type sensor device and a sensor device temperature variable means heating the sensor device and changing the heating temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas detector for detecting a plurality of types of gases.

[0002]

2. Description of the Related Art For detecting a combustible gas such as carbon monoxide, methane or hydrogen, a catalytic combustion type gas sensor element having a carrier such as alumina carrying an oxidation catalyst such as platinum has been used.

[0003] Here, Japanese Patent Application Laid-Open No. Sho 63 discloses a technique in which by subjecting a catalytic combustion type sensor element to a silicone vapor treatment, only hydrogen among various combustible gases can be made sensitive.
No. 30751, for example. Alternatively, by providing activated carbon or other adsorbent as a filter around the sensor element, gas other than for the purpose of detection is prevented from reaching the sensor element, thereby providing selectivity to the gas.

However, in these conventional techniques, it is necessary to provide a plurality of sensor elements in order to detect a plurality of gases, which increases the cost and also requires the calibration of each sensor element. , And the size of the detection unit increases, which makes it difficult to make the gas detection device compact.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the above-mentioned conventional problems, that is, to provide a gas detection device capable of detecting a plurality of types of gases with one sensor element. I do.

[0006]

According to a first aspect of the present invention, there is provided a gas detection device including a contact combustion type sensor element, wherein the sensor element is heated and its heating temperature is reduced. This is a gas detection device having a sensor element temperature varying means for changing.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a gas detector according to the present invention,
In addition to the contact combustion type sensor element, a comparison element (temperature compensation element) having substantially the same structure but having no sensitivity to the detection target gas is provided, and a bridge circuit is configured.
The influence of the temperature change of the surrounding measurement atmosphere can be eliminated. It is desirable that this comparison element be kept at the same temperature as the contact combustion sensor element.

The contact combustion type sensor element is used after being heated to a temperature suitable for contact combustion by a heating means such as a heater. The sensor element temperature varying means in the gas detection device of the present invention changes the temperature of this sensor element. Is what you can do. Such a sensor element temperature varying means can be constituted by a heater and a heater power supply (voltage control, chopper control, etc.) capable of changing the output.

In an atmosphere containing hydrogen, carbon monoxide and methane, the temperature of the sensor element which can be set by the sensor element temperature varying means is not sensitive to carbon monoxide and methane while being sensitive only to hydrogen. There are three levels: temperature that has no sensitivity, temperature that has sensitivity to hydrogen and carbon monoxide but has no sensitivity to methane, and temperature that has sensitivity to all of hydrogen, carbon monoxide and methane. Thus, the respective concentrations of hydrogen, carbon monoxide, and methane can be detected.

FIG. 1 shows the relationship between the sensor element temperature and the sensor output (by a thin film type microsensor) in an atmosphere having hydrogen, carbon monoxide, or methane alone. The X axis of the graph is a voltage value applied to a micro heater for heating the sensor, and corresponds to the sensor element temperature.

The temperature is a temperature that is sensitive only to hydrogen but not to carbon monoxide and methane, and a temperature is sensitive to hydrogen and carbon monoxide but not to methane. Temperature, and furthermore, temperature, is a temperature sensitive to all of hydrogen, carbon monoxide and methane.

Since the sensor element output for hydrogen, the sensor element output for carbon monoxide, and the sensor element output for methane do not interfere with each other, the sensor output in the case of a mixed gas is the sum of the output of the single gas at that temperature. Become.

[0013] In the gas detection device of the present invention, a sensor element temperature periodically changing means for periodically changing the heating temperature of the contact combustion type sensor element between the three stages, and the sensor element output value at each temperature. By providing a gas concentration calculating means for checking and calculating respective concentrations of hydrogen, carbon monoxide and methane gas in the detection atmosphere from these output values, it is possible to detect these three kinds of gases almost simultaneously.

[0014] Such a sensor element temperature periodically changing means combines a heater and a heater power supply capable of changing the output with a timer means, and also checks the sensor element output value at each temperature. Gas concentration calculating means for calculating the concentrations of hydrogen, carbon monoxide and methane gas in the detection atmosphere from the values can be configured by combining an A / D converter and a microprocessor.

Further, if the sensor element temperature periodic change means has a period during which the sensor element is not heated when changing the heating temperature of the contact combustion type sensor element between the above three stages, The power can be greatly reduced, the battery operation of the gas detection device can be facilitated, the usable period thereof can be greatly increased, the deterioration of the sensor element can be reduced, and its life can be prolonged.

Here, the gas detection device of the present invention will be described.
This will be described with reference to the drawings. FIG. 2 is a block diagram of an example of the gas detection device of the present invention. This gas detection device includes a contact combustion sensor element α1 and a comparison element α2, and a sensor element temperature varying means β for heating the sensor element and changing the heating temperature is provided near these elements. This sensor element temperature varying means β changes the heating temperature of the heater β1a disposed in the sensor element α1, the heater β1b disposed in the vicinity of the comparison element α2, the heater output variable power supply β2, and the contact combustion sensor element to hydrogen. In an atmosphere containing carbon monoxide and methane, a temperature sensitive to only hydrogen, a temperature sensitive to hydrogen and carbon monoxide, and a temperature sensitive to all of hydrogen, carbon monoxide and methane And a means for periodically changing the sensor element temperature β3 during the above three stages.

The sensor element α1 and the comparison element α2
Is a combination of a coil-type sensor element or a coil-type comparison element composed of a platinum wire having a coil portion around which a catalyst-carrying carrier or a non-catalyst-carrying carrier is arranged, or a diaphragm provided on or on a silicon substrate. A thin-film microsensor having a sensor element and a comparison element each composed of a platinum thin film wire and a catalyst-carrying carrier film or a catalyst-non-carrying carrier film may be used. However, in the case of the latter thin-film type microsensor, since it is easy to reduce the heat capacity, the power consumption can be kept low, and the battery driving time of the gas detection device can be extended.

In these sensor elements / comparative elements, the output lines may be separate from the heaters or may be used for the same purpose. However, since they are easy to manufacture and low in cost, they are usually connected to the output lines. It is also used as a heater.

The output of the sensor element α1 is introduced to gas concentration calculating means γ for calculating the concentrations of hydrogen, carbon monoxide and methane gas in the detection atmosphere from the sensor element output value at each temperature of the catalytic combustion type sensor element. The gas concentration calculation means γ calculates the gas concentration from the sensor temperature variable means β, the output of the sensor element output based on which of the three temperatures, and the output of the comparison element, and records the gas concentration. The gas type and concentration are output to means (not shown), display means δ, and the like.

FIG. 3A is a circuit diagram of the gas detection device whose block diagram is shown in FIG. In the drawing, reference numeral 1 denotes a detection unit, in which a catalytic combustion sensor element (not shown), a comparison element (not shown), and a heater 1 are provided.
a (in this example, the heater 1a is also used as an output line of these elements). The outputs of the catalytic combustion sensor element and the comparison element inside the detection section 1 are introduced into the MPU 2 from an input boat 2ia with an A / D converter via a bridge circuit (not shown). The temperature of the sensor element and the comparison element is heated to a required temperature by the output voltage variable power supply 1b and the heater 1a in the detection unit 1.

The MPU 2 is provided with an output port 2oa for controlling the output of the power supply 1b, and is connected to the power supply 1b. Further, the MPU 2 has a CPU 2c for controlling and calculating.
p, the output control value of the power supply 1b corresponding to the program of the CPU 2cp and the sensor element temperature in FIG.
ROM2 for storing data for various controls such as
ro (see FIG. 3B), and R for storing various variables such as timers T1 to T3, measured values a to c, and variables A to C.
AM2ra (see FIG. 3 (c)), and an output port 2ob for outputting to the LCD display unit 3 for displaying the type of gas and its measured value.

The operation of the gas detector according to the present invention will be described with reference to the flowchart shown in FIG. After starting, T is output port 2oa in step S1.
And the sensor element temperature is set to a temperature that is sensitive to only hydrogen but insensitive to carbon monoxide and methane. After a predetermined time t1 set in steps S2 and S3, the output of the detection unit is changed to the input port 2ia.
And stored in the RAM 2ra as a variable a.

Next, in step S5, T is output to the output port 2oa, and the sensor element temperature is set to a temperature that is sensitive to hydrogen and carbon monoxide but insensitive to methane. After a predetermined time t2 set in steps S6 and S7, the output of the detection unit is input from the input port 2ia and stored in the RAM 2ra as a variable b.

Further, in step S9, T is output to the output port 2oa, and the sensor element temperature is set to a temperature that is sensitive to all of hydrogen, carbon monoxide, and methane. After a predetermined time t3 set in steps S10 and S11, the output of the detection unit is input from the input port 2ia and stored in the RAM 2ra as a variable c.

Next, in steps S13 to S15, from the variables a, b, and c stored in the RAM, a signal value C corresponding to the methane gas concentration, a signal value B corresponding to the carbon monoxide gas concentration, and a signal corresponding to the hydrogen gas concentration. A value A is obtained by calculation, and a hydrogen gas concentration f (A), a carbon dioxide gas concentration f ′ (B), and a methane gas concentration f ″ (B) are calculated from these values, and these values are displayed on the LCD from the output port 2oa. The data is output and displayed on the unit 3. Thereafter, the process returns to step S1, and steps S1 to S16 are repeated thereafter.

As is clear from the above description, in this embodiment, the heaters β1a and β1b in FIG.
In addition, the heater output variable power supply is connected to the power supply 1b, the sensor element temperature periodic change means β3 and the gas concentration calculation means are connected to the MPU2.
Respectively.

In the above example, the sensor element of the detection unit,
Although the comparison element is always heated, for example, in step S5
By inserting a step of interrupting the heating of the detection unit for a certain period between steps S9 and S10, between steps S9 and S10, and between steps S16 and S1, the power consumption can be reduced and the sensor life can be extended. The effect can be obtained.

In particular, in the case of a thin film type microsensor, the time required for the sensor output to stabilize after the start of energization of the heater is short, so that a heater heating time of 50 to 200 milliseconds × 3 times is sufficient. As described above, it is possible to measure hydrogen, carbon monoxide and methane gas in a short heating time, and it is possible to extremely reduce power consumption by performing such a measurement once every 30 seconds, for example. Yes, and long-term measurement is possible even when driven by a battery.

[0029]

The gas detector according to the present invention is an excellent gas detector capable of detecting a plurality of types of gases such as hydrogen, carbon monoxide and methane with one detecting element.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a sensor element temperature and a sensor output in an atmosphere having hydrogen, carbon monoxide, or methane alone.

FIG. 2 is a block diagram of an example of the gas detection device of the present invention.

FIG. 3 is a circuit diagram of the gas detection device whose block diagram is shown in FIG.

FIG. 4 is a flowchart showing an operation of the gas detection device of FIG.

[Explanation of symbols]

 α1 Contact combustion sensor element α2 Comparison element β Sensor element temperature variable means β1 heater β2 Heater output variable power supply β3 Sensor element temperature periodic change means γ Gas concentration calculation means δ Display means

Claims (4)

[Claims] 1. A gas detecting device comprising a contact combustion type sensor element, and a sensor element temperature varying means for heating the sensor element and changing a heating temperature thereof. 2. The heating temperature of the sensor element, which can be set by the sensor element temperature varying means, is set to a temperature that is sensitive only to hydrogen in an atmosphere containing hydrogen, carbon monoxide, and methane. 2. The gas detection device according to claim 1, wherein the gas detection device has three stages: a temperature having sensitivity to hydrogen, and a temperature having sensitivity to all of hydrogen, carbon monoxide, and methane. 3. The sensor element temperature varying means includes a sensor element temperature periodically changing means for periodically changing the heating temperature of the contact combustion type sensor element between the three stages, and the temperature of each of the three stages. 3. The gas detection device according to claim 1, further comprising: gas concentration calculation means for calculating respective concentrations of hydrogen, carbon monoxide, and methane gas in the detection atmosphere from the sensor element output value at step (b). . 4. The sensor element temperature periodic change means has a period during which the heating of the sensor element is not performed when the heating temperature of the contact combustion type sensor element is changed between the three stages. The gas detection device according to claim 3, wherein