JPS61105451A - Heat conduction type gas detecting element - Google Patents

Abstract

PURPOSE:To detect inflammable gas with high precision by using a platinum wire as a base and covering its surface with a material which never catalyzes it. CONSTITUTION:A comparing element 4 contains standard gas hermetically is bridge-connected to fixed resistances 5 and 6 in a pair with a gas detecting element 1; a power source 7 is connected to the input terminal and a display meter 8 is connected to the output terminal. The detecting element 1 and comparing element 4 are supplied with electric power when in operation and a detection line rises in temperature to maintain constant temperature. When sample gas is flowed in from the gas intake of the detecting element 1 in said state, the surface of the detection line 1 contacts the inflammable gas across metal which never catalyzes it and heat is absorbed in proportion to the thickness to cause a temperature drop, thereby decreasing electric resistance. Consequently, there is a difference in resistance generated from the comparing element 4 and an output signal proportional to the thickness of the inflammable gas is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a thermally conductive gas detector, and more particularly to a gas detection element using a platinum wire as a detection wire.

(Prior art) Thermal conduction type gas detectors usually have two resistance wires connected in a bridge, fully energized, and one resistance wire used as the detection section for the fourth gas to be tested, and the other resistance wire used as the comparison section. Exposure to standard gas as sample 1 gas and e! The temperature difference between two resistance wires caused by the difference in thermal conductivity of the quasi-gas is detected as a resistance change.

By the way, the detection wire of this thermal conduction type gas detector meets the requirements of high temperature resistance coefficient and high temperature corrosion resistance.
Platinum wire is used.

However, since platinum has a strong oxidation catalytic effect, when a sample gas containing flammable gases such as butane and propane is detected using a thermal conductive gas detector using a platinum wire, this IIr There is a problem in that the flammable gas catalytically burns on the surface of the platinum wire, raising the temperature of the platinum wire by 1-1, causing a temperature change unrelated to the thermal conductivity of the sample gas, and lowering the detection accuracy.

(Objective) In view of such problems, it is an object of the present invention to provide a thermally conductive gas detector using a platinum wire that can detect combustible gas with high accuracy.

That is, the present invention is characterized in that a platinum wire is used as a base, and the surface of the wire is coated with a substance that does not interfere with the catalytic action.

(Structure I &) The details of the present invention will be explained below based on illustrated embodiments.

FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 denotes a gas detection element which is a characteristic part of the present invention, and a detection line 10 formed by forming a coil of strands of wire to be described later. The cap 12 is welded to a stay 11.11 which also serves as a lead wire, and has a cap 12 with a sample gas inlet 12a bored in its upper part.

Figures 2(a) and 2(b) show examples of the gas detection wires described above. Group No. 2 in Figure 1 is a platinum wire stretched to a predetermined wire diameter, and the surface is coated by sputtering or the like. Evenly coated with gold (Au)! 3 so that platinum is not exposed to the outside.

[Example] Gold (^U) was physically deposited to a thickness of about 14 m by sputtering on the surface of a platinum wire with a diameter of 10 to 25 μLm, and this was formed into a coil shape and attached to a stay.

Figure 1IJ3 shows an example of a gas detection circuit using the above-mentioned gas detection element, and the reference numeral 4 in the figure is a comparison element having a standard gas sealed inside. It is configured such that it is paired with a fixed resistor 5.6 and connected in a bridge, a power supply 7 is connected to the input end, and a display meter 8 is connected to the output end.

When the device is activated in this embodiment, the detection element! The comparison element 4 is supplied with power from the 'nl source 7, and the detection line is heated to about 400 to 500°C and maintained at a constant temperature.

In this state, the signal of the detection element l.

When a sample gas containing a flammable gas such as butane or propane is flowing in from the gas inlet 12 of the pump, the detection line lO is detected by passing the surface of the sample gas through the gold layer 3 (Fig. 2), which does not have a catalytic effect. I
When it comes into contact with Ir flammable gas, heat is taken away in proportion to the concentration of Ir flammable gas, the temperature decreases, and the electrical resistance decreases. This results in a resistance value of X! between the comparison element 4 and the resistance value. (An output signal proportional to the concentration of combustible gas is generated.

Needless to say, the surface of the detection line IO is made of gold (Au).
Since the sample gas is coated with , there is no possibility of catalytic oxidation of the combustible gas contained in the sample gas, and there is no risk of abnormal temperature changes.

In the above-mentioned examples, the coating was made with gold (Au), but it may also be coated with a heat-resistant material that does not exhibit an oxidation catalytic action, such as a gold (Au) alloy that does not contain a catalytic metal, α-alumina, or a fluororesin. It has a similar effect.

(Effects) As described above, according to the present invention, since the detection wire is a platinum wire whose surface is coated with a heat-resistant material that does not have catalytic oxidation, flammable gas does not undergo catalytic combustion. The resistance change of the detection wire is used only for the thermal conductivity and concentration of the combustible gas, which not only makes it possible to detect combustible gas with high accuracy, but also prevents the detection wire from abnormally overheating and prevents the detection element from overheating. Lifespan can be significantly extended.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an apparatus showing an embodiment of the present invention;
Figures (A) and (B) are a cross-sectional view showing an example of a detection line used in the device, and Figure wS3 is a block diagram showing an example of a gas detection circuit using a gas detection element. 1...Gas detection element lo...Detection line 2...
・Platinum wire 3... Gold 12... Sample gas inflow [113... Cap applicant Riken Keiki Co., Ltd. Agent Patent attorney Kei Nishikawa Katsuhiko Kimura

Claims (1)

[Claims] A thermally conductive gas detection element consisting of a detection wire coated with a heat-resistant material that does not exhibit an oxidation catalyst and stretched over the surface of a thin platinum wire.