JPS62174643A - Combustible gas sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a combustible gas sensor, and more specifically, to a combustible gas sensor employing a field effect transistor type configuration.

<Prior art> As shown in FIG. 5, a conventional combustible gas sensor has been used for a direct 8! A power supply (12) and an ammeter etc. (13) are connected in series, and the above elements (
11) to approximately 100°C to 400°C.
) was provided with a configuration in which a power supply (15) was connected in series.

Furthermore, a field effect transistor type (hereinafter abbreviated as FET type) hydrogen gas sensor has been provided in which the gate electrode of the field effect transistor is made of palladium (Pd).

<Problems to be Solved by the Invention> In the flammable gas sensor having the configuration shown in FIG. This not only complicates the configuration, but also requires a heater (1
4) has the problem of causing a gas explosion.

Further, there is a problem in that the gas selectivity is poor and the method is similarly sensitive to similar flammable gases such as hydrogen gas and hydrocarbon gas. For example, even if a sensor is used to detect a leak of flammable gas, it will also be sensitive to the alcohol gas generated when sake is heated, resulting in the same situation as when detecting a leak of flammable gas. The problem is that it can cause

In the above FET type hydrogen sensor, palladium (P
Since the H+ ions decomposed and formed by the catalytic action in d) accumulate in the gate electrode, it is only possible to measure the rate of change in the hydrogen gas concentration due to their sequential accumulation, and the absolute value of the hydrogen gas concentration can only be measured. The problem is that it cannot be measured.

<Object of the invention> This invention was made in view of the above problems,
It can eliminate the risk of gas explosion, and
It is an object of the present invention to provide a combustible gas sensor that can improve the selectivity of combustible gases and can also accurately measure the concentration of combustible gases.

Means for Solving the Problems> In order to achieve the above object, the flammable gas sensor of the present invention comprises one of the gate electrode and the source electrode of a field effect transistor made of platinum metal, and the other made of platinum metal. A gas-permeable proton conductor membrane is formed, which is made of a metal that does not react with flammable gas, and integrally extends over both of the electrodes.

However, silver can be used as the metal that does not react with the flammable gas.

In the flammable gas sensor with the above configuration, combustible gas is guided through the gas-permeable proton conductive membrane to the electrode made of platinum metal, and is decomposed and formed by the catalytic action of platinum metal to generate electrons. The protons that accumulate, decompose, and form are
The concentration of the flammable gas is influenced by the potential of the electrode, which is made of a metal that conducts freely through the gas-permeable proton conductor membrane and prevents recombination with the electrons mentioned above, and does not react with the flammable gas. It can be held at a predetermined potential without being affected.

<Example> Hereinafter, embodiments will be described in detail with reference to the accompanying drawings showing examples.

FIG. 1 is a schematic diagram showing an embodiment of the combustible gas sensor of the present invention, in which an n-type source region [21 and a drain region (3) are formed at predetermined positions on the surface of a p-type substrate (1). In addition, an n-type channel region (4) is formed between the source region (2) and the drain region (3), and the p-type substrate except for a portion corresponding to the source region (2) is formed. The entire surface of (1) is covered with an insulating film (5). Then, a gate electrode (6) made of platinum is formed on the insulating film (5) corresponding to the channel region (4),
a source electrode made of silver (forming a force) in contact with said source region (2), and further said gate electrode (6);
A solid electrolyte membrane (8) as a gas permeable proton conductive membrane is formed to cover the source electrode and the insulating membrane (5).

Note that (9) is a DC power supply, and (g)) is an ammeter, which are connected in series between the source region (2) and the drain region (3).

The operation of the combustible gas sensor having the above configuration is as follows.

When hydrogen gas is introduced as a measurement gas as shown by arrow A in FIG. At the surface of the gate electrode (6), 12 →
2H" +28 2 days + 1/202 + 2e- + H20. Moreover, since the H+ ions move freely in the solid electrolyte membrane (8), the above reversible reaction does not occur frequently, and the solid electrolyte membrane (8) As the amount of hydrogen gas reaching the gate electrode (6) through 8) increases, the potential becomes deeper (see FIG. 2A).

On the other hand, in the source electrode (7), since silver is not sensitive to hydrogen gas, it continues to be held at a predetermined potential even if the concentration of hydrogen gas changes (see FIG. 2B).

Therefore, a potential depending on the concentration of hydrogen gas is applied between the source and gate electrodes, and when a constant voltage is applied between the source and drain electrodes, the potential decreases as the concentration of hydrogen gas increases. (
(See Figure 2C).

Furthermore, since the H+ ions generated in the vicinity of the gate electrode (6) during the above operation are stored without being wasted, it is not recommended to use a particularly high impedance measuring device. not necessary,
An ordinary ammeter can be used to measure the exact concentration of hydrogen gas.

Moreover, although only the concentration measurement of hydrogen gas has been described above, the concentration measurement of -acid carbon gas can also be carried out in the same manner.

That is, -carbon oxide gas also undergoes a reversible reaction in the same way as hydrogen gas, specifically Co + HO-GO2+ 2 H" + 2 e2
F+" + 1/20 +28->1-(2
It is 0. Therefore, the concentration of carbon monoxide gas can be measured using the electrons generated by the above reaction.

FIG. 3 is a schematic diagram showing another embodiment, and the only difference from the above embodiment is that the gate electrode (6) is made of silver, and the source electrode (7'I) is made of platinum.

Therefore, the gate electrode (6) is held at a predetermined potential regardless of the concentration of hydrogen gas, and the source electrode (7'I) becomes a deep potential as the concentration of hydrogen gas increases. A potential is applied between the electrodes that changes in the opposite way to that in the above example depending on the concentration of hydrogen gas.
When a constant voltage is applied between the source and drain electrodes, the current characteristic increases as the concentration of hydrogen gas increases (see FIG. 4).

Note that this invention is not limited to the above embodiments; for example, it is possible to use a calomel electrode in place of the silver electrode, or to use an electrode made of another platinum metal in place of the platinum electrode. In addition, the measurement range can be changed by changing the gas permeability of the solid electrolyte membrane (8), and a plurality of combustible gas sensors with different measurement ranges can be installed in parallel and can be selectively controlled by a switch (not shown). It is possible to make it work, and various other design changes can be made without changing the gist of the invention.

<Effects of the Invention> As described above, the present invention configures a field effect transistor using an electrode that is sensitive to combustible gas and an electrode that is not sensitive to flammable gas, and also that the surface is covered with a gas permeable proton conductive membrane. This has the unique effect of making it possible to accurately measure the concentration of combustible gas using a conventional measuring device while ensuring that the danger of gas soot is eliminated.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment of the flammable gas sensor of the present invention, FIG. 2 is a characteristic diagram explaining the operation of the combustible gas sensor, FIG. 3 is a schematic diagram showing other embodiments, and FIG. The figure is a characteristic diagram, and Figure 5 is a schematic diagram showing a conventional combustible gas sensor. (6)...Gate electrode, (7)...Source electrode, (
8)...Solid electrolyte membrane (A) Hydrogen gas amount Figure 1 Figure 2

Claims (1)

[Claims] 1. Gate electrode of field effect transistor; and one of the source electrodes is made of platinum metal. one with combustible gas and the other with flammable gas. It is made of non-reactive metal and is placed on both the above electrodes. Gas permeable proton conduction that integrally covers the Flammable, characterized by the formation of a body membrane gas sensor. 2. Silver is a metal that does not react with flammable gases. The combustible material according to claim 1 above sexual gas sensor.