JPS6220500B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a gas detection element based on electrical resistance measurement, and when used in combination with a temperature compensation element, for example, the resistance temperature characteristic is made the same as that of the temperature compensation element to improve gas detection sensitivity. The present invention relates to a gas sensing element that improves.

Generally, conventionally known gas detection elements are made of metal oxides such as stannic oxide, zinc oxide, or ferric oxide, as well as platinum-based catalysts such as Pd and Pt, as well as Sb,
Research has been conducted to improve gas sensitivity by adding Ai, Fe, Ni, Zn, Si, Ti, Zr, etc., but the temperature characteristics have not been considered, and in fact, gas detection with better gas sensitivity than conventional methods has been carried out. Although many elements are known, there are almost no gas sensing elements with excellent temperature characteristics.

Therefore, when performing gas detection using a conventionally known gas detection element, measurements have been performed while compensating the element temperature characteristics to a specific temperature that ensures the highest gas sensitivity.

However, in the method of maintaining the element temperature at a specific temperature, it is difficult to maintain the gas sensitivity characteristics constant because the element temperature changes due to fluctuations in the heating power supply voltage and changes in the environmental temperature. .

In addition, conventional methods for compensating the temperature characteristics of gas detection elements have been to use stabilized power supplies and Chener diodes to deal with fluctuations in the power supply voltage, and to use bimetals and thermistors to deal with environmental temperature changes. Compensation methods tend to require complicated electrical circuits, are expensive, and have a narrow compensation range.

Therefore, the inventors of the present application
No. 73470) proposed a temperature compensation element that can be used in conjunction with a gas detection element to reliably maintain the gas sensitivity of the gas detection element at a high level.

This temperature compensation element is a new metal oxide semiconductor that has the same resistance coefficient as the gas detection element but has almost no gas sensitivity. It is composed of a metal oxide semiconductor element composed of a sintered body whose main components are stannic oxide and zinc oxide blended in a range of 5%.

That is, for example, if paldium chloride is added to stannic oxide, the propane gas sensitivity will be improved, but if rubidium or iridium compounds are added to stannic oxide, the propane gas sensitivity will be improved. Gas sensitivity is completely lost and the drag coefficient remains unchanged.

To explain this in more detail, FIG. 1 shows the propane gas detection characteristics of elements in which various catalysts are added to stannic oxide. According to this, the dopant showed higher sensitivity than the undoped stannic oxide element, but it showed the same sensitivity for osmium and rhodium as the undoped stannic oxide element, and for rubidium it showed the same sensitivity as the unadded stannic oxide element. This has the effect of causing a loss of gas detection ability, and when an element is manufactured by firing iridium at a lower temperature than this, the propane gas detection ability is lost.

This effect was obtained as a result of converting an n-type semiconductor into a p-type semiconductor by controlling the valence, and by utilizing this phenomenon, temperature compensation of the gas sensing element can be performed.

This will be explained with reference to FIG. 2. FIG. 2 shows a comparison of the resistance-temperature characteristics of the gas sensing element and the temperature compensating element of the original application.

Here, the gas detection element is 93wt% stannic oxide,
The main components used were 1wt% palladium chloride, 1wt% sintering aid, and 5wt% gas component. A shows the resistance temperature curve of the sensing element in air, and C shows the resistance temperature curve of the sensing element in air containing 0.1 V% of propane gas.

In addition, the temperature compensation element is 92wt% stannic oxide, 1wt
% Palladium Chloride, 1wt% Rubidium Chloride, 1wt
% sintering aid and 5 wt% glass component were used. B shows the resistance temperature curve of the temperature compensation element in air, and D shows the resistance temperature curve of the temperature compensation element in air containing 0.1 V% of propane gas.

According to Figure 2, the detection element is A before and after gas detection.
Measurements are made at the element temperature when the electrical resistance ratio of It is necessary to compensate.
On the other hand, as is clear from FIG. 2, the electric resistance ratio between C and D is always constant regardless of the element temperature, so it can be used as a temperature compensating element for the sensing element.

The original application utilized this phenomenon to propose a gas detection device consisting of a gas detection element and a temperature compensation element.

However, when the electrical resistance ratio is always constant regardless of the element temperature, as shown in C and D in Figure 2, this gas detection device is temperature compensated and can detect gas with high accuracy; If the types of gases or the components of the sensing elements are different, this ratio may not be constant, and in such cases, highly accurate gas detection cannot be performed.

Therefore, in this invention, as mentioned above, we researched a method that allows accurate gas detection even when the electrical resistance ratio of the gas detection element and the temperature compensation element is different. It was found that this contributes to a decrease in the temperature coefficient,
This invention was completed based on this knowledge.

FIG. 3 is a resistance-temperature characteristic curve of the device showing that the osmium compound contributes to lowering the temperature coefficient of resistance of the device. Here, A is rubidium chloride
Resistance-temperature curve of a stannic oxide element doped with 0.7wt%, B is a resistance-temperature curve of a stannic oxide element doped with 1.7wt% iridium chloride, C is osmium oxide
Resistance temperature curve of stannic oxide element added with 1.4wt%, D is resistance temperature curve of stannic oxide element added with 0.6wt% rhodium powder, E is palladium chloride
The resistance temperature curve of a stannic oxide element doped with 1wt% is shown.

As is clear from this, no decrease in the temperature coefficient of resistance was observed for rubidium, iridium, and paldium, but osmium oxide contributed to a decrease in the temperature coefficient of resistance.

Furthermore, as shown in Figure 1, osmium compounds exhibit gas sensitivity comparable to that of additive-free stannic oxide elements, so they are not affected by gases and can be incorporated into gas detection elements. .

Therefore, in this invention, in a gas detection element composed of a sintered body mainly composed of stannic oxide and zinc oxide, 0.1 wt% of the osmium compound is used.
and 3wt%, and the electrical resistance ratio is adjusted to be the same as the electrical resistance ratio of the temperature compensating element.

In this case, the amount of osmium compound added is
Below 0.1 wt%, the effect of compensating for variations in device characteristics due to ambient temperature decreases, and above 3 wt%, it becomes necessary to consider the gas sensing and selection ability of the compound.

Furthermore, the osmium compound may be added to the temperature compensating element to make its electrical resistance ratio the same as that of the gas sensing element.

In this case, the compounding components and proportions of the temperature compensation element and the gas detection element differ depending on the type of detection gas, and when the detection gas is propane, for example, paldium chloride and osmium oxide are blended with stannic oxide. For the gas detection element, a temperature compensation element in which osmium oxide is mixed with stannic oxide can be used.

Furthermore, by blending an osmium compound into the gas sensing element and adjusting its electrical resistance ratio, it is possible to use it alone to perform accurate gas detection without using it together with a temperature compensating element.

Next, a compensation method using the gas detection element according to the present invention will be explained. This compensation uses a device in which a temperature compensation circuit incorporating a temperature compensation element is added to a detection circuit incorporating the detection element according to the present invention. This can be done by doing.

For example, a circuit device may be constructed by incorporating the sensing element according to the present invention on one side of a bridge circuit and a temperature compensation element on the other side, and adjusting the electrical resistance value when gas containing the gas to be detected passes through the sensing element. The measurement is performed while being compensated by a temperature compensation element, and the amount of gas to be detected in the gas is determined from the measured value.

In this case, if the temperatures of the sensing element and the temperature compensating element are not the same, the electric resistance ratio between the sensing element and the temperature compensating element cannot be constant, and the compensation effect cannot be exhibited.

However, it is difficult to make the temperatures of the sensing element and the temperature compensation element the same because they are affected by power supply voltage fluctuations and environmental temperature changes.

Therefore, in this embodiment, in order to avoid being affected by power supply voltage fluctuations and environmental changes, one surface of the heatable electric insulating substrate 1 is provided with electrodes 2a and 2b at both ends, as shown in FIG. A heating resistor 3 is provided, a heating power source 4 is connected to the electrodes 2a and 2b, and electrodes 5a and 5 are connected to the other side of the substrate 1 at both ends.
5b and electrodes 7a at both ends,
A temperature compensation element 8 having a temperature compensation element 7b is provided, and a blitz circuit for gas detection is further comprised of the gas detection element 6, the temperature compensation element 8, a fixed resistor R, and a variable resistor R'.

During gas detection and measurement, the heating resistor 3 is heated by the heating power source 4, and the gas detection is performed while compensating the temperature of the gas detection element 6 and temperature compensation element 8 under the same heating conditions.

In this case, since the gas detection element 6 and the temperature compensation element 8 are placed under the same heating conditions, measurement can be performed without being affected by power supply voltage fluctuations or environmental temperature changes. can take accurate temperature compensated measurements.

In the embodiment shown in FIG. 4, the heating resistor 3 is provided on the back surface of the heatable electrical insulating substrate 1, and the heating resistor 3 is heated. However, the heating resistor 3 may not be provided. If the sensor is not affected by power supply voltage fluctuations or environmental temperature changes, the sensing element and the temperature compensation element may be provided on the same substrate.

On the other hand, in the above embodiment, an example was described in which the temperature compensation element is used to compensate the temperature of the gas detection element. Temperature-compensated gas sensing can be performed without using an element.

Although propane gas was described in this example, carbon monoxide gas, urban Temperature compensation for gas detection, such as gas, can also be performed.

Figure 5 shows the selectivity characteristics of propane gas (solid line) and carbon monoxide gas (dashed line) when palladium and rubidium are added to stannic oxide. By using this, it is possible to detect gases containing two or more types of gases.

FIG. 6 shows an embodiment of gas detection when two or more types of gases are included. ', a temperature compensation element 8' is provided,
As shown in FIG. 4, a bridge circuit incorporating a gas sensing element 6 and a temperature compensating element 8 is constructed, and a bridge circuit incorporating a gas sensing element 6' and a temperature compensating element 8' is constructed.

When performing gas detection measurement, the heating resistor 3 is heated by the heating power source 4, and the gas detection element 6,
Gas detection is performed while temperature compensating the temperature compensating elements 6' and 8' under the same heating condition.

In this case, if gas-selective elements are used as the gas detection elements 6, 6', two types of gases, for example propane and carbon monoxide, are detected by separate elements.

Therefore, it is possible to measure many types of gases simultaneously and accurately with temperature compensation.

Furthermore, the gas detection device as in the embodiment described above is free of failures, can instantaneously and reliably compensate for changes in the temperature of weak elements, and can be made inexpensive and compact.

Next, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the following examples unless it goes beyond the gist of the invention.

Example The gas sensitivity characteristics of a gas sensing element whose main components are 92.6wt% stannic oxide, 1.4wt% osmium oxide, 1wt% sintering aid, and 5wt% glass are shown in Figure 1 (◎
(straight line), and the resistance-temperature characteristics were as shown in Fig. 3 (c).

In addition, when using the above gas detection element as the temperature compensation element 8, as the gas detection element 6,
93wt% stannic oxide, 1wt% paldium chloride,
1wt% sintering aid, 1.4wt to 5wt% glass component composition
% of osmium oxide and fired.
This element was used because it exhibited a resistance-temperature characteristic that was substantially the same as that of the temperature compensation element 8 described above.

Then, both of these elements are printed on an electric insulator substrate 1, and fired in an electric furnace at 650°C to 800°C.
When installed in the electrical circuit shown in the figure to detect and measure propane gas, gas sensitivity could be measured without being affected by power supply fluctuations or environmental temperature changes.

[Brief explanation of the drawing]

Figure 1 shows the gas detection characteristics of the element with various catalysts added. Figure 2 shows the electrical resistance characteristics with respect to the surface temperature of the element. Figure 3 shows the gas detection characteristics of the element with various catalysts added. 4 is a schematic diagram of a circuit device showing an embodiment of the present invention. FIG. 5 is a diagram showing gas selection characteristics when various catalysts are added. FIG. 6 is a diagram showing an embodiment in which two or more types of gas are detected simultaneously.

Claims (1)

[Claims] 1. In a gas detection element that measures the electrical resistance of a sintered body whose main components are stannic oxide and zinc oxide,
A gas sensing element characterized in that the gas sensing element contains an osmium compound in a range of 0.1wt% to 3wt%.