JP2001272367A - Reaction heat detection type gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect and measure a detection objective gas concentration in a tested gas, such as ozone without having to use reaction promoters, such as a catalyst. SOLUTION: A temperature of a sensor is set to be higher than a thermal cracking temperature of a test objective gas sort and to be a temperature which suppresses a reaction, causing variations in a detection property, so that oxidative decomposition of the detection objective gas is progressed without using any reaction promoter such as a catalyst, and then the concentration of the test objective gas in the tested gas is measured. In this case, two gas sensors are used, and one of the gas sensors measures a temperature change due to decomposition heat, when the element is heated at a temperature above the decomposition heat, while the other sensor eliminates influence of a temperature change of the tested gas without being influenced by the reaction heat due to thermal decomposition, when its temperature is set to a room temperature or to be slightly higher than the room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas sensor for detecting and measuring the concentration of a gas to be detected in a test gas such as ozone without using a reaction promoting substance such as a catalyst.

[0002]

2. Description of the Related Art A gas sensor of the type which detects a change in the temperature of reaction heat needs to measure the temperature of a test gas by some method to compensate for the temperature unless the temperature of the test gas is constant. Conventionally, a contact combustion type sensor has been known as a gas sensor for detecting a temperature change due to reaction heat close to this type. The contact combustion type sensor usually includes a sensing element to which a catalyst is added and a temperature compensation element having no catalytic activity, and both elements are operated at the same temperature as a bridge connection, and at the same time, temperature compensation is performed.

[0003]

In the above-mentioned catalytic combustion type sensor, in order to suppress the reaction in the compensating element, the operating temperature must be lower than the thermal decomposition temperature of the gas to be detected. Utilization is essential. In many catalysts, the activity generally changes greatly depending on the state of the catalyst, and there are many catalysts that cause so-called catalyst poisoning depending on the kind of gas contacted. In particular, this effect is significant when a strongly oxidizing gas such as ozone, hydrogen fluoride, or a silicon-containing compound or a product remains as a solid after decomposition. The conventional catalytic combustion type gas sensor based on bridge connection can easily compensate for temperature, but requires the use of a catalyst, so it can be easily decomposed with no suitable catalyst or easily decomposed with a slight heating. It is difficult to detect the gas that causes the poisoning or the gas that causes the catalyst poisoning. Examples of those corresponding to these gases include silane, trichlorosilane, and tetraethoxysilane. After decomposition, the silicon-containing compound such as silane causes silica to adhere to the surface of the sensing element and changes the catalytic activity.

Conventionally, ozone gas is generally determined at low and high concentrations by ultraviolet absorption spectroscopy, but the detection device is expensive. Methods for measuring the heat of decomposition for detecting ozone at a high concentration have also been proposed, but all of these methods were based on the premise of catalytic decomposition, so that their stability was poor and practical application was difficult. Ozone itself changes the catalytic activity of ozone itself, and when artificially generated, nitrogen oxide gas is often produced as a by-product, which not only changes the catalytic activity,
If the temperature is lower than 550 ° C., the solid oxide may adhere to the sensing element surface.

Therefore, by heating the element above the thermal decomposition temperature of the gas to be detected without using a catalyst and measuring the thermal decomposition heat of the gas, a gas sensor which is in principle free from catalyst poisoning and is stable for a long period of time. Can be realized. However, as a trade-off in this case, if temperature compensation is performed with a bridge connection, the gas to be detected is thermally decomposed even with the compensating element, so that there is a dilemma that temperature compensation cannot be performed.

[0006]

Accordingly, in the present invention, two gas sensors are used, and one gas sensor heats the element more than the heat of thermal decomposition to observe a temperature change due to the heat of decomposition, and the other sensor is used. By setting the temperature at room temperature or slightly higher than room temperature, the influence of the temperature change of the test gas is removed without being affected by the heat of reaction due to thermal decomposition. That is, the present invention relates to a sensor for detecting the amount of heat generated or absorbed when a gas to be detected is decomposed or oxidized by coming into contact with a high-temperature gas sensor as a temperature change. By setting the temperature higher than the thermal decomposition temperature of the gas and suppressing the reaction that changes the detection characteristics, the oxidative decomposition of the gas to be detected proceeds without using a reaction accelerator such as a catalyst, The concentration of the detection target gas in the inside is measured.

The present invention also provides a sensor for detecting the amount of heat generated or absorbed when a gas to be detected is decomposed or oxidized by contact with a high-temperature gas sensor as a temperature change. The temperature of the gas sensor is set to a temperature higher than the thermal decomposition temperature of the gas type to be detected and to suppress a reaction that changes the detection characteristics, and the temperature of the compensation element is set to the temperature of the gas to be detected. Alternatively, the temperature of the test gas is measured at a temperature lower than the thermal decomposition temperature, and the temperature is compensated by electronic calculation or calculation by software. In the above two cases, the detection target gas includes ozone, silane, trichlorosilane, tetraethoxysilane, and the like.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a conceptual diagram of an embodiment of the present invention in which ozone gas is measured using a temperature-compensated gas sensor of the type that measures platinum resistance. Gas sensor 1 and temperature compensator 2 for detecting temperature with platinum resistance
Are elements having the same characteristics and are placed in the same test gas atmosphere, here, ozone. Gas sensor 1
The operation temperature of the two elements is different by supplying different currents to the compensation element 2 and the compensation element 2, respectively. However, the temperature compensation is performed by placing them in the same environment and adding them with different multiplication factors.

If a current I is supplied from the constant current source 3 to the gas sensor 1, the gas is heated to a temperature (about 550 ° C.) higher than the thermal decomposition temperature of the gas to be detected. The thermal decomposition rate of ozone is about 0.0295 L at 127 ° C. mel ^-1 s ^-1
It is reported that the temperature of the sensing element is about 100
Heating up to 230 ° C., which is higher by 230 ° C., enables detection of ozone. However, when nitrogen oxide gas coexists, the solidified nitrogen oxide adheres to the sensing element, and thus the amount of nitrogen gas becomes 550.
It is desirable to operate at a temperature of at least ℃. Further, the specific current source 4 supplies the compensating element 2 with 1/1 of the power
When a current I / 10 of 0 flows, the temperature of the compensating element 2 becomes about 100
° C, but not to the thermal decomposition temperature of the gas to be detected. The temperature coefficient of the platinum resistance depends on the temperature, and the temperature coefficient at 100 ° C. is about 1.4 times the temperature coefficient at 500 ° C.
Therefore, if the temperature of the test gas fluctuates, the output voltages of the gas sensor 1 and the compensating element 2 also fluctuate.
Since the magnitude of the variation is proportional to the current, it will be about seven times different.

Therefore, if the ratio of the amplification degree between the amplifier 5 on the compensation element 2 side and the amplifier 6 on the sensor 1 side is set to about 7 times and the outputs are added, the output is maintained even if the temperature of the gas to be detected fluctuates. The signal does not fluctuate and temperature compensation is realized. At this time, since the operating temperature of the gas sensor 1 and that of the compensating element 2 are different, the resistance ratio is also different, and an offset is generated in the output voltage. , The output of the adder circuit 8 also becomes zero. In this state, if the detection target gas (ozone) is contained in the test gas, an extra temperature rise corresponding to the heat of thermal decomposition is obtained as an output signal.

Although the actual temperature coefficient of the platinum resistor slightly varies depending on the temperature, the difference in temperature dependency can be compensated by adjusting the ratio of the amplification degree between the amplifier 5 and the amplifier 6. Although the above description has been made with reference to an analog operation by an electronic circuit, the signals of the gas sensor 1 and the compensating element 2
After the / D conversion, the calculation can be performed using a computer. Further, although the description has been made using a platinum resistor for temperature measurement, the present invention can be applied to a case where a thermistor or a thermocouple is used. FIG. 2 shows an output example of the sensor, in which an output voltage proportional to the ozone concentration is obtained.

[0012]

Since the present invention is constructed as described above, it is particularly difficult to detect a hardly decomposable gas without a suitable catalyst, a gas which can be easily decomposed by heating a little, or a gas which causes catalyst poisoning. In addition to providing a means to measure ozone gas stably inexpensively over a long period of time without using expensive conventional ultraviolet absorption spectroscopy detection devices, catalytically poisoned catalysts provide stable detection. Even a gas type that cannot be used has a remarkable effect, such as the detection being possible.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a temperature-compensated gas sensor that measures platinum resistance.

FIG. 2 is a graph showing output characteristics of a sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Compensation element 3, 4 Constant current source 5, 6 Amplifier 7 Offset circuit 8 Operation circuit

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 599115273 Shinji Okazaki 353-3 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Shoji Asakura 1-31-3, Nakazawa, Asahi-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Eiji Nakagawa 40-12-809 Denen Chofuhonmachi, Ota-ku, Tokyo (72) Inventor Shinji Okazaki 353-3 Hazawa-cho, Kanagawa-ku, Yokohama, Kanagawa Prefecture (72) Inventor Hironori Shimizu Ginza, Chuo-ku, Tokyo 7-14-14 Ebara Corporation (72) Inventor Isamu Iwamoto 7-14-14 Ginza, Chuo-ku, Tokyo F-term within Ebara Corporation (reference) 2G060 AA01 AB01 AB15 AE19 AF02 AF07 BA03 BB02 BB09 BD02 HA01 HC02 HC10 HC13 HE01 KA03

Claims (4)

[Claims] 1. A sensor for detecting, as a temperature change, the amount of heat generated or absorbed when a detection target gas is decomposed or oxidized by contact with a high-temperature gas sensor,
By setting the temperature of the sensor to a temperature higher than the thermal decomposition temperature of the gas species to be detected and to suppress the reaction that changes the detection characteristics, the oxidation of the gas to be detected can be performed without using a reaction promoting substance such as a catalyst. A gas sensor for measuring the concentration of a gas to be detected in a gas to be detected, wherein the gas is subjected to decomposition to prevent a change in the detection characteristics caused by the reaction of the gas to be detected or an interfering gas with time. 2. The gas sensor according to claim 1, wherein the gas to be detected is ozone, and the temperature of the sensor is set to about 550 ° C. 3. A sensor for detecting the amount of heat generated or absorbed when a gas to be detected is decomposed or oxidized by coming into contact with a high-temperature gas sensor as a temperature change, and having the same or similar temperature characteristics for temperature compensation. Wherein the temperature of the gas sensor according to claim 1 is set to a temperature higher than the thermal decomposition temperature of the gas species to be detected and a temperature that suppresses a reaction that changes the detection characteristics, and the temperature of the compensation element is set to the temperature of the gas to be detected. A temperature-compensated gas sensor that measures the temperature of a test gas by setting it at a temperature lower than the temperature or the thermal decomposition temperature, and performs temperature compensation from electronic calculations or calculations by software. 4. The gas sensor according to claim 3, wherein the gas to be detected is ozone, and the temperature of the gas sensor is set to about 550 ° C.