Selection of Flammable Gas Sensors
The combustible gas sensor is a gas-electric conversion element. It can convert the information of combustible gas concentration into analog signal, and then convert the analog signal into digital signal through A/D conversion unit and send it to microprocessor for corresponding operation. Therefore, the combustible gas sensor is a key part of the system, which will directly affect the performance of the system, so the choice of economic, stable and accurate combustible gas sensor is the primary task of designing the system.
When choosing flammable gas sensors, the following aspects should be chosen:
(1) Selection according to the type of gas detected
(2) Sensitivity
(3) Linearity and stability
(4) Response time
At present, sensors for combustible gases mainly include semiconductor sensors, solid electrolyte gas sensors, contact combustion gas sensors, polymer gas sensors, electrochemical gas sensors and so on. Because of the variety of combustible gases, one type of gas sensor often can not detect all combustible gases. 。 Contact combustion gas sensor can be divided into direct contact combustion sensor and catalytic contact combustion sensor. Its working principle is that the gas-sensitive material can be oxidized and burned by combustible gas under the electrified state or under the action of catalyst. The combustion makes the electric heating wire warm up, so that its resistance value changes. Semiconductor gas sensors are heated by a constant DC power supply. When there is no combustible gas, there is a high resistance state between the two poles of the semiconductor, and the sensor has no signal output. When combustible gas exists in the air and is adsorbed on the oxide sintered body, it causes the change of semiconductor conductivity or thermal conductivity, and makes its resistance value smaller, thus converting the measured gas concentration information into electrical signal. Because the contact combustion gas sensor uses the combustible gas oxidation combustion to raise the temperature of the electric heating wire to detect the combustible gas, this type of sensor is insensitive to the non-combustible gas and will not cause cross-infection of other gases. Moreover, the sensor is less affected by ambient temperature and humidity, and has stable performance. Catalytic combustion gas sensor adopts bridge principle to form detection circuit, which has good linearity and sensitivity. Semiconductor gas sensor is exposed in the environment for high temperature detection, so the interference caused by gas is difficult to overcome, and it is prone to false alarm. At the same time, it is vulnerable to the influence of temperature and humidity, and its dispersion is relatively large.