Gas detector is the device for measuring the gas leakage concentration, mainly meaning the portable or handheld gas detector. The working principle is inspection of the gas type in the air with the gas sensor, so the sensor is used to detect the gas type and content. In general, the gas sensor defined by the inspection purpose, all the sensor used to measure the gas type and leavel named the gas sensor. No matter it with the physical method, or chemical method.

Semiconductor Sensor

It use some metal oxide semiconductor materials, under the certain temperature, the conductivity changes with the composition of the ambient gas. For example, the alcohol sensor, it with the principle of using the Tin Dioxide under high temperature with the alcohol gas, the resistance will be a sharp reduction.

Advantages:

It could be effectively used to test: Methane, Ethane, Propane, Butane, Ethanol, Formaldehyde, Carbon Monoxide, Carbon Dioxide, Ethylene, etc. It with low cost, suitable for civil gas detection. The following gas sensor is successful: Methane(Natural gas, Biogas), Alcohol, Carbon Monoxide, Hydrogen Sulfide, Ammonia. High quality sensor could used for industrial detection.

Disadvantages:

The stablility is not good, easily affected by the environment; and the output parameter is not certain. So it unavaible for the working place with high inspection demands.

Catalytic Combustion Sensor

It with the principle of on the surface of the platinum resistance preparing the anti high temperature catalyst layer, under the certain temperature, the combustible gas will catalytic combustion on the surface. Then the temperature of platinum resistance will rise, the resistance changes, the change value is the functions of the combustible gas concentration.

Advantage:

It selectively detect the flammable gas, which cann’t be burned, the sensor will no respond. Catalytic combustion sensor measure accurate, respond quickly, long working life. Play an important role in combustible gas detection.

Disadvantage:

Most of the organic vapors have toxic effect on the sensor.

Electrochemical Sensor

Some flammable gas or toxic gas with the electrochemical activity, could be electrochemical oxidation or reduction. Using these reactions, we can identify the gas composition and inspect the gas concentration. Electrochemical sensor also could be classified as the following types:

1.      Original battery type gas sensor, with the same principle of the dry battery. But the difference is the battery carbon manganese electrode was replaced by a gas electrode. Take the Oxygen sensor as an example, the oxygen in the cathode is reduced, the electron flow to the anode through the current meter, where the lead metal is oxidized. The magnitude of the current is directly related to the concentration of oxygen. This kind of sensor could used to detect the Oxygen O2, Sulfur Dioxide, Chlorine, etc.

2.      Constant potential electrolysis pool type gas sensor, the sensor for detection of reducing gas is very effective, its principle and primary cell type sensor is not the same, the electrochemical reaction is occurred in the current compulsory, the sensor is a kind of real Coulomb analysis. The sensor has been successfully used in the detection of carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine, and other gases. It is the main sensor for the detection of toxic and harmful gases.

3.      Concentration difference cell gas sensor and gas electrochemical activity has on both sides of the electrochemical cell, the spontaneous formation of the concentration difference of electric potential and electromotive force and the size of the gas concentration, the sensor of the successful example is the car with oxygen sensors and solid electrolyte type oxide carbon sensor.

4.      Limiting current type gas sensor with a measurement of the concentration of oxygen sensor using electrochemical pool in the limiting current and carrier concentration related to the principle of preparation of oxygen concentration sensor, oxygen detection for automobile, steel and oxygen concentration detection.

Infrared Sensor

This gas sensor mainly used to detect the Carbon dioxide CO2, Methane CH4.