The Concept of Gas Sensitive Resistor
Gas sensitive resistor is a kind of semiconductor sensitive device. It uses the mechanism of gas adsorption to change the conductivity of semiconductor itself. Gas-sensitive resistor can be used to convert the composition and concentration of a certain gas into resistance variation, and then into current and voltage signals.
Types of gas sensitive resistors
(1) N-type gas-sensitive resistor
When methane, carbon monoxide, natural gas, gas, liquefied petroleum gas, acetylene, hydrogen and other gases are detected, the resistance value of N-type gas resistor decreases.
(2) P-type gas-sensitive resistor
When flammable gas is detected, the resistance value of P-type gas resistor will increase, but when oxygen, chlorine and carbon dioxide are detected, the resistance value will decrease.
Gas Sensitive Resistor Structure
The schematic diagram of the gas sensitive resistor is shown below.
It can be seen from the figure that the gas sensor is mainly composed of explosion-proof net, tube seat, electrode, encapsulated glass, heating wire and oxide.
Main parameters of gas sensitive resistor
The product of heating voltage and heating current.
Under working conditions, the voltage between the two poles of the gas sensitive resistor.
Under the optimum working conditions, the resistance value of gas sensitive resistor varies with the gas concentration after contacting the gas. If a voltage measurement method is used, the value is equal to the ratio of the voltage drop on the load resistance before and after contact with a certain gas.
Under the optimum working conditions, the time required for the voltage of the load resistance to change to the specified value after contacting the gas to be measured.
Under the optimum working conditions, the time required for the voltage on the load resistance to return to the specified value after the gas is separated from the measured value.
Characteristic of Gas Sensitive Resistor
The following figure shows the Sensitivity-temperature characteristics of gas-sensitive resistors. It can be seen from the curve that the electrical conductivity changes little at room temperature. When the temperature rises, the electrical conductivity changes greatly. Therefore, the gas resistor needs to be heated when it is used.
Resistance-Gas Concentration Characteristics
The following figure shows the resistance-gas concentration characteristic curve of the gas sensitive resistor. It can be seen from the figure that the gas sensitive resistor has high sensitivity to ether, ethanol, hydrogen and n-ethane.