Working principle and structural characteristics of surface mount diode gas sensor

As we all know, gas sensors are generally divided into surface mount diode type, contact combustion type, chemical reaction type, optical interference type, thermal conduction type, infrared absorption scattering type, etc.

Among them, surface mount diode gas sensors are more widely used.

The main components of a surface mount diode gas sensor are: gas sensing part, heating wire, and explosion-proof mesh. The gas sensing part is achieved by using SnO2 Fe2O2、

Sensors with sensitizers such as Pt and Pd added to metal oxides such as ZnO2. The selectivity of the sensor is controlled by the amount of sensitizer added, for example, for ZnO2

Series sensors, if Pt is added, the sensor has high sensitivity to propane and isobutane; If Pd is added, it is more sensitive to CO and H2.

The gas sensor is made of a ceramic diode as the frame, covered with a sensitive membrane material, and measured using gold-plated pins at both ends of the membrane. The most commonly used materials for sensitive membranes are

Metal oxides, polymer materials, and colloidal sensitive films. Its two key parts are the heating resistor and the gas sensitive film. Connecting gas sensitive materials with gold electrodes

At both ends, make it equivalent to a resistance that varies with the concentration of the external gas being measured. Due to the high thermal stability of metal oxides, and the fact that these sensors only

The surface layer of the patch diode undergoes reversible oxidation-reduction reactions, while the internal chemical structure of the patch diode remains unchanged.

So, long-term use can also achieve high stability. The principle is as follows: Once metal oxides are heated, oxygen in the air will be transferred from the metal oxide patch

The donor energy level of diode crystal particles takes away electrons and adsorbs negative electrons on the crystal surface, increasing the surface potential and hindering the movement of conductive electrons

The gas sensor has a constant resistance value in the air. At this point, the reducing gas undergoes an oxidation reaction with the oxygen adsorbed on the surface of the chip diode, due to the gas molecules'

The desorption effect causes a change in the surface potential, therefore, the resistance value of the sensor needs to change. For reducing gases, the resistance value decreases; For oxidizing properties

Gas increases the resistance value. In this way, the concentration of gas can be detected based on the change in resistance value.