SEMI CONDUCTOR


Metal Oxide Semiconductor

GAS TYPE DETECED

Combustible gas; Toxic gas

PRINCIPLE OF OPERATION

Made of a metal oxide that changes resistance in response to the presence of a gas; this change is measured and translated into a concentration reading.

PRICIPALS OF OPERATION

A semiconducting material (metal oxide) is applied to a nonconducting substance (substrate) between two electrodes. The substrate is heated to a temperature at which the presence of the gas can cause a reversible change in the conductivity of the semi-conducting material. When no gas is present, oxygen is ionized onto the surface and the sensor becomes semi-conductive; when molecules of the gas of interest are present, they replace the oxygen ions, decreasing the resistance between the electrodes. This change is measured electrically and is proportional to the concentration of the gas being measured.


READING - PPM

PROS:

High sensitivity (detects low concentrations); wide operating temperature range; long life.

CONS:

Non-specific (cross-sensitive to other compounds); nonlinear output; sensitive to changes in humidity: subject to poisoning.