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
High sensitivity (detects low concentrations); wide operating
temperature range; long life.
Non-specific (cross-sensitive to other compounds); nonlinear
output; sensitive to changes in humidity: subject to poisoning.