GAS TYPE DETECTION
Combustible gas; Toxic gases
PRINCIPLE OF OPERATION
Measures the gas sample's ability to transmit heat by
comparing it with a reference gas (usually air).
Two sensors (detecting sensor and compensating sensor)
are built into a Wheatstone Bridge. The detecting sensor is
exposed to the gas of interest; the compensating sensor is
enclosed in a sealed compartment filled with clean air.
Exposure to the gas sample causes the detecting sensor to
cool, changing the electrical resistance. This change is
proportional to the gas concentration. The compensating
sensor is used to verify that the temperature change is
caused by the gas of interest and not by ambient
temperature or other factors.
PPM; up to 100% by volume
Wide measuring range.
Non-specific (cross-sensitive to other compounds);
does not work with gases with thermal conductivities (TCs)
close to one (that of air, NH3, CO, NO, O2, N2); gases with
TCs of less than one are more difficult to measure; output
signal not always linear.