TERMAL CONDUCTIVITY

Thermal Conductivity

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).

DESCRIPTION 

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.

READINGS:

PPM; up to 100% by volume

PROS:

Wide measuring range.

CONS:

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.