A physical online gas analyzer. According to the principle that different gases have different heat conductivity, the content of some components in the mixture can be calculated by measuring the thermal conductivity of the mixture.
This kind of online gas analyser is simple and reliable, suitable for many kinds of gas, and it is a basic analyzer. However, it is difficult to directly measure the thermal conductivity of gas, so in fact, the change of thermal conductivity of gas is often converted into the change of electrical resistance, and then measured by electric bridge.
There are two kinds of thermistor elements in the thermal online gas analyzers: semiconductor sensitive element and metal resistance wire. Semiconductor sensor has small volume, small thermal inertia and large resistance temperature coefficient, so it has high sensitivity and small time lag.
The ball shaped metal oxide is sintered on the platinum coil as the sensing element, and then the same platinum coil with equal internal resistance and heat output is wound with the non-reactive material as the compensation element. These two components are used as two arms to form the bridge circuit, that is, the measuring circuit.
When the semiconductor metal oxide sensing element absorbs the measured gas, the conductivity and thermal conductivity change, and the heat dissipation state of the element also changes. As the resistance of the platinum coil changes with the temperature change of the element, the bridge has an unbalanced voltage output, on which the concentration of gas can be detected.
Thermal conductivity gas analyzer has a wide range of applications, in addition to being commonly used to analyze the content of hydrogen, ammonia, carbon dioxide, sulfur dioxide and low concentration of combustible gas, it can also be used as a detector in chromatographic analyzer to analyze other components.