2 - 2
INZ-TN4ZAFE-E
2.2 Principle of operation
Two platinum wires are stretched along center lines of two slots respectively formed through a
metal block.
The platinum wires are heated to approx. 100°C with a DC current (bridge current). The two
slots form a sample chamber and a reference chamber respectively, and the platinum wires form a
Wheatstone bridge in combination with two fixed resistors arranged outside the chambers. When
thermal conductivity of sample gas changes, temperature of the platinum changes to vary its
electrical resistance in the sample chamber, whereas temperature and resistance of the platinum
wire do not change in the reference chamber in which thermal conductivity of a reference gas is
kept always constant.
Therefore, the Wheatstone bridge generates a voltage signal depending on kinds and concentration
of the sample gas.
The thermal conductivity gas analyzer is constructed as shown in Fig. 2-1.
Table 2-1 lists thermal conductivities of typical gas components, and Table 2-2 summarizes
indicating deviations due to interfering components in measurements with the thermal conductivity
gas analyzer.
Sample gas
DC constant
current
Measuring
chamber
Reference
chamber
Reference gas
sealing
DC amplifer
Fixed
resister
Fixed
resister
Fig.2-1 Structural View of Thermal Conductivity Gas Analyzer
