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Gas Out
130
˚
C
60
˚
C
Gas In
Figure 2.1: Schematic drawing of thermal conductivity measurement. The sensor is comprised in the
stainless steel block which is kept at a constant temperature.
The FTC320 contains a thermal conductivity sensor to analyze the quantitative composition of gas mix-
tures. The measurement is based on the heat transfer between a heat source and a heat sink.
The measuring gas is led through a stainless steel block that is kept at a constant temperature of
63
◦
C (for most applications). The block temperature is stabilized using a control loop - it serves as
a heat sink of constant temperature. A micro mechanically manufactured membrane with a thin-film
resistor serves as heat source. A control loop stabilizes the membrane temperature at 135
◦
C (for most
applications).
Above and below the membrane two small cavities are etched into the silicon. These cavites are filled
with measuring gas by diffusion. The surfaces opposite to the membrane are thermally connected with
the heat sink. Through maintaining a constant temperature gradient between the two opposite surfaces,
the heat flow is dependant of the gas mixture’s thermal conductivity alone. Hence the voltage needed
to keep the membrane temperature constant is a reliable measure for the thermal conductivity of the
mixture and can be used further to determine the gas mixture’s composition.
File name:
FTC320Ex Operating Manual_1.09KD201009MPO3V02.pdf
Содержание FTC320
Страница 45: ......
