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MEASURING PRINCIPLE
2 - 10
ETC00781(1) Series 100 e 10/2001
2.3 Thermal Conductivity Measurement
To measure gases like Hydrogen (H
2
), Argon (Ar) or Helium (He), the measurement method of
thermal conductivity (TC) will be used.
2.3.1 Sensor Design
The sensor consists of four small PT 100 resistors arranged in a Wheatstone Bridge which is
mounted into a block made of either aluminum, stainless steel or hastelloy, depending on the
application (e.g. stainless steel / hastelloy for corrosive gases). The block is thermostatted to
supress influence of external temperature change.
Fig. 2-7: Thermal conductivity sensor
2.3.2 Analysis Cell
Both the volume of the block and the mass of the resistors have been minimized on order
to obtain short response time.
The block contains two gas paths for sample and reference gas, whereat the reference gas
path is closed for standard applications. Always two sensors are located in the sample and
the reference gas path. The resistors are full glass packaged to withstand agressive gases.
The material in contact with the gases are glass, Gold, Aluminum, stainless steel and
Hastelloy, so a high resistance against corrosion by agressive gases is provided by this
cell.
THERMAL CONDUCTIVITY (TC) MEASUREMENT