Thermo Scientific FOCUS GC, Instruction Manual, Page: 173 / 356

Chapter 9
TCD Overview Thermal Conductivity Detector (TCD)
Instruction Manual 173
Figure 9-1. TCD Filaments and Gas Flows
When the filaments are properly powered, they heat at a temperature (resistance)
that is a function of the thermal conductivity of the gas flowing through the
filaments. When a chromatographic component elutes in the analytical channel, a
change takes place in the heat transfer followed by a variation of the filament
temperature. The signal polarity is a function of the thermal conductivity of the
component relative to the reference gas and to the user-selected polarity of the
filament power supply.
WARNING! The TCD filaments are sensitive to impurities present in the carrier, reference, and
make-up gas supplies. To ensure correct detector operation, you should use oxygen
and water vapor traps in the carrier gas and the make-up gas supply lines. We
suggest that you install an OXICLEAR filter (PN 281 131 40) before connecting the
gas to the GC.
1.Measure Cell A.Reference Gas
2.Reference Cell B.Make-up Gas
3.Column