Thermal Conductivity Detector - Siemens Maxum II Service Manual

Thermal Conductivity Detector

The Thermal Conductivity Detector (TCD) is a concentration-responsive detector of moderate
sensitivity. The detector cell, containing the sensing element, is a flameproof/explosion-proof
unit located in the chromatograph oven. The TCD is the only Maxum II detector type that is
not mounted in the detector compartment.
The TCD works on the principle that the thermal conductivity of the carrier gas is different than
the thermal conductivity of the sample components. This means that the carrier gas conducts
either more or less heat from the heated element than the sample components. The electronic
circuits sense the change in heat flow and produce a proportional analog voltage signal. Two
types of TCD are used within the Maxum II.
● Thermistor Model – This TCD type uses thermistors. It includes six independent
measurement cells and two reference cells. This detector connects to the IS TCD DPM,
located in the electronics cabinet.
● Filament Model – For higher temperature requirements a 2-cell TCD is available that uses
filaments for thermal conductivity sensing. The 2-Cell Filament TCD is often used as an
Inter‑Column Detector in conjunction with an FPD or FID application. This detector typically
connects to a dedicated input channel on the Base DPM.
Maxum Edition II Detectors
Service Manual, May 2018, A5E42019847001
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