CompactGC manual
11
3.4
Detectors
Four detectors are available: Thermal Conductivity Detector (TCD), Flame Ionisation
Detector (FID), Pulsed Discharge Detector (PDD) and Photo Ionisation Detector (PID)
(available end 2003). Up to three of these detectors can be configured in the
CompactGC.
TCD
The TCD is a very widely used detector for analysis of gases, but in principle all
components with different thermal conductivity in relation to the carrier gas can be
detected. The response is concentration dependant: a higher column flow or make-up
flow results in a decreased sensitivity.
This detector is a dual channel microvolume cell with two filaments on constant mean
temperature. See figure 3.4.
Figure 3.4: TCD detector
Operation principle
The filaments are continuously losing heat to the wall of the detectorcell by the thermal
conducting carrier gas (see figure 3.5). When a component with a different thermal
conductivity compared to the carrier gas passes the filament, the electronic circuit in
which both filaments are integrated (Wheatstone bridge) is adjusting the current to
maintain the constant filament temperature. This current change is dependant on the
component concentration, and is converted to a chromatographic signal that can be
handled by the data system.
analysis flow
reference flow
dual filaments
