Detector Systems
Thermal conductivity detector (TCD)
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TCD-to-FID series connection
The following describes, for a TCD whose exhaust vent returns to the
inside of the oven, connecting the TCD to an FID.
If necessary (see NOTE below), exchange the standard FID jet for the
0.030•inchjet (Part No. 18789•80070).Information about jet exchange
is available in Chapter 8, Preventive Maintenance.
Note: Use of the 0.030•inchjet is necessary only in cases where FID
flame lighting problems occur due to increased gas flow rate through the
FID, or TCD response is affected adversely due to the increased back
pressure on the TCD.
Since the 0.030•inchjet reduces FID sensitivity, it is recommended that
operation with the standard 0.018•inchjet be tried first, before deciding
to switch to the 0.030•inchjet.
Inside the oven, connect the TCD oven•returnexhaust vent tube to
the base of the FID using the TCD•to•FIDjumper tube (Part No.
19302•80600)and standard 1/8•inchstainless steel swage•typenuts
and ferrules.
Ferrules should be preset, and two wrenches should be used in
opposition in tightening the nut to prevent twisting the tube.
Note: Use of the TCD•to•FIDjumper tube is critical to achieve lowest
possible detector background noise.
This completes series connection of an FID with a TCD.
Filament passivation
The TCD filament is a tungsten•rheniumalloy whose surface has been
chemically passivated.
Passivation protects against damage due to O
, but chemically active
components such as acids and halogenated compounds may attack the
