Detector Systems

Thermal conductivity detector (TCD)

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

149