
1 of 24
Jun 2001
Agilent 6890 Gas Chromatograph Service Manual
330
Thermal Conductivity Detector
(TCD)
Theory of operation
The TCD responds to any compounds whose thermal conductivity is different
from the thermal conductivity of the carrier gas alone. The TCD cell is a dual
channel device, with an empty flow path and a path containing a detector
filament. A switching valve alternates between sending the column effluent
(containing analytes) through the empty and the active flow paths. When the
column effluent flows through the empty channel, a pure stream of reference
gas maintains an equilibrium through the filament path. The reference gas is
used to compare thermal conductivity changes caused by the column effluent.
A gas with high thermal conductivity, such as helium, is used as the carrier/
make-up/reference gas. When the analyte is present in the gas stream, the
thermal conductivity drops, and less heat is lost to the cavity wall. Under
constant applied voltage, a silicon nitride coated filament in the TCD cell will
heat up and its resistance will increase. This change is what is recorded and
measured for the chromatogram.
Figure 330-1
The Thermal Conductivity Detector (TCD)
Pneumatic lines
Detector body
Heater/sensor cable
Filament leads
∆
PRT leads
(under cover)
Содержание 6890 Series
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Страница 195: ...260 Solvent Vapor Exit Accessory Leak testing 10 of 10 Jun 2001 Inlets Agilent 6890 Gas Chromatograph Service Manual ...
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Страница 389: ...360 Auxiliary EPC Replacement procedures 16 of 16 Jun 2001 Detectors Agilent 6890 Gas Chromatograph Service Manual ...
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Страница 479: ...520 Gases Supplying valve actuator air 14 of 14 Jun 2001 Site Preparation Agilent 6890 Gas Chromatograph Service Manual ...
Страница 485: ...530 Power Grounding 6 of 6 Jun 2001 Site Preparation Agilent 6890 Gas Chromatograph Service Manual ...
Страница 491: ...540 Instrument Specifications Detectors 6 of 6 Jun 2001 Site Preparation Agilent 6890 Gas Chromatograph Service Manual ...
Страница 492: ...600 Performance Verification How to check the performance of the 6890 instrument 610 Checkout Chromatograms ...
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Страница 555: ...840 Shutdowns 10 of 10 Jun 2001 Error Codes and Internal Diagnostics Agilent 6890 Gas Chromatograph Service Manual ...
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Страница 637: ...1110 Valves Liquid sample valves 6 of 6 Jun 2001 Valves Agilent 6890 Gas Chromatograph Service Manual ...
Страница 647: ...1120 Valve Box Removing the valve box assembly 10 of 10 Jun 2001 Valves Agilent 6890 Gas Chromatograph Service Manual ...
Страница 675: ...1150 Troubleshooting Pressure check 6 of 6 Jun 2001 Valves Agilent 6890 Gas Chromatograph Service Manual ...
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Страница 717: ...1225 Main Board 6890N Fuses 6 of 6 Jun 2001 Electrical Agilent 6890 Gas Chromatograph Service Manual ...
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