Revision 4
4
12/15/2018
2.2.3 Thermal Conductivity Detector
A thermal conductivity detector (TCD) is used to detect the amount of each individual
component as it elutes from the chromatograph columns (Figure 2-3). The TCD is housed
inside the chromatograph oven and is kept at a very stable temperature to minimize drift.
Figure 2-3: Thermal Conductivity Detector
The TCD consists of 2 thermistor beads housed in separate compartments, the Reference
Cell and the Measure Cell.
When there are no components eluting from the column(s), both of the thermistors are
exposed to carrier gas and will be at the same temperature and thus have the same
resistance. In this case the Wheatstone Bridge is balanced and the voltage from the circuit
will remain at zero. The outlet of the column is plumbed to the Measurement cell so that
when a compound elutes from the column it passes through the Measurement cell while the
Reference cell contains only carrier gas.
Heat from the Measure thermistor will be transferred away from the Thermistor by the gas
that passes through the Measure Cell. The amount of heat that is transferred will depend on
the amount of gas that is flowing past and that gas’s ability to conduct heat (its thermal
conductivity). The temperature of the Measure Thermistor, and thus its resistance, will
change. In this case the Wheatstone Bridge will become unbalanced and a voltage
deflection will be observed.
Содержание AccuChrome MA2963
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Страница 124: ...Revision 4 111 12 15 2018 Figure 12 1 PLGC Power Connections Figure 12 2 Relays Wiring Diagram ...
Страница 125: ...Revision 4 112 12 15 2018 Figure 12 3 Analog Outputs Loop Powered Mode Figure 12 4 Analog Outputs Self Powered Mode ...
Страница 126: ...Revision 4 113 12 15 2018 Figure 12 5 Isolated RS 485 Port Connection Figure 12 6 Isolated RS 232 Connections ...
Страница 129: ...Revision 4 116 12 15 2018 Figure 12 11 Oven RTD and TCD Connections Figure 12 12 Arcnet AC485 Twisted Pair Connection ...
Страница 130: ...Revision 4 117 12 15 2018 Figure 12 13 Oven Heater Connection Figure 12 14 GC Valves Connections ...
Страница 131: ...Revision 4 118 12 15 2018 Figure 12 15 Solenoids 5 to 10 Connections Figure 12 16 Solenoids 1 to 4 Connections ...
Страница 132: ...Revision 4 119 12 15 2018 Figure 12 17 Digital Inputs Connections Figure 12 18 Cabinet Heater Connection ...
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