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Jun 2001
Agilent 6890 Gas Chromatograph Service Manual
250
Volatiles Interface
Theory of operation
The volatiles interface (VI) introduces a gas sample into the gas
chromatograph (GC) from an external device such as the headspace, purge
and trap, or air toxics samplers. The interface has a small volume and is highly
inert, thus ensuring high sensitivity and resolution for applications requiring
trace level detection.
Total flow to the interface is measured by a flow sensor and is divided into
two streams. One stream connects to the purge regulator; the other connects
to a frit block. At the frit block, the flow is further divided. The first stream
goes to the gas-phase sampler and from there is introduced into the interface.
The second stream, called the pressure sensing line, passes through the frit
block and is measured by a pressure sensor. This stream also provides a trickle
flow to the interface.
There are three modes of operation available—split, splitless, and direct. The
pneumatics vary for each operating mode and are discussed in more detail
later in this chapter. The volatiles interface is not supplied with manual
pressure control.
Split mode
When you introduce a sample in the split mode, a small amount of the sample
enters the column while the major portion exits from the split vent. The ratio
of split flow to column flow is controlled by the user. The split mode is
primarily used for high concentration samples when you can afford to lose
most of the sample out the split vent and for samples that cannot be diluted.
During Pre Run, during sampling,
and
after sampling,
total flow to the
interface is measured by a flow sensor and controlled by a proportional valve.
Flow at the head of the column is back-pressure regulated. Pressure is sensed
upstream from the proportional valve.
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Страница 27: ...24 of 24 Jun 2001 Contents Contents Agilent 6890 Gas Chromatograph Service Manual ...
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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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