Agilent Technologies 6890 Series Service Manual page 374

360 Auxiliary EPC
Theory of operation
The auxiliary EPC channels are controlled by a pressure setpoint. To work
properly, there must be adequate flow resistance downstream of the pressure
sensor. The auxiliary channel pneumatics manifold provides a frit-type
restrictor for each channel. Four frits are available:
Frit Marking
Blue Dot
Red Dot
Brown Dot
None (brass tube)
The Red Dot frit is in all three channels when the instrument is shipped.
The figures on the next two pages show approximate pressure/flow
relationships for the three Dot frits, assuming there is no significant
additional resistance downstream of the frits.
If the Zero resistance frit is installed, the user must provide flow resistance
downstream and generate the pressure/flow relationships.
WARNING When hydrogen is used, dangerously high flows are possible if insufficient
flow resistance is provided downstream of the supply tube. Always use either
the High (Blue Dot) or Medium (Red Dot) frit with hydrogen.
External flow restrictor (Type 2 manifold)
Use an external flow restrictor (part no. G1530-80380) on each auxiliary EPC
channel to be used for a flammable gas (i.e., hydrogen). The restrictor prevents
excessive gas flow in the event of a leak in the manifold or its input fitting.
External flow restrictor
Jun 2001
Flow Resistance
High
Medium
Low
Zero
Detectors
Agilent 6890 Gas Chromatograph Service Manual
Part no.
19234-60660
19231-60770
19231-60610
G1570-20540
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