Flow and Pressure Control Part 1. Electronic Pneumatic Control (EPC)
Auxiliary channels
66
Auxiliary channels
Three additional auxiliary pressure control channels are available as an option.
They are controlled by the Aux 3, Aux 4, and Aux 5 tables (Aux 1 and 2 are heater
controls).
If an auxiliary channel is specified as the Inlet during column configuration,
the channel allows run time programming as well as three-ramp programming.
The most common case of this is when a gas sampling valve is used.
The auxiliary 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:
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.
Frit marking Flow resistance Part no.
Blue Dot High 19234-60660
Red Dot Medium 19231-60770
Brown Dot Low 19231-60610
None (brass tube) Zero G1570-20540
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