8
Installing an Auxiliary Pressure Control Module
Install the new module
Changing the flow restrictors (optional)
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.
Figure 1 and Figure 2 show approximate pressure/flow relationships for the
three dot frits, assuming there is no significant 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. You may
also want to use the restrictor kit that comes with this accessory. Its
installation document describes using it for the 6890 GC, but still applies to
the 6850 GC.
Frit marking
Flow resistance
Agilent part number
Blue Dot
High
19234-60660
Red Dot
Medium
19231-60770
Brown Dot
Low
19231-60610
None (brass tube)
Zero
G1570-20540
