User guide

158 Advanced User Guide
7 Flow and Pressure Modules
Pressure Control Modules
The PCM is a general purpose module with two independent
control channels, designated 1 and 2. The general name of a
PCM module is PCM #, where the # (actually, a letter) identifies
the PCM (there can be up to 3 installed).
The two channels are not identical. Channel 1 is a simple
forward- pressure regulated channel that maintains constant
flow through a fixed restrictor.
Channel 2 may be used either as a forward- pressure regulator
or as a back- pressure regulator, simply by reversing the input
and output connections. The back pressure mode can be very
useful with a gas sampling valve, where it ensures that the
sample pressure in the loop remains constant.