Epc Overview; Repairing Epc Modules - Agilent Technologies 7820A Service Manual

EPC overview

Repairing EPC modules

126
Agilent 7820 GC Service
An Electronic Pneumatic Controller (EPC) module senses gas
pressure or mass flow and controls that pressure or flow.
There are 3 kinds of EPC modules:

Inlet flow modules

Detector flow modules

Pneumatic control modules (PCM)
Inlet modules are each designed for specific inlets.
A PCM has one control channels, intended for carrier gas.
The 7820A can control up to 4 EPC modules. Each has a
particular purpose and is limited to a particular location in the
EPC carrier.
Repairs on EPC modules should be in this order:
1 Verify the EPC module is receiving 24 VDC power, the green
LED is ON, and the EPC appears configured in the GC
display.
Compare the Communication buss connection with an adjacent
module that has a good power and signal connection.
If detector flows are incorrect, reload the correct frit values for the
detector body.
Replace proportional valve or valves for flow or pressure
problems.
Replace the module only after checking items 1 and 2 (when
dealing with power issues).
Repairs should be verified by the following:

Zero the pressure channels before performing any
verification tests.

Inlets: With the inlet capped, perform pressure decay test.
With column installed, compare calculated flow reading from