HP 5890 SERIES II Service Manual page 46

Electronic Pressure Control 1 second to 99%
Safety Shutdown (Standard): If the system is unable to reach or maintain pressure set point value after
45 seconds the following 3 things happen. The alarm relay is triggered and the alarm sounds immedi-
ately. Pressure Control Valve shuts off all but a few ml/min of flow (bypass flow still permitted). The
oven and all heated zones are shut down.
This is a Fatal Error. The only way to recover is to power cycle the GC. If the leak has not been fixed,
the same sequence will repeat.
The Column head pressure may be controlled by either of two systems, Manual Presure Control (MPC)
or Electronic Pressure Control (EPC)
The MPC in an uncomplicated system consisting of 1) a manually adjustable forward pressure regulator
which sets the pressure in the inlet and 2) a factory preset forward pressure regulator allowing 10 to 20
ml/min to escape to vent pulling septum bleed with it.
Possible failures could include pluged restrictor in the inlet to the FPR. This would prevent the inlet from
reaching pressure setpoint. The FPR could be stuck open allowing the injection port to go to the same
pressure as the source gas tank. It could be stuck in the closed position preventing the injection point
from reaching the setpoint. Leaks in any of the tubing connections would also prevent the injection port
from reaching or maintaining pressure setpoint. Leaks at the Septum, Column fitting, Septum Purge
Control, Column Head Pressure gage or Purge Vent restrictor could also make injection port pressure
control difficult. These leaks should be checked by capping off the injection port or suspected part to
isolate it rather then using soap solution leak detection fluid.
The EPC uses a digitally controlled proportional control valve and electronic presssure transducer to
perform the same functions as the MPC' s manual forward pressure control and column head pressure
gage. One additional feature of the EPC is a bypass flow line designed to protect the column with a
small flow (.1 to 3 ml/min) in the event that the proportional control valve or electronics would fail. The
same plugging or leak considerations as the MPC apply with the addition of the possiblity of electronic
failures to either the proportional valve, pressure transducer or electronic control board. These will be
verified by substitution.
Symptoms and possible causes
Not enough pressure.
1. Septum leaks or is missing
2. Column is broken
3. Column ferrule seal leaks
4. Gas supply is off
5. Supply pressure may not be achieveable with the column is use.
Pressure goes to 0 or max.
1. Configuration is wrong
Not Ready light flickers
(oscillating pressure)
1. Septum and/or column connection leaks.
2. Pressure set higher than the operating limit
SVC 3- 3
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