10 Settings
Operation Manual 143
Maintaining EPC calibration—inlets, detectors, PCM,
PSD, and AUX
The EPC gas control modules contain flow and/or pressure sensors that are calibrated at the
factory. Sensitivity (slope of the curve) is quite stable, but zero offset requires periodic
updating.
Flow sensors
All inlet modules use flow sensors, as do PSDs, and channel 1 of a PCM. If the Auto flow zero
feature is selected, they are zeroed automatically after each run. This is the recommended
setting. They can also be zeroed manually—see “To zero a specific flow or pressure sensor”.”
Pressure sensors
All EPC control modules use pressure sensors. They must be zeroed individually. There is no
automatic zero for pressure sensors.
Auto Zero flow
A useful calibration option is Auto Zero flow. When selected, after the end of a run, the GC
shuts down the flow of gases to an inlet, waits for the flow to drop to zero, measures and
stores the flow sensor output, and turns the gas back on. This takes about two seconds. The
zero offset is used to correct future flow measurements.
Auto zero septum purge
This is similar to Auto zero flow, but is for the septum purge flow.
Zero conditions
Flow sensors are zeroed with the carrier gas connected and flowing.
Pressure sensors are zeroed with the supply gas line disconnected from the gas control
module.
Zero intervals
Table 15 Flow and Pressure Sensor Zero Intervals
Sensor type Module type Zero interval
Flow All Use Auto flow zero and/or
Auto zero septum purge
Pressure Inlets
Small capillary columns
(id 0.32 mm)
Every 12 months
Large capillary columns
(id > 0.32 mm)
At 3 months, at 6 months,
then every 12 months
Auxiliary channels Every 12 months
Detector gases Every 12 months
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