100 Agilent 7890 Series Troubleshooting
4 GC Not Ready Symptoms
The Measured Column Flow Does Not Equal the Displayed Flow
If the actual column flow does not match the calculated flow
displayed on the GC within 10%, do the following:
• Verify that the measured flows are corrected to 25 °C and
1 atmosphere.
• Verify that the correct column dimensions are configured
accurately, including the actual (trimmed) column length.
• A short (<15 m) 0.58 to 0.75 mm id WCOT column is being
used with a split/splitless capillary inlet. The total flow
controller is set for a high flow rate, which creates some
pressure in the inlet and causes column flow even with a
setpoint pressure of zero. (In these situations, an actual
pressure may be shown on the display, even with a zero
setpoint.) With short, 530 to 750 mm columns, keep the total
flow rate as low as possible (for example, 20 to 30 mL/min).
Install a longer column with higher resistance (for example,
15 to 30 m).
• The split vent line or trap may be partly plugged, creating an
actual inlet pressure higher than the setpoint pressure.
Check for a restriction in the split vent line. See To Run the
Inlet Trap Check.
• If using a Mass Selective Detector, verify the column outlet
for the transfer line is set to MSD.
• Make sure that the auto flow zero is turned on. As applicable,
zero the flow and pressure sensor for the flow module. If this
does not solve the problem, replace the flow module.
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