12 Maintaining the NPD
To Replace the NPD Bead Assembly
Maintaining Your GC 195
16 Close the NPD cover, install the GC detector top cover, and install the electronics top cover.
All covers must be closed to get a stable NPD baseline.
17 Exit maintenance mode. Select Maintenance > Instrument > Perform Maintenance >
Maintenance Mode > Finished.
18 Restore normal NPD operating gas flows.
19 With all gases on, heat the detector to 150 °C and hold for about 15 minutes, then increase
the temperature to 250 °C and hold for 15 minutes.
20 Increase the temperature to operating value (310 to 320 °C recommended). Allow
15 minutes for equilibration.
21 Check the NPD leakage current. See “To Check the NPD Leakage Current” on page 201. If
> 2.0 pA, verify bead installation or see the Troubleshooting manual.
22 If using an Agilent data system, connect to the instrument.
23 Restore the analytical method. Confirm the detector hydrogen, air, makeup gas flow rates.
24 Start the Adjust offset process. Enter the desired offset in the Target offset field.An offset
of 25 to 30 pA is sufficient for most applications. The bead life may be shortened at a
higher offset.
25 Reset the bead counter.
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