200 Agilent 7890 Series Troubleshooting
8 Troubleshooting Tasks
To Measure NPD Leakage Current
1 Load the analytical method.
2 Set the NPD Adjust Offset to Off and the Bead Voltage to 0.00 V.
• Leave the NPD at operating temperature.
• Leave flows on or off.
3 Press [Front Det] or [Back Det], then scroll to Output.
4 Verify that the output (leakage current) is stable and
< 1.0 pA.
5 The output should slowly drop toward 0.0 pA, and should
stabilize in the tenths of a picoamp. Current > 2.0pA
indicates a problem.
If the current is > 2.0pA, do the following:
• Inspect the jet for contamination.
• Check the column or column adapter fitting for leaks.
• Ensure that the metal sealing ring is not crushed or
misaligned. See To Maintain the NPD Collector, Ceramic
Insulators, and Jet
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