HP 5890 Series II Plus Reference Manual page 183

Preventive Maintenance
Nitrogen-phosphorus detector (NPD)
3. Remove the Teflon spacer and stainless steel spring spacer from the
top of the collector body.
4. Loosen the setscrew in the Teflon portion of the collector body.
5. Grasping the collector at its top end (to avoid contaminating its
detecting end), withdraw it from the collector body. Some resistance to
this occurs until the O•ringseal becomes free.
6. Noting the following, reassemble in the reverse order:
7. Inspect the brass collar; note that the hole through it is slightly larger
on one side than the other. Install the brass collar onto the end of the
collector so the side with the larger hole is toward the collector body.
8. Press the assembly together firmly by pressing down on the brass
collar while holding the collector body. Make sure the sealing O•ring
has seated itself into the collector body.
9. While holding the assembly together, note Figure 8•16to verify the
collector is correctly positioned. If so, tighten the setscrew in the
collector body to secure the collector.
If the collector is extended too far beyond the lower end of the
collector body, it is likely the brass collar is installed upside down.
Reposition the collector in the collector body, reinstall the brass collar,
and press the assembly together again.
10. While holding the assembly together, replace the transformer lead
into the brass collar (loosening the setscrew further may be
necessary). Orient the collar so the lead is adjacent to the transformer
The O•ringseal should be placed onto the collector. The collector is then
inserted into the collector body from the top. Insert it only far enough to
extend a few millimeters past the bottom face of the collector body.
The stainless steel spring spacer must be installed with its tabs toward
the collector body (against the stainless steel portion).
The Teflon spacer must be mounted with its flat (ungrooved) side toward
the collector body (against the stainless steel spring spacer).
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