HP 5890 Series II Plus Reference Manual page 187

Preventive Maintenance
Nitrogen-phosphorus detector (NPD)
All collectors should be washed off with GE grade hexane or a similar
solvent before reinstalling in the instrument to remove any grease,
fingerprints, or other contaminants. Soak the entire collector in a vial of
hexane for several minutes (2-10). Remove the collector, touching only
the top portion, and scrub the lower, outer collector tube with a clean
wipe soaked with hexane. Dry off the excess hexane solvent.
Place a new O•ringon the collector and place it into the collector body
assembly from the top. Carefully position the collector tube so that the
bevel on the outer tube is positioned properly in relation to the bottom
edge of the collector body. Tighten the collector holding screw firmly
against the collector tube. This connection is both a mechanical
connection and an electrical contact.
Complete the collector assembly as follows: Wear clean, lint•freegloves
to avoid contaminating the collector assembly; (1) make sure the O•ring
is depressed into the groove in the collector body; (2) examine the
collector sealing gasket for wear or cracks and replace if necessary; (3)
place the stainless steel spacer/spring onto the collector/body assembly;
(4) place the Teflon spacer on top of the spring•the side with the groove
faces up; (5) if necessary, replace the bottom transformer secondary wire
into the hole in the collector body and tighten the setscrew onto the wire
connector.
Attach the brass collar to the top of the collector tube and tighten the
collar•holdingscrew. The smaller hole in the brass collar faces up.
Insert the top transformer secondary wire into the slot in the brass collar
and tighten the wire•holdingscrew on the bare wire. This must be a
good electrical connection, but take care and do not completely cut the
wire with the screw.
Carefully position the transformer/collector body assembly into the cover
and fasten the Teflon insulator of the collector body in place with the two
screws. Do not overtighten the screws into the Teflon and strip the
threads.
Carefully position the transformer with both end covers in place between
the threaded standoffs and fasten in place with the two screws. Place the
assembled detector cover in place onto the detector base and fasten in
place with the three screws.
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