PCM-2 Manual.pdf - Voss Associates

This revised PCM-2 gas proportional detector design operates at voltages which approach the
physical limits of corona and arc discharge detection probe of its type. It is therefore very important
that the detector chamber is clean and free of any sharp metal burrs or raised metal scratches to
preclude any potential for corona discharge at normal operating voltages. A visual inspection of the
probe chamber prior to assembly and a conscientious effort to ensure its cleanliness throughout the
assembly process are essential in order to successfully build PCM-2 detectors. The following
manufacturing process steps must be performed in the order listed for all three sizes of PCM-2
detector assemblies to maximize their consistency and performance and to minimize the potential for
high voltage test failure.
This procedure is outlined for the production build of new detectors using new component parts
which are ready for assembly. For fielded detector assemblies which are to be rebuilt, complete
disassembly must first be performed and the components restored to their original surface finish and
cleanliness conditions. This requires that the retaining spring clips be removed and reformed to their
original 90 degree shape, the mylar face discarded and the internal anode wires removed and
discarded. Then remove the plastic or brass elbows and plastic quick-connect couplings hom the
probe chamber. The high voltage insulator(s) and banana jack(s) can then be removed and the high
voltage jumper wire(s) unsoldered from them. Removal of the PTFE (teflon) turret posts, caps and
brass turret spindles is not recommended, however, it will be necessary to remove the two turret caps
at each channel end in order to replace the anode wire springs there. If the PTFE turret assemblies are
damaged or for any other reason require replacement, they should be manually unscrewed from the
press studs on which they are installed. Removed turrets should be replaced and not reused in the
detector assembly. The probe chamber shall at this point be ready by rebuilding per the following
process steps.
For assembling PCM-2 gas proportional detector assemblies VP11534560, VP11534561 and
VPl1534562 perform the following:
1. Remove the probe chamber from the plastic bag packaging and, with gloved hands. visually
inspect the probe chamber for any noticeable nicks, scratches, burrs or other raised metal on
the bottom and sides of the pan and around the pipe threaded holes. Lightly sand and/or
Scotchbrite any raised metal or scratched areas to restore to a smooth surface finish. Avoid
over-abrading so as not to break through metal surface finish or plating. If all internal
surfaces of the probe chamber are clean and uniformly smooth and scratch-free, proceed to
step 4.
Wipe any abrasive residue from the pan with a clean lint-free cloth and isopropyl alcohol.
Thoroughly clean by scrub washing the internal surfaces of the detector pan using a soft bristle
brush and a mild detergent and hot water solution.
3. Rinse the detector pan thoroughly with hot water. Wipe away excess water with a clean lintfree
cloth or "Kim-Wipe" and blow dry all internal surfaces of the probe chamber with dry
nitrogen.
11000-A308/PCM-2 Oet. Assy. Procedure/Revision/March 1994 2