PCM-2 Manual.pdf - Voss Associates

This test procedure defines the necessary operations to perform high voltage and gas
leakage checks required to verify proper and reliable performance of the original and revised
PCM-2 gas proportional detector designs. The high voltage test is required to check that the
detector does not exhibit excessive corona discharge or "arcing" at its nominal operating
voitage. Excessive arcing can cause the detector to be electrically "noisy". thereby reducing
its overall alpha sensitivity beyond thresholds defined for etfective usage in the PCM-2. The
gas leakage test is required to verify that the completed detector assembly has an adequate gas
seal. "Leaky" detectors can cause excessive and costly P-l 0 counting gas consumption and
lead to reduced overall PCM-2 detection performance.
The following tests apply to all three sizes of original PCM-2 detector assemblies (part numbers)
YP11534245, YP11534246, YP11534247) and revised PCM-2 detector assemblies
(part numbers) YP1l534560, 'YP11534561, YP11534562).
ARC TEST:
Equipment needed:
1. "High-pot" tester with arc detection capability and a voltage capacity
of at least 1800 vdc.
2. A source of P-l 0 counting gas regulated to approximately 5 psi.
3. Vacuum pump and vacuum gage ( 0-30 in. Hg vacuum)
4. I flat and rigid steel or aluminum piate measuring 8" X 38".
5. Several medium-sized C-clamps or bench-mounted quick fixturing clamps.
6. Several wooden spreader blocks.
7. Plastic tubing and detector hose-barbed quick-connect fittings as required.
8. Smoked Plexiglass or Lexan plate(s) 1/8" thick measuring 36-3/8" X 7-1/4".
19-5/8" X 6-1/2" and 8-7/8" X 6-1/2" tor long, medium and small probes
respectively.
Setup and testing:
This test can either be performed on completely constructed probe assemblies
or in support of mass assembly operations, on incomplete probes which have
only been built up to the point of mylar "facing".
I. First purge all air from the probe by flushing with P-I 0 gas. Because
the presence of air in the probe chamber can cause erroneously
successful test results, the noted purging procedure must be
closely followed;
a) For completed (myiar faced) probes. connect up the source of
counting gas to one of the probe's fittings and an exhaust hose to the
other allowing it to purge at a flow rate of 200 cc/min tor:
]0429-A525/PCM-2 Oet. Voltage & Leak Test Procedure/Revision/March ]994