PCM-2 Manual.pdf - Voss Associates

18. Hold the probe upright with its open face facing slightly downward and blow all internal
surfaces clean with canned air or dry nitrogen gas.
CAUTION:
DO NOT use compressed shop air in-line hdJiil"Rcai!1lts wiii contami.nate Rilil:enrnai
probe chamber surfaces.
19. Lay the probe face-down onto a unifonnly stretched and canned air "hlown" mylar sheet
kaving a minimum 2 in. wide mylar excess all around. Mylar should be stretched onto a
clean smooth sheet of cardboard to avoid puncturing the mylar and for subsequent razor blade
trimming. Apply a very thin spread of clear vacuum grease (DOW-CORNING High
Vacuum Grease # 976) to the outer flanges of the probe chamber all around. Install the ......
20. Cut two 2 in. long lengths of double-sticky conductive copper tape and affix at each of the
probe's short sides. off-center, with one end of the tape near the gasket face per print. Seeure
the tape finnly to the gasket and down onto the external (back) surface of the probe chamber
and peel off the remaining tape liners.
21. Trim the mylar around the probe with a sharp razor blade and smooth mylar over gasket on
all four sides and over onto exposed copper tape at ends. Neatly gather up the mylar at each
corner of the probe and laying and Scotch tape it over onto its baek surface.
22. Lay the probe chamber ring (outer frame) face-down on bench and insert prepared probe
chamber face-down into it pushing down uniformly on the probe all around until mylar face is
firmly seated against the inside surface of the chamber ring. If excessive resistance is
encountered between the chamber and ring remove the prepared chamber, apply a thin
film of clear liquid silicone lubricant to the inner sides of the ring and then reinstall the
probe chamber.
23. Trim the excess mylar around the probe at the edge of the chamber ring with a sharp razor
blade, making sure to trim around and not cut through the two mylar/cooper tape pieces at
each of the probe assembly. Cover each of these mylar/tape pieces over with lengths of
Scotch tape.
24. With the probe assembly face-down on a flat rigid surface, apply a uniformly distributed
clamping force on the back surface of the probe chamber so as to compress the probe gasket
.005 to .015 in. all around, thereby creating the necessary gas seal. A set-up of wooden load
spreader blocks and C-clamps or bench mounted quick-clamps works well for this clamping
operation (reference Figure 1).
25. With sufficient clamping force applied to the probe assembly, install the spring clips in the
slots grooves located all around on the ring and chamber respectively per print. If the detector
is being rebuilt with used spring clip parts, bend each of the spring clips back to a 90 degree
or slightly acute angle with a pair of pliers prior to reinstalling them onto the probe assembly.
If the spring clips show any crazing, cracks or other signs of work hardening fatigue or if the
11000-A308/PCM-2 Det. Assy. Procedure/Revision/March 1994 6