Loadlock Gauge problem/observations possibly crash related

Eric Perozziello eap at gloworm.Stanford.EDU
Sun Feb 17 17:52:26 PST 2002


Just a few extra details on the several problems this weekend:

Crashes seem to be related to a loadlock pumpdown timeout error. 
The pressure in the loadlock drops, and then seems to hit some 
kind of "base" pressure which is above the required (~80mT) setpoint
pressure for venting, loading, etc.  The "base" pressure is usually different
each time (from 120 mT to 700 mT).  

I can think of three possible causes of this:
1). pump problem
2). leak
or 3). gauge error.

Since it is intermittent, and sometimes pumps quite normally, 
and the leakup rate seems normal, 1&2 seem less likely.  Also, 
I've seen it pump down to "good" base, then fail on a subsequent
pumpdown with no actions that would create a leak inbetween. 

It seems as if the pirani CC gauge is giving a bad reading, but there
is no other readout to verify this reading (There is a baratron 
on the loadlock, but I don't know where to read this).  

-Eric



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