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User name R. Michaels
Log entry time 20:07:47 on January 16, 2005
Entry number 139388
This entry is a followup to: 139364
keyword=re: negative deadtimes
For halog end-of-run entries, the deadtime uses the final scaler reading,
so it can be a problem(fixable) if T7 or others roll over (high rate).
For datamon, the deadtime is differential over 4 sec. I think it is
true that when T7 rolls over it appears negative but still increases,
so the differences are still ok except at the moment of rollover.
I will check to see if this is true but someone can comment if they know.
Deadtime may also appear negative if the beam is unstable, particularly
if prescale factors are high. This is correctable offline. Another
reason for bogus deadtimes could be double counting in scalers, which
is dangerous.
If datamon shows nonsense during STABLE beam, give me a call and I'll
check it. In that case it needs to be understood and fixed.
A copy of this log entry has been emailed to: reitz@jlab.org,gayou@jlab.org,saw@jlab.org