User name R. Michaels
Log entry time 16:42:18 on July20,2006
Entry number 174574
This entry is a followup to: 174525
keyword=L-arm offset too high; gates too wide (BPM)
Ok, I think I know what's wrong now with Left-arm BPM readout.
The data with autogain but beam off shows saturation on 4
channels (note, 2 BPM and 2 Raster), see fig 1.
The data with forced gain = 0 has no saturation on BPM, but of
course the two Raster signals that saturated were not affected
(obviously). Also the pedestals are wide on both HRS DAQs
because I think the ADC gate is too wide (250 nsec). Normally
for the BPM/rater ADC the ADC gate width is only 50 nsec. This
improves the headroom.
How the ADC works (apparently): For signals above 8192 channels,
you enter a "no man's land" and may get hits at 16384 (see peak at
far right). This is no good. Ideally, data should stay below 8192.
Therefore we need fine adjustment of negative offset, and narrower
gate width, such that both pedestal and data appear in the range.
Should have done it a week ago, admittedly ...