Hello there..
today I spent some time w/ Karen to look at this C/flasher issue. The
first thing that was pretty clear is that you can get 0-5 KHz of tube
noise with flasher off. Those signals are indeed several volts in
amplitude and there is not much we can do about it.
However, if my scope triggers on the flasher pin-diode out *then* - at
least for RC0 - I see pulses of about 1 V. There are all very stable and
reproducible and (by looking at their average on the scope) all well
matched. Only one tube in RC0 was maybe 30 % away from the average.
This is different then what reported yesterday (although I had to guess
that yesterday's shifts used the default voltages. There is no such info
on the messy logbook)
The tube noise is high but still not so high to bother us when we put a
C box in coinc with the signal from another detector (tof, paddle, nc)
We clearly can't trigger on the C itself in order to gain match since the
cosmic/flasher rate is <<< tube noise (KHz).
However, when checking gains with the flasher we can trigger on the pin diode.
A pulse of 1 V is still too high for the A-adder. I could reduce the pulse
height by either 100 or 30 % by simply "making a bad connection" upstairs.
Once I did try this and concluded it didn't work but of course I was also
triggering on tube noise then.. Instead, loosening the connection clearly does
work but is painful and slow.
I also tried to put a tiny bit of (transparent) tape on the input fiber
but this killed the signal completely.
Tomorrow I hope some of you will be around. I'll be happy to systematically go
over this. Check all input on the scope (have to be inside the analog adder range)
then take a true flasher run upstairs. Still for some boxes, the noise (defined
as total rate) can be some factors of 10/20 different... That I can not explain but
we'll hopefully understand it.
-- t
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Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124
research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
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