I saw no flasher trigger on the scalers although the flasher was
on. Investigating with a scope in the D Tunnel, I noted the photodiode
signal was small (about 20-25mV). This signal gets split in half and then
sent to a discriminator to form the flasher trigger. The disc threshold is
set to 15mV, so it's not surprising there were no triggers.
I've sent the photodiode signal to a LeCroy PM amplifier before the
discriminator. There's a small negative DC offset then (-10mV). I've
changed the disc thr back to 25mV (as it was before 7/9, when we added the
flasher trigger). This discriminator also is used for Cerenkov signals;
25mV was the standard threshold before the flasher required 15mV.
Perhaps someone more knowledgeable about the flasher/photodiode can
improve the signal, and remove the amplifier, set the disc thr back to 15mV.
Karen
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