From gilman Tue Mar 18 18:55:09 1997 Date: Tue, 18 Mar 1997 18:55:06 -0500 From: Ronald Gilman To: rom@cebaf.gov, bogdanw@cebaf.gov, mliang@cebaf.gov Subject: fpp fake helicity signal documentation Cc: gilman, rutt@cebaf.gov, jones@cebaf.gov Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Content-MD5: bJAGuqcyb0KNnZ6SuJ4VNg== I have setup a fake helicity signal generator, and brought the signals to the hadron arm detector stack. The details: Generator: LeCroy 2323A dual gate and delay in slots 3+4 of CAMAC crate at bottom of rack CH01b06, in Hall A counting house. The outputs from this module appear to be ~ -0.7 V, less than (what I think of as) the NIM standard -0.8 V. Thus, the delay outputs do not retrigger the module; I rediscrimate them first. The signals are currently set to be 33.3 ms long, with time between signals of ~ 40 ns. The signals go downstairs to the equipment aisle through patch 1H75B03, numbers 17+18. The signals are connected with 4 foot BNC cables to the patch to the hadron arm "nose", through numbers 9+10. At the back of the detector stack, 10 foot BNC cables bring the signals to patch 161B, numbers D5+D6, which takes them upstairs to the top level of the stack. I checked the signals on the scope; I see signals like those upstairs, except for ~us rounding of the edges. The difficult part of putting the simple correlated test helicity scheme remains to be done. rg From gilman Mon Mar 24 18:10:05 1997 Date: Mon, 24 Mar 1997 18:09:57 -0500 From: Ronald Gilman To: segal@cebaf.gov, rom@cebaf.gov, mliang@cebaf.gov, jones@cebaf.gov, bogdanw@cebaf.gov Subject: helicity gating ... for this weekend Cc: gilman, rutt@cebaf.gov, kum@cebaf.gov Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Content-MD5: rYI2S8R7jbEu36FGF89thg== The helicity gating circuitry is set up on the hadron arm. Mark and MeMe have seen it. The boxes are in the bottom / NIM crate in the center rack upstairs in the hadron arm. For each helicity channel, the circuit looks as follows... signal | | linear fan out-----\ | | | | GO output Phillips gate+delay | from TS 150 us delay | | | | | | | | Phillips gate+delay | assorted level regenerate ~17 ms gate | shifting | | | | | | | | | input a input b input c LeCroy 465 coincidence module linear output logical output (100 ns wide) | | / \ | / \ | gate FB event to ``mlu/ts'' for ADC ungated and helicity scalers gated scalers The 150 us delay time is to blank off the polarization stabilization period of 100 us, with some saftey margin. Re-AND-ing with the input pulse makes sure the trailing edge of the gates are fine. The gas Cerenkov scaler is the nominal "h-" scaler, while the spare scaler is the nominal "h+" scaler. The other scalers are unchanged. (Maja is currently using the scintillatorL.R scaler for aerogel Cerenkov.) The scaler channels used are 9/10 for +/- on each of the 3 "mlu/ts" scalers. Other than the fact that the ``first'' and ``last'' helicity pulses in the run may not be a full 1/60 s long, the scalers for the two helicities should be ~equal, about ~50% of the ungated scaler -- note however that the "h+" scaler all the h+ pulses but no h- pulses, and similarly for the "h-" scaler. For the event data, I have put the long helicity gates into: h+ gate into channel 15 of the S1 and gas Cerenkov 4413 discriminators h- gate into channel 16 of the S1 and gas Cerenkov 4413 discriminators So by looking at the detector map, it should be clear on which ADC channels to look for pedestals / overflows. The only remaining issues are to perform a few cosmic checks of the system (all scalers count the same if un-helicity gated, helicity gated scalers count ~1/2 ungated scaler), and to bring the real helicity signal into the hut. Too, it would be good to familiarize a selected few additional people with the logic. If you disagree with this setup, please speak to me before you change things on your own. We need all this capability for our data this weekend. rg