Log entry time 20:32:14 on July17,2001

Entry number 66513

Followups:

• 66525 07/17/01 21:16 gilman helicity signals II

In the past two days, we (RG, WK, JP) have looked 

at the helicity signals to see if we can understand 

the origin of the helicity asymmetry problems seen.



1) Our "+" and "-" helicity signals originate from the "delayed helicity"

signal from MCC, with "+" the signal, and "-" the complement.



2) The basic scheme is, e.g., for + signal:

   signal --> 500 us delay --> start "+" latch --> ADCS, scaler gates, scalers

             \--> stop +-+ phase latch

  a) Lecroy gate and delays on right arm are digitally set to 500 us, both phases

      on scope agreed with each other and 500 us to < 10 us. Did not check better.

  b) Phillips gate and delays on left arm are screwdriver set to 500 us. Offsetting

      trigger on the scope, we could see both phases have delays set to 499-500 us

      with few tenths of us jitter.



3) We also looked on the scope at input +/- signals to see if they were constant

at about 33.3 ms (ignoring the occasional double widths from, eg, -++- helicity

sequence). Jitter in the pulse lengths appeared to be at the few times 10^-4

level, and there was no indication of systematic difference between "+" and "-"

phases.



Thus: there is no evidence that either input helicity pulse width variation

or setting of gate and delays can lead to the 10^-3 time asymmetries seen.

Note: time base stability of scope is unknown to me, and observations only

lasted for several minutes, so long term stability is uncertain.