FYI: Relative timing of MPS and Helicity state signals seems to have shifted.

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User name brads

Log entry time 17:45:16 on October 21, 2009

Entry number 296014

Followups:

296017 10/21/09 18:17 brads NIM MPS signal quality to Moller DAQ is marginal (fixed for FADC Moller DAQ)
296908 10/29/09 14:36 E.Chudakov Moller - helicity signals

keyword=FYI: Relative timing of MPS and Helicity state signals seems to have shifted.

On August 7th I measured the relative timing of the MPS and HEL signals I took from the old Moller DAQ. At that time the Helicity signal lagged the MPS pulse by 25 usecs.
OLD timing

MPS ---------+            +-------------------------------------
             |____________|
              <- 500 us ->
             .
             .
HEL      ---------+ <----------- 33 ms -----------> +------------
             .    |_______________//________________|
             .    .
         --> .    . <-- 25 us

As of this morning the leading edge of the two signals are basically right on top of each other. CURRENT timing

MPS ---------+            +-------------------------------------
             |____________|
              <- 500 us ->
             .
             .
HEL ---------+ <----------- 33 ms -----------> +----------------
             |_______________//________________|
             .
          -->.<-- only a few hundred nanosec difference now

Note that this seems to be a shift back to the configuration of pre-2007. This is noted on Eugene's "Helicity signals" page here. Actually, now that I look more closely that link shows a 250us MPS interval, but the interval is now 500us (and has been at least since I measured it back in August).

Note that this shift impact the (old and new) Moller readouts slightly. The helicity status is readout at the MPS leading edge. Before it read the same helicity window status associated with the scaler information from that window. Now, the stored helicity will be for the NEXT helicity window (relative to the scaler data).

A copy of this log entry has been emailed to: rom, brads, gen, glamazdi, camsonne