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    User name R. Michaels

    Log entry time 11:33:37 on April29,2008

    Entry number 235792

    Followups:

    keyword=HAPPEX DAQ tests

    There's no beam until ~3 pm, so we do some tests of the HAPPEX
    DAQ to see if it screws up the helicity (last week's observation).

    Run 4381 ... mostly T8 ... check baseline performance
    --> helicity looks ok

    Run 4382 ... deliberately unplug helicity pulse (check if
    it's what we're looking at). --> helicity all -1 (and some 0
    due to MPS blanking). -> ok.

    Run 4383 ... repeat of 4381

    Next we run HAPPEX DAQ.

    Run 4384 ... with HAPPEX DAQ run 40837.
    We can see in the data that the "simplified" helicity looks good,
    and also looks good on a scope. However, the "complicated" helicity
    (result of 3 gate generators) is indeed screwed up on a scope.

    Run 4385 ... using "complicated" helicity. Still running HAPPEX.
    --> See the bad asymmetry (hel +1 more than hel -1). This
    reproduces the problem observed last week.

    Run 4386 ... back to "simplified" helicity. Still running HAPPEX.
    --> helicity ok again.

    Looking at the signals on a scope, I found that a signal from
    channel 0 of the FLEXIO of HAPPEX DAQ was causing the problem.
    It goes to a NIM/ECL chan 14 which is adjacent to chan 13 where
    the helicity feeds in. A glitch appears on this signal which
    fools the gate generators. This must be due to crosstalk through
    this NIM/ECL module. The output of chan 14 goes to the patch
    panel on a cable labelled "Moller synch". I asked E. Chudakov
    about this and he will check later (question is: why does Moller
    need a signal from HAPPEX ? If it doesn't can we remove it ?).
    We will continue to use the "simplified helicity" (bypass the 3
    gate generators) but I would also like to unplug the cable from
    HAPPEX DAQ FLEXIO chan 0, since I think it plays no role.