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    User name gilman

    Log entry time 14:43:34 on January 9,2003

    Entry number 91216

    Followups:

    keyword=helicity setup

    After Bob's confirmation with the VTOF that we really are delayed 9 cycles, instead
    of 8, I have tweaked the timing of the delays we put on the helicity and QRT signals
    that we send to the spectrometers.

    We use the transitions of the helicity signal to generate 200 us delayed
    start and stops which are then used to generate the delayed helicity signal.
    We delay it 200 us so that during the 500 us MPS=false time, we can readout
    the scalers with T9 event and get the helicity of the last pulse (that is, the helicity
    of the pulse presumably 8 pulses earlier when in the usual delayed reporting
    mode) that was integrated by the scalers. I have changed the delay from
    200 us to 350 us. It should be stable to a couple us.

    (Aside: MPS is the signal that tells us when the helicity is stable. It is
    roughly true for 33 ms, false for 0.5 ms, and iterate...)

    The QRT signal tells us when it is the first pulse of a group of 4.
    The pattern is always +--+ or -++-, chosen pseudorandomly,
    so one can always uniqely find the first one, in the middle of 1001-0110
    or 0110-1001 patterns, for example. But QRT makes recognizing the first
    one trivial.

    The QRT pulse is generated by a 200 us delay, and has a fixed "33" ms
    width. Over time, the module width had narrowed a few tenths of a percent,
    so that the T-->F transition was 100 us delayed, whereas the F-->T transition
    was delayed 200 us. Since Seonho's analysis saw only QRT=False for the T9,
    this leads to the suggestion that for unknown reasons we typically read out the
    scalers 150 +/- 50 us after MPS goes false, rather than nearly instantly as
    we expect. I have readjusted the width of the QRT pulse, and increased the
    delay to 350 us.

    We have just started runs 20244/1243 (no, I don't know why we are out of sync.)
    with this adjusted timing. It would be good to see if we see QRT=True in 1/4 T9 events.