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    User name V. Sulkosky

    Log entry time 20:39:25 on October 26, 2008

    Entry number 244792

    This entry is a followup to: 244738

    keyword=BPM/Raster Work Summary

    This afternoon, I returned to the Hall to investigate and fix the
    BPM signals that were still saturating. In the end, I adjusted the
    attentuation and offsets to reduce the signals after the modules as much
    as possible. The signals are now, without beam, between -15 to -20 mV.

    I should warn we have run out of adjustment and there is no more range
    left on these boards. With these changes, we definitely need a
    Bull's eye scan. Until then, the BPM readout in spot++ will not give
    the correct beam position.

    A few notes:

    1) The signals from the BPMs before the attenuators are between -0.6 to
    -0.75 V. We expect these signals to be about 1 V, but from all my
    conversations with Bob, I thought these signals were supposed to be
    positive not negative.

    2) The attenuators are suppose to attenuate and invert the signal, since
    the 1881 these signals are plugged into expect a negative signal that
    will not saturate the ADC. We have typically set these modules so
    that the output after the module is less than -50 mV.

    3) As far as I know no changes were made to the BPM system or their
    readout in the spectrometers. The signals were teed-off at the
    patch panel behind the green wall to add the signals to the
    BigBite DAQ. We removed these connections and as I expected there
    was no change in the raw BPM signals as measured in the left HRS.

    4) After our tests, Bryan re-added the tees for the BigBite DAQ.

    5) I also checked the ADC gate width for this TDC, I found it to be
    about 250 ns.

    My big concern is that something unexpected happened and changed in the
    system. At the moment, we are unsure what that was, but it might have
    to do with the signals' polarity.

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