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    User name R. Feuerbach

    Log entry time 13:32:55 on March 28, 2005

    Entry number 142640

    This entry is a followup to: 142547

    keyword=Shifting of coincidence time

    Ramesh noticed that the coincidence time has apparently moved bewteen the two run periods. I believe this is related to the problem mentioned in 141597 with the Lecroy 1875A module used by S2 and for the coincidence time measurement.

    Occassionally, this module spontaneously "shifts" the effective time of the common-start used by the TDC. In the past, this shift has been on the order of a few nanoseconds.

    This is something that must be monitored by the shift workers, since it is possible for this shift to be large enough to push the S2 signals out-of-range. The short-term solution is then to power-cycle the Fastbus crate, which appears to restore the TDC to a sane state.

    A copy of this log entry has been emailed to: rsubedi