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MPS signal problem durring HAPPEX

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    User name M Friend

    Log entry time 17:39:27 on February 4,2010

    Entry number 309173

    Followups:

    keyword=MPS signal problem durring HAPPEX

    During HAPPEX there are several Compton runs where the FADC DAQ MPS scaler counted 2 MPS's during a single CODA readout (see Compton run 19457, for example). It was originally thought that this was due to the DAQ taking too long to read out some MPS's. This is not the case however. Instead, when this happens, no helicity reads are missing: the MPS scaler gets 2 counts but the helicity pattern is not missing any events. Furthermore, the double firing of the MPS signal only happens between 0->1 helicity transitions, so that the MPS double firing MUST know about the helicity board setting.

    As an example, the pattern of helicity reads (where -1 represents an extra count in the MPS scaler) looks like:
    0 -1 1 1 0 -1 1 0 0 1 0 -1 1 1 0 0 1 1 0 1 0 0 -1 1 1 0 0 -1 1 0 1

    The theory is that sometimes the MPS signal is slightly ratter (between 0->1 helicity transitions) and is double firing our scaler. HAS ANYONE ELSE NOTICED A RATTY MPS SIGNAL? This signal comes directly from a counting house patch panel.