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    User name Moffit

    Log entry time 12:28:20 on June 8,2004

    Entry number 124950

    keyword=Access Activities... HAPPEX Detector Pedestal Checks

    Noticed that the pedestal signal levels for the HAPPEX Detector and Profile Scanner in the Left Arm Happex DAQ were around 10k and very noisy.  Determined from this that I had used the wrong polarity TwinAx cable to plug them in to the Happex ADC.
    After switching the cables... noise in the HAPPEX Detector channel went down to an RMS of ~4.5chan... with a signal level of around 4.5k.  It appears to also respond in the correct way to changes in the LED pulser.  Profile scanner PMT also looks better.
    The right arm:
        The HAPPEX detector noise into the HAPPEX ADC is around 12-15channels (attachment 1).  Using a thick TwinAx cable with capacitor connecting the grounds, causes the RMS to go down to ~3.5channels (attachment 2).
        However... the signal is pretty much useless for counting mode.  Looks like quite a lot of ringing.  Removing the capacitor doesn't cure this effect (for counting mode).
    David and I decided to go back to using the regular RG-58 cable for now.  A move to use the thick TwinAx would mean a few hours of cable movement.. maybe we'll still have time later today (waiting for beam).

    FIGURE 1

    FIGURE 2