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Entry  Tue Feb 15 23:19:54 2011, Frank, DailyProgress, BEAT, some (minor) calibration problem found frequency_drift.pngfull_error_signal.png
    Reply  Tue Feb 15 23:33:51 2011, tara, DailyProgress, BEAT, some (minor) calibration problem found 
       Reply  Wed Feb 16 09:14:14 2011, Frank, DailyProgress, BEAT, some (minor) calibration problem found 
Message ID: 498     Entry time: Tue Feb 15 23:19:54 2011     Reply to this: 499
Author: Frank 
Type: DailyProgress 
Category: BEAT 
Subject: some (minor) calibration problem found 

Found at least two (minor) problems:

  1. So far i measured the zero-crossing of the mixer signal and both peak values and modeled the signal using a sine.
    For calibration i used the slope of the sine near the zero-crossing.
    As the frequency range for pi in shift is about 60MHz the function is almost linear for the range we measure over 24h (~2MHz).
    Today i measured the mixer signal in small steps and compared both techniques. The result surprised me a little bit:
    full_error_signal.png
  2.  

    it is not a lot of difference in slope but it is surprisingly linear over a range of 40MHz!

  3. the channel which contains the calibrated VCO monitor signal uses a wrong sign.
    The fit is right, but i remembered that i exchanged the BNC to 2-pole LEMO connector some time ago because it had the wrong sign.
    However, the frequency tuning curve i measured with the old (wrong) cable.
    I used the right sign on my computer but implemented the wrong one in EPICS, so that data was/is wrong. Will change that tomorrow.
    This can't explain the problems i had last week as i used Matlab to convert the monitor signal into frequency, not that channel.
    Anyway, this is how the data i took last night (19h) looks like using the right slope (see item 1):
    frequency_drift.png
    so i think once the EPICS channel is fixed we can trust that channel
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