= FM ILT Grating control analysis =

== Measurements (2nd FM ILT run) ==

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* Nominal:
   * Stability after homing not reproducable 
      * 22nd afternoon: 6 homings followed by stable situation (10 digits noise 
        peak-to-peak)
      * 22nd evening: no single home followed by stable situation (60 peak-to-peak)
   * Disabling/enabling the controller improves the stability
      * Disable : always brought the noise to few (3-4) digits peak-to-peak.
      * Enable : always brought the noise te 10 digits peak-to-peak
      * But a new homing or movement to extremes of the range degrades the stability
        again to 60 peak-to-peak.
   * High torque
      * Disabling the controller at extreme positions in the range produces 
        large amplitude swing-back (plot will follow)
   * Friction ?
      * Several disablings of the grating controller at position 500000 produced
        swing-backs in different directions.  To be checked if this is correllated 
        with the direction we come from (we have the data, looking into that now)

* Redundant: 
   * On the 21st in the afternoon and evening, disabling the grating controller 
     in the redundant chain did not reduce the oscillations.  During a 40 minutes
     measurement where we left the controller disabled, we collected enough data
     to have a good S/N in the hall sensor readout - in the plots in attachment you can
     see that a significant peak is seen in hall B and the inductosyn readout around
     8.4Hz.  Hall A was in a flat part of the sine curve.
     (FILT_GratingCharact_20070221_26_curPosHallAFft.png