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