K. Arai, J. Kissel

Implementing AC/DC watchdog for Quad/Triple SUS

AD/DC watchdogs have been implemented for Quad/Triple suspensions. The snapshot of one of the MEDM screens is attached.

Those watchdogs have different signal processing chains and thus have different purposes:

- DC watchdog monitors the positions of the OSEM flags and interrupt the actuation of that suspension level if any of the sensor signal hit the high or low thresholds.
- AC watchdog monitors the RMS values of certain signals and interrupt the actuation of that suspension level if the RMS reaches the threshold level.

The signals being monitored (i.e. OSEM sensor signals, OPLEV sensor signals, Coil outputs, etc) are individually processed by the filters called "band limiting filters". The AC watchdog employs the RMS module to obtain the RMS value of the signal. This RMS block has the time constant of ~7sec (See this entry). Then the output of the bandlim filters or those of the RMS blocks are compared with the thresholds.

Bandlim filters: For the DC one, this filter cleans up the sensor signals by attenuating at the high frequency (e.g. f>~10Hz) band where the sensor noise dominates the sensor output.  For the AC one, the filter usually employs "AC coupling" as we may not want to include the huge DC value of the OSEM output in the RMS calculation. One possible configuration for the OSEMs is to calculate the velocity of the signal by differentiating the OSEM signals (i.e. to multiply (2 pi f)). Again the high frequency components are to be attenuatedfor the same reason as the DC case.

Currently the bandlim filters are mostly empty (= do nothing). They are to be filled by the preparations scripts with easyquack.