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Message ID: 2311     Entry time: Tue Mar 19 16:39:20 2019
Author: anchal 
Type: DailyProgress 
Category: FSS 
Subject: Need to track down 60 Hz spike source in FSS 

The bad news...

  • We were curious on actual actuation signal being sent to EOM by the TTFSS boxes.
  • So we opened the north path and hooked up clips to TP4 in D090183. This point is used for PCMON signal.
  • We found that there is a strong ~5V spike happening at this point at a rate of 60 Hz.
  • This spike rails the EOM and hands of the error correction to pzt which happens slower.
  • But when we increase the common gain in our circuit, this spike makes everything unstable at a much smaller gain then what we want to use.
  • This is clearly a leak from AC supply, from where and how is unknown at the moment.

The good news...

  • We got something to work at and hopefully this is our culprit.
  • If we get to remove this and increase our common gains high in FSS, we might get a deeper look in the noise.

Steps ahead:

☐ Reroute AC power cables separate from signal cables.

☐ Add chokes or loop cables around ferrite cores to increase impedance to ground loop current.

☐ Shield the FSS 37 wires cable with aluminium foil.

☐ Add a thick grouning from table to rack.

☐ Grounding all DC supplies to a single point in a star configuration with thick metal/wire.

☐ Check all DC power supplies if they are leaking these 60 Hz spikes.

☐ Removing the AC power strips from the table sides. Connect the camera power cables far way from table top.


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