40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Entry  Fri Oct 23 16:41:06 2020, Koji, Update, IOO, Excess laser freq noise investigation plot.pdf
    Reply  Mon Oct 26 13:35:58 2020, Koji, Update, IOO, Excess laser freq noise investigation 6x
       Reply  Mon Oct 26 17:26:26 2020, gautam, Update, IOO, Excess laser freq noise investigation 
Message ID: 15644     Entry time: Mon Oct 26 17:26:26 2020     In reply to: 15643
Author: gautam 
Type: Update 
Category: IOO 
Subject: Excess laser freq noise investigation 

Apart from the questionable wiring on the Acromags, one other important difference is in the way the connections were made between the old VME crates to the Eurocrate backplanes, and how we do it now. The thick cables had their sheilds connected to the eurocrate ground (or at least, there was a dedicated ground lug on those cables which we screwed on to the ground terminals on the Eurocrate backplanes). However, in our current configuration, we interface the Acromag ADCs and DACs to the backplane via these adaptor boards. The shields of the DSUB cables are presumably NOT connected to the Eurocrate grounds. This should also be investigated as one potential cause of the grounding issue - while on some of the Eurocrate modules, the P1/P2 connectors may have either the "A" or "C" row of connectors shorted to ground, some may not, and the TTFSS may suffer from such an issue?

Note that we have this problem in all of the slow machines that were upgraded to Acromag (if this turns out to be the issue). 


In fact, the problem was the grounding issue (presumably on the IOO racks).

ELOG V3.1.3-