aLIGO LHO Logbook

H1 SUS

nicolas.smith@LIGO.ORG - posted 15:20, Friday 07 November 2014 - last comment - 17:28, Friday 07 November 2014(14922)

Current monitor readback of ETMY L1 LR osem has offset, not obviously a problem

I wanted to see if our ETMY F2P problems were saturation related. So I looked at the current monitors for the L1 OSEMs.

One thing that was quickly noticed is that while the three others show <100 counts in the readback when there is no drive signal, the LR coil shows -4000 counts. (For scale, saturation occurs around 13000 counts for the three normal looking coils).

This would seem to indicate some problem, possibly removing a third of our range in one direction of one of our coils. However, when you actually drive the coils to saturation, they all seem to have the same range from the point of view of the DAC, just with LR readback offset from zero by 4000 counts.

So this could just be a problem in the readback, not clear without looking at the analog electronics.

Comments related to this report

jeffrey.kissel@LIGO.ORG - 17:28, Friday 07 November 2014 (14930)

Link

J. Kissel, N. Smith-Lefebvre

After Nic showed me some of the details of what he found, I saw that a lot of the channels had an offset of not just 4000 [cts], but an infamous value 4300 [ct]. This could very well be an old nasty problem in the analog electronics where one leg of the SCSI connector on the back of the ADC card in the IO chassis shorted. It's best described here:
LLO aLOG 1857
Most likely these offsets have been there since these chassis were first cabled up, and never fixed.

Other instances where this bug bit us:
LHO aLOG 5385
LLO aLOG 1853

I'll add this to Integration Issue 9, which continues to gather dust.