Around 2:30 on August 7, 2012 I attached 5 grounding plugs to the "TEST IN" connections at the Y end station.  At this time, all ITMY and ETMY coil driver boxes (for TOP, UIM, and PUM) have grounding plugs connected to each of the TEST IN connections.  I then took some power spectra measurements of the coil driver NoiseMonitor channels to see what effect the grounding plugs have on the coil driver noise.

Starting with ETMY, the UIM driver board didn't exhibit any significant change between COIL IN and TEST IN configurations.  This is because the noise in the coil drivers is dominated by component noise, and selecting the TEST IN state allows one to see the component noise without the added DAC noise.

The ETMY PUM driver board is dominated by DAC noise, since the PUM driver is not filtered as much as the UIM board in the lowest noise mode.  Therefore when we switch to the TEST IN state, the expectation is that the noise in all coil drivers should drop to the component self-noise level.  This is what we are seeing now, as compared to Jeff K's alog #3111 when the noise levels increased and the frequency dependence was different for those channels.

https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=3111

For the ITMY, the UIM behavior is generally the same as on ETMY coil drivers.  However, the ITMY PUM driver shows an increase in noise after switching to the TEST INPUT with grounding plug attached.