Krishna
I took a quick look at the data from the PEM STS at EndY, which is mounted on the BRSY platform. The channels are mentioned in 33533.
First plot shows the GND STS (used by SEI) and the PEM STS converted to angle units (by multiplying by w^2/g) in comparison to the BRSY - rX. The wind-speed during this time was less than 2-3 m/s. The GND STS sees less signal than the BRS below ~50 mHz, but the PEM STS sees a lot more. The second plot shows the coherence between some channels and the third plot shows the X-direction signal. The Z channel is not recorded so I can't access it through ligodv-web.
The source of extra noise in the PEM STS could be - a) Insufficient mass centering or b) Extra temperature noise either on the STS case or the table it sits on; more insulation to the table and the STS case might help...
When allowed (Tuesday?) we could go check the centering and center it up as needed--Hugh
On Tuesday went to EndY to Check on and Center the PEM STS Masses
Upon arrival checked the mass measurements right away: U V & W were -3.7 -1.8 & -12V. The X axis is generated from U V & W but the Y signal comes just from V & W. See manual for axis mapping.
While the W mass is clearly out to lunch, U is also high >2volts. However, as W contributes to both X & Y signals (but with different weightings) you'd think both X & Y signals would be noisy. One might even argue that Y(North on STS Manual) would be even worse than X.
This morning, Thursday ~0930pst, with an IFO Lockloss, we went to the VEA again to check and found the U V & W masses exactly where I recorded them almost two days ago after nearly two hours of centering attempts: 9.9 12.9 & -13.5V. After recording the voltages this morning, we hit the centering button and left the VEA.
Now see the attached 60 hours of minute trends. Before the Tuesday mass centering activity, the X & Y time series values suggest fairly zero'd signals; I did zoomed in and they are. During the interum ~2 days before this morning's look, the Y signal was pined to a rail. Noting my U V & W voltages, before Tuesday just W was on it's rail but after Tuesday, essentially all 3 masses were at or near a rail. This further suggests you can not just look at the X Y & Z signals to assess the mass centering.
So, clearly, waiting for the masses to come off their rail did not yield results. In addition, it appears there is a higher frequency noise on the channels showing up on X after Tuesday and now on Y after this morning's centering.. We will go measure the mass voltages when allowed. I did leave some leads hanging off the monitor port for voltage measuring but they are mostly insulated and I don't think they are causing noise. However, we'll remove these next time just in case.
Meanwhile, the positive glitches seen on the time series (average is still under the min trace but the max [black] is way higher than the average) are not continuous. I guess these show up as the 1/f noise starting around 40Hz on the spectra, second attachment. The reference traces are 1200utc 31 Jan (before the Tuesday activities.) Note the higher noise on the X (pink) trace compared to the Y signal (cyan.) I checked the wind, it did not seem to be an issue at that time.
I have to just throw this in and run.
Here is a comparison of the SEI Ground STS and the the PEM unit on the BRS. These have some gain difference I don't understand yet but I made them the same by multiplying by the ratio at the useism. At this BW, the PEM is not happy.
