corey.gray@LIGO.ORG - posted 21:41, Thursday 24 June 2010 - last comment - 09:37, Monday 28 June 2010(18)
Displacement Sensor & GS13 Spectra: What's Wrong With Our H3 GS13?
Today, dtt was used to obtain spectra for the LHO HAM ISI Assy #1 located at the SEI Test Stand. This measurement was run with the dial indicators disconnected. Two measurements were run: The first one ("T1") had H1V1H2V2 Displancement Sensors & ALL GS13's. The second measurement ("T2"), had H3V3 Displacement Sensors. Two measurements were needed because of the ~0.3Hz noise seen between both Displacement Sensor "mini-racks".
One blaring feature (see attached spectra) is the H3 GS13---something looks amiss with it. Checked the rack for anything obviously wrong, but all HAM Interface Chasis looked fine.
Vincent suggested putting a 300count vertical offset on the H3 Actuator, and this clearly showed something wrong with this GS13 (see attached screenshot).
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The screenshot I tried attaching above didn't seem to work (it was a .tiff screen shot from a Mac & was treated as a quicktime file when I tried clicking it from the log). Attached here is a .jpg version of the same file. Hopefully this works.
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I am attaching a Power Spectrum from last week. It looks like H3 was fine. Also, looking at the time series, it seems that there is some signal, but much lower (about two order of magnitudes on the power spectrum). Could it be a BIO filter improperly switched?
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Are Fabrice's spectra with the table locked, and Corey's without? The high-frequency (>10 Hz) structure has changed dramatically on *all* the sensors between those two spetra. If these two spectra were taken with the table in the exact same state, then this might be another clue...
(Vincent L., Richard M., Corey G.) There is no BIO for the SEI Test Stand. And yes, it should be noted that the spectra from Fabrice's post was from a couple weeks ago. It was a quick one we ran with the SYSTEM LOCKED (we were performing a quick check to investigate the 0.3Hz signal on the Displacement Sensor Mini-Racks). So, it was wrong for me to say everything looked good from that spectra--I had assumed assumed the ISI was un-locked. Last Friday, we performed a few more checks on the GS13. The most telltale check was a cable swap. From the "feedthrough interface", the GS13 Horiz/Vert cable runs to the H/V location. Here is a connection to a plug which splits into two separate cables--one goes to the Horiz GS13 & the other goes to the Vert GS13. We unplugged the H3/V3 cable here, and ran it to the H1/V1 cable. Dataviewer showed that the problem stayed with the H3-GS13 (i.e. H1 was now ugly). Therefore something is wrong with H3 GS13. Reconnected cables to their original configuration. As another check, we locked up the Table and ran another power spectrum [attached]. Sure enough, we had similar results to what we saw a couple of weeks ago (i.e. Fabrice's post)---where all the spectra, for the most part, look similar. Thinking their may be a mounting issue, or something wrong with the mechanical structure of the GS13 inside, we will take a look for any rubbing in the area of H3/V3. We'll then take off the H3 door, and perform some checks on H3 (while watching with DV & quick spectra).
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