corey.gray@LIGO.ORG - posted 11:43, Monday 28 June 2010 - last comment - 13:40, Monday 28 June 2010(31)
Swapping H3 GS-13 From Assy #1
It has been shown there have been issues with our H3 GS-13. Before pulling out the GS-13, the ISI table was visually checked for mechanical shorts (none were found). As another system/pod check, the ISI table was tilted in a couple of different states(by placing weight on table) such that the pod would be angled "down" & angled "up". H3 is unique in that it is the GS13 whose axis is perpendicular to the Support Tubes (vs. H1 & H2 who are symmetrically angled wrt the Support Tubes). For our set up, the "crane-Southern" Support Tube is the side where the "TOP & unfixed" end of the H3 GS13 is. The "crane-northern" end of the GS13 is where the "BOTTOM & bolted-down" end of the GS13 is. Because of this geometry, it was easy to put weight on the table such that we tilt the TOP or BOTTOM of the GS13. With the TOP tilted down, we did not notice any change in the H3 performance (we were looking at DataViewer, the signal looked noisy, and would only show big seismic bumps and then quickly damp that out, and return to the noisy state). With the BOTTOM tilted down, H3's performance totally changed---for the better. H3's signal looked like its fellow H1 & H2. A Power Spectrum confirmed that H3 looked like the other GS13s when the BOTTOM was tilted down. The attachment's top plot shows the GS13s with the ISI weight down on the Northern end of the table. The bottom plot shows a balanced & unlocked ISI from last week (where we had an ugly H3). After this, we decided to swap this GS13 for our one & only extra Horizontal GS13. For documentation, there is a Serial Number on the base flanges for these guys. Original/old H3 GS13 is S/N 046 New H3 GS13 is S/N 068 Will post performance of our new H3 after the swap is made (not a trivial or quick task).
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Entry above was made by Corey Gray (When I'm logged in, not sure why I have to enter the "author name" every time I do something here).
[Corey, Hugh, Jim, Mitchell] Back in business! After about 90minutes we had a new H3 ready to go. Like I said it wasn't trivial. It took 3 people garbed up inside working for 90minutes. There are also tons of bolts which had to be dealt with--always scary because one always has the fear of possibly galling a bolt. But yes, once the GS13 was securely installed, one could clearly see that its signal on Dataviewer was much better (and more like H1 & H2). The table is probably not ideally level (due to the swap work), but went ahead and ran a high-resolution power spectrum [attached], and the results clearly point out a better looking H3. As for the old H3 GS13-- * When was it last tested? (right before it was sent up?) * What should we do with this GS13? (send to LLO?) * Do we have any more spares? (we just have one Vertical spare now)
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