jeffrey.kissel@LIGO.ORG - posted 12:49, Tuesday 16 May 2017 - last comment - 15:03, Tuesday 16 May 2017(36208)
HVAC Upgrade at EY means H1 SUS ETMY (and likely TMS) Has Drifted / Sagged
J. Kissel Charge measurements prefer the test mass suspension's optical levers be very well centered on their QPDs before starting. As I was centering the optics manually this morning, I found the H1 SUS ETMY suspension suspiciously low (pointed down) in pitch. After some investigation, I've learned that we're taking the opportunity during the break to upgrade the EY VEA HVAC system. After trending the optical lever, the L2 OSEMs in Pitch, and M0 OSEM in Vertical, coupled with the (formerly correct?) channel for temperature, I can see some sort of obvious, large, drift in the suspension that would be easily explained by VEA temperature excursions. I merely post this as a reminder that once we get the VEA temperature back under control -- and back to the VEA's former temperature set point, we'll need to re-assess ETMY and TMSY suspension alignments. For now, I've left ETMY with its alignment centered on the optical lever.
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A little more poking around reveals that the Y-End Beam Rotation Sensor also sees an effect of the HVAC upgrade's resulting temperature changes in the Y VEA. Namely, it shows / confirms the ~3 hour, +/- (1 deg F / 0.5 deg C) oscillation in temperature reported by the FMCS channel and by the ETMY optical lever (presumably the vacuum system's effective low-pass filter is filtering out this "fast" oscillation). Note, that the variance in the VEW temperature previously was only about (+/- 0.25 deg F / 0.1 deg C). Since this is seen in both the optical lever and in the beam rotation sensor, I'm quite confident that this is a real temperature swing. Further note -- the static temperature has also changed after the upgrade. We used to hold the VEA at 68.0 deg F / 20 deg C, but it appears as though the upgrade has left the VEA at 67.1 deg F / 19.5 deg C. This likely explains the long term sag / pitch of the ETM. John will write a more detailed log later, but upon pointing this out to him, he adjusted the HEATING OFFSET and COOLING OFFSET in the new HVAC control system in hopes to reduce the ~3 hour temperature oscillation. He changed the values from 1 deg F to 0.25 deg F (though the system echoed back that these are now set to 0.0 deg F). He'll work with Bubba to change the static temperature.
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J. Kissel Also note that PCAL Y sees a substantial effect of the large temperature excursions seen in the VEA during the upgrade as well, indicating that there is still some temperature sensitivity left in the system, like what was seen back in January (see, e.g. LHO aLOG 34153). The gross clipping has gone away since the temperature has *mostly* recovered, but -- presumably because of the 0.5 deg C difference in static temperature, the RXPD is reporting 0.2% higher displacement than before the HVAC upgrade. Further, one can see the ~3 hour oscillation in the RX and TX PDs.
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For the record I have changed two parameters in the ENDY VEA heat/cool control.
Both "Heating Offset" and "Cooling offset" were set to 1F. I reduced these both to 0.5 after discovering that the system would not accept 0.25. The setpoint is 68F (which it was before)
The control routines may need fine tuning to get back to the control level we had before this upgrade. We await the Apollo expert for this.
See the attached screen shot. An updated temperature trend is also attached and shows a response to our changes.
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