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Reports until 08:57, Friday 14 August 2026
H1 CDS (DetChar, PEM)
david.barker@LIGO.ORG - posted 08:57, Friday 14 August 2026 - last comment - 14:59, Wednesday 26 August 2026(91537)
Corner Station PEM Accelerometer mismatch identified and fixed

Miranda, Dave:

Over the past week we have documented the LHO PEM accelerometers and produced an as-built  wiring drawing

This was in response to a possible misreading of accelerometer(s) with the wrong channel names.

We found three accelerometers with incorrect names, which date back to pre-O4, so I'm tagging DETCHAR.

The accelerometer Was being readout as this channel
H1:PEM-CS_ACC_LVEAFLOOR_HAM6_Z_DQ H1:PEM-CS_ACC_BEAMTUBE_SRTUBE_X_DQ
H1:PEM-CS_ACC_BEAMTUBE_SRTUBE_X_DQ H1:PEM-CS_ACC_EBAY_FLOOR_Z_DQ
H1:PEM-CS_ACC_EBAY_FLOOR_Z_DQ H1:PEM-CS_ACC_LVEAFLOOR_HAM6_Z_DQ

We fixed this at 16:00 Thursday 13th August 2026 PDT by remapping the BNC connections on the front panel of APC1. The cable going to port12 was moved to port13, that going to port13 was moved to port14 and that going to port14 was moved to port12.

We tap-tested the EBAY_FLOOR accelerometer at 16:10 and this showed up on H1:PEM-CS_ACC_EBAY_FLOOR_Z_DQ

Comments related to this report
mirandarose.claypool@LIGO.ORG - 09:39, Friday 21 August 2026 (91637)CDS, DetChar, PEM
Link

For detchar: Based on our (dave, robert, my) best guesses, this error starts on JAN 26th 2024 when the ENdevcos, as well as the signal conditioners for the accelerometers, were replaced (alog 75592). This is post end of O4a (Jan 16th 2024), so the data for O4a is okay, but the data for O4b/c is affected. This means that if there's an hveto round winner/trigger/pemcheck correlation/etc for one of the three channels on the right, it will instead be data from the detector on the left column. For clarity:

  • If the trigger says H1:PEM-CS_ACC_BEAMTUBE_SRTUBE_X_DQ, then the data is actually from the lvea floor accelerometer, H1:PEM-CS_ACC_LVEAFLOOR_HAM6_Z_DQ.
  • If the trigger says H1:PEM-CS_ACC_EBAY_FLOOR_Z_DQ, then the data is actually from the beamtube accelerometer, H1:PEM-CS_ACC_BEAMTUBE_SRTUBE_X_DQ.
  • if the trigger says H1:PEM-CS_ACC_LVEAFLOOR_HAM6_Z_DQ, then the data is actually from ebay accelerometer, H1:PEM-CS_ACC_EBAY_FLOOR_Z_DQ.

Here are some examples that I hope help clarify (as I was also confused):

  • When Dave and I tapped the ebay floor accelerometer with a pen, there was a spike on the ham6 floor accelerometer channel. So, H1:PEM-CS_ACC_LVEAFLOOR_HAM6_Z_DQ was incorrectly reading data from the ebay floor accelerometer and not the lvea floor accelerometer. 
  • Likewise, when Robert unplugged the srtube accelerometer, the ebay floor z channel disappeared. So, the H1:PEM-CS_ACC_EBAY_FLOOR_Z_DQ channel was receiving information from the srtube accelerometer.
  •  I've also attached spectra that shows a few days before and after the switch, Jan 25th and Jan 29th, 2024. You can see the channel names change for the different spectra while retaining the same shape.
Images attached to this comment
mirandarose.claypool@LIGO.ORG - 14:59, Wednesday 26 August 2026 (91694)CDS, DetChar
Link

Dave noticed that the switch on the power conditioner for H1:PEM-CS_ACC_HAM7_Y was set to x1 (visible in the wiring diagram, v6), while all the other switches were set to x10. Today, Robert and I went in and switched it to x10 at 11:30 AM PDT. We both believe this was related to the ENdevco replacements on Jan 26th, 2024. I looked at the spectra before and after replacement (Jan 24th, 2024 and Jan 29th, 2024, attached below), and then today after we flipped it. As you can see, the spectra now has the correct order of magnitude. 

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