pep.covas@LIGO.ORG - posted 15:37, Thursday 15 June 2017 - last comment - 17:34, Wednesday 28 March 2018(36917)
New line at 86 Hz related to PCALX channels
A new line at 86 Hz has appeared in the DARM channels after the vent. After running BruCo, I've seen that that frequency was coherent with some PCAL channels: https://ldas-jobs.ligo-wa.caltech.edu/~pep.covas/bruco/1181560000/ I attach two different plots showing the differences between before/after the vent for the DARM channels and for three different PCALX channels . The "before" data is from 07/05/2017 09:00 UTC, and the "after" data is from 15/06/2017 09:00 UTC.
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I compared the de-whitened calibrated x-end Pcal TX PD channel (applying the appropriate [;1,1] filtering) with the de-whitened CAL-DELTAL_EXTERNAL just to check that the height is about right. Indeed, this does appear about right (see attached image). When H1 drops out of lock, we will perform some quick tests to see if we can determine what is wrong.
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Pep C., Evan G. We localized the time to when this line turned on, at 00:24 May 31 2017 UTC (see attached). Now we investigate what changed at that time.
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Evan, the frequency of the high-frequency calibration line we are running from X-end changed at this same time (plot attached). With large amplitudes of lines we are running, due to non-linear effects, they tend to produce many other lines in the spectra. It is possible that this is due to the current line (5950 Hz) we are running. We can definitely test this by changing the frequency and see if 86 Hz goes away (the line features strongly depends on what HF line we are running).
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Thanks for pointing this out, Shivaraj. It's quite weird how this is appearing, perhaps beating against other harmonics of the calibration lines?