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Reports until 00:56, Wednesday 18 March 2015
H1 CDS
sheila.dwyer@LIGO.ORG - posted 00:56, Wednesday 18 March 2015 - last comment - 08:21, Wednesday 18 March 2015(17327)
can we trust DTT coherences?

Sheila, Kiwamu, Dan

We have had several occasions where we are trying to make a driven measurement, we can clearly see our drive orders of magnitude above the DARM noise, but we get no coherence according to DTT.  The first screenshot attached shows the coherence from my drive into the DHARD pitch loop to several channels that in principle all contain the same information:

H1:CAL-DELTAL_EXTERNAL_DQ, H1:LSC-DARM_IN1, and H1:LSC-DARM_OUT_DQ.  You can see all of these channels have different coherences, but I don't understand why.  Since I'm not driving the DARM filter bank, DARM IN and DARM OUT should be exactly the same information with a linear filter applied, and the CAL channel is the sum of these two channels with some calibration applied.  

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Comments related to this report
daniel.sigg@LIGO.ORG - 08:21, Wednesday 18 March 2015 (17332)

Hmm. Since OUT is the worst, followed by IN and then CAL, I am wondering if we get the single treatment?

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