Virgo Logbook

AdV-DAQ (Calibration)

rolland, estevez, mours - 19:30 Friday 17 August 2018 (42467)

Calibration shift

Modification of the calibration lines around 60 Hz and 355 Hz + addition of calibration lines with PCal

This is done in order to have frequencies multiple of 0.125 Hz to test Hrec with lower latency (test will be done with shorter FFTs of 8 s)

13h55 UTC, restart of CALnoise and update of the Hrec configuration

BS	WE	NE	PR	WE_PCAL	NE_PCAL
				35.0	36.5
61.0	61.5	62.5	63.0	60.5	63.5
356.0	356.5	357.5	358.0	355.5	359.0

A small line at 1012.5 Hz has been added to NE and WE calibration signals. Its amplitude have been set to be seen in SC_MIR_Z_CORR channel, but not in DARM. The goal is to monitor the injection path from Acl the to DSPs (in particular the delay) without being seen in DARM. This line will be monitored by the process TFMoni.

Injections with the PCals

PCal at NE and WE switched on at 14h10 UTC, with their three calibration lines. Note that their frequencies will be updated in the coming months for h(t) monitoring purpose.

On the NE and WE cameras, the small PCal beam spot is visible close to the center of the mirror when the main beam is switched off. The bright spot seen on top-right is an image of the PCal injection bench due to diffuse PCal light (1047 nm).

14h25 start some injections of lines with PCal and then with end EM actuators (this will be analysed to calibrate the EM actuators with respect to the PCals) (10 Hz to 200 Hz)
14h35 start injections from 10 Hz to 500 Hz
14h40 start injection of a single line around 80 Hz to compare results with previous measurements where a series of lines were injected

Note: NE PCal photodiode was not switched on during the measurements. Only the WE injections can be analyzed.

More usual calibration injections

14h45 to 15h measurement for calibration transfer from mirrors to marionettes.
15h manual unlock.
15h02 measurement of CAL to Sc delays.
15h05 start to relock with NI, WI relays kept closed in HP mode. We had some issues with "SSFS synchro", which was probably resulted from the LNFS being free. It worked once Julia had relocked the LNFS on the timing system. ITF relocked around 16h25 UTC.
16h35 to 17h measurements for calibration transfer from input to end mirrors.
Manual unlock
17h20 : Tune B1p phases at 6, 8 and 56 MHz and start free Michelson measurements.

Remarks

Suspension DSPs: the delays from the CAL channels generated by Acl to the Sc channels sent back by the DSPs are the same for all the mirrors (714 µs) as expected. But they are all different for the NE, WE and BS marionettes (between 980 and 1200 µs) while there where all the same at 915 µs in the past. Something wrong is probably on-going on the injection path to the marionettes.
There is still aliasing of the CAL channels into the Sc channels (see Sc_NI,WI,BS_MIR_CORR around 17h27 UTC)

Around 15h30 UTC, we found that the Vbias of PCAL_NE_PD2 had the wrong sign and fixed it. This is related to the replacement of the photodiode made during last week (6_9 August) to investigate the presence of a lot of 50 Hz lines in this photodiode. It is the same with the new one, so we will have to continue investigation. The offset of this channel must be retuned.

Comments to this report:

estevez, rolland - 18:27 Tuesday 21 August 2018 (42492)

First analysis of the PCal data from the calibration shift

PCal injections were done both on WE and NE with a new method called "Pcal to Mir". (Unfortunately, we did not manage to have data on NE because of photodiodes switched off.)
However, on WE, the analysis gave the model of the WE mirror actuator as shown in the figure.
The gain of WE actuator is fitted at 0.38 µm/V which is in agreement within 5% with the measurements at 0.40 µm/V done with the "In to End" method.

This result is encouraging since it is the first measurement we've done and the PCals are not yet fully operationnal.
The WE PCal is likely to have an uncertainty of ~10% on the power for the moment, but a more precise calibration of it will be done in the coming weeks with a better powermeter.

Images attached to this comment

rolland, masserot - 18:35 Tuesday 28 August 2018 (42556)

The "aliasing" effect seen on BS, NI and WI during the free Michelson data is also present on NE and WE. It looks like aliasing around 2.5 kHz, while the extension is done between channels from 10 kHz to 40 kHz, hence it is not really aliasing but some other effet, possible mixing of the sample order?

figure 1: LSC_CORR and Sc_MIR_Z_CORR for NE and WE : there is clearly some noise in Sc channels at high frequency
figure 2 : zoom on LSC_CORR between 0 and 1 kHz, and zoom on Sc_MIR_Z_CORR between 4 and 5 kHz. The structure of the LSC_CORR signals between 0 to 1 kHz are seen on Sc_MIR_Z_CORR between 5 and 4 kHz.

Images attached to this comment

rolland, estevez, verkindt - 17:10 Wednesday 29 August 2018 (42575)

Calibration lines at 1012.5 Hz to monitor the CALnoise to DSP actuation path

We have checked that the line at 1012.5 Hz sent to NE and WE since August 17th are useful for monitoring the actuation path from CALnoise to the DSPs. The first plot shows the coherence, modulus and phase of the transfer function from CAL_WE,NE,MIR_Z_CORR to Sc_WE,NE_MIR_Z_CORR, which has a very good coherence when the ITF is in LOW_NOISE_3 mode (the name of the channels is misleading : the TF are indeed computed at 1012.5 Hz, not around 60 Hz, we will update the channel names).

When the coherence is good, the modulus is around 0.98 (it may get closer to 1 when the issue of communication/sample usage between Acl and DSP will be fixed), and the phase is stable around 0.75 rad, which converts to a delay of 713 µs (since there is a 2pi jump at lower frequency when doing the full phase measurement). This delay is indeed consistent with the delay that we measured (714 µs) from CAL to Sc channels when injecting white noise without any control during weekly calibration injections. Hence it confirms that these monitoring lines will permit to pinpoint with low latency any change in the transmission from CALNoise to the suspension DSPs. A flag will be added in the DMS to trigger an alert when there is a modification, which means either a communication issue either an on-purpose modification and the need to re-calibrate the actuation path.

In addition to NE, WE mirrors, lines at 1012.5 Hz have been added end of this morning to the BS, PR, NI and WI mirrors, and to the NE, WE and BS marionettes. They have low amplitude so that they should not be visible in DARM.

rolland - 17:08 Thursday 30 August 2018 (42586)

The missing plot...

Images attached to this comment

rolland, verkindt, estevez - 11:37 Tuesday 16 October 2018 (43090)

The calibration lines at 1012.5 Hz have been moved to 2012.5 Hz around 9h25 UTC today (for all mirrors and marionettes).

This will improve the precision of the monitoring of CAL to Sc transfer functions down to the percent level (instead of 5%/10µs in the past weeks). It will also reduce the (already low) visibility of the line in DARM.

The TFMoni and CaliMoni configurations, and DMS flags are being updated accordingly.