jenne.driggers@LIGO.ORG - posted 14:27, Friday 19 May 2023 - last comment - 08:47, Tuesday 29 August 2023(69757)
Confusing config for PCALY line 4
Evan Goetz noticed that there is a mismatch between the Pcal injected frequency and "matching" demodulator for PCALY line 4. This line at 24.5 Hz is in place for temporary monitoring of the thermalization effects on calibration, eg, alog 69478. I don't think that this is detrimentally affecting our calibration at this time, so I'm not going to call Jeff while he's on vacation. He can take a look Monday morning to make it more clear which frequency is supposed to be where.
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Ya, unfortunately, because the PCAL oscillator numbers and DEMOD oscillator numbers within their name are defined by front-end code, then you have to do some nasty MEDM trickery that results in this confusing display. In short -- the DEMOD can demodulate any arbitrary frequency, and as long as the *local* oscillator within the DEMOD matches the real signal, then you'll get a sensible answer. In this case, we're using the PCALY LINE4 demod to demod the 24.5 Hz line that's driven by awg with the CAL_AWG_LINES gaudian, so there *is* no end station OSC frequency we can display on this user interface. So, the former mapping of the PCALY LINE4 DEMOD to the PCALY OSC FREQ still shown on the screen (which drives the 2084.01 Hz line), but is meaningless.
Same goes for the PCALXY comparison line display that's shown in the background.
Jenne concluded the right thing -- that this does not impact the output of the calibrated data:
(a) The front-end demodulation of the systematic error pipeline is NOT the primary monitor (produced by GDS)
(b) the 24.5 Hz line is temporary, and (hopefully) will be turned off once the run starts
(c) the PCALXY comparison is, this far, just a monitor and not used to correct any live data.
In the fullness of time this user interface will be cleaned up, but in the mad scramble to make sense of all of these new features some things have been sloppy and confusing. I promise those commissioning the systems are aware of this sloppiness and successfully dancing around it for the time being.
I've committed the local changes to the MEDM screen that resolve this confusion. See
/opt/rtcds/userapps/release/cal/common/medm
CAL_CS_PCAL_COMPARISON.adl
as of rev 26174.
HOWEVER -- we should really modify this screen to use a local-to-each-IFO macro file, since the oscillator number used to drive these PCAL lines (and any PCAL line) is pretty arbitrary, and not, in general, synchronized between sites.