edmond.merilh@LIGO.ORG - posted 15:56, Wednesday 15 April 2015 - last comment - 18:06, Wednesday 15 April 2015(17890)
SUS Noisemon noise study
I've taken Amplitude Spectral Density measurements on all of the suspension coil drivers that utilize the quad monitor bd. Below are screenshots of the data from the ones that I think may require some investigation. This data will be commited to SVN.
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In list form, these are the suspects: ETMX L2 UR -- (State 1 too large) BS M2 UL, UR -- (State 1 & 2 too large on UL, No change in noise between states for UR) ETMY L1 UL, LL, LR (No change in noise between states) PR3 M3 LR -- (No change in noise between states) PRM M3 LR -- (No change in noise between states) SRM M3 UL, LL, LR -- (No change in noise between states) SR3 M2 UL, UR, LR -- (UL close to ADC noise, UR, LR no change in noise between states) SR3 M3 UR, LR -- (No change in noise between states) Ed didn't mention, but these measurements are not calibrated, i.e. they're in units of ADC counts of monitor board voltage (hence the comparison between ADC noise in counts). To calibrate into current across the coils, one needs to invert (divide by) the response of the noise monitor circuit (D070480), zpk([0,0,0,0],[5,5,5,5,4.8e3,4.8e3],196) which takes you to, Vout, the voltage across the differential legs of the output op-amps, before the output impedance network of each driver, then you need to divide Vout by the output impedance network and the coil, to get the current across the coil, Ic, Ic = Vout / (2*coilDriver.Zout + osemCoil.Zc). Note that these are suspects because we've simply played the "this performance doesn't look like the others" game. As the list of suspects is smaller than "all of the noise monitors," we can now focus our attention here so it's less overwhelming to get answers to questions like - is it right? - why doesn't it look like the others? - is it the driver response itself or the monitor? etc.