J. Kissel

I've processed the absolute actuator strength measurements for ETMX from 2019-01-14 (last week Monday just after reverting the bias voltage to "430 V"; see LHO aLOG 46414).

The (unscaled**) answers are as follows:
    Actuator | Strength (N/ct)
    UIM      | 7.933e-08 (+7.445e-11,-7.316e-11) or (+0.09385%,-0.09222%)
    PUM      | 6.56e-10 (+3.021e-13,-3.022e-13) or (+0.04605%,-0.04607%)
    TST      | 4.863e-12 (+1.719e-15,-1.71e-15) or (+0.03536%,-0.03517%)
or in physical units (i.e. removing all of the well-known quantities in the electronics chain and leaving only the fundamental force-per-fundamental-drive-unit):
    Actuator | Strength
    UIM      | 1.69 (N/A)
    PUM      | 0.03203 (N/A)
    TST      | 4.554e-11 (N/V^2)
where N is Newtons of force, ct is 18-bit DAC counts *, A is current in the coil of the OSEM, and V^2 -- assuming a requested bias voltage of 9.3 V_DAC = (40 V_ESD/V_DAC * 9.3 V_DAC) V_ESD = 372 V_ESD.

* Remember -- ETMX's ESD electronics chain is driven by a 20 bit DAC, changed out in Oct 2018 (see LHO aLOG 44905). However, we've compensated for this swap with a factor of 4.0 in the ESDOUTF filters of ETMX, down stream of the excitation point of the measurement, and thus the "count" drive is still an 18-bit DAC count.

However,
(a) ** These measurements were taken with the PCAL Y RX PD used as absolute reference, and were taken before the PCALY RX PD absolute scale was updated (see LHO aLOG 46449). So these answers need to be scaled:
           PCAL OLD   DARM ERR
H_oldref = -------- * --------
           DARM ERR   SUS EXC
           
           PCAL NEW   
H_scaled = -------- * H_oldref
           PCAL OLD
where (new/old) = 0.9759 for PCALY RX PD as reported in LHO:46449.

(b) It's dreadfully obvious from the measurement that our model has plenty of frequency-dependent systematic error. I also know the following:
    (i) We have not updated the dynamical model of the QUAD to include updated known-to-exist, non-"falls as simple f^(2*istage)," high-frequency dynamics . Were still using the old O2 dynamical model which has ETMY's (former) violin mode frequencies ("the Shapiro Effect" impacting primarily the PUM stage, see LHO aLOG 16057), and does not include the UIM stage actuator's funky resonances (see LHO aLOG 38295).
    (ii) We have not measured, and thus not well-compensated, any stage of SUS ETMX's driver electronics. We're still using the "off-the-shelf," "same compensation for each quadrant" compensation.
As such, I've restricted the frequency region of the fit to where there is no (OK, much less) frequency-dependence in the residual between model and measurement. This is not necessarily the right thing to do, but we won't know until we clean up the known causes of frequency dependence mentioned just above.

The PCAL RX PD channel calibration has been updated since this measurement, I'm actively working on getting an updated dynamical model, and I'll measure the coil/ESD driver transfer functions next Tuesday. But if we must update the front-end calibration sooner than we can get a new set of measurements (after updating the coil/ESD driver compensation) then we could use these scaled values:

The (scaled) answers are as follows:
    Actuator | Scaled Strength (N/ct)
    UIM      | 7.7418e-08
    PUM      | 6.4019e-10
    TST      | 4.7458e-12
or in physical units:
    Actuator | Strength
    UIM      | 1.6493 (N/A)
    PUM      | 0.031258 (N/A)
    TST      | 4.4442e-11 (N/V^2)

I have not updated anything in the front-end calibration. I'm going to process the sensing function measurement from 2019-01-19 (LHO:46530) and confirm that I can re-construct the DARM open loop gain transfer function well with these actuator numbers, and then I'll push an update to the calibration into the front-end.

See comment to this log describing the details of *how* I processed these measurements with the new pyDARM infrastructure.