Method
Since I am mainly concerned with the actuator part of the OSEM, I chose to do this measurement at the output cables for the coil drivers in 1X4. See schematic for pin-mapping. There are several parts in between my measurement point and the actual coils but I figured it's a good check to figure out if measurements made from this point yield sensible results. The slow bias voltages were ramped off under damping (to avoid un-necessarily kicking the optics when disconnecting cables) and then the suspension watchdogs were shutdown for the duration of the measurement.
I used an LCR meter to measure R and L - as prescribed by Koji, the probe leads were shorted and the readback nulled to return 0. Then for R, I corroborated the values measured with the LCR meter against a Fluke DMM (they turned out to be within +/- 0.5 ohms of the value reported by the BK Precision LCR meter which I think is reasonable).
Result
PRM
Pin1-9 (UL) / R = 30.6Ω / L=3.23mH
Pin2-10 (LL) / R = 30.3Ω / L=3.24mH
Pin3-11 (UR) / R = 30.6Ω / L=3.25mH
Pin4-12 (LR) / R = 31.8Ω / L=3.22mH
Pin5-13 (SD) / R = 30.0Ω / L=3.25mH
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BS
Pin1-9 (UL) / R = 31.7Ω / L=3.29mH
Pin2-10 (LL) / R = 29.7Ω / L=3.26mH
Pin3-11 (UR) / R = 29.8Ω / L=3.30mH
Pin4-12 (LR) / R = 29.7Ω / L=3.27mH
Pin5-13 (SD) / R = 29.0Ω / L=3.24mH
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Conclusions
On the basis of this measurement, I see no problems with the OSEM actuators - the wire resistances to the flange seem comparable to the nominal OSEM resistance of ~13 ohms, but this isn't outrageous I guess. But I don't know how to reconcile this with Koji's measurement at the flange - I guess I can't definitively rule out the wire resistance being 30 ohms and the OSEMs being ~1 ohm as Koji measured. How to reconcile this with the funky PRM actuator measurement? Possibilities, the way I see it, are:
- Magnets on PRM are weird in some way. Note that the free-swinging measurement for the PRM showed some unexpected features.
- The imbalance is coming from one of the drive chain - could be a busted current buffer for example.
- The measurement technique was wrong.
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