aLIGO LHO Logbook

H1 SUS

oli.patane@LIGO.ORG - posted 09:59, Thursday 25 June 2026 - last comment - 19:50, Monday 29 June 2026(90747)

QOSEM SatAmp to QOSEM Cable Resistance

Jeff, Betsy, Arnaud, Oli

Yesterday afternoon we went to the BBSS QOSEM satamp and checked the coil resistance. We did this by putting the BBSS in SAFE and then unplugging the Satamp to Duopus cables one by one. Each of these three cables have the pins for two QOSEMs, split as CH1 + CH2, CH3 + CH4, and CH5 + CH6. Each cable was unplugged and then the pins for each coil probed. Below are the results. These values are all pretty similar.

Coil Resistance (Satamp to Duopus)
	CH1-2 (SUS_BS_81)		CH3-4 (SUS_BS_82)		CH5-6 (SUS_BS_83)
Channel	CH1	CH2	CH3	CH4	CH5	CH6
CH Coil Pins	23 -> 10	18 -> 5	23 -> 10	18 -> 5	23 -> 10	18 -> 5
OSEM Mapping	F1	F2	F3	SD	LF	RT
Coil Resistance	39.1 +/- 0.1 Ohm	40.0 +/- 0.2 Ohm	39.0 +/- 0.2 Ohm	39.7 +/- 0.2 Ohm	40.0 +/- 1.5 Ohm	40.5 +/- 0.5 Ohm
Notes					Larger than normal variation

Comments related to this report

jeffrey.kissel@LIGO.ORG - 09:22, Friday 26 June 2026 (90773)

Link

Picture of the setup: (in this instance) the QOSEM CH 3-4 (i.e. F3 and SD) SUS_BS_82 cable is disconnected at the QOSEM satamp in SUS-R2, and its "to chamber" end is connected to a standard D25 breakout board. Clip leads are connected across the pins as described above to gather the coil resistance.

These results are as expected: the QOSEMs are up-cycle bodies and coils from BOSEMs, which are known to have resistance of ~40 [Ohm], in this case 40 +/- 2.5%.

Note, this is markedly different than the 35 +/- 10% [Ohm] -- 31.5 to 38.5 [Ohm] -- assumed in LHO:90743. Maybe Tom is assuming that this is the coil resistance if measured directly at the coil flexi-circuit terminals, and the "extra" resistance is from the long cable run to the chamber which is what we typically measure.

However, the 2.5% spread in coil resistance values between F1, F2, and F3, is NOT enough of an imbalance to explain the worrisome P to Y cross-coupling seen at DC (LHO:90728 and LHO:90739) and in the M1 to M1 transfer functions (LHO:90765).

Images attached to this comment

thomas.roocke@LIGO.ORG - 19:50, Monday 29 June 2026 (90817)

Link

Indeed, the ~35ohm nominal coil resistance I quoted in LHO:90743 is measured at the QOSEM uDB9, so not including cable or feedthrough resistance.

After assembly I measured the coil reistance of these LHO BBSS QOSEMs to be:

QOSEM SN	LHO BBSS Channel	Coil Resistance at uDB9
S2600012	F1 / CH1	34.6
S2600009	F2 / CH2	35.6
S2600013	F3 / CH3	35.1
S2600008	LF / CH5	35.7
S2600011	RT / CH6	36.4
S2600010	SD / CH4	35.6