[Tom, Oli]

Summary: There is a polarity flip between the BOSEM and QOSEM coils due to the wiring of the QOSEM flexi-circuit. To maintain consistency with existing BOSEM controls a sign flip should be implemented in CDS coil drives.

When commissioning the damping loops for the BBSS on the teststand, we noticed that there was a sign flip required in the QOSEM coil drive for the loops to be stable, when copying over the existing BOSEM damping. See LHO alog 90441. After some investigation, this sign flip is due to a polarity flip in the wiring from the coil drivers to the QOSEM coils. The QOSEM coils are wound in the same direction as the BOSEM coils, however on the QOSEM flexi-circuit I accidentally flip the coil connections with respect to that of the BOSEM. All QOSEM version to do date suffer from the coil sign flip. 

In the attached screenshot, we see the BOSEM flexi-circuit has this weird flip between the coil pads (on the very left) and the uDB9 connection. I did not copy this flip over to the QOSEM flexi, which has caused this coil polarity flip.