When we transition DARM control from EX to EY, we ramp off the DARM input into the EX test/PUM/UIM filter banks.

Since the UIM filter bank has an integrator, this leaves a static offset on the output of this filter bank which is cancelled by the offloading of IMC-F to the UIMs.

However, depending on the size of the offset, this can use up a significant amount of the control range of the offloading (which is set by a digital limiter). Today, the EX offloading was hitting this limiter, causing IMC-F offloading to stop and start (see attachment).

Since the offloading signals were trending even further toward saturation (i.e., greater likelihood of IMC-F saturating and causing lockloss), I dropped the interferometer out of observing and zeroed this offset using two one-minute ramps.

We should modify the ISC_LOCK guardian to do this automatically during lock acquisition.