Update 8-Feb-2024: The MODS1 blue IMCS quad cell appears to be working and there is no evidence that the workflow modification is still needed. The initial problem has not clearly been resolved, however, so please report any imcslock failures of MODS1B to support staff.

19-Sep-2023: During the restart of MODS1 post summer shutdown 2023, and issue with the MODS1 blue quadcell which is used for the IMCS lock was found.

The noisy/zero bias on the MODS1 blue IMCS quad cell signal happens when the blue CCD system is in continuous erase mode between exposures.  While we actively troubleshoot the issue, there is a temporary solution that involves an adjustment to the work-flow. The work-around is to manually turn off continuous erase mode just before a script does the first imcslock following pointing to a new field or when the instrument is reconfigured (for example, reconfiguring from imaging for target acquisition to take spectra).  Support staff will provide the instructions to the workflow when operating MODS if needed.

Once the IMCS is locked on, during exposures it will stay locked on because when the shutter is open and exposed to light it is not constantly erasing itself.

The team is making excellent progress in determining the source of this issue.  Please follow along here to see if this workaround is still needed in the future.