I created a modified QPD block called QPD_WITH_SATURATION_CTRL, which is available in /opt/rtcds/userapps/trunk/isc/common/model/QPD.mdl.

This block has a custom made saturation block after the SUM output, before dividing the Pitch/Yaw signals with SUM.

The saturation thresholds can be specified through EPICS PVs. This EPICS controllable saturation block is available in

/opt/rtcds/userapps/trunk/isc/common/models/C_Code.mdl