Why does the PI200 FAST OUT drift or saturate?

When the fast integrator is enabled, even a small DC offset in the error signal is integrated over time. This causes the FAST OUT voltage to drift and can eventually drive it into saturation.

When acquiring a lock, disable the fast integrator while positioning the system close to the desired lock point, then enable it when closing the feedback loop.

If necessary, the setpoint or a slow actuator can be used to reduce the offset and prevent the fast integrator from saturating.