I used to the Moku:Pro laser lockbox to maintain the small Michelson IFO in B102 at an ajustable point on the fringe. The Moku input is a photodiode signal at the output, and the Moku output goes to the piezo controller's external input, which in turn drives a ring piezo on one of the end mirrors. 

On the attached photos you see the Moku setup, photodiode signal (red), error signal (blue), and scanning signal (green) used to acquire the lock. The second photo shows the system in lock. I have not optimised the control loop, so it is not very robust. Next step will be to measure transfer functions for the piezo actuator.