I have inserted a rudimentary PID function into the manual simulation code as a way to test whether or not the PID function is changing the defocus values in the desired manner.

I am currently determining the ratio of ring heater power to the steady-state defocus as a way of measuring the scale of the response.

This ought to give a good way of measuring the scale needed to convert the calculated actuator response into an actual load.

I've attached the rudimentary code below. (The actuator isn't feeding into the heater at the moment, but inserting the "actuation" variable into the load expression is all that is required.)

% function out = model
%
% ITMPlusRing.m
%
% Model exported on Jun 24 2013, 16:24 by COMSOL 4.3.0.151.

u = zeros(1,2);
e = zeros(1,3);
mtime = 0;
deltat = 600;