I have some king of heating system: heater (that I can control current for final power control) and a thermocouple (for measuring the temperature). I also have a device that can record temperatures from thermocouple. I would like to take a transfer function of my system for my PID-alike algorithms testing in Matlab. How can I do it? I am wandering if setting the heater for some low power and recording the temperatures is enough. How can I generate tf in matlab out of that king os step response? I have full version of Matlab with all toolboxes (especially Control System Toolbox).