I have two sets time aligned of data. The first we can call the "step" the second the "step response". The step in reality represents the applied change in temperature of a hotplate, from ambient to a higher value over a few minutes - therefore an fairly "soft" step. The step response is the decreasing resistance of a calibrated NTC thermister on a PCB on top of the hotplate. I want to model the step response as an RC circuit in order characterize the thermal conduction properties of the PCB. How do I compute these two data sets to give me estimates of R and C?

Any help will be much appreciated. I'm a very poor mathematician. Is there a program that will churn the numbers and pop out the right answer!? (well...I can hope).

Terence