Although it seems that I use a proper heater range (as I can regulate with PI using say ~ 10% of this range), I am unable to set a P large enough, to obtain oscillations with I = 0. Even P = 1000 will not be enough. Using the next heater range (where only a few percent are enough to regulate) will not solve the problem: P = 1000 still does not provide oscillations.
It appears that the P conversion to heating power is just too low (by the way, what is the unit for P ?).
My second question is: since firmware version 1.5 that I have, has there been some improvement for the regulation or autotune function, and can I load a more efficient firmware ?
Last Edit: Feb 8, 2019 7:54:41 GMT -5 by lfruchter
Post by Lake Shore Jeff M on Feb 8, 2019 8:42:58 GMT -5
If your system has a large thermal mass, you may never be able to get it to oscillate. P is a multiplier of the error in temperature. You can figure its scaling out by setting P to say 100, I and D to 0, and then put in a fixed error. So if the reading is 20 K and you put in a setpoint of 21 K, the heater will turn on to a certain percentage. The P scaling is just the amount of heater percentage per K.
In regards to updating the firmware. Version 1.5 is about 9 releases behind so I would highly recommend doing the update, although, there are no defined changes for the regulation or Autotuning functions.
- low range: 140 %/K - med range: 45% /K - high range: 20% /K
As a controller potentially can be used to drive very different systems, is there a way to change the proportionality between P and % of heating range, to adapt to the different cases ? As it is, I am left only with a change of the maximum power delivered, which is a bit annoying for safety.