I’m very happy to finally have my mashing system operational and last night I did a test run with water and some towels covering the false bottom of my mash tun (simulating a grain bed).
The system is fast and responsive and I was impressed with its general performance, but it overshot when reaching mash temperature and again when trying to settle at desired mash temp. I didn’t run the test long enough, but looking at the graph I’m not sure that it would settle at all. Not within the time frame of a normal mash. The same thing happened when I simulated the step to a mash out. A little overshoot wouldn’t bother me if it settles within a few minutes time, but the heat loss from my setup is so low that the temperature didn’t fall back down to the desired mash temp until 15 and 20 minutes after it overshot. That is too long for a 60 min mash. Let me provide some pictures:
Graph of mash simulation:
Zoomed in graph of reaching mash temp:
Zoomed in graph of reaching mash out temp:
I was tempted to try some manual tuning using Ziegler-Nichols method, but I realised that I have two PIDs working in a pair here: The MT-PID is driving the RIMS-PID setpoint. This got me confused on how to proceed.
Any help on the tuning and on how to proceed with reducing the overshoot and decrease settling time is greatly appreciated!