Peter_I:
Very simple:Commercial PID-controllers (My first one was a second-hand Eurotherm, the next four has been cheap chinese controllers... they all work fine, but the eurotherm is the best by a small margin).
The eurotherm did not have an autotune function. It was fun to do the datalogging and Ziegler-Nichols, but it is so much easier to push AT and lean back.I use a slowcooker controlled by the PID through the aforementioned SSR, and it works great.
I have also used a ricecooker (higher wattage, easier tuning) and a BIG pot insulated with a towel and heated by an immersion heater.Tuning is important for stable temperature.... and do not trust the temperature calibration! One of the controllers were 4° off when I got it. Thermocouples can be a little tricky too, and be a couple of degrees of the mark.
(Relative temperature is easy, absolute temperature is a little harder)
I have used Type K couples, but Pt1000 or LM35 would be a wiser choice for the low temperature region of gastronomy.
Thanks for the info! I was planning on just using a PID controller. Most of the DIY Sous Vide cookers use one. I guess I am using the Arduino, just because I wanted a learn more about the Arduino.