Right now i'm using a digital controll to maintain temperature.((johnson A419 ithink)) I have just recently became aware that PID controlls even exist
I am reading everything i can on how they work.
I believe i would like to use one in my still operation
I would appreciate some help.
I see many are sold on ebay. Some with and some without a probe or solid state relay. Also, there seem to be diferent types of probes.
The johnson controll works fine but this is a hobby and it has me hooked
You do not control a still by controlling the temperature, though it can be a useful guide to monitoring where you are in the run, and overtemp alarms are certainly useful.
The vapour temperature is determined by the composition of the vapour. You can influence the composition, especially in a reflux column, but you cannot change it (or temps) arbitrarily. A vapour composition of 75% ethanol/25% water is always going to be the same temp (85ºC). Basic physics.
All you can really control is the amount of power you put into the thing, and hence the rate it generates vapour.
Trying to drive it by temp, especially in a pot still, is an exercise in chasing your tail.
You most definitely DO NOT want to control a still with a PID controller. PID controllers are useful when you're trying to maintain a certain temperature in a system that has some lag time when heating. The PID controller, if properly tuned, will prevent overshoot and hold the temperature at the setpoint by varying the heat input.
When you're distilling, you're boiling the liquid - so the temperature is going to stay at the boiling point as long as you're giving it enough heat. The temperature can NOT go any higher. Giving the system more heat will just increase the rate at which the liquid boils.
Therefore, you want to manually vary the amount of heat input to get the desired product flowrate for a given reflux, which is something you do not want a controller doing for you. Or - keep the heat input the same and vary the reflux to change your flowrate. It all depends on your still and how you want to manage it. I play around with both throughout the run.
Once, during Prohibition, I was forced to live for days on nothing but food and water. W.C. Fields
