PID questions

[StirCrazy]

Originally Posted by ScubaSteve

Doing dual input control systems is a PITA. Actually building it isn't really an issue but tuning and making it stable is. The simplest set-up is have it set-up such that you are essentially using the temperature difference between the two probes but that only works for certain applications.

Can you give me a pretty good decription of what you are trying to accomplish? I need to know what is part of the system that you are trying to control (like size and number of tanks, where your heating elements are located, how you are moving the flow about, etc). I'll try me best to draw up the most stable configuration for you.

ok so what I am doing is an electric smoker. so I need a PID to maintain a setpoing temp. I found some with rise also so I can program it to sit at 120 degrees for 2 hours then 130 for an hour then 140 for an hour so going up 10 degrees every hour till it hits 180 then hold. this would only be one type of smoke, the rest would be a set temp till I turn it off.

the other probe I was hoping I could stick it into a hunk of meat and have it display the meat temp and then set off an alarm at a specific temp and then when another temp is reached I was hoping I could have it adjust the main temp. so for an example when the meat reaches 180, drop the cabnet temp from 225 to 180 for a holding tempature.

I can do everything buy buying to cheep PID's except for the hold temp thing which isn't a hugh deal would just be nice, but I was hoping to be able to get away with just one if I can.

this is the one I was thinking of using for the main control if I do a two PID setup.
http://www.auberins.com/index.php?ma...&products_id=5

Steve