Simple Heating Circuit

[drodgers 0]

Good morning....I am new to mr plc. and new to setting up a heating circuit I am experiencing an issue with setting up a very simple heating circuit using AB Compactlogix 5370 , 1734-IT2I t'couple card, k type t'couple System is simple Setpoint 300 F high limit 305 F low limit 295 F I want to turn the heater on and have the PID cycle the contactor as necessary to reach and maintain desired set-point does anyone have any sample logic? Do I need to mess with gains? Thanks!

[HKU_MS 0]

PID loops are never simple if you have a 10 degree temp. range you are controlling with on/off control you probably can get by with latching and unlatching an output. You would need to have a purpose to set up an analog control loop such as cutting in and out multiple contacts to hold to within one or two degrees to need to use a PID loop if you do use one yes you will have to find the proper level for each gain there are several post here already on how to set up PID gains.

[mhowasso 5]

Yes, I agree. PID is one way but they can be a lot of trouble (regardless of what some claim). Especially on an Oven where variables can change continuously. Ovens can have their own personality depending on age, insulation, door seals, fan circulation, heating elements, thermocouple type, etc. etc. I have 35 Ovens that had PID controllers (that was always giving trouble) and I took them all out and put a PLC with Feed forward logic. I use a mercury relay and feed forward logic in my PLC and I can hold the temp in a 2000 degree F oven within 5 degrees with no problem and it is easy to maintain and troubleshoot. I use a 3 phase mercury relay for switching the power on and off at the speed you want to ramp up the temp and then hold it there. then ramp it down if required. You will have to play with the ramp speed timing when you get within a few degrees of your set point to prevent overshoot and undershoot to the desired target (set point). There might be other ways also, but the feed forward is simple to program and it works. But, everybody has there own way they are comfortable with. Edited 20 Sep 2014 by mhowasso