approach to controlling heating elements

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jward
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Joined: Sun Oct 04, 2009 9:38 pm
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approach to controlling heating elements

Post by jward »

Looking for suggestions on controlling heatings elements.

I need to control the HLT and Boil kettle elements, but they shouldn't run at the same time to prevent tripping the circuit breaker. I was trying to use PID to control the HLT; set the boil element on and switch to duty cycle to maintain boil; using ladder logic to turn one off if the processes turn both on. That wasn't working well with the ladder logic I was using.

What approach should I use to keep the elements from running at the same time?
jward
Posts: 69
Joined: Sun Oct 04, 2009 9:38 pm
Bot?: No

Re: approach to controlling heating elements

Post by jward »

I got the ladder logic working the way I envisioned. I think I had to stop using outputs as rung inputs to themselves as output. I never liked recursion. Out0 is controlled in a process using PID for the HLT. OUT1 controlled with a state using direct on until 200F and then exits to a state that runs OUT1 via Duty cycle to maintain the boil. OUT8 controls the SSR/HLT heating element and OUT9 controls the SSR/Boil Kettle heating element. This ladder logic runs OUT8 and OUT9 ensuring only one runs at a time.
ladder-logic.PNG
ladder-logic.PNG (20.14 KiB) Viewed 6946 times
I expect that using registers in the processes instead of OUT0 and OUT1 would be better approach after I learn the ins and outs of registers.... Feel free to share your advise.
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