- #1
PID algorithm for constant temperature controller.
- Thread starter gputowski
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SUMMARY
The discussion focuses on developing a PID algorithm for a heating controller, emphasizing the importance of managing time lag in the system. The formula for the PID controller is defined as: Controller output = proportional gain P × error + integral gain I × ∫(error) + derivative gain D × d(error)/dt. Participants highlight the need to regulate both the ON and OFF times of the relay, suggesting that a single formula may not suffice. Instead, they recommend using short ON-OFF intervals and potentially incorporating Pulse Width Modulation (PWM) to enhance control accuracy.
PREREQUISITES- Understanding of PID control theory
- Familiarity with heating control systems
- Knowledge of time lag effects in thermal processes
- Basic principles of Pulse Width Modulation (PWM)
- Research the implementation of PID controllers in heating applications
- Explore the effects of time lag on control systems
- Learn about Bang-Bang control and its mathematical foundations
- Investigate the use of PWM in enhancing control precision
Engineers, control system designers, and anyone involved in developing or optimizing heating control systems will benefit from this discussion.
- #2
gputowski
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Any idea?
- #3
jim hardy
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Just what do you mean by
One PID algorithm is
Controller output = proportional gain P X error + integral gain I X ∫(error) + derivative gain D X d(error)/dt
?gputowski said:
One PID algorithm is
Controller output = proportional gain P X error + integral gain I X ∫(error) + derivative gain D X d(error)/dt
- #4
Svein
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The one thing you need to remember when trying to regulate a heating controller is the time lag through whatever you are trying to regulate. This lag can easily run into hours.
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jim hardy
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Slope of temperature curve during that first on-cycle should give a clue about process thermal capacity, and maybe that time lag mentioned by svein..
- #6
gputowski
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Thank You for the answer.
I know the formula for PID. But If You have seen my first drawing You should see that We are regulating the time when the relay is ON. We all supposed to regulate the time when the relay is OFF. Is it possible to make it by one formula or I will have to make two formula with time: first when the relay is ON second when the relay is OFF and make a loop.Greg
I know the formula for PID. But If You have seen my first drawing You should see that We are regulating the time when the relay is ON. We all supposed to regulate the time when the relay is OFF. Is it possible to make it by one formula or I will have to make two formula with time: first when the relay is ON second when the relay is OFF and make a loop.Greg
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jim hardy
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I'm not sure i understand that statement.gputowski said:
ONtime is (1-OFFtime).
You're mixing linear control with" on-off control" here, sometimes that's called "Bang-Bang control"
and the math of that is another world. I won't go there myself
From a quick search:
Here's a paper...
http://dimacs.rutgers.edu/Workshops/AIMS/slides/SLafrica4.pdf
and a couple references
http://en.wikipedia.org/wiki/Bang–bang_control
http://cds.linear.com/docs/en/datasheet/1041fa.pdf
http://liberzon.csl.illinois.edu/teaching/cvoc/node86.html
Your best bet is to keep your on-off intervals short compared to the process time constants and treat it as linear
or insert a PWM at your controller output.
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