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PID algorithm for constant temperature controller.
- Thread starter gputowski
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In summary, Greg is looking for help to write the coorect PID algorithm for heating controller. He has sent a graph and references to someone who can help.
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gputowski
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Any idea?
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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
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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..
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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.
Related to PID algorithm for constant temperature controller.
1. What is a PID algorithm for a constant temperature controller?
A PID algorithm, or Proportional-Integral-Derivative algorithm, is a common control strategy used in temperature controllers to maintain a constant temperature. It calculates an error value by comparing the measured temperature to the desired setpoint, and then adjusts the output accordingly using proportional, integral, and derivative terms.
2. How does a PID algorithm work?
A PID algorithm works by continuously monitoring the error between the current temperature and the desired setpoint. The proportional term immediately adjusts the output based on the magnitude of the error, the integral term accounts for any accumulated error over time, and the derivative term anticipates future changes in the error. These terms work together to minimize the error and maintain a constant temperature.
3. What are the benefits of using a PID algorithm for a constant temperature controller?
A PID algorithm offers several benefits, including improved accuracy and stability compared to other control strategies, the ability to handle nonlinear and time-varying systems, and the ability to adapt to changes in the system over time.
4. Are there any limitations to using a PID algorithm?
While PID algorithms are effective in many cases, they may not work well for highly nonlinear or complex systems. They also require tuning of the proportional, integral, and derivative terms to achieve optimal performance, which can be time-consuming and challenging.
5. How can I tune a PID algorithm for my specific temperature controller?
The best way to tune a PID algorithm is through trial and error or by using specialized software. Some guidelines for tuning include starting with a low proportional gain and gradually increasing it until the system becomes unstable, then backing off to a lower value. The integral and derivative terms can then be adjusted to improve performance further. It may also be helpful to consult with experts or reference materials specific to your temperature controller and application.