LabVIEW
RT - PID Gains - where and when to use them
I'm not asking you to read a book on how to fish; I'm giving you a fishing rod and asking you to show me what you can and can't do with it.
I'm doing this because you did not respond to any of the answers to your original question. Without a response, we can't understand your thoughts, thus we can't figure out how to write an answer that you'd find helpful. Thus, I asked follow-up questions to get you to reveal your thoughts/knowledge.
Here they are again -- answers to your original question, "When and where to use PID gains?":
@nathand wrote:
A PID controller has, as inputs, a process variable and a setpoint. The process variable is the parameter you want to control, such as temperature. The setpoint is the desired value of the process variable. Let's say you do have a temperature control system where there is both a heating system and a cooling system.... The two systems could both be driven by PID and share the same setpoint and process variable. Some control options for this system:
- a single PID controller with one set of gains, where a negative output drives the cooling system and a positive output drives the heater (or some variation on this), if both the heater and chiller have similar performance characteristics.
- two PID controllers, each with a set of gains, one controlling the heating and one controlling the cooler.
- a combination of these two: a single controller with gains that are selected based on the setpoint or process variable, which is known as gain scheduling. The advantage to a single controller is that you'd never have the two controllers fighting each other.
You could also have a code that controls several similar processes (for examply, multiple identical temperature chambers). In that situation you could have a single set of PID gains but multiple controllers each with a different setpoint and process variable.
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@JKSH wrote:
> Where and when to use PID Gains?
Answer: Whereever and whenever you want to use a PID controller.
e.g. Since you want your temperature to be under PID control, your temperature controller needs a set of PID gains. However, since your fan is under on/off control (not PID control), your fan controller won't have a set of PID gains.
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Nimgaard wrote:
They are input to the PID controller, weighing the different parts of the PID controller (P, I and D). So each PID controller needs a set of PID Gain parameters.
If you create a new instance of the PID controller then yes, you will need to add PID gains to that controller.
The more complex question is, what numbers do you want to put into the parameters? Using the same parameters as input to several PID controllers is most often a bad idea. You should calculate gain parameters for each controller indiviudally.
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An example (simplified): If you control a quad-copter then you have 4 motors that you control. And the motors control the behaviour of the copter. But the motors dont get PID gains. However you might have one controller each for pitch/roll/yaw that is combined into control signals for the motors. And each of those controllers will have PID gains.
...and Nimgaard has written much more, trying very hard to help you.
You have been shown how to fish by 3 people, using 3 different techniques. Please be proactive and tell us which parts were helpful and which parts you need further clarification with. Ask us follow-up questions regarding what we've already written. (e.g. "Why did you spin the fishing reel this way?", "What does _____ have to do with PID gains?")
If you want one PID controller to regulate temperature, you do something like this:
If you want multiple PID controllers to regulate temperature, you do something like this:
Does this help? Is this example complex enough? What do you find unclear?
