Hi Guys After spending a couple of days playing with this thing I have a question or two. 1 After you get the mode oscilating how do you get it to stop do you have to continue to adjust all three or do you do one at a time.
You should adjust one at a time: Adjust -> observe results -> adjust -> observe -> etc. untill you are happy. ;-)
2 How do you know if you are heading in the right direction what will make the oscilations slow.It seems to me that it goes at the same rate all the time with the same amplification regardless of settings.Is there one property that effects the rate and one the amplification or once again is it a combination of all three.
Generally: reduce proportional gain (Kp), reduce derivative time (Td) and increase integrator time (Ti).
There is no one property that effects the rate or frequency of the oscilations. We usually want to get the amplitude of the oscilations as small as possible, the frequency is more or less tied to the resonance-frequency of the process that is controlled.
Any help you can give or something you should read(other than the ones in FG.I have read them but still am stumped)would be greatly appreciated.
You could try searching for "PID controller tuning" in your favourite search engine.
P.S Clarification.Where it says in the setup that Ti should be set to infinity does mean writing "inf" were a number would normally be.
No, it means setting the value as high as possible. I'm, not sure if "inf" would be recogniced as infinity.
In the latest CVS version this has been addressed. You can set the integrator time to 0 (zero). Now if you look at the PID algorithm you'll see that this does not make sense because it would lead to a division by zero. On the other hand setting Ti to the highest possible value might be a bit awkward, and the highest possible value for a double might be platform dependant. So I've decided to use zero to completely eliminate the intergator action from the controller. The code recognices setting Ti to zero and then removes the integrator action.
Short answer: when it says that Ti should be set to infinity, set it to 0.0 (zero).
The same can be said for derivative time (Td). Setting Td to zero would in the previous version lead to a division by zero. The new version recognices this and skips that particular piece of code (where the error is filtered).
Summary: Set Ti to zero to completely eliminate integrator action. Set Td to zero to completely eliminate derivative action.
-- Roy Vegard Ovesen
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