Feedforward PID control problems

hoping for a little help with the feed forward vi.
I have two inputs to a PID function, the Process variable (PV) being slightly behind (phase lag) the set point (SP).
This little bit of phase lag causes some unnecessary error in the PID algorithm.
I believe that feedforward VI is used to correct this type of problem.
The PV is from a load cell if it matters, recording around 1Htz cyclic load.
I can utilize the PID feedforward VI and plot its input vs output and see that it is indeed creating the necessary phase change (shown below in figure).
However, when i put the phase changed signal into the main PID vi, it somehow dosent seem to ever change/correct the phase offset of the PV signal that is coming in, its like its really not being used except that at very large vales (ie 0.2min) it just becomes unstable..
I have tried both lead and lag for both the PV and SP for every conceivable values between 0.000001 and 10min..
The feedforward VI does create amplitude changes between the inputs and outputs at small time levels (ie 0.001min) of which i am correcting for manually. Yet, The output signal without the feedforward vi seems to always better than with it.
Attachments:
v65PIDLL.vi ‏175 KB

hi george,
Thank you for checking in.
Im starting to get a handle on this after 3 or 4 days.
Basics are that the PID function is used for feedback.
It compares a setpoint (the desired state) to feedback state (process variable) in order to compute the error term which is then used for feedback.
Sometiems the set point feedback has a time delay in it and thus, creates a little extra error in the comparision and makes it hard to get the PID accuracy perfect.
So with a feedback load control system, there is a delay in the time the load cell is read to be compared to the desired state.
So what "lead lag vi" does iscreate a delay or lead in one of the signals so there can be a better computation of error.
Where it gets tricky is that lead lag vi also creates a offset and amplutide change in the set point on certain conditions such as larger phase shifts and smaller times delays,.
This in many cases makes a worse computation of error than the loss of phase shift by itself.
And in trying to correct for this offset and amplutide change, i was making mistakes which reduced the size of the error term.
But i did some things to try to keep this simple and the output is still not perfect, but better.
of course, i should add a discliamer, trying to help if anyone reads it, but im not a proffessional, i just play one on TV

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So although we have scaled the inputs to the PID controller, a problem is that there is a phase delay. An image of this is attached. Green is the PID output, red is the set point, and white the reading from the load cell. The amplitudes and DC levels are not perfectly adjusted as it is as close as it can get, I think, until the phase is corrected. So this particular phase delay seems to be because there is a time difference between the time the sinusoidal set point is created and the time the load cell (feedback PV) is sampled.
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Ill attach the main program.
Attachments:
v65PID.vi ‏171 KB

nevermind.. doing simple mistake.
sorry..

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I work on a closed loop PID controlled problem (Labview 8.5) and I have a couple of questions in order to make some progress!
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Attachments:
Control.vi ‏277 KB
ReadBinar.vi ‏162 KB

Hello Zach!
First of all, I want to thank you for your kind interest on my problem!!
I must describe you the desired process with the Control.vi. There are two AI channels writing down the acceleration of a structure in two different points (for velocity reasons I use Binary Type storage for my data). One AO channel for structure sinusoid excitation (shaker) and two CO channels for controlling two solenoid valves with which I want to control my structure acceleration (minimize it as well and fast as possible)!!
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With best regards!
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Attachments:
Control.vi ‏288 KB
equal within tolerance.vi ‏9 KB
ReadBinar.vi ‏163 KB

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I think with a timed loop you can run reasonable good timing down to 1 mSecond. I think 1 mSecond is the lower limit for non realtime systems like Windows/windows CE. And if you have the PID toolkit this will supply you with the functions you need. You do not need an extra CE PID toolkit. This because the touch panel module run under your standard Labview environment. But I do not know if all the functions in the PID tool like fuzzy logic are compatible with CE. Have you also considered Windows Embedded as OS for your module. With windows Embedded you can run standard Labview built exe files
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asdfs wrote:
Per my other posts, I am testing a friend's software to see if this is what we would like to use. I would prefer to use their software for our initial work to help offset the cost of the software. Problem is their software is 8.0 pro without the extra PID stuff. I am curious how one gets started creating a custom PID algorithm to be used in series between an input and an output. I have viewed several tutorials but all seem to simply point at the PID toolkit that is not availalbe to me right now. I realize it might be more work to create one but probably the only option at this point.
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PID control loop.vi ‏33 KB

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Attachments:
29092012.vi ‏32 KB

Apparently, in the Execution tab, the only option ticked is "Auto Handling of Menus at Launch", and i unticked it, try to run the program, and it worked.
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