Help, I can't get my PID feedback loop to work on PCI-7344 controller

[Yoni]

Hello,
I've encountered problems using the onboard PID feedback loop feature on controller 7344. I have an analog feedback source which should control a servo axis. (the axis should move in order to keep the feedback voltage at a constant value) I set up the program, set up the hardware, the hardware seems to work perfectly well, but every time I run the darn thing the axis (and the feedback) start vibrating very rapidly between high voltage (+/- 9 volts or so) no matter what PID parameters I enter. (even when I set them all to 0). BTW, when I use the "read following error" it gives me a correct value.
HELP!!! has anybody encountered such a problem or know what to do?
attached to this message i
s my program (which doesn't work.) any help will be greatly appreciated.
thanks
Yoni

[Brent_R]

Hello Yoni,

It seems the problem is with the code and not the PID values you have tried. The one main problem I see here is that you are disabling the axes right before sending the trajectory commands in the loop. With nothing wired, the default input to Enable Axes.flx is all axes disabled. Add a control or constant like you did in the previous call and reenable the axes you need. Also, you do not need the Enable ADC.flx command, because this is automatically handled by Configure Axis Resources.flx. Finally, the positions in Load Target Position.flx and Read Position.flx are in counts, not in volts.

I would recommend giving this a try in the 1-D Interactive section in MAX first, then try running one of the simple example programs in:

C:\Program Files\N
ational Instruments\LabVIEW 6.1\examples\Motion\FlexMotion\One Axis.llb

Regards,

Brent R.
Applications Engineer
National Instruments