can I run two PIDs from the same vi?

[smartlander]

Hi

I want to control speed of the rotating shaft and force applied by the pneumatic cylinder using two different PIDs from the same program.
I managed to get two PIDs to work separatly using PID control loop VI`s supplied with labview 6.1 (I got Kc, I and D right, so there is no overshoot). When I try to run both PIDs within my vi they don`t work. I again tried various gains and managed to get one PID to work but not the other. Then through trial and error I managed to get a second PID to work but I had to change refresh time of the FOR loop from 100msec to 1msec.
Does anyone have experience with running two PIDs in the same program? Does the timing of the FOR loop influence PID contorller? Does equiring of other data while run
ning PID has effect on the PID?
I would really appreciate any comments/help. I am pretty thrustrated at this time 🙂
Thanks"

[JR_A.]

The timing of the FOR loop will influence your PID control, which is a fundamental part of PID control. Acquiring data doesn't affect the PID although it could affect the timing of the loops. For instance if you only have one DAQ card you would want to have it all in one loop because you can not have two AI sessions open to the same card.

For more detailed information on PID I would recommend reading the "PID Control Toolset User Manual" which should have been installed to your machine but can also be found at : PID Control Toolset User Manual"

Regards,

JR A.
Application Engineer
National Instruments