Author Topic: DP620 PID delay problem  (Read 4585 times)

campodavila

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DP620 PID delay problem
« on: July 08, 2013, 09:54:00 AM »
 Hi everyone.
anyone can help me.

In a DP620 DISPLAY I have a PID block that controls the inching(brake) of a H1 axial piston pump from Sauer-danfoss.
the problem is that the PID block is executed in each execution loop(about 10msec) and the brake reaction time H1 pump is much higher, so for the pid work properly  I need  that the pid to run once every 10 times(for example) that the main loop is executed.

┬┐how can i program it?

thanks a lot

Offline Richard

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Re: DP620 PID delay problem
« Reply #1 on: July 08, 2013, 11:46:58 AM »
Hi,

I've used several PID controls for both motor speed control and cylinder position control but I always put the control in the controller that driving the output and recieving the feedback.  Do you have a good reason for putting the control in the display and sending the output and feedback over CAN?

I have found that display loop time can vary greatly too depending on what screen you are in and what is displayed.  I've had loop times that vary from 50-165 mS depending on the screen that is viewed at the time.

Can you put the PID control in the controller where the loop time in probably more constant?

If not then the PID block gives the ability to run (normal operation), hold the integrator or reset using the Rst/Hld input.  I've never tried this but maybe you experiment with counting the loops and switching the control from hold to normal at every fifth or tenth positive transition.  (feed a true into an OR gate and NOT the output back to the second input so it oscillates with each loop, then also use the OR output to feed into a loop counter which will control the Rst/Hld of the PID ).

I hope this helps,

Richard


campodavila

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Re: DP620 PID delay problem
« Reply #2 on: July 08, 2013, 02:56:42 PM »
thanks Richard

I have not controller in the suystem , only I have the Display, I will try using the Rst/Hld input.


jose