Control old servodrives with analog input with a PID in RSLogix

[peryklez 0]

Hello I need some help to program a PID in rslogix 5000 ladder. I program a PID to control a servodrive that need a +-10 vdc input to run forward and backward where 0 is stopped and +10 is the faster forward and -10 the faster backward move. The problem is that i just can control the drive with an output from a control logix of 0 to 10 vdc and the drive moves to the SP , the PV is an encoder count with the 1769-HSC module, it slightly pass the SP, but since the PID is only control from 0 to 10 it arrives to 0 vcd and don't return the drive to the SP, been the PV sligtly great than the SP, anyone that help me to know how to program the output to work from -10 to +10 and have the pid remain at 0 vdc when it arrives to the SP?.

[MrAutomation 20]

If you program the PID to have an output of -10 to +10, it will automatically return to 0 when it's in position. More accurately, it will find the output that maintains a stable PV, which happens to be 0V in your circumstance. You will need fairly high Gain/Integral values to ensure your drive stops in position and doesn't overshoot.

[peryklez 0]

i guest i will have to test, i scale the PID in the rslogix from 0 to 100 % and put max 35% to ensure an output of 3.5 vdc maximum so the servomotor don´t run so fast, if i change from -10 to +10 vdc will the pid start to run in 0 vdc or will start at -10 vdc? thats what im dont know and i am afraid that the servomotor confuses since the pid down know the decelerarion needed to change direction, thats what i was thinking in use a low gain so the pid reacts slower and try by steps. B.R.

[Ken Roach 194]

I realize this isn't answering your question, but when I need to control an old servo drive with a Logix-based system, I go to the old 1756-M02AE Analog and Encoder motion control module. The motion module has already solved all of the control issues you are experiencing, along with position control and axis coordination. Doing this with a CompactLogix, and ordinary analog module, and an HSC is making it far more complex than it needs to be.

[peryklez 0]

Similar option for a compact logix?

[Ken Roach 194]

No, there are no analog motion control modules for the CompactLogix, only SERCOS and EtherNet/IP CIP motion.