Proportional Valve Control

[Bluenoser337]

Hi: I am looking to retrofit a machine that has a hydraulic pump, providing tension and speed on some driven wheels. There is presently an old stand-alone closed loop control board controlling the pump swivel angle by positioning the spool on a proportional valve. Feedback to the card includes spool position, swivel angle position and pump pressure. Output from the card is 2-wire to the proportional valve. I want to eliminate the control board and have the new PLC do everything. I can get all the feedback signals that used to go to the card converted to 4-20mA...that's no problem. I'm not sure what the proportional valve uses (voltage or current) but I hope to find out by model number. Question is: This seems like it should be a fairly simple and typical PID application for a modern PLC. Is there anything I am missing that a 20 year old control board can do that the PLC can't? Any comments appreciated!! Thanks!! RB

 

[PNachtwey]

Does the old control card have a micro controller on it? If so there may be extra 'smarts' in the card than just a PID. If not then the PID is probably analog with op amps and pots. Analog PIDs work with infinite resolution and infinite speed. It is hard for a micro controller to match this speed let alone a PLC that has a slow and irregular scan time.

A lot depends on how quickly and accurately the PID must respond to load changes. If the pump works pretty much in a steady state condition you should be able to get by with a PLC.


Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

 

[Bluenoser337]

Modern PLCs can be set up so specific functions can be executed independent of the main program scan so, we are good there. I have since found out that the old control card supplies a pulsing output to supply power and control signal to the valve simultaneously, so I need some thing in the middle between the PLC and the valve...trying to find my best option now. Thanks!! RB

 

[PNachtwey]

A PID has one output. What is it going to control? Spool position, swivel position or pressure? Now what?


Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

 

[Bluenoser337]

Hi PNachtwey...the old control card has a single PID output signal as well.