Proportional Hydraulic Valves - How-to?

This is my first time using hydraulic proportional valves, and I'm sure I'm just making them more complicated than need be. I was just going to barrel into the code and make something that works, but surely someone here has already figured it all out and can share?

I have an Allen Bradley PLC (1769-L30ER), with an analog output card (1769-IF8) that drives the proportional valve with 4-20ma. The only feedback I have is an extend, extend decel, retract decel, retract prox switches. I need the cylinder to move from extend to retract and back again as fast as possible, with ramp up and down for acc/dec. Fairly straight-forward application.

Can you all share examples of how you handled this in the past to get me started in the right direction?

Any reason you didn't want to use motion?

Sounds like you need to figure out.
Max speed/setpoint (for process or analog valve)
Speed/setpoint (hard coded or operator input)
Ramp up rate
Ramp down rate

With a little more effort you should be able to figure out the reverse direction with a smooth ramp up/down to the other direction.

Welcome to the forum!

You didn't say but is your proportional valve set up for full A-port/neutral/full B-port position to be at 4/12/20mA, -20/0/+20mA or something else? If it's 4/12/20mA, you'll be able to use the 4-20mA output as is. If the valve requires anything outside the range of the analog output, you'll need a signal isolator to deliver the appropriate signal.

I would also suggest making your flags of the appropriate size so that your decel proxes are tripped over the entire distance between the decel and full travel limits. This'll help ensure consistent speed regardless of your move start point.

Can you all share examples of how you handled this in the past to get me started in the right direction?

Click to expand...

Can you tell us what the application is so we can tell you?
I haven't done anything like you suggest since the early 1980s. We didn't use a proportional valve. We had a high and low speed bang-bang valve. I was also driving the actuator into a hard stop so precision positioning wasn't required. A proportional valve seems like overkill without some sort of feed back that is continuous.
If you had a real position feed back you can calculate a ramp up and ramp down as a function of position but limits switches don't permit that. You can try ramping up and ramping down as a function of time after hitting a limit switch but this will not be consistent as loads and temperatures change.
You will spend a lot of time using trial and error to get this to work the way you want and will always be fiddling with it