Getting rid of pots

I would like some info or examples please. We have a hydraulic system using proportional valves to control the pressure and flow. This system now uses potentiometers through IC boards to control this. I would like to change this to using a key pad on C-more touch screen and analog output cards. The plc is a Direct Logic 350 (KOYO). I am not sure of how to do this any thoughts greatly welcome.

I have several questions.

what it the hydraulic system controlling?
how will the system handle an open circuit? will it shut down or tell the system to go wide open?

what happens if the plc faults? what will it shut down? can you stand the downtime to replace the card? what if you don't have a card and it's out of stock?

before proceeding, may I suggest that you ask a lot if what if questions and have a backup plan if the plc faults, dies, or you don't have the spare parts.

not slamming you, just want you to ask lots of questions and have a backup plan.

james

All good questions from James, but a lot of the times the system has to be upgraded because the IC board controlling the hydraulics is no longer made.

As for the solutions, is the system actually controlling something with a PID loop for example, or is it just driving the proportional solenoid?

If it is a direct control of the output solenoid, one option is to control a motor that moves the pot for you. I never would have thought about this as a solution, but I have a few machines with it. It is ****, as expected.

Depending on how the input of the card where the pot is connected, there could be a chance of being able to connect the IO card directly. I would say though that this is either unlikely or you wouldn't have the documentation to do it.

Lastly, if you know the valves you are controlling and what signal they take (they may not take signal as such and just react on current, bear in mind the number of solenoids), then you can get an hydraulic amplifier or driver (I have a soft spot for Wandfluh) and connect that to your analog output on the PLC.

Either way, do bear in mind what the system does and more importantly the current standards for said system because once you touch it, it has to meet current standards.

This hydraulic system controls the up and down cylinder and the indexing of a plating line. There are a few reasons for wanting to change this. One the pots are real sensitive and slightest adjustment has quite the effect on movement. Another is the risk of someone else not knowing the previous making an adjustment and causing downtime and tearing something up. Another is to make a smoother transition when the line starts to go up or down and indexing. We have the cards to replace with and there are more than enough safety sensors on the line for different faults. If there is a fault the machine stops of course.

The pots send a 0-10vdc signal to the IC boards.

since you have explained your process, two questions still needs to be addressed.

how will the system react to an open wire situation?
how will the system react to a plc fault?
in this situation, we have 2 conditions, #1. the output is 0 volts, the system should remain still. #2. the system is at 10 volts, ????? Being familiar with your operation, I believe that you should investigate this to prevent any chemicals from being spilled.

james

yes using analog outputs is good way to deal with this,keep the limits better as to avoid hih or low signals.