4-20 mA controlled 0-24vdc potentiometer??

the_superfly5

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T
Join Date
Jul 2010
Location
Orlando
Posts
6
Hey,

I need to control a 0-24 vdc potentiometer with an analog signal from my PLC. Any ideas on how to accomplish this? Thanks ahead of time!
 
One idea is to hook up the 4-20 signal to a servo motor attached to the pot.
I have other ideas too.
 
Wow, It's been a long time since I saw a real motor operated pot.

We had one that ran the speed reference of an old extruder DC drive which had no isolated reference input.

It worked just fine until curiosity caused someone to tweak the end limits of the actuator, but it was easy enough to set it back to normal.

Either superfly is dealing with a motor operated pot application, or he has his "to's" and "from's" mixed up. Maybe he just needs to get a signal from a human operated pot "to" a PLC analog input card?

http://www.basler.com/html/html/potentiometer.htm
 
Last edited:
I have an actuated valve on a small hydraulic system that is controlled by a range of dc voltage (0 - 24vdc = 0 - 100%.) This modulates the pressure in the hydraulic system. I could use a human operated pot, but the customer would like to control the percentage via the HMI rather than deal with human control.
 
Yikes. This is a perfect example of why supplying as much info as possible right up front is a good idea. I suspect that you are headed for trouble with your current approach.

Most proportional hydraulic valves are not pure DC. A dither signal is applied to the voltage command supplied to the valve coil - so a valve amplifier card made for the purpose is usually used. There are a number of products on the market that will accept a 4-20mA or 10V input command and supply the correct kind of PWM signal to the proportional valve.

Give us some information on the hydraulic valve you are using and we can help you.
 
Well... you really need a signal conditioner then, though backwards of the normal isolator type.

My first thought would be to use two three-way isolators, with the outputs in series. The ones I linked have fully floating outputs, so you can wire them in series. Set each one for the same base span, say 0-10VDC in = 0-12VDC out. Wire the inputs in parallel. Now your 0-10VDC analog out from the PLC becomes 0-24VDC out to your valve.

0 to 24VDC however sounds like an odd control voltage. Virtually all devices out now run on 4-20mA, or 0-10VDC, or one of the similar standards. Are you absolutely sure the valve takes a 0 to 24VDC variable reference? What is the actual part number and manufacturer?

Most hydraulic proportioning valves nowadays might take a 24VDC power supply, and have a separate control input, be it voltage or current.
 
manny solid state proportional relay should serve you in this APP the direct application servo valve control
And if you like to do test...using a direct PWM output from your PLC with a choke coil and a capacitor to smouth the output...

but the idea of a servo motor on the a pot is way overkill....

Sometimes we say : Why make it easy when it can be so complicated :)
 
OkiePC said:
Wow, It's been a long time since I saw a real motor operated pot.

We had one that ran the speed reference of an old extruder DC drive which had no isolated reference input.

It worked just fine until curiosity caused someone to tweak the end limits of the actuator, but it was easy enough to set it back to normal.

Either superfly is dealing with a motor operated pot application, or he has his "to's" and "from's" mixed up. Maybe he just needs to get a signal from a human operated pot "to" a PLC analog input card?

http://www.basler.com/html/html/potentiometer.htm
Click to expand...
Printing presses still use the MOP even today.
(Existing controls that is)
 

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