4-20mA Output to 10k Pot

[ds7891]

I have a very old device that the speed is being controlled by a 10k POT.

Would like to automate the speed using an Analog Output 4-20mA or a 0-10v output card.

I measured across the POT connections on the old device and the excitiation voltage is only 2.2vdc.

Does anyone make a device to convert Analog to a POT?

I have used a POT to Analog converter, but now I need it the other way around.

My last ditch effort is to use a Motorized POT


Thanks

 

[osmanmom]

your info missing something

 

[BlueAltezza]

I've used an analog isolator when I need to do something similar with some DC motors & drives from Minarik:
https://www.minarikdrives.com/p-17357-pcm4.aspx

I don't know if that would work for you, but I'm sure other manufacturers makes isolation modules like that.

 

[GaryS]

Why not us an MOP Motor Operated Pot
A quick search found this it looks like it should do what you need

http://www.carotron.com/systeminterfacecomponents/mopgen/

 

[James Mcquade]

I agree with osmanmom.

1. you need to sketch out the circuit and know what it does.
2. look up the device being controlled, find the model number, look up the manual, and see what it says. is it a 0-10 volt, ma signal?
3. select analog output, current or voltage.

regards,
james

 

[BryanG]

I was researching something else and saw this and filed it away for future reference. It gets you close to what you want but I haven't found a simple 4-20mA to Digital Potentiometer. There must be someone who has joined the ends together.

http://www.analog.com/media/en/news...ection-guide/Choosing_the_Correct_Digipot.pdf

http://www.resistorguide.com/digital-potentiometer/

You can get them with an up/down interface, serial, I²C or SPI.

This shows that someone has thought about it:
https://www.maximintegrated.com/en/app-notes/index.mvp/id/4051

 

[spaderkung]

I would guess the pot is there for a voltage reference, but with an old device and not too much description it's hard to say. You have measured on the device but have to measure also across the pot to get the maximum voltage. Then you know what range and resolution you have to supply. I beleive many of the links above are to devices that already include a control function, but maybe you want to do that yourself.

 

[Saffa]

If the device is outputting 2.2V to the pot and all 3 legs are used then you need a 4-20mA to voltage converter with a programmable output range that can be set to 0-2.2V.

If only 2 legs of the pot are being used then it's a current reference which is more tricky. You would need to measure the current at zero and full range and see if you can find a suitable converter

 

[Bit_Bucket_07]

Why not us an MOP Motor Operated Pot
A quick search found this it looks like it should do what you need

http://www.carotron.com/systeminterfacecomponents/mopgen/

In the past (circa 1980), I've use MOPs with digital output control. A current to voltage signal isolator could simulate the potentiometer input, but it would depend upon whether the drive's input would accept a voltage signal from an external voltage source.

 

[ds7891]

Delete Post

 

[keithkyll]

If this is a 90 VDC controller, the pot is most likely at line voltage relative to ground. Must have model number of controller first.

 

[rupej]

If it really is a 0-2.2V pot, and there's no way to change that, I would just use a 0-10V output, and scale the output device to 0-2.2V and be done.

 

[Lare]

If it really is a 0-2.2V pot, and there's no way to change that, I would just use a 0-10V output, and scale the output device to 0-2.2V and be done.

On that case you would also need passive PLC analog output. Potentiometer gets voltage from device. PLC can't supply potentiometers power directly to same pins than potentiometer.

Normal PLC analog output can be used if there is output loop powerd isolator between PLC and device. Weidmuller have at least them.

http://www.clrwtr.com/PDF/Weidmuller/Weidmuller-Output-Current-Loop-Supply.pdf

Another way is connect plc output to wiper pin and ground. On that case you need to remove potentiometer from device so that different voltages don't mux.

 

[ds7891]

I got more information.

Ends up that the 10k pot is wired to a Valve Controller, which outputs a 0-100ma signal to a hydraulic valve.

The Valve Controller....well, I have that in my hands, and there is not a single part number on it. And honestly, it looks semi-custom.

I did talk to the manufacture of the Hydraulic Valve, and they weren't sure what controller I had by explaining the looks of it. They suggested ffinding a signal converter to get my PLC signal (4-20 or 0-10v) converted to 0-100ma.

The operating range of the Hydrualic valve is really 14-85ma FYI.

Any suggestions on a signal converter?

 

[V0N_hydro]

I was looking to control the speed of a turbine with a PLC as I often do but for this particular one the path of least resistance was to get a Woodward UG-Actuator which takes 0-100mA signal from the governor and has a shaft takeoff from the turbine to make hydraulic power to control the steam valve, and a woodward 2301D governor which outputs a 0-100mA signal to the actuator.

example 2301: http://www.govconsys.com/pdf/Woodwa... Digital Control for Small Steam turbines.pdf