convert 4-20mA to 2-10V


Thread Starter

J-F Portala

Hi listers,

I have a little electrical problem.
I have sensors which output is in 4-20mA. My acquisition board accepts only 0-10V.
What is the better way to trasform 4-20mA signal in voltage.
I think a 500 ohms resistor is not sufficient to give me a clean signal. What I have to add to this signal ?

I have the similar problem with an encoder which gives me a 24V output. I would like share it to several PLCs, but the signal will decrease according to the number of PLCs.

I have another application where I have an encoder (24V) and my counter board accepts only TTL signal. What do I have to apply to this signal in order to keep clean signals?

thank you for your help
[email protected]
SoViLor company
Yokagawa has a product which converts 4-20mA to 1-10 Vdc signal.
Product no. is JUXTA J Series . Try this.


Meeuwis Bouw

Let the 4-20 mA current pass through a 500 ohm resistor. Thee voltage drop over the resistor will be 2-10 Volt. Exactly.
Meeuwis Bouw,
Superfos Packaging.
Why don't you think a resistor will give you a clean signal? Dropping resistors have been used to convert 4-20 signals into voltages for decades. You need a precision resistor and almost any instrument company can provide them.

Jake Thompson

Check out RED LION controls, they make a bunch of din rale mount products that convert signals form one to another. I have had the same
situation and have had great luck with these. Also look under, they make a bunch of signal converters.
Good Luck!

Robert Scott

There is nothing wrong with using a 500-ohm
resistor to convert 4-20mA to 2-10V. In fact I can't think of anything better you could do. Of course you still need a source of loop power,
which your acquisition system probably doesn't
provide. But that can be as simple as a nice clean 24-V power supply. Just watch your ground references to make sure you don't create
any ground loops.

Regarding the sharing of an encoder between
several PLCs, I don't know why the signal should decrease according to the number of PLCs, unless the PLCs present an unduly high loading. If that is the case, you might have to insert some high-current buffers.

If you are trying to bring 24-V signals down to TTL level, then a simple voltage divider should work. If you are worried about exceeding the safe input voltage of the TTL circuits, you might want to include some diode protection to
the +5V rail.

James Johnson

Your 500 ohm resistor is a good option, provided you use a high precision resistor. Many analog PLC cards actually contain resistors to
convert the 4-20 ma signal to a voltage in their input circuitry. You will need to be carfull to check the maximum loop resistance when
using this solution.
Another option is to use a 4-20ma to 0-10v converter module. Action Pak makes modules like this.

Good luck,
James Johnson
How about just using a 500 ohm precision resistor?
4ma X 500 = 2V
20ma X 500 = 10V

This will work if your current source can drive a 500 ohm load and if you can ground one end of the resistor. If the resistor is in the middle of
the current loop, then make sure that your receiving device can stand the common mode voltage.

Jerry Miille
There will be a considerable loss in resolution to convert the live zero 4-20 mA signal to a 2 - 10 Vdc signal and then scale it in software.

There is also a concern for a ground loop. If the 4-20 mA has a field reference and the Data Acq board also has a ground, it will not work.

If the 4-20 is coming from a two-wire transmitter, where is the power coming
from. If from the DA board, this is another source of a ground loop. Industry standard approach is to use a signal converter to accept the 4- 20 mA input, provide isolation and noise immunity (EMI & RFI), and present a 0-10 Vdc signal to the board. The same module can also provide operating power to the field transmitter if it is a two-wire device. All of this for under $250 is an inexpensive way to guarantee a quality measurement.

Is the encoder signal 0-24 Vdc or is it a 24 Volt pulse. There are different solutions for either case.

Feel free to contact me off-line if I can be of further help

Bud Adler
Director, Business Development
Moore Industries-International, Inc.
The Interface Solution Experts
[email protected]
Office: 407.324.9389
Cell: 407.353.2727
Fax: 561.828.2232
First, is the 4-20 mas device capable of being overranged (most can go to 22ma or even higher)?
Next, how does your A/I card handle an overrange situation? Does it go to max counts and stop? Or does it give a bad value indication? Is this important for your control? If overrange is possible, you might consider converting the signal to 1-5 VDC using a 250 ohm resistor and setting the appropriate range in the logic. This assumes that you have sufficient resolution in your A/D conversion (minimum of 12 bit - 4095 counts) to meet the accuracy needs of your system.

John Beck
ControlSystem Specialist - retired