# 4-20ma to 0-10 volt conversion

Discussion in 'Electronic Basics' started by [email protected], Mar 21, 2007.

1. ### Guest

Does anyone know of a single ic that will take a 4-20ma signal and
convert it to a 0-10 volt signal ???

It looks like someone would produce such a beast by now....but my
google searches have turned up nothing.

~:>

2. ### Tom BiasiGuest

Can you settle for 2 to 10 Volts?

3. ### Paul E. SchoenGuest

Yes, a 500 ohm resistor. Add a 2 volt battery and you have 0-8 volts. A 625
ohm resistor and a 2.5 volt battery (or offset) gives you 0-10 VDC.

Usually a 4-20 mA signal is a control loop which allows transducers to take
their power from the loop supply, and change the current according to what
they measure. The display can be as simple as an analog meter with the
pointer offset below the zero point, or can be an electronic digital
display powered from the loop. Power can come from any device in the loop,
or a separate battery or supply.

Paul

4. ### JamieGuest

you just use a voltage network to feed the transmitter from converter.
with this network, you can use an Op-amp with dual rail supply or
some negative offset to give you 0 volts at 4 ma's
something like a 24 DC supply using a 100 ohm Resistor to supply
the transmitter. The op-amp simply uses both inputs to monitor the
offset of the voltage on this resistor, which will translate to a
voltage output..

5. ### Anthony FremontGuest

A 1/2W 500 Ohm resistor will give you a 2V to 10V signal. You can use a
smaller resistor and an op-amp to not place so much load on the line.
Outside of using a resistor, you could measure the magnetic field coming off
the wire, but that's getting out there.

If you have to have 0-10V, you could do it something like this and use
another op-amp to double the voltage output:
http://pdfserv.maxim-ic.com/en/an/AN823.pdf

6. ### ChrisGuest

An operational amplifier is versatile and capable of performing the
conversion. Assuming you have a single 15V supply, here's an LM324-
based circuit that will do the job fairly well (view in fixed font or M

| VCC
| +
| |
| .-.
| 12K| |
| | |
| '-' VCC
| | +
| .-. |\| Set For Vo = 0V
| 1K| |<-------|+\ at I(in) = 4mA
| | | | >-o--------.(1V)
| '-' .---|-/ | |
| | | |/| | | ___
| === | GND | | .---|___|---.
| GND | | | | 25.5K |
| '--------' | | |
| | ___ | |\ |
| + |\ '---|___|-o---|-\ |
| o----o-------|+\ ___ 10.2K | >----o---o Vo
|I(in) | | >-o--|___|-o-------------|+/
| .-. .---|-/ | 10.2K | |/
| 249| | | |/ | .-.
| | | | | 25.5K| |
| '-' | | | |
| - | '--------' '-'
| o----o |
| | ===
| === GND
| GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The 249 ohm terminating resistor for your current loop will produce a
1 to 5 V input at the first op amp. The second op amp is supposed to
produce a 1.0V reference to subtract from the 1-5V. The resistors on
the third op amp are set up to provide a gain of 2.5 for the
difference -- 0-4V becomes 0-10V.

These are standard 1% resistor values. If you need/want 5%
components, try using 30K and 12K in place of the 10.2K and 25.5K. If
you need more accuracy, you might want to replace the LM324 with a
lower drift single supply quad op amp, and use a voltage reference

Good luck
Chris

7. ### jasenGuest

If you can live with a 2-10V output the "chip" is called a 500 ohm resistor
(2 1K resistors in parallel)

if that's not suitable something can probably be done using an op-amp.

Bye.
Jasen

8. ### MassiveProngGuest

There is 4 to 20mA NON-LINEAR range for instrumentation. There is
also
4 to 20mA LINEAR range for instrumentation.

Our IR thermometers offered 0 to 1 volt conversion as an option, but
I do not recall 0 to 10V.