1-3vdc analog input to 4-20ma

B

Thread Starter

Bobby Gauthier

I have a modem that has some built in i/o. Great! But the analog input has a 1-3 Volt input.
The standards that we use are 1-5vdc or 4-20ma.
I need to know of a module or some other way to make this a 4-20ma input so it is usable.
Any help would be greatly appreciated.
 
R
A simple crude way might be to connect a diode in series with a resistor.

You have a span of 2 Volts instead of normal 4 so my guess is the resistor would be 125 Ohms
You would need to offset the volts to get 1V @ 4mA that's where the diode comes in it would give 0.6 Volts which would add to the 0.5 Volts across the resistor @ 4ma or 1.1 Volts.

From there a simple voltage divider across the diode would allow you to trim the 0.6 down to 0.5 or you could use a lower value resistor and input range 1.1 - 3.0

Good luck
Roy
 
R
Forgive me if I double post

A 125 Ohm resistor in series with a diode will give 1.1 to 3.1 Volts (4-20 mA)
Use a Voltage divider to reduce the 0.6 Volts across the diode to 0.5 or a smaller resistor and have a range 0.6 to 3.0

Hope this helps
Roy
 
D
Roy can you help me?

In an older post you had a circuit diagram for a 4-20mA simulator that could work with 2 or 4 wire systems....I need to build a 2 wire simulator..do you still have a diagram available

Kind Regards
Dave
 
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