Arduino and 0...20 and 4...20mA current loop sensors

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brainfart
 
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Arduino and 0...20 and 4...20mA current loop sensors

Post by brainfart »

I have a bunch of industrial sensors, e.g. pressure transducers, that output current. How can I connect them to the arduino? I seem to remember a trick involving a resistor turning that current signal into a voltage, but I'm not quite sure right now how to do this and I'd rather ask first before I sacrificing anything to the blue smoke demons.

brainfart
 
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Re: Arduino and 0...20 and 4...20mA current loop sensors

Post by brainfart »

Ok, I seem to remeber that it is possible to convert a 20mA signal to 5Vwith a 250 Ohm resistor... Can anyone elaborate?

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adafruit_support_bill
 
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Re: Arduino and 0...20 and 4...20mA current loop sensors

Post by adafruit_support_bill »

Ohm's law is what you are looking for: V=IR
The voltage drop (V) across your resistor will be equal to the resistance (R) times the current (I) flowing through it.

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Re: Arduino and 0...20 and 4...20mA current loop sensors

Post by brainfart »

Yes, I remember that , so in principle I measure the voltage drop across a 250 ohm resistor placed into the current loop with my arduino. Regardless if that current loop utilizes 20 or so volts. That's what I was somewhat afraid of.

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Re: Arduino and 0...20 and 4...20mA current loop sensors

Post by adafruit_support_bill »

Regardless if that current loop utilizes 20 or so volts.
By definition, if it is a 4-20mA loop, any (Ohm's) law-abiding resistor will give you the right voltage drop. Current loops are used to eliminate the effect of wire resistance over a long run. If there is a lot of resistance, the line driver will increase the voltage as necessary to achieve the appropriate current. Any resistor inserted at any point in that loop will still obey Ohm's law.

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Re: Arduino and 0...20 and 4...20mA current loop sensors

Post by brainfart »

Thank you.

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