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1 ohm to 100 kilo ohms are called medium resistance and once I read somewhere that the shunt method is recommended in this interval but I don't remember where. I want to document a shunt resistor method used with 500ohm and I want to find a standard such as IEC, ISO ect. to verify what we do obeys to a standard.

How can I find it?

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  • \$\begingroup\$ Not sure about standards, but a 500 ohm resistor will drop 10 volts and dissipate 0.2 W when you push 20 mA through it. Seems like it might be a little on the large side, though I'm not entirely sure what you want to do with it. \$\endgroup\$ – alex.forencich Oct 21 '15 at 8:10
  • \$\begingroup\$ current loop measurement \$\endgroup\$ – user16307 Oct 21 '15 at 8:19
  • \$\begingroup\$ a daq hardware will read voltages from the shunt \$\endgroup\$ – user16307 Oct 21 '15 at 8:19
  • \$\begingroup\$ Ah, I see. What is the input voltage range of the DAQ hardware? \$\endgroup\$ – alex.forencich Oct 21 '15 at 8:33
  • \$\begingroup\$ -9.9 to 9.9 Volts \$\endgroup\$ – user16307 Oct 21 '15 at 9:27
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The most common shunt resistance for 4-20ma current loop systems is probably 250 ohms, but 500 ohms and values lower than 250 ohms are also used. The most common supply voltage seems to be 24 volts. With a 24 volt supply, and 250 ohms shunts, up to 4 receivers can be connected in series with one transmitter. I doubt very much that there is a standard for this. If you can't find a definitive answer, look for web sites of manufacturers of commercial 4-20ma equipment and see if they cite any standards. Individual user companies may have their own standards.

Here is some reference material:

Murata PDF

National Instruments html

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