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Application Note: Creating a 4-20 Ma Current Loop on the ACT-1B and ACT-3

From Monarch Instrument

Think of the IO port as a variable resistor that regulates the current to 4-20 ma in the loop. All the other
devices in the loop are represented as a resistor equal to the input resistance of all the devices combined.
This maximum allowable value for this resistance depends on the power supply used.

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