When to use: Use this when designing or troubleshooting a 4–20 mA current loop to verify the power supply has enough compliance voltage to drive the full-scale 20 mA signal through the wire, barriers, indicators, and the transmitter itself. The maximum total loop resistance is set by the difference between the supply voltage and the transmitter's minimum operating voltage. Use the span/zero converter to translate a measured mA value into percent of span and engineering units.