4-20 mA PLC Calculator
To connect our float switches to a PLC for 4-20mA output, wire the switch with two resistors as show below. Consult your PLC’s datasheet for input resistance (impedance) on analog input pins*. Type this and your operating voltage into the specifications below to have a resistance value chosen for you. Find the closest value resistor and enter those values into the Chosen R1 and R2 sections . This will show you the actual mA expected.
*Common PLC input impedance values for most Allen Bradley, ABB, IDEC, and Siemens controllers are 250Ω, 280Ω, 300Ω, and 500Ω.