Operation These sensors can be used to monitor motors, pumps, machine tools, conveyors or other electrical loads where an analog representation of the load current is required over a wide range of currents. The output can sense proper fan, pump or motor operation and failure, including belt or bearing loss as well as monitor machine feed rates and tool wear. These 4-20 mA sensors are loop powered devices that require an external 15-42 Vdc power supply. The total power supply must be 10 Vdc + (Rl * 20 mA) where RI is the input resistance of the device measuring the signal. Therefore, if Rl is 250 ohms, the minimum power supply is 15 Vdc. These sensors also have a linear output of 4 - 20 mA over all six selectable ranges (three ranges each for the ? and ? devices). A connection diagram is shown below. The line current is calculated as Iline = (Iloop - 4 mA) * Irange / 16.