The ST420-DI is an analog-output shaft speed sensor/transmitter. It detects magnetic pulses from a rotating shaft-mounted pulser target (disc or wrap) and outputs a smooth, continuous 4-20mA analog signal in direct proportion to the pulse frequency (rotating shaft speed). See the Output Function graph on p. 4. The ST420-DI combines a magnetic pulse detector, signal processing and 2-wire loop-powered 4-20mA circuitry into a sealed stainless-steel M18x1 sensor housing with NPT conduit port.