analog - Frequency Key Shift technique to superpose the digital communication on top of 4–20 mA signals - Electrical Engineering Stack Exchange
Instrumentation training - HART – Highway Addressable Remote Transducer Protocol: HART is a digital signal that rides on a standard 4 mA … 20 mA process control loop. In the field of
KPFH Smart Positioner HART 4-20 mA
Design an optimized circuit for HART-enabled 4- to 20-mA inputs - Embedded Computing Design