Isolated 4 mA to 20 mA/HART Temperature and Pressure Industrial Transmitter Using a Low Power, Precision, 24-Bit, Sigma-Delta ADC

Circuit is an isolated smart industrial field instrument that interfaces to many types of analog sensors such as temperature (Pt100, Pt1000 and thermocouple) or bridge pressure sensors. The instrument communicates via a 4 mA to 20 mA analog output and a highway addressable remote transducer (HART) interface. HART is a digital 2-way communication in which a 1 mA peak-to-peak frequency shift keyed (FSK) signal is modulated on top of the standard 4 mA to 20 mA analog current signal. The HART interface allows features such as remote calibration, fault interrogation and transmission of process variables, which are necessary in applications such as temperature and pressure control