Complete 4 mA to 20 mA Loop Powered Field Instrument with HART Interface (CN0267)
The circuit shown in Figure 1 is a complete smart industrial, loop powered field instrument with 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 peakto- peak frequency-shift-keyed (FSK) signal is modulated on top of the standard 4 mA to 20 mA analog current signal. This allows features such as remote calibration, fault interrogation, and transmission of process variables, which are necessary in applications such as temperature and pressure control.
This circuit has been compliance tested, verified, and registered by the HART Communication Foundation (HCF). This successful registration provides circuit designers with a high level of confidence using one or all of the components in the circuit.
The circuit uses the ADuCM360, an ultralow power, precision analog microcontroller, the AD5421, a 16-bit, 4 mA to 20 mA, loop powered digital-to-analog converter (DAC), and the AD5700, the industry’s lowest power and smallest footprint HARTcompliant IC modem.
Figure 1. 4 mA to 20 mA, Loop Powered Field Instrument with HART Interface (Simplified Schematic: All Connections and Decoupling Not Shown)
Figure 1A. DEMO-AD5700D2Z Printed Circuit Board (Pressure Sensor Not Included)
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