The 4–20mA current loop has been widely used as an analog communication interface in industrial applications. It facilitates transmission of data from remote sensors over a twisted-pair cable to a programmable logic controller (PLC) in a control center. Simplicity, reliable data transfer over long distances, good noise immunity, and low implementation cost make this interface well suited for long-term industrial process control and automated monitoring of remote objects.
To no one’s surprise, industry is evolving just like all electronic applications today. It has more stringent demands. There are new requirements for higher accuracy, lower power, reliable operation over an extended -40°C to +105°C industrial temperature range, added security and system protection, and implementation of the digital Highway Addressable Remote Transducer (HART®) protocol. Collectively, these requirements make the design of today’s 4–20mA current loop quite challenging.
This reference design explains how to develop a 4–20mA current-loop transmitter, analyze its performance, and select the components that meet rigorous industrial requirements. Test data for error analysis, overtemperature characterization data, schematics, and analysis software are provided.
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