The HART Communication Protocol (Highway Addressable Remote Transducer) is a hybrid analog+digital industrial automation open protocol. Its most notable advantage is that it can communicate over legacy 4–20 mA analog instrumentation current loops, sharing the pair of wires used by the analog only host systems. HART is widely used in process and instrumentation systems ranging from small automation applications up to the highly sophisticated industrial applications.

According to Emerson,^[1] due to the huge installed base of 4–20 mA systems throughout the world, the HART Protocol is one of the most popular industrial protocols today. HART protocol has made a good transition protocol for users who wished to use the legacy 4–20 mA signals, but wanted to implement a "smart" protocol.

The protocol was developed by Rosemount Inc., built off the Bell 202 early communications standard in the mid-1980s as a proprietary digital communication protocol for their smart field instruments. Soon it evolved into HART and in 1986 it was made an open protocol. Since then, the capabilities of the protocol have been enhanced by successive revisions to the specification.

Here is a close up of the SDAFE-HART Module:

The PI-SPI-DIN-2x4MIO has two slots for SDAFE-HART Modules and the PI-SPI-DIN-RTC-RS485-4AI-4KO-8DI had four slots for SDAFE-HART modules.

It is up to the end user to develop and write their own HART protocol software.

We will provide our test software in Python code (Command 0 and 33 for the Rosemount 2880) to help the end user get started. Here is a screenshot of the above transmitters in action!