HART

Two wires are used for this communication network. When a 4-20 mA analog signal is sent, a digital signal is superimposed on it. Nodes that received the signals use the digital signal separated from the analog signal. The transmission rate of digital signals is 1200 Hz when the bit is turned ON and 2200 Hz when the bit is turned OFF, which are not very fast. One-to-one wiring is basically recommended, but this network also supports multidrop connection with multiple devices.

Analog signal

Digital signal

With the HART communication protocol, communication is performed when the master sends a command instruction and a slave sends back a response.

Data is sent and received using a digital signal superimposed on an analog signal. To read the digital signal, the master and slaves need to separate it from the analog signal.

This function automatically sends a message when a slave has a value exceeding a threshold or an error occurs.

HART communication is slow, with transmission rates of just 2200 Hz when the bit is turned OFF and 1200 Hz when the bit is turned ON. It is mainly used for wiring checks, output calibration, and similar purposes via a network, instead of large-volume data communication. In large-scale facilities, such as plants, a HART network can be used to reduce the amount of checking work when devices are located away from controllers.

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November 2015