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HART over IP for industrial automation networks

Posted: 30 Jan 2013     Print Version  Bookmark and Share

Keywords:highway addressable remote transducer  Transport Layer  TCP 

In today's competitive landscape, all companies aim to reduce operation costs, deliver products rapidly, and improve product quality. The highway addressable remote transducer (HART) protocol directly contributes to these business goals by providing cost savings in:

 • Commissioning and installation
 • Plant operations and improved quality
 • Maintenance


The HART Protocol was developed in the mid-1980s by Rosemount Inc, The protocol was soon published for free use by anyone, and in 1990 the HART User Group was formed. In 1993, the registered trademark and all rights in the protocol were transferred to the HART Communication Foundation (HCF).

Figure 1: Typical HART Over IP network.

What is HART over IP?
The HART Protocol is the global standard for sending and receiving digital information across analogue wires between smart devices and control or monitoring systems.

The principle objective of the HART Protocol is to establish standards that allow host applications and field devices from differing companies to work with each other as a system. Even if a system component is replaced with a similar device from another company, the system should still function properly.

Accordingly, HART promotes interoperability in many ways:

 • Compatibility with the 4-20mA loop allows a HART device to work with existing plant systems.
 • Providing a well defined Physical Layers for devices to communicate over.
 • Specifying Data Link Layer framing, error detection and bus arbitration requirements to ensure the integrity of communications.
 • Requiring all devices to support all Universal Commands.
HART is a bi-directional communication protocol that provides data access between intelligent field instruments and host systems. A host can be any software application from technician's hand-held device or laptop to a plant's process control. The HART TCP/IP Communication Interface is a Transport Layer specification.

HART host system: Client
The HART client allows a user application to implement information exchange with a remote device. The client builds a HART request with information sent by the user application to the client interface. The request is then sent to the UDP or TCP port of the server.

HART TCP device: Server
A HART Device (server) listens for a HART request on particular port. The request is processed and a response is returned to the client that made the request.

How HART technology works
HART broadly operates in two modes that are described below.

Master slave mode: HART technology is a master/slave protocol, which means that a smart field (slave) device only speaks when spoken to by a master.

Burst mode: In Burst mode, the master instructs the slave device to continuously broadcast a standard HART reply message. The master receives the message at the higher rate until it instructs the slave to stop bursting.

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