HART - Digital Transformation for Analog Instruments

HART is by far the largest digital communications technology deployed in the process industries with over 40 million field instruments supporting HART technology installed worldwide.

HART is the global standard for sending and receiving digital information across the 4-20mA analog current loops that connect the vast majority of field instruments with distributed control systems. HART technology offers a reliable, long-term solution for plant operators who seek the benefits of intelligent devices with digital communication, while preserving existing investments in analog instrumentation and plant wiring. Much more than a communication protocol, with HART technology process plants have access to a wealth of digital process, maintenance, and diagnostic information. Information that is valuable throughout the plant lifecycle from design, to installation and configuration, through operation, and finally maintenance.

HART is simple, reliable, and easy to use. 

The FieldComm Group owns the HART specifications and provides specification development, training, and product registration services associated with the technology. Since it’s initial release in the 1990s, HART has become an IEC standard, undergone three major revisions, and preserved backward compatibility with all prior releases. 

Hart Explained

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, asset management, safety or other system using any control platform. Communication occurs between two HART-enabled devices, typically a smart field device and a control or monitoring system. Instrumentation grade wiring and standard termination practices assure reliable communication. 

HART provides two simultaneous communication channels, one analog, the other digital:  

  • A 4-20mA signal communicates the primary measured value (PV) as an analog  value of current using the wiring that provides power to the instrument.  The host system then converts the current value to a physical value according to parameters defined by HART Software.  For example, 7 mA = 80 degrees F.  

  • Digital device information is communicated by encoding  a digital signal, generally using a technique known as Frequency Shift Keying on the same 4-20mA wiring used for analog communications. The digital signal contains information from the device including PV, device status, diagnostics, and additional measured or calculated values, etc.  

Together, the two communication channels provide a complete field communications solution that is easy to design, simple to use, low cost and extremely reliable. 



Ethernet networks have been pervasive in office environments for decades. But in process facilities, 2-wire 4-20mA wiring has been the norm.  Slowly, Ethernet and IP networks are growing towards the process plant floor.  To address this growth FieldComm Group offers HART-IP support.

HART-IP allows host level systems and asset management applications to access and integrate measurement and device diagnostics information from HART-enabled field devices using the existing plant Ethernet networking infrastructure.

HART-IP is a simple-to-use, high-level application technology that is independent of the underlying media. Thus HART-IP operates with redundant Ethernet media as well as mesh or ring topologies. Similarly, HART-IP can run over Power over Ethernet (PoE) for such infrastructure and devices. Speeds of 10 Mbit/s, 100 Mbit/s, and 1 Gbit/s etc. are supported.

Because the application layer is the same for HART field devices as HART-IP, time consuming and error-prone data mapping (using Modbus RTU or TCP/IP) is eliminated, making HART-IP the most simple to use and suitable backhaul network for WirelessHART gateways and 4-20mA HART multiplexers and remote I/O.

HART-IP offers the most straightforward method to access large amounts of all the standard HART information available in a HART device coming from products that concentrate many measurement points into a single output.  It allows the information from these devices to be brought up to the Ethernet level easily, without the need to go through any translation processes and with no loss of information.

HART-IP Features and Benefits
Feature Benefit
10 Mbit/s - 1Gbit/s support Operates with existing infrastructure
HART Application Layer Simple integration with existing control and asset management systems
Ethernet TCP/IP protocol

Shared bandwidth with existing applications.

No requirement for customized Ethernet protocol




WirelessHART - How it works

WirelessHART is a wireless communications protocol for process automation applications. It adds wireless capabilities to HART technology while maintaining compatibility with existing HART devices, commands, and tools. By design, WirelessHART using mesh networking technology. Each device in a mesh network can serve as a router for messages from other devices. In other words, a device doesn't have to communicate directly to a gateway, but just forward its message to the next closest device. This extends the range of the network and provides redundant communication routes to increase reliability, particularly in the difficult radio environment found in process facilities.

Each WirelessHART network includes three main elements:

  • Wireless field devices connected to process or plant equipment.  This device could be a device with WirelessHART built in or an existing installed HART-enabled device with a WirelessHART adapter attached to it.
  • Gateways enable communication between these devices and host applications connected to a high-speed backbone or other existing plant communications network.
  • A Network Manager is responsible for configuring the network, scheduling communications between devices, managing message routes, and monitoring network health. The Network Manager can be integrated into the gateway, host application, or process automation controller.

For flexibility to meet different application requirements, the WirelessHART standard supports multiple messaging modes including one-way publishing of process and control values, spontaneous notification by exception, ad-hoc request/response, and auto-segmented block transfers of large data sets. These capabilities allow communications to be tailored to application requirements thereby reducing power usage and overhead.

WirelessHART Security  

WirelessHART employs robust security measures to protect the network and secure the data at all times. These measures include the latest security techniques to provide the highest levels of protection available.

Protects Valuable Information – It’s Automatic

  • Robust, multi-tiered, always-on security
  • Industry standard 128-bit AES encryption
  • Unique encryption key for each message
  • Data integrity and device authentication
  • Rotate encryption keys used to join the network – automatic or on-demand

Protects Wireless Network

  • Channel hopping for security protection and co-existence
  • Multiple levels of security keys for access
  • Indication of failed access attempts – a rogue device
  • Reports message integrity and authentication failures
  • Safe from Wi-Fi type Internet attacks