A Process Data Bridge with HART

Summary

Moving critical plant floor data into higher level control and information systems—within a manufacturing facility or into the cloud—no longer must be difficult or expensive. The combination of the Industrial Internet of Things (IIoT), industrial Ethernet backbones and wireless networks means there is a quick and seamless way to share process data with the entire corporate infrastructure. And the devices to build the bridge may already be installed.

HART, a communication protocol that has been around since the early ‘80s, is the foundation for the more than 40 million HART devices currently installed worldwide. HART enabled devices superimpose a digital signal upon their 4-20mA process signal so that it can contain additional process measurements and other variables: instrument status, diagnostic data, alarms, calibration values, alert messages, etc. This data can then be shared from smart HART digital field instruments to mid- and higher-level control, asset management and data information systems without having to upgrade expensive process control interface equipment. This whitepaper excerpt explains how. (See the full paper for more information or visit the FieldComm Group website for a more in depth and complete primer on HART.)
 

Information hierarchies

As the desire to exchange data between industrial and business systems has become more commonplace, the separate information hierarchy levels outlined in the ISA 95 model (Figure 1) have started to coalesce. In prior years, data and information that needed to be exchanged between the lowest plant floor levels 0-2 and the upper Enterprise Resource Planning (ERP) level 4 required expensive Manufacturing Execution Systems (MES) products or custom coding—and oftentimes both. The free flow of information has introduced a new set of ubiquitous terms, standards and phrases such as IIoT, smart factory, cloud automation and Industry 4.0.

Protocol revisions

It is important to note that HART data uses specifically defined universal and custom commands outlined within the HART specification. The HART specification has also had updates to the protocol, referred to as revisions, which have additional capabilities. Most HART devices operating in the field today utilize revision 5, 6 or 7.

HART field devices also are compliant to a certain HART revision. Most field devices released within the last 20 years support HART revision 5, 6 or 7. Each new revision of HART offers different features and capabilities, but all field devices—regardless of revision—still support backwards compatibility with HART hosts and handheld communicators.

HART interface options

There are many HART interface options: HART enabled 4-20mA input cards, HART multiplexer (Mux) systems, slide-in PLC gateway cards, custom-coded software interfaces for asset management and MES/ERP systems, and standalone gateways that typically convert the HART data to some other proprietary or open industry format.

Many PLC and BPCS cards installed in legacy systems don’t have the capability to read the HART data superimposed on the 4-20mA signal. However, each control system vendor usually has an alternative card or offers an upgrade path for the CPU/controller and input cards to read HART.

HART multiplexers are common. Typically, their interface is a custom RS-422, RS- 485 or RS-232 serial connection and the multiplexer is custom-configured for a particular vendor’s hardware interface, asset management system or control system. Some PLC and BPCS companies offer slide-in chassis-type gateway cards that read the HART data and offer a proprietary backend communication connection to the system.

Often, each of these options is quite costly. The most expensive but also most specific HART interface is the one written by a programmer.

Another interface option is a standalone HART gateway. These most often provide the most economical pathway to extracting HART data from field devices. They usually offer one to four channels or ports that allow several HART devices to be multi-dropped for maximum data concentration (Figure 3).

Configuration of IIoT devices

For many years, end users have had to deal with custom and proprietary configuration packages from vendors for advanced capability devices. This typically leads to several custom software packages that users must learn, get IT support and permission for and become familiar with. Most IIoT capable devices are not straight forward field instruments and therefore small handheld configurators are not convenient for setup and configuration. In fact, many HART protocol gateways often require complex database mapping and programming software.

When sourcing or specifying an IIoT device, investigate what the programming interface will be. Several open standards and software packages that vendors have access to prevent the need for custom or expensive programming software utilities. We recommend looking for devices that support FDT/DTM technology for programming, so free software like PACTware can be used.
 
_{All figures courtesy of Moore Industries, Inc.
This feature originally appeared in the April 2024 isue of InTech digital magazine.}