April 01, 2011

Dear Control Engineering: Is HART 7 strictly a wireless protocol, or does it also cover wired devices? What version of HART are most manufacturers using with wired devices these days?

Given the number of protocols circulating these days, it's no wonder that they can get confusing. So we put this question to Ron Helson, executive director of the HART Communication Foundation. Here's his answer:

HART 7 is more than just a wireless protocol, the HART 7 standard applies to the full range of measurement, control, and automation systems products based on the HART Communication Protocol – whether wired or wireless. The WirelessHART capability is getting the most attention, but HART 7 provides many new capabilities beneficial to industry users in both wired and wireless products. Examples include:

1) Report by Exception—enables devices to push information to the control or asset management system without the system having to poll the device with a standard HART command. If there is a process or device status change, the device will automatically advise you.

2) Time-Stamped Data—a valuable tool that adds a time stamp to process data readings sent to the host system which is helpful in evaluating the sequence of events or analyzing problems that have occurred.

HART Communication Foundation policies encourage manufacturers to design new devices and update existing devices to the latest HART version. Consequently many manufacturers are updating their device and systems products to HART 7. 

While this updating is going on, the vast majority of wired devices installed in user plants and available on the market today are built to the HART 5 standard. However, because all HART versions are backward compatible and interoperable with each other, the HART version is mostly transparent to the user. Each HART version builds on the functionality of the previous versions without taking anything away—the functionality of HART 5 is included in HART 6; the functionality of HART 5 and HART 6 is included in HART 7. This backward / forward compatibility preserves investments of both users and manufacturers as it enables a HART 5 control system to communicate with a new HART 7 device the same as it communicates with a HART 5 device. It also means that control system built to the latest HART 7 standard can communicate with all versions of HART devices – HART 5, HART 6 or HART 7. 

--Ron Helson, executive director of the HART Communication Foundation

www.hartcomm.org