Because Wi-Fi, in turn, is a wireless network that can accommodate standard TCP/IP communications, Phoenix Contact's backhaul approach will soon benefit from another new HART protocol enhancement: HART IP. Phoenix Contact's first WirelessHART backhaul offering relied on Modbus/TCP to bring monitoring points back to the host system. Soon, they'll be changing over to HART IP over Wi-Fi in new implementations, which will make it easier to communicate all the richness of HART devices' diagnostic data as well as up to eight process variables.
While communication of HART data over other Ethernet-based protocols certainly was doable in the past, with HART IP "all that mapping goes away," explains Emerson's Bob Karschnia. "HART IP also allows for a standardized flow of data into historians, control systems and other plant applications," he says. "Compared with using OPC, Modbus/TCIP, EtherNetIP -- the end user doesn't need to worry about it." All information in a HART device is available to the host system is available using standard HART commands. HART IP is expected to find a home as well in the direct communications of more complex, non-loop-powered instruments that deal with a lot of data, such gas analyzers and four-wire transmitters.
The HART Protocol now also includes a number of other enhancements such as new, larger command strings, more process variables (up to eight now), longer tag-names, and headroom for additional supplier names and model numbers (the number of HART devices and manufacturers having exceeded the original authors' envisioned upper limit). Other new capabilities defined in the specification focus primarily on patterns in the communication signals themselves: for example, alarms by exception, rate-of-change alarms, time-stamped data, and triggered bursts.
The current HART Protocol also defines for the first time test parameters and tools for ensuring the interoperability of devices and host systems. This is a non-trivial process for the vendor community, especially suppliers of host systems that must demonstrate the deft handling of even "worst-case" implementations by device manufacturers, but should ultimately pay dividends for the end user community. Device manufacturers, meanwhile have a somewhat easier time of it, as they are free to pick and choose what advanced features they will implement in order to differentiate their products.
The Future Is Bright
As the HART Protocol approaches its third decade of development and the HART Communication Foundation turns 20, it's clear that the movement's best years may well lie ahead. HART underpins the connectivity of a wide range of current and legacy field devices and host systems, and more are set to debut in the coming months. "We're looking at HART communication as being here long term; we're adding it to every new product we build," says Scott Saunders, chief operating office for Moore Industries-International, maker of a broad range of specialized signal conversion devices.
"There's just an enormous base of knowledge," adds Jeff Dobos, president of ProComSol, maker of PC-based HART communications and diagnostics software. "People know how to use it, and they want to use what they know; wiring is simpler, and wireless is an option," Dobos says. "Further, there are more and more suppliers using HART," he says. "Competition is strong, prices are down, and innovation continues to drive forward."
Gary Cusick, vice president of MACTek Corp., a manufacturer of interface devices for both wired and WirelessHART, is a bit less reserved about the technology's continued potential. "We believe HART technology is the best available field communication protocol for process automation applications – for new and existing plants," he says. "Users have spoken and have overwhelmingly selected HART communication as the world's leading field protocol."