WirelessHART Opens New Horizons
The latest version of the HART standard is most notable for its extension to wireless field network communications. WirelessHART, which has achieved global standard status as IEC 62591, leverages the time-synchronized mesh protocol (TSMP) developed by Dust Networks, now part of instrumentation subsystem supplier Linear Technology, to communicate process variables as well as instrument diagnostics over a robust but low power communication network.
"In the early 2000s, our vision was that you should be able to put a sensor anywhere," says Joy Weiss, Dust Networks president. "We knew that in order for our vision to take off, customers had to trust that [our wireless network] was as good as the wires they had before." Coincidently, a number of suppliers in the process control industry began actively seeking a wireless solution that would provide multiple years of battery life together with high network reliability in industrial environments. The resulting standard effectively grafted the long established wired HART taxonomy onto Dust's wireless mesh network, adding a wireless communication option to the HART portfolio and making it relatively straightforward to integrate wireless monitoring points and wireless device management into existing control systems and wired HART device management methodologies.
As evidence of the uptake of WirelessHART, a just completed survey of Control readers indicates that 28% of readers already have wireless field networks up and running in their plants (see figure). Further, WirelessHART leads the pack among readers with active wireless networks or plans to deploy them: more than a third indicated they have settled on WirelessHART. Another measure of WirelessHART acceptance is the number of instrument manufacturers that are being told by their users that they need something that will fit into their wireless infrastructure, Weiss notes. "Sometimes it's their first HART implementation -- they're going straight to WirelessHART," she says.
WirelessHART mesh networks also can be used effectively in combination with other wireless technologies, notes Garrett Schmidt, product manager, wireless I/O and networks, for Phoenix Contact in the Americas. The company offers a longer range, powered Wi-Fi device to backhaul local sub-networks of WirelessHART devices. The number of devices on each WirelessHART sub-network depends on topology and desired measurement update rate, adds Dave Burrell, a wireless product specialist, also with Phoenix Contact. "The range is 25-100 devices per [backhaul] node, with 25-50 being typical," Burrell says.
A key benefit of WirelessHART for users is that it's low cost and easy to add new process measurements. When implementing a WirelessHART solution there's no need to disturb crumbling or capacity-limited wired infrastructure.
HART Leading Wireless Adoption
A just completed survey of Control subscribers shows that the implementation of wireless instrument networks continues to gather momentum. A full 27% say they currently are using wireless field instrument networks (first pie chart) and another 21% intend to test one in the future. The other half of respondents are equally split among the undecided and those who do not intend to implement wireless field instrument networks. WirelessHART also leads the pack (second pie chart) among respondents who have decided on a wireless instrument network protocol.
Which of the following statements best characterizes your current or planned usage of wireless instrument networks?