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There are many wireless protocols, but there is only one wireless protocol deliberately built as an extension of an existing wired sensor network protocol and to work with the applications, tools, and people you already have: WirelessHART.
In short, Wireless + HART = WirelessHART.
“WirelessHART was designed by the industry experts who created the HART Communication technology,” says Ed Ladd, director of technology programs for the HART Communication Foundation, “and drawing on the experience of more than 26 million installed HART-enabled field devices, WirelessHART is designed to address the critical demands of industrial plant environments and to complement, work alongside, and extend the capabilities of wired HART.”
“WirelessHART,” says Emerson’s chief strategic officer, Peter Zornio, “removes the limits and unleashes the HART technology in a way that wasn’t possible when channeled through conduit.”
WirelessHART is also unique in that it provides for an adapter that is not just a wire replacement or a protocol converter, but an intelligent HART-enabled device and powerful system integration tool. This adapter now makes it easier than ever to leverage the intelligence in existing HART devices already installed in your plant. The WirelessHART adapter can be attached to any existing wired HART device, enabling wireless access to the “stranded data” inside the intelligent HART device. Consequently, the WirelessHART adapter provides a cost-efficient connection for integrating the intelligent capabilities of HART devices into control and asset management systems.
“The wireless adapter makes this transition very easy,” says Thomas Holmes, CEO of MACTek Corporation. “By using the installed device, say a HART 5 device from any supplier, the user can add a wireless adapter allowing HART data from the device to be communicated to the gateway.”
Any manufacturer’s gateway will work.
WirelessHART, like every other portion of the HART 7 specification, is completely backward-compatible with all previous versions of the HART specification, and wireless adapters can be installed on any existing HART device, regardless of protocol version.
The main secret to the success of WirelessHART installations is the mesh. Using the global standard IEEE 802.15.4 2.4 GHz radio and channel-hopping technology, WirelessHART installations are flexible, secure, reliable, and simple.
All field devices have the same wireless capabilities, and as the number of devices in the mesh grows, the more secure and reliable it becomes. The more devices in the mesh, the greater the number of pathways exist from any single device to an access point, from an access point to any single device, or from a device to another device.
At the same time, the user experience mimics using wired HART, with the same tools and practices users have become familiar with. The same command structure is also used in WirelessHART, and WirelessHART is compatible with HART-enabled control systems and EDDL.
“End users get a state-of-the-art standard wireless infrastructure,” says Emerson‘s Zornio, “supported by a full set of vendors they know and trust, so they can invest with confidence. At the same, time,” Zornio goes on, “WirelessHART builds on the experience, knowledge, work practices, and investments end users have made in HART over the last 15+ years.”
The WirelessHART network consists of field devices, adapters, access points, and gateways. Somewhere on the network, either built into a gateway or separately, are the Network Manager and the Security Manager. No devices are network end points, or reduced function devices to be orphaned by changing signal conditions.
Every WirelessHART field device and adapter is also a router. Since every device is a router, the result “path diversity.” Path diversity means that messages route around obstacles and interference sources regardless of the physical location of the device in the network.
The Network Manager maintains and updates routes. It establishes links between neighboring devices, and it allocates bandwidth. There is a single Network Manager (can be redundant) in a WirelessHART network that can manage multiple gateways and access points. The number of access points needed is determined by the number of devices and average update period, using a simple formula (see “HART 7: Installing and Making Systems Work” in this issue). Geographic location may also be a factor. The more devices you add, the more access points. Multiple access points per gateway mean redundancy and faster throughput, and even better “path diversity.”
All communication paths in the mesh network are continuously exercised (primary and redundant). All WirelessHART devices are routing-capable to maximize the number of possible redundant pathways, increase the reliability, and simplify network design.
WirelessHART technology’s priority-based routing enhances reliability. Its first priority is to keep the network operational. Second is to deliver the process monitoring and control data. Third, enable management and troubleshooting of the devices. Fourth, deliver the alarms. All alarms are time-stamped and latched. That way alarms are never lost, and the alarm log details in what order the problems occurred.
User deployment and operation is simple. WirelessHART devices are configured using the same tools as wired HART devices. Only the Join Key and Network ID need to be loaded into the device for it to join the network. These items can be loaded by the user or preloaded at the factory, and the device does the rest. The device joins the network and, working with the Network Manager, it embeds itself in the mesh. The Network Manager then continuously grooms the mesh to ensure reliable, low-latency communications as plant conditions change and evolve.
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