Today, automation professionals in a process plant have a choice to make for new installations: wired or wireless? For plants with existing wired and wireless infrastructure, the choice hinges on a straight comparison of the two technologies and the application of the solution that makes sense.
The International Electrotechnical Commission (IEC) approved WirelessHART in March 2010 as IEC 62591, and ISA-100 was approved in September 2014 as IEC 62734. For the purposes of this article, wireless refers only to wireless sensor systems, and not to other wireless technologies such as 802.11 Wi-Fi.
WirelessHART is a self-organizing mesh technology in which field devices form robust wireless networks to dynamically mitigate obstacles in the process environment. Other wireless technologies employ similar strategies, with varying degrees of effectiveness.
[sidebar id =1]Wireless technologies do not require communication wiring and related infrastructure. Some wireless devices require power wiring, but the vast majority of deployments utilize battery power, and thus operate completely without wires. Wireless networks communicate data back to host systems securely and reliably, and can be applied to both control and monitoring applications.
A WirelessHART installation requires, first of all, a wireless instrument transmitting data according to the IEC 62591 WirelessHART standard. If a transmitter does not have WirelessHART, a wireless adapter can be installed on most existing two- or four-wire devices.
With WirelessHART, each wireless device transmits to a gateway managing a specific wireless field network. Typically, the gateway is assigned to a process unit. Each gateway manages its own wireless field network and can have an assigned HART tag like any HART device. Each wireless field network in a plant has a unique network ID to prevent devices from attempting to join the wrong network.
WirelessHART devices can communicate through each other to send messages to the gateway, forming a self-organizing “mesh.” The mesh extends the range of a device beyond that of its own radio. For example, a wireless device may be several hundred feet away from the gateway with obstacles between, but power-efficient “hops” through neighboring devices closer to the gateway ensure a reliable, extended range. The gateway connects to the DCS via a wired or wireless high-speed link, typically Ethernet.
[sidebar id =2]The chief advantage of wireless systems is that they can be installed virtually anywhere in an efficient, timely, and cost-effective manner. Battery-powered transmitters require no wired infrastructure or local power supply, so they can be far away from a process unit’s wired fieldbus and power wiring. They can also be installed in locations where supplying power and cabling would be too expensive or hazardous. This flexibility means that there are benefits to using wireless in both Greenfield capital projects and existing Brownfield facilities.
Greenfield capital projects typically want to make 10 to 20 percent of traditionally wired signals wireless. Engineering, procurement, and construction contractors and plant owners see strategically incorporating wireless as beneficial in terms of reducing physical fixed infrastructure. They also use wireless technology to manage schedule risk and cost escalation/containment and to reduce space requirements and weight.
Wireless can reduce schedule and cost impacts because there is always the potential for scope creep and additional I/O as projects progress. The later in the project a change comes, the greater the risk of jeopardizing the project schedule and budget. Wireless can usually accommodate these changes better than fieldbus.
Quite often, additional measurements are eliminated from the design of a new or retrofit project because those signals are deemed too costly to implement during the capital expenditure phase of a project. If those measurements are needed later, adding wired instrumentation can be much more costly than wireless solutions. On these types of Brownfield projects, wireless solutions are a good way of supporting operational excellence programs to improve plant productivity and reliability and compliance to emerging environmental and safety legislation.
A plantwide wireless network can be installed with minimal disruption to fixed infrastructure such as wiring, conduits, and cable trays. For example, a major chemical company in Europe implemented a plantwide wireless infrastructure to enable operational expenditure programs. The first application was an energy project to monitor steam traps. The company installed wireless acoustic transmitters to listen for acoustic signatures and monitor temperature—both vital signs related to steam trap operation. The steam trap monitors took only two days to install, and they generated a complete return on investment (ROI) in six weeks through detection and remediation of previously unknown losses.
In another application, a global contractor reported that adopting wireless solutions cut commissioning time by 50 percent. It also streamlined the design and engineering process, saving 10 hours per measurement point. Using wireless helped them maintain the project schedule and improved their ability to manage change on the project.
A third leading wireless application is fixed asset inspections per IEC 60079 Part 17, which requires plants to continuously monitor electrical equipment in hazardous areas. This directive obliges maintenance personnel to manually check instrument cable glands, cables, terminal field junction boxes, safety barriers, trunking, ducting, pipes, and conduit for leaks, corrosion, tightness, and similar problems. Wireless transmitters do not require wired infrastructure, thus eliminating this costly maintenance task.
The low-power nature of WirelessHART devices allows them to operate for several years without replacing the battery. Configurable update rates conserve battery life by choosing the most appropriate rate for a particular application, typically within a range of 1 second to 1 hour. Most applications today are “monitoring” and therefore only need infrequent updates. WirelessHART transmitters can in certain circumstances be used in real-time control applications, but this requires higher update rates, in some cases necessitating wired power.
Many projects have a very attractive ROI when using wireless due to the elimination of installation and maintenance costs. In these situations, wireless can quickly deliver an investment payback, with ongoing benefits.
Wireless will become more popular because it can monitor anything, anywhere. Also, it can be easily installed in both new and old plants. Industry-leading process plants will install both wired and wireless infrastructure and use whichever is most efficient and effective in each situation.
