Wireless Networking moves from Instruments to Infrastructure
01 February 2008
Three major wireless providers, Honeywell, Emerson, and Invensys are pursuing widely different approaches—with specific benefits and weaknesses—but have clearly articulated long-term strategies and resources to achieve their goals.
Photo courtesy of Emerson Process Management
In the early days, the key phrase was wireless instrumentation and the benefits it would bring. During the past year, the distributed control system (DCS) vendors expanded on this idea: now they talk about wireless infrastructure as their key goal. They want to connect more than instruments; the intention now is to provide a wireless backbone for everything that needs to be communicated in a plant, from sensor information to portable HMIs to mobile telephones.
And, fading into the background, are concerns about security and reliability of wireless networks. The issue is still there, but end users appear to be increasingly won over to the wireless networking concept. And some are hinting that the technology may be appropriate for some mission-critical control applications, although that’s a topic more reserved for the future.
35 million wireless devices
Honeywell Process Solutions was first major player on the market, introducing its XYR 5000 wireless instruments in 2003. Without a question, its wireless pedigree has great depth. Various divisions of Honeywell have researched and marketed millions of wireless devices in areas as from avionics to building automation, some of them in missioncritical applications.
When Honeywell rolled out its OneWireless platform in 2006, it was clearly aiming at infrastructure, including not only instruments but wireless mobile operator stations, employee tracking, and voice communications. For instrument communications, Honeywell chose a variant of SP-100 (the ISA wireless standard that is expected to be completed in 2008), but says it recognises others may prefer the WirelessHART platform (based on 802.15.4; a mesh networking technology operating in the 2.4GHz ISM radio band using DSSS radios with channel hopping) and has prototyped these radios as well.
Honeywell’s recent acquisitions in instrumentation companies, such as InterCorr for corrosion monitoring, and Enraf for tank level monitoring and custody transfer, as well as its new alliance with Krohne for flow measurement, show a renewed interest in instruments at the field level. However, Paul Orzeske, EMEA general manager, says his company is not interested in commodity sensor products, but will pursue sensors that are ‘highly differentiated’ and extend the Experion product range.
Externally powered iNodes
Honeywell developed SP-100 based devices believing the standard will be more robust and efficient in bandwidth use, especially when contrasted with WirelessHART. ‘Why would you want a pager when you can have a Blackberry?’ is the way Honeywell’s VP Harsh Chitale compares the two standards. Honeywell’s OneWireless uses externally powered multi-nodes called iNodes’ scattered throughout the coverage area. These communicate with each other and provide a backhaul to bring information to a gateway where it passes into the larger wired network to the DCS. Individual instruments do not mesh with each other or act as repeaters. They simply broadcast data to the iNodes, which take it to the gateway. The meshing action takes place between iNodes, not at the instruments. For safety, at least two iNodes receive data from each instrument, creating a redundant path.
Honeywell has created a network with low latency and very deterministic communication which is critical for closed loop control functions. Alex Chernoguzov, Honeywell engineering system architect explains, ‘While we know initial applications will predominantly include slower-speed monitoring and alerting, we intentionally architected the system so that customers can, in the future, add control and higher speed data communication using existing wireless infrastructure. If you design a system to monitor only, it is hard to upgrade it to accommodate control. If you design the system for control, it is easy to do monitoring. So, we intentionally designed it with high reliability, high throughput and a high degree of determinism and latency control to support multiple-use applications. ‘In addition, customers asked us to support fast alerting. Many people don’t understand the difference between monitoring and alerting. Monitoring means you send a value back periodically no matter what. Alerting means that you send a value back immediately if a threshold is reached. A good example is a level sensor for a tank. For monitoring purposes, you might only need the value updated every 30 seconds.’ During an overflow, ‘you don’t want to wait 30 seconds, you want to know right now. That’s alerting, and it looks a lot like control because it requires minimal latency, guaranteed delivery, etc.’
Moving beyond instrument communications—whether or not that ultimately will be SP-100 or WirelessHART or something else—the nodes also provide WiFi connectivity (802.11 g) for wider bandwidth applications such as laptop computers; mobile HMI and control room interfaces; employee tracking and voice and video communication. In fact there are three aerials on each node: one for the instruments, one for WiFi, and an third for the nodes to communicate with each other.
In its early efforts, Honeywell learned ‘that there’s a very finite amount of air space available at these plants, and a lot of them today are already using other wireless applications,’ says Jeff Becker, Honeywell’s director of global wireless business. ‘Because wireless is a shared medium, you start to hit interference limits. You can only run so many applications at the same time before they start to step on top of each other.
‘Honeywell decided to co-ordinate wireless use rather than have many point solutions that could interfere with each other. Customers don’t want to manage it, so OneWireless made a whole lot of sense.’
Emerson’s Smart Wireless
In January 2007, Emerson Process Management launched its Smart Wireless instrumentation system, identifying Dust Networks as a partner providing the 802.15.4 embedded wireless modules, which has become the WirelessHART standard. Later in the same year, Emerson announced it had concluded an agreement with Cisco to provide a ‘complete solution’ for wireless factory networking, including management applications such as worker mobility, VoIP, and video applications.
This first introduction reflects the importance Emerson places on the lowest level of the factory networking hierarchy: 45% of its $5.7 billion revenue in the previous year came from field instruments, while another 31% came from valves and regulators. Connecting these devices, Emerson asserts, does not have to be complicated.
‘Bob Karschnia, VP of technology for Rosemount says, ‘We introduced our Smart Pack as a simple way for people to try it easily and with a limited number of devices. We have other customers that are ordering equipment and installing it as fast as they can. That’s really a big statement, because people in oil refineries and chemical plants and power plants are all busy today, but these people are taking time out to get these installed and are actually using them.’
Each one of Emerson’s wireless devices functions as a transmitter, receiver, and a repeater. They form communication links with each other, support their network partners as needed, and report to a larger system when there are disturbances in the links.
All instrumentation in this scenario is battery powered, and only one gateway point needs external power and a wired network connection. Dust Networks says its TSMP (time synchronised mesh protocol) is very efficient with power consumption, allowing battery life of several years and longer even in adverse conditions. Consequently, there is effectively no need to add wiring to the communication devices.
Everything in a Dust/Emerson platform is optimised to maximise battery life, or at least make it predictable. Individual devices minimise power consumption and communicate data in bursts of 10 ms. Instruments not practical for battery powering will require mains or some other method.
Under Emerson’s current application of the SmartMesh XT protocol, the shortest reporting interval for an instrument is 15 seconds. However, individual devices can be called upon by neighbours to relay data even when they have no data of their own to send. Devices closest to the gateway see the most relaying activity, however the network can be optimised to ensure that no single devices have to bear more than their share. This spreads activity through the network and stabilises battery life. Emerson predicts that with effective optimisation, any device, regardless of its position in the network, should operate at least 5 years.
Of the protocols examined here, the Dust / Emerson solution with its multihop mesh networking has the highest potential for latency in communication since data may have to jump from device to device before reaching the gateway. This does increase transit time, although the practical effect is debatable in the context of an instrument’s data reporting interval. If a temperature transmitter, for example, only has to send its value every 15 sec or 30 sec, then a few extra milliseconds of latency will not disturb the operation.
With the SmartMesh XT approach, each hop adds 31.2 ms, so if an instrument is ten hops from the gateway (which could be the case for some on the fringes of a huge network) latency is 312.5 ms. More typically, a network will require three or four hops, so latency will be about 100 to 135 ms. In most installations, up to 30% of the devices in a network talk directly to the gateway, so those have no extra hops. There are strategies to mitigate latency, but some can reduce battery life.
Emerson and Cisco
In late 2007 Emerson announced it would collaborate with Cisco to provide WiFi plant network solutions for its customers. The networks will use Cisco’s Unified Wireless Architecture offering which includes Cicso’s 1500 Series wireless mesh access points, controllers, network management software, and plant applications such as communication, tracking, video, and worker mobility tools. Emerson says it will manage the projects and deliver the solutions by working with Cisco, and will thus eliminate the need for a ‘complex wireless overlay network.’ Cisco’s Wireless Control System will centralise the configuration and management of the plant’s WiFi network.
Emerson is also busy developing new instruments to add to its field devices. At the same time it made the Cisco announcement, it said that it was also adding to its wireless instrument portfolio a ‘discrete transmitter’ to connect to digital points, a vibration transmitter, a remote operations controller, and in collaboration with Rohrback Cosasco Systems, a corrosion monitor.
Invensys: the technology agnostics
The third wireless technology is driven by Apprion (www.apprion.com) and its industrial partner, Invensys. The two say wireless has huge potential but must be approached with a plan. A plant-wide assessment is a critical first step. They cite studies that say wireless networks require more management than
comparable wired counterparts. Users that build haphazardly will ultimately find a mess of conflicting communication.
Second, they say, no single vendor technology is sufficient to exploit all that wireless has to offer. Therefore, infrastructure has to work with a variety of approaches and vendors. Ian McPherson, VP of products for Apprion says, ‘The needs of the application are going to drive people to one of three propositions: you can have low latency, high bandwidth, or long battery life. You can’t reconcile all of those in one technology. Our ability to be technology agnostic doesn’t mean you should have anything and everything, but you can have choice of multiple vendors to find the best for
any application or networking challenge.’
This being the case, McPherson expects to see plants with multiple sensor networks operating side-by-side depending on the nature of the tasks they perform. The Apprion infrastructure will keep them all working together co-operatively, he says.
Moreover, a well managed wireless network can perform any wired functions and more. Apprion describes its infrastructure as a cloud that covers a plant and can do virtually anything. Invensys supplies applications that operate within this cloud, and when fully deployed, it can integrate with any wireless instrumentation platform, and handle walk around HMIs, personnel tracking, condition monitoring, voice and video communication, etc. An end user can select devices from any supplier, using point-to-point or mesh networking. Invensys characterises this as ‘both vendor-independent and standards-agnostic.’
Apprion’s hardware approach is to deploy externally powered nodes, called Ionizers, around the plant. Like Honeywell’s OneWireless, these have multiple radios to communicate with each other and a variety of devices. Ultimately, all information travels via a WiMax backhaul that connects all the Ionizers. However, the Ionizers will not necessarily be able to communicate directly with all individual wireless devices. For example, a group of Emerson Smart Wireless instruments may still use the Emerson gateway as the access point. If that gateway can be wired to the larger plant network, it might not communicate with the
Apprion system at all except to share security and network management functions. This approach will have the least appeal to a company who wants to approach wireless incrementally. The infrastructure has to be built before applications can be implemented, and that represents a major expense compared to a buying just a few points. The infrastructure is scalable but not really designed for small installations. But once the system is in place, applications are simple to add since most possibilities should have been considered
n the site survey.
System design and management play to Apprion and Invensys’ strengths, since neither have wireless process instrumentation. This is in contrast to Emerson and Honeywell, which have much hardware available and more on the way. Hesh Kagan, strategic technology director at Invensys Process Systems, explains, ‘We’re developing wireless instrumentation, but many of our systems today are being used with competitive instrumentation in the wireless world, just as it is in the wired world. We’re about working with customers to develop an ongoing strategy. Wireless is just an enabling technology. Our whole message is the InFusion model of integrating the whole enterprise.’
One interesting element of this discussion is the convergence of technologies. All three are moving in the direction of offering full scale, managed wireless infrastructure solutions. Given the potential for interconnectedness, does that make the choice of initial vendor all the more critical or much less important?
‘Some day there may be software defined or cognitive radios that could run different protocols on a single radio, but that’s many generations from now, says Apprion’s Mr. McPherson. Until that day, approaching wireless technology, like any technology, should begin with understanding your applications.
Peter Welander, Control Engineering in the U.S., contributed to this article
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