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Smart-but-Simple Wireless Sensor Networking


There is currently a tremendous amount of energy and attention focused on industrial wireless. Standards are being developed, major automation vendors are announcing products, and expert opinions are everywhere in magazine articles, blogs, and at conferences. While the technology is interesting and essential, let’s keep in sight the only reason wireless matters: to make operating a plant more cost-efficient, safer, and more predictable. If wireless adds complexity, then it will fail.

In this article we will discuss the concept of “smart-but-simple” networking and its ability to reliably deliver process information without burdening the plant with new systems, consultants, or workload.

The term smart-but-simple refers to a new generation of wireless sensor networking (WSN) products. Unlike WiFi networks, which tend to be line-powered and connect workers to their applications, WSNs are typically battery-powered and connect field devices to monitoring and control systems for the purposes of gaining more insight into your processes, your plant, and your assets. Unlike prior-generation point-to-point and star-connected wireless networks, WSNs are able to dynamically adapt to the environment to provide extremely high long-term reliability.

Today, WSNs are gaining acceptance in a wide variety of industrial applications ranging from tank level to motor vibration to relief valve monitoring. In the future, WSNs will evolve to serve a wide range of monitoring and control needs. Smart-but-simple WSN products embed self-forming and self-healing intelligence in the network to ensure simple installation and long-term reliability. The network is smart so that the user experience is simple. These networks monitor their RF environment and node-to-node connectivity and continually adapt to ensure extremely high end-to-end reliability – without user intervention.

Smart Networks Deliver Reliability and ROI

Point-to-point and bus-connected networks have worked well in wired systems, so why not just translate this architecture into wireless networks? The unique challenge of wireless is that the strength and availability of individual communication links continually vary in time. Unlike wired communication links, which remain fairly constant for the life of the device, wireless links are affected in unpredictable ways by environmental conditions, new obstacles, delivery trucks, other wireless systems, etc. A particular communication link between two devices may vary from rock-solid to unstable during the course of a day, given the wide range of potential interference.

Luckily, each individual link varies differently in time and space, and if one link is experiencing trouble, there is a good chance that another link can successfully get the message through. To take advantage of this property, a wireless network must provide a way for data to flow on strong links and clear frequencies while avoiding weak links and congested frequencies. Providing multiple redundant routes is typically referred to as mesh routing and the use of multiple different frequencies is referred to as frequency or channel hopping. Frequency hopping and mesh routing is an extremely powerful combination, providing highly reliable wireless communication in challenging industrial environments. By leveraging the inherent diversity offered by wireless connections, a frequency-hopping mesh simply sidesteps interference and obstacles to ensure data reaches its destination – even if several individual links fail or specific frequencies are congested with traffic. The primary advantage of smart-but-simple WSNs is that frequency-hopping and mesh-routing intelligence is embedded right in the network so you don’t need to roll a truck or call a wireless expert if a link goes down.

 
Figure 1. Frequency hopping and mesh routing are key enablers of reliable wireless networking. Each node in a frequency-hopping mesh network has at least two available routes and uses a different frequency for each subsequent transmission.

If It’s Not Simple, It’s Not a Solution

The primary economic value of wireless is its ability to simplify the task of installing, commissioning, operating, and maintaining sensors to monitor and control the plant. After all, the sensors are the same, the systems are the same, and the data is the same as in wired applications. The difference with wireless sensing is the ease with which you can access parts of the plant or processes that were impractical before due to the cost and complexity of running wire. This increased reach into the plant gives leading companies the visibility and insight they need to increase the efficiency of their operation to the next level.

Of course, these benefits can only be gained once the wireless network is installed and is reliably delivering data. Any solution that makes things more complex is not delivering on the promise of wireless and it will not help plant operators economically solve their problems. The entire reason WSNs are generating interest in industrial applications is that real-world deployments in oil and gas refineries, chemical plants, pharmaceutical plants, and food and beverage facilities, to name a few, have proven reliability and have delivered up to 90% reductions in installation costs compared to their wired counterparts. The only way to realize this is to have a network that is smart enough to enable successful implementation by instrument technicians using the same tools and training they have today.

When all is said and done, the user experience must be “it just works.” Smart-but-simple WSNs embed self-organizing and self-healing intelligence in the network. This intelligence enables each node to scan its environment, identify neighboring nodes, and establish routes – all without human intervention. If the wireless solution requires new skills, new tools, new consultants, or new systems to get up and running, the economics become murky.

To fully gain the benefit of wireless, the installed system must also be very easy to extend or expand. Application requirements change, new measurement points are added, and new applications are layered in to serve new business needs. If each addition or expansion requires a team of wireless specialists, solution payback erodes quickly.

WirelessHART – A Smart-but-Simple Wireless Standard

The HART® Communication Foundation has been working for the past two years on developing WirelessHART™, a wireless extension to the HART communication protocol. The WirelessHART standard has recently been released as part of the new HART 7 specification, and it effectively combines smart-but-simple wireless networking with established tools and practices to provide the easiest end-user solution.

Dust Networks has worked closely with the HART Foundation and its members to bring best-in-breed wireless networking technology to the process industries. Dust Networks’ pioneering TSMP™ technology is a foundational building block of the standard, which utilizes mesh networking, time synchronization, and frequency hopping to ensure wireless deployments are extremely reliable, ultra low-power, and easy to install and manage.

By keeping an eye on the need for an it just works user experience, the HART Communication Foundation has developed a standard that will deliver the promise of wireless to the plant floor. The impact of WirelessHART will be far and wide: With an installed base of over 24 million devices and another 2+ million added yearly, HART is the dominant smart instrument communication standard in the process industries. Every one of these devices can be installed, managed, and maintained using existing tools and practices. Adding the ease and flexibility of wireless to the mix promises to be a revolution in plant efficiency, safety, and uptime.

 
Figure 2. WirelessHART applications (courtesy of HART Communication Foundation)

Smart-but-Simple Plus Standards Puts You in the Driver’s Seat

The new WirelessHART standard combines the benefits of smart-but-simple networking with established and well understood tools to effectively deliver the promise of WSN to the process industries. Several companies, including ABB, Emerson, Endress+Hauser, Pepperl+Fuchs, Siemens, and Yokogawa, have stated their support for WirelessHART, and products will begin to come to market in 2008. These products will be enabled by embedded WSN technology providers, including Dust Networks, which announced its SmartMesh IA-510™ WirelessHART-compliant products in September 2007. Get detailed information on WirelessHART.

We are right around the corner from a revolution in plant efficiency, uptime, and safety. While wireless is the key enabling technology, the revolution is in the flexibility and agility with which plant operators can gain new insights and leverage real-time information to improve the way they run their plants. Only a system that is extremely simple to deploy, reconfigure, and expand will deliver on the promise of wireless by putting you in the drivers’ seat.


 Overview of WirelessHART*

WirelessHART is the new interoperable wireless communication standard for the process industries. It adds wireless communication capabilities to process measurement and control devices based on the HART Communication Protocol, while maintaining compatibility and ease of use characteristics with existing HART devices and tools.

Each WirelessHART network includes three main elements:

  • Wireless field devices connected to process or plant equipment.
  • Gateways that enable communication between these devices and host applications connected to a high-speed backbone or other existing plant communications network.
  • A Network Manager responsible for configuring the network, scheduling communications between devices, managing message routes, and monitoring network health. The Network Manager can be integrated into the gateway, host application, or process automation controller.

The network uses IEEE 802.15.4-compatible radios operating in the 2.4GHz Industrial, Scientific, and Medical radio band. The radios employ direct-sequence spread spectrum technology and channel (frequency) hopping for communication security and reliability, as well as TDMA synchronized latency-controlled communications between devices on the network. This technology has been proven in field trials and real plant installations across a broad range of process industry applications.

Each device in the mesh network can serve as a router for messages from other devices. In other words, a device doesn’t have to communicate directly to a gateway, but just forward its message to the next closest device. This extends the range of the network and provides redundant communication routes to increase reliability. The Network Manager determines the redundant routes based on latency, efficiency, and reliability. To ensure the redundant routes remain open and unobstructed, messages continuously alternate between the redundant paths. Consequently, like the Internet, if a message is unable to reach its destination by one path, it is automatically rerouted to follow a known-good redundant path with no loss of data.

The mesh design also makes adding or moving devices easy. As long as a device is within range of others in the network, it can communicate.

For flexibility to meet different application requirements, the WirelessHART protocol supports multiple messaging modes, including one-way publishing of process and control values, spontaneous notification by exception, ad-hoc request/response, and auto-segmented block transfers of large data sets. These capabilities allow communications to be tailored to application requirements, thereby reducing power usage and overhead. 

*Source: WirelessHART website

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