Industrial Wireless Sensor Networks

By Lynnette Reese, Mouser Electronics

Industrial wireless sensor networks (WSN) are projected to increase by 553% in the next five years, to nearly 24 million installed sensor points. Recent developments in wireless communication, power efficiency, extreme miniaturization (such as made possible by MEMS sensors) and embedded computing technologies have led to the rise of viable wireless sensor networks for demanding Industrial environments. Other reasons for this growth are that WSNs are at acceptable reliability levels for most industrial uses, the advent of WSN standards specifically for industrial systems, and increasing awareness and education about the benefits of WSNs. It looks as if wireless has reached a tipping point in the Industrial sector. WSNs are creating new uses, solutions, and applications, offer enormous benefits to many industries, and are essentially changing the paradigm by which industry operates. Key to all of this is that integrated chip solutions are now offered at prices the market can afford.

A wireless sensor network is a network of up to thousands of tiny autonomous sensors (or nodes) physically distributed in a space. These sensors are effectively linked, and communicate peer-to-peer with each other via radio frequency (RF) waves where they monitor and communicate local status or conditions, such as temperature, vibration, pressure, pollutants, motion, and so forth (see Figure 1.) These smart sensors can automatically supervise processes and require no manual intervention unless a process fault occurs that cannot be corrected via action of the smart node or via human commands initiated remotely.

The smart sensors/nodes cooperatively hand off data to other smart sensors through many possible paths in the network, potentially leading to a main location where the information may be viewed by a human, further processed and stored, or otherwise acted upon. The redundancy of multiple communication paths looks something like a mesh when all possible paths between nodes are drawn. Each sensor or node may be as small as a pepper flake and yet have a processor, a tiny memory (e.g., 12Kb on-chip RAM), low data rates (40 Kb/s), and a short range (most are 100' or less), all with low energy consumption. Lower energy consumption is now possible due to lower cost, higher integration, more refined power management capability, and the application of smarter algorithms. In addition to that, energy harvesting takes power budgets to net zero consumption, and battery-less intelligent operation opens up solutions uniquely made possible by this emerging technology.

Wireless capability offers huge benefits. Adding remote sensors (often with some local decision-making capability) without the cost of laying cables or wires results in saving labor, energy, and materials as well as creating process improvements through improved monitoring and correction from anywhere, since smart phones are an ideal human operator/maintenance interface. Productivity increases when operators no longer have to travel to obtain remote data or replace batteries in hard-to-reach or hazardous places. WSNs are faster to install and much easier to relocate compared to wired solutions. They are extremely scalable and link-reliable, and offer real-time capability and energy independence when deployed with energy-harvesting devices. WSN is finding its way into industrial applications such as machine health (e.g., vibration analysis), manufacturing, condition-based maintenance, automated metering, remote monitoring, inventory, vehicle and personnel management, and many other areas of operations management. Equipment can be maintained when necessary, per sensor input. When maintenance is performed earlier and when needed the life of the equipment is lengthened and reduces waste (for a greener plant) versus the old way of performing maintenance on a time-based schedule whether it's needed or not. This is known as “condition-based maintenance.”

Efficient Wireless Communication

Two major challenges to the adoption of new technology are cost and whether or not standards exist. In the consumer market, Blue-Ray won as a standard over HD-DVD. Both formats were announced a decade ago. Competition between standards is counter-productive. Industrial WSNs are not immune. WirelessHART and ISA100-11.a are relatively new, and developed specifically for industrial use, where two of the most critical factors are reliability and real-time response. These two standards are very different from consumer-related wireless protocols. A protocol is a set of conventions or rules for data transfer for addressing, signaling, error detection, and authentication required for sending information over a communication channel.

Industrial wireless networks may demand near real-time and cannot tolerate the high latency levels that are acceptable for VoIP, for example. For wired field devices, an Ethernet latency of only 10ms is acceptable. Wireless Sensor Networks are no different. Thus, a major feature of wireless mesh networks is the preponderance of redundant nodes with store-and-forward packet switching functions; the same basis on which the robust nuclear-proof ARPANET, progenitor to the Internet, is known for. If large chunks of the network fail, the majority of remaining nodes in the network are unaffected. This is related to another benefit of WSN: they are self-healing. If a node is removed, the other nodes will simply use other neighboring nodes to relay information. If a new node is added, it begins transmitting and relaying packets as if it had been there all along.

Industrial WSNs can function with deterministic performance if the protocol is considered. A deterministic system is a system where there is no randomness in generating future states of the system. This means that response times are predictable; there is predictable network latency, fault tolerance, and a connection-based topology. Much of determinism relies on the efficiency of the routing algorithms that are used in any protocol, wired or not. This is where industrial standards most benefit WSN implementation and redundancy, high-reliability and low complexity are common demands of industrial networks.

Network security is also of grave concern in industrial control systems. The anonymity of a wireless network is not enough to keep it safe from hackers, and this is a growing concern. Encryption is applicable to Industrial WSNs and

Mouser offers several wireless sensor networking products. A prime example of an energy-independent WSN is the Powercast Wireless Sensor System, which has RF-energy harvesting modules that work together to transmit accurate temperature and humidity measurements in real-time through a wide range of industry standard protocols on 802.15.4 hardware.

In general, WSNs began as proprietary solutions offered by automation vendors to solve previously impossible problems or replace expensive solutions. Proprietary solutions are not open, so the solutions are something of a “black box” to users. This acts to impede the organic growth of innovation, since only the vendor has access to the tools for research and development in proprietary protocols.

The main characteristics of a WSN include:

• Nodes can easily be relocated
• Can automatically handle node failures
• Nodes are similar in function and behavior
• Easily scalable to grow into larger networks with thousands of nodes
• Suitable for harsh environmental conditions since there are no cables and low or no power maintenance
• Easy to use; adding a node is as simple as placing and activating it (low or no configuration requirements)
• Low power consumption
• Very low power consumption for nodes that use batteries or harvest energy

Table of Protocols Used in Industrial Wireless Networks

The future of wireless sensor networks is in concepts such as “ambient intelligence,” which is a term that refers to the pervasiveness of wireless computing such that a physical space is embedded with a variety of nodes that sense and implement control based on the requirements of the immediate environment. Wireless technology is not going to stop improving any time soon. The new IEEE 802.11ac standard will deliver transfer rates three or four times faster than the present 802.11n Wi-Fi, with data rates of up to 1.3 Gbps. And so Industrial networks will improve. The paradigm for Industrial networking is shifting as wireless allows us to do things we could not do before, or creates new functionality that we didn't know we needed.

 Lynnette Reese is a technical consultant at Mouser and holds a B.S. in Electrical Engineering from Louisiana State University. Prior to her position at Mouser, she completed a combined 15 years in technical marketing in embedded hardware and software with Texas Instruments, Freescale, and Cypress Semiconductor. She enjoys gadgets of all types and is an aspiring geek goddess.