Why Go Wireless: Weighing the Benefits and Challenges of Wireless Remote Monitoring
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Significant time and money has been invested into researching the use of wireless technology for remote monitoring. Yet, significant wireless deployments are just beginning to materialize in industry. There are many advantages to eliminating cables in remote monitoring applications, but there are also many challenges. As standards such as Wi-Fi (IEEE 802.11) and ZigBee (based on IEEE 802.15.4) continue to mature for use in wireless sensor networks (WSNs), those challenges are being addressed. Discover how wireless technology has evolved for measurement applications and learn key considerations for designing wireless remote monitoring applications.
Table of Contents
Benefits of Wireless Remote Monitoring
The two primary motivations for choosing a wireless network over a wired approach are the flexibility and the cost-savings associated with eliminating cables and wires.
Flexibility
| With no wires or cables to route, a wireless monitoring system is inherently more flexible than a traditional network. You are not locked into a fixed network topology or system setup, leaving open the possibility for additions, upgrades, extensions, and so on. This convenience means there is less overhead associated with setting up a measurement, and less overhead means more opportunity for taking additional measurements for added insight into your system. Wireless also extends the portability of your data acquisition. Field measurements can be time-consuming and costly. With wireless sensors, setup time is significantly reduced. | NI Wi-Fi DAQ  Watch the six-minute Wi-Fi data acquisition guided tour » |
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For many applications, wires and cables are not a practical option. For example, moving or rotating equipment, such as a crane or oil drill head, requires the festooning of cables or the use of slip rings. These mechanical additions add complexity to the system and require regular maintenance. Slip rings in particular can wear out and degrade signal integrity. A wireless approach eliminates the need for such additions, by allowing the sensors themselves to rotate or move with the device under test. Signal integrity can also improve by bringing the analog-to-digital conversion closer to the actual signal source. |
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Figure 1. Festooning cables can be a costly alternative to using a wireless measurement system.
Cost
The flexibility of wireless remote monitoring systems can translate into large cost savings. For example, consider the case of a factory floor, where machine health is crucial to proper operation of the plant. Cost savings can be achieved at two levels: reduced downtime and installation labor. More diagnostic measurements give you increased visibility into the health of your machines and the efficiency of your processes. Each sensor added can potentially reduce downtime by giving you insight into when a part is about to fail. With more data you can also respond quickly to maintenance issues or prevent them entirely. However, this added insight must be weighed against the cost of additional measurements. The expense of running cables or wires in an industrial environment cannot be ignored when calculating the return-on-investment (ROI) of a new monitoring system. Take into account the engineering effort, materials, and system downtime, and the cost for running cables in a plant can range from $10s per foot to $1000s per foot. If these measurements are highly distributed, the cost associated with adding a sensor can quickly negate any diagnostic benefit. Wireless monitoring systems require less installation and maintenance cost.
Challenges of Wireless Remote Monitoring
The financial benefits of using wireless for remote monitoring are compelling; yet, industry has been slow to adopt the technology. Security, reliability, integration, and power are all challenges that must be overcome before there is widespread adoption of wireless measurement systems.
Security and Reliability
Security is the number one concern for many engineers and scientists considering wireless. The reasoning behind this is due in large part to the failings of early wireless standards such as wired equivalent privacy (WEP), which did not prevent unauthorized access well. There are two main components of network security that must be addressed before wireless is widely adopted: authentication and encryption.
A wireless network is inherently more accessible than a wired network (such as Ethernet) because it is not a closed system: data travels through the air. There are many options for restricting wireless network access, however. ZigBee and other low-power personal area networks (PANs) have a limited broadcast range, making it easier to limit the physical coverage area. For larger systems, standards such as IEEE 802.11X have evolved to provide authentication on wireless networks based on the Extensible Authentication Protocol (EAP). Clients on the network must identify themselves before being granted access to the network. There are other less sophisticated strategies for preventing unauthorized network access as well. Good security practice for wireless networks includes MAC and/or Internet Protocol (IP) address filtering and service set identifier (SSID) suppression.
Even if data is accessible to an unauthorized user, it is not necessarily intelligible. Data encryption on wireless networks has evolved significantly over the last decade from clear-text broadcasts to 128-bit cryptography. The Advanced Encryption Standard (AES) is now an NIST standard and a requirement for all U.S. government installations. Both ZigBee and Wi-Fi have the option for 128-bit AES encryption.
Read more about wireless network security for data acquisition applications.
Integration with Existing Systems
A common solution to wireless security vulnerabilities has been proprietary networking protocols. Many wireless sensor vendors use a proprietary network because its details are not publicly available. The problem with this solution is two-fold. One, if the details of such a protocol are ever leaked, the entire system is compromised. And two, proprietary networks are difficult to integrate with existing wired systems. If you choose a proprietary protocol, you are locked into using network components from a specific vendor that may not be interoperable with your existing equipment. This is also true of the software. Turn-key data-logging software is not typically open – modifications are difficult if not impossible. The risks of a vendor-defined solution can be great if that vendor becomes unavailable in the future. Choosing a standards-based wireless solution mitigates those risks by giving you options.
The advantages of using a standards-based wireless network include lower costs, interchangeable products from different suppliers, and established best practices. Also, standards such as IEEE 802.11 are readily incorporated with existing Ethernet-based systems. Choosing an open software system is equally important for integration and scalability. NI LabVIEW, for example, is capable of communicating with both proprietary and standards-based wireless networks.
Learn how to simplify wireless remote monitoring applications with LabVIEW and Wi-Fi DAQ.
Battery Life
A third potential challenge for wireless networks is power, though it is application specific. For most applications there is a tradeoff between power consumption and the amount of data you can collect. Wi-Fi, for example, requires more power than ZigBee, but can stream continuous waveform data. ZigBee and 802.15.4 on the other hand can run for years on batteries by limiting the amount of data they collect and the frequency with which they transmit it. Alternative energy sources are also in research, including solar panels and microgenerators that can convert vibrations into electrical energy.
The Future of Wireless
According to a study by Venture Development Corporation, the worldwide market for wireless measurement devices and services is expected to reach over $US 1.5 billion by 20121.
Current and Forecast Worldwide Shipments of Wireless (RF/Microwave) Products Under Study for Industrial On-Site Monitoring & Control Applications Segmented by Network Interface Classes (U.S. Dollars in Millions)1
Wireless networking protocols have matured to overcome the challenges associated with earlier technology. With standards such as Wi-Fi and ZigBee and open software such as LabVIEW wireless remote monitoring will continue to see strong adoption.
References
1James K. Taylor Venture Development Corporation. The Worldwide Market for RF/Microwave Wireless Monitoring and Control Products in Discrete and Process Manufacturing. March 2008.
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