wireless Measurement

 Wireless communication offers many benefits for measurement applications, including lower wiring costs and remote monitoring capabilities. However, choosing a technology and method of implementation can be difficult without knowing the strength and weaknesses of each wireless standard.

Benefits of Wireless

The main benefit of wireless technology for measurement applications is the ability to minimize or avoid the use of wires and cables. Depending on the nature of the application and environment, physical wiring can be expensive, inconvenient, or even impossible. Examples include moving/turning platforms, mobile applications (for example, vehicles or cranes), and structures that complicate wiring installation.
Wireless communications also extends the distance, or range, of data acquisition and I/O beyond what is practical with wiring. Therefore, large scale operations, such as water treatment facilities and tank farms, widely use wireless technologies. While the initial investment required for wireless networking hardware may be higher than that of traditional wired hardware, the total system cost including installation expenses and operating costs is generally significantly lower.
When choosing to implement a wireless network, there are several factors that you should take into consideration:

• Performance
• Range
• Security

Performance
When considering performance, it is important to consider the size of the spectrum, distance, data rate, power, number of users, and technology compatibility.
Even though different wireless standards define specific data rates, in practice, you can only expect to see a data rate of about 30 percent or less of the theoretical maximum throughput in a practical application. Factors such as RF interference and the number of users influence the performance of wireless networks. In addition, if you are using multiple compatible standards, the faster standard is typically limited by the slower standard. For example, when using 802.11b and 802.11g components on the same network, the 802.11g components slow to the data rate of 802.11b.
There is a constant trade-off between range and throughput. Your hardware should autosense signal strength (unless you tell it otherwise), and back off the transmission rate if your signal gets weak. If you are using 802.11b for example, it automatically backs the rate down from 11 Mb/s to 5.5, 2, and even 1 Mb/s. For most Internet connections this bandwidth is still sufficient.
Range
Generally, the range of a wireless device decreases as frequency increases, but that is not always the case. Tests show that 802.11g has the same, or perhaps slightly better, range than 802.11b, even though they use the same frequency. There are devices on the market that are designed to add wireless range for laptops by increasing the power of the card past the Wi-Fi certification limit of 100 mW. Before purchasing additional access points for your system, consider adding an extended range card if your local governing body permits it.
Directional antennas usually make the most sense in point-to-point use. They focus the signal into a narrow beam instead of letting it radiate in all directions like the isotropic antenna found in your base station. What you will find is that the higher the gain of the antenna, the narrower the focus of that beam. Thus, as the gain increases, so does the need to properly aim the antenna. This increases the risk of the receiver missing the transmitted data if not aligned properly. Directional antennas are typically sold by their gain rating. You can observe the effect of the gain in the “beam width” descriptions of each antenna.
Security
A primary concern when installing wireless networks is security. The rapid growth and popularity of wireless networks in both the commercial and residential market led to implementation for many diverse applications, including the transmitting private information. The need for privacy drove the development of wireless security protocols and continues to spur efforts to make wireless a more secure technology.
The original 802.11 standard included a security protocol called Wired Equivalent Privacy (WEP), which encrypted data packets well enough to keep out most eavesdroppers but still had some weaknesses. The industry needed a stronger encryption/authentication system, which led to the implementation of IEEE 802.11i (commonly known as WPA2). WPA2 provides the Extensible Authentication Protocol (EAP) and the Advanced Encryption Standard (AES), a 128-bit cryptographic algorithm endorsed by NIST and required in all US government facilities.
Another security measure is to minimize the propagation of radio waves outside the physically controlled area of a facility. This causes the wireless network to be more secure because of the reduction of the potential for eavesdropping and denial of service attacks.
You can find more information on wireless security here.

Wireless Technologies for Measurement and Automation

Over the past several years, wireless communication technologies have become ubiquitous, largely due to consumer electronics. There are hundreds of wireless equipment manufacturers and just as many standards. Understanding the benefits and shortcomings of each technology can make the selection process easier. This is especially important in measurement and automation where measurement data cannot be compromised, even when relying on radio waves.
There are two distinct wireless technologies that are suited for measurement-based applications:  IEEE 802.11 b/g (Wi-Fi) and IEEE 802.15.4 (ZigBee).  IEEE 802.11 offers high bandwidth and high security, and is well suited for applications in which you need to stream waveform data wirelessly across a secure link.  IEEE 802.15.4 has lower bandwidth than IEEE 802.11 but has longer range, requires lower power, and can accommodate the reliable mesh networking topology, making it well-suited for long-term monitoring applications. National Instruments offers wireless measurement devices that take advantage of the benefits of each of these protocols.  To learn more about the tradeoffs between these two protocols, read the Selecting the Right Wireless Technology whitepaper.

Adding Wireless Capabilities to a Measurement System

National Instruments offers two kinds of wireless measurement devices:  NI Wi-Fi DAQ and NI Wireless Sensor Networks.  Visit the wireless measurement devices product guide to read an in-depth whitepaper on these two wireless measurement platforms.

NI Wi-Fi DAQ

NI Wi-Fi data acquisition (DAQ) devices deliver simple, secure measurements with high-performance streaming capabilities on standard, trusted technologies. You can view data in real time, streaming dynamic waveform measurements at up to 51.2 kS/s per channel. In addition, built-in signal conditioning provides connectivity for a variety of sensors, including thermocouples, accelerometers, load cells, and so on. These devices take advantage of NI C Series measurement and control modules, also used for USB data acquisition and NI CompactRIO programmable automation controllers (PACs).

NI Wi-Fi DAQ

Using WPA2, the highest commercially available network security, Wi-Fi DAQ devices protect your system from unwanted access. Authentication ensures that only authorized devices have network access and encryption prevents data packets from being intercepted. Wi-Fi DAQ devices support multiple Extensible Authentication Protocol (EAP) methods that provide for mutual authentication between the DAQ devices and wireless access points. They also support 128-bit AES encryption, endorsed by NIST and required in all US government facilities. With strong security protocols, you can incorporate wireless connectivity with existing enterprise networks safely.
Wi-Fi DAQ devices include NI-DAQmx driver and measurement services software with intuitive application programming interfaces, configuration utilities, I/O assistants, and tools designed to reduce system setup, configuration, and development time.

NI Wireless Sensor Networks

National Instruments Wireless Sensor Networks (WSN) offer reliable, low-power measurement nodes that operate for up to three years on 4 AA batteries and can be deployed for long-term, remote operation. The NI WSN protocol based on IEEE 802.15.4 technology provides a low-power communication standard that offers mesh routing capabilities to extend network distance and reliability. 

The high-accuracy NI WSN measurement nodes provide four analog input channels and four digital input/output channels for easy sensor connectivity, while four AA alkaline cells deliver up to a three-year lifetime. You can configure each digital channel as input, sinking output, or sourcing output. The WSN-3202 also offers an up to 12 V, 20 mA sensor power output line that draws from the battery or external power supply to drive external sensors. 

These rugged devices feature industrial shock and vibration specifications and -40 to 70 °C temperature ratings. You can combine them with the NI WSN-3291 outdoor weatherproof enclosure for long-term, outdoor deployments. A 2.4 GHz, IEEE 802.15.4 radio provides a 300 m outdoor range with line of sight and allows the measurement nodes to form a reliable mesh network. When you configure the nodes as mesh routers, they must remain on at all times to send and receive data across the network. In this case, it is recommended that you power them with an external source such as a 9 to 30 V supply, solar panel, or larger battery.