Wi-Fi Extends the Reach of Data Acquisition

In today’s diverse world of data acquisition, it can be difficult and costly—if not impossible—to achieve wired access to your sensors. Fortunately, vendors are offering wireless systems that provide the bandwidth necessary to support DAQ functionality in a variety of application areas—monitoring bridges and other large structures; analyzing on-track performance of vehicles; monitoring the efficiency of solar-cell systems; collecting data to enhance the design of heating, ventilation, and air-conditioning (HVAC) systems; and monitoring noise and vibration at construction sites to assure compliance with neighborhood regulations.

To serve applications like these, manufacturers such as Agilent Technologies and National Instruments are offering wireless-ready DAQ products. The selection includes what NI calls its second-generation wireless DAQ platform (Figure 1), which extends first-generation product measurement support; and Agilent Technologies’ 34972A DAQ platform (Figure 2), which uses LXI as a bridge to Wi-Fi and cellular communications capability.

Figure 1. National Instruments’ Second-Generation Wireless DAQ Technology
Courtesy of National Instruments

Figure 2. Wireless-Ready LXI-Enabled 34972A DAQ Platform
Courtesy of Agilent Technologies 

Tami Pippert, DAQ product manager at Agilent, noted that the company was motivated to develop wireless DAQ capability. “The reality of market data acquisition needs and applications,” she said, “is that all types of environments and connectivity challenges exist involving extreme temperature or other environmental conditions, moving vehicles, and remote locations with limited connection options and accessibility.”

She cited a few specific examples of applications in which Agilent’s wireless DAQ technology finds use: “High-speed track-testing engineers capture vehicle temperatures and download to a central computer for analysis; refrigeration manufacturers monitor refrigeration temperatures; and engineers working on the design of new HVAC systems collect  temperature and voltage data from equipment located in the remote areas of industrial sites with high acoustic noise”—an undesirable location for engineers to spend considerable time gathering data.

From Pipelines to Marine Vehicles

NI’s wireless DAQ hardware finds use in several application areas. Jean-Michel Chalons of SAPHIR and Henri Campagna of dB Vib Consulting have used NI LabVIEW software, the NI Sound and Vibration Measurement Suite, and NI Wi-Fi data acquisition devices to develop the PC-based Surveillance of Acoustics and Vibration in the Environment (SAVE) system to wirelessly monitor acoustics and vibrations at construction sites.1 They report the system is being used by Gaz de France to monitor gas pipelines, Électricité de France to monitor power generators, and AdduX to monitor assembly line noise.

Jeremiah Fasl of the University of Texas/Austin discussed using the technology to study the collapse of a 120-ft bridge with an intentionally fractured girder. He noted, “We used the NI WLS-9237 Wi-Fi DAQ module to instrument the load cell that determined the weight of the road base applied to the bridge. The wireless system provided the measurement accuracy needed to calculate the collapse load quickly while eliminating wires that would have caused safety issues.”2

In still other applications, Rodney Tan of UCSI University used an NI WLS-9163 wireless C Series DAQ module to develop a solar cell efficiency assessment system that acquires voltage and temperature readings.3 Francisco Jesús Velasco of the Universidad de Cantabria Escuela Técnica Superior de Naútica employed LabVIEW software to implement wireless communications through a web server to develop “a remote experimentation platform using autonomous in-scale physical models to carry out trials and maneuvers that verify marine vehicle stability and steerability as well as create a software support system to perform the guidance, navigation, and control (GNC) of the platform.”4

Relying on Wi-Fi and LXI

Both Agilent’s and NI’s wireless DAQ implementations employ Wi-Fi. Jim Schwartz, product marketing engineer at NI, said Wi-Fi has some pretty distinct advantages. “From a data acquisition standpoint, what is important is the amount of data you can send over a particular protocol, and Wi-Fi is definitely one of the highest—we are able to stream full-rate accelerometer data at 51 kS/s.” He noted that the company does offer wireless sensor node products based on Zigbee, which are used for slower, monitoring-type applications.

“Zigbee is cool because it is so low power, and battery life extends up to three years so there are some serious advantages there,” Schwartz said. “But from a purely data acquisition approach, the advantages that come with Wi-Fi are huge. You can use the built-in infrastructure of your building; you can couple directly with laptops or almost any device that supports Wi-Fi.”

As for distance, Schwartz said many applications are line-of-site. Although Wi-Fi transmission distances degrade significantly indoors in the presence of walls, wires, and other wireless devices, Wi-Fi has a typical range of around a hundred meters for line-of-sight applications.

In addition to Wi-Fi, the Agilent approach makes use of the LXI technology incorporated into its 34972A DAQ platform (Figure 2). Explained Pippert, “Using the new 34972A, with built-in LAN/LXI and USB I/O capability as the foundation, we have enabled users to take advantage of [wireless DAQ] capabilities. If users combine the LAN capabilities of the 34972A with its built-in web-browser capabilities along with a wireless router, they have wireless access to a full data acquisition solution.”

The Agilent 34972A consists of a three-slot mainframe with a built-in 6½-digit DMM and eight different switch and control modules. The product features a built-in USB interface so it can easily connect to a PC or laptop without the need to purchase additional IO cards or converter interfaces. However, the 34972A need not be connected to a computer in a field application. Users can employ a USB flash drive to upload datalogging configurations into the 34972A and transfer large data sets back to the computer.

But it is the LXI interface that opens the door to wireless data acquisition applications. With respect to Wi-Fi-based DAQ applications, Pippert said, “The Agilent 34972A DAQ wireless solution uses the standard IEEE 802.11 wireless LAN for instrument communications and capitalizes on millions of engineering hours invested in product development, security, and product robustness.” She went on to explain that easy-to-use LXI instrument tools make configuration and operation of the wireless network simple, adding that the LXI-compliant 34972A, with its built-in web browser capabilities, can be combined with a wireless bridge to connect seamlessly to a wireless LAN network.

As for data security in a Wi-Fi environment, according to an Agilent publication, “After a decade of real-life field testing and improvements, 802.11n encryption methods have matured and are extremely robust. The latest method (WPA2) uses advanced encryption scheme (AES) coding. AES has been carefully scrutinized worldwide and adopted by many governmental groups because of its effectiveness.”5

To maximize wireless LAN security, you should choose WPA2-AES encryption, create a strong key by using at least 13 randomized characters, turn off SSID broadcast, and change the default router’s administrator login and password.

Using a Travel Router

One specific approach to setting up a wireless data acquisition system is to use a TRENDnet TEW-654TR Travel Router to augment the 34972A, such as when collecting various temperatures, DC voltages, and AC voltages during design of an HVAC system.6

You can employ two methods to set up the travel router. In the first method (the simpler one), the travel router operates in access-point mode (Figure 3a). Your computer communicates directly with the 34972A through the travel router. This method requires no additional WLAN. As a result, you will not be able to access any other websites or instruments with your computer; however, other computers will be able to communicate wirelessly with the 34972A.

Figure 3a. TEW-654TR Travel Router Operating in Access-Point Mode
Source: Agilent Technologies 

In the second approach, the travel router operates in client mode (Figure 3b). This slightly more complicated wireless connection method provides additional benefits. Your computer communicates with a central access point, as does the 34972A, through the travel router. This method requires the availability of an additional WLAN, but it enables your computer to access other websites and instruments.

Figure 3b. TEW-654TR Travel Router Operating in Client Mode Mode
Source: Agilent Technologies 

Adding Mobile App Support

Mobile engineering apps7 are part of Agilent’s wireless DAQ solution as well. Explained Pippert, “Additionally, we’ve created a free Agilent application for iPhone, iPad, and iPod [to enable users to] easily control the data acquisition/switch unit. [The app] enables customers to set up, monitor, and control measurements remotely from wherever they are. Additionally, for both Apple and Android smart-device users, we have developed a tool kit to make it easy to create Android and Apple applications to address electronic test instruments. The tools help to control, transfer, and plot the data from test and measurement instruments for wireless DAQ as well as many other applications.”

Neil Forcier, an applications engineer with Agilent’s system products division, demonstrated the programming tools in an online video.8 He noted that while there are many PC tools available to support test and measurement applications development, that isn’t the case with mobile device apps, a situation Agilent is working to change. To that end, Agilent is offering Android and iOS device programming tools that facilitate connecting to instruments, controlling data, and plotting the data they generate.

According to Chris Delvizis, a product manager for data acquisition products at NI, the company began releasing its first-generation wireless DAQ products in 2007, and the SAVE, bridge-collapse test, solar-cell assessment system, and autonomous marine vehicle applications cited in references 1 through 4 employ that technology. He added that at NIWeek 2011, NI introduced its second-generation platform in the form of a one-slot NI CompactDAQ chassis that supports wireless, USB, and Ethernet buses.

The new NI cDAQ-9191, cDAQ-9181, and cDAQ-9171 chassis accommodate all NI C Series modules for the NI CompactDAQ platform and can be used in conjunction with the existing four- and eight-slot chassis. With modules designed for almost any sensor, the NI CompactDAQ platform eliminates the fixed functionality of traditional sensor measurement systems and gives engineers and scientists the ability to increase productivity while decreasing overall cost.

New metal enclosures make the chassis more resistant to environmental damage as compared to the previous plastic sleeves. The chassis operate in a temperature range of 0 to 55°C and can withstand up to 30g shock and 3g vibration.

Delvizis noted that the new chassis can be used with more than 50 C Series modules vs. 10 or 11 for the first-generation product. In addition, multiple electrical and sensor connectivity options can be combined with any chassis to create customized systems specific to the needs of numerous applications. “The big change,” he said, “is the breadth of measurement modules that [the second-generation product] now supports.”

Among the features, NI Signal Streaming technology delivers high-bandwidth capabilities that make it possible to achieve sustained high-speed and bidirectional data streams over USB and Ethernet as well as wireless buses. Zero-configuration networking technology simplifies initial setup, eliminating the need for IT involvement in network setup and integration.

NI-DAQmx driver software, included with each NI CompactDAQ chassis, enables engineers and scientists to log data for simple experiments or develop a complete test system in NI LabVIEW, NI LabWindows/CVI, ANSI C/C++, or Microsoft Visual Studio .NET. A consistent API enables an application developed for an NI CompactDAQ wireless chassis to work with an NI CompactDAQ USB or Ethernet chassis without any modifications to the software. In addition, all new NI CompactDAQ chassis now support the controller area network (CAN) C Series module for optimal communications across various networks.

Delvizis noted that each C Series module includes the analog/digital converter as well as the signal-conditioning and the connectivity features necessary to support common measurements—from thermocouples to load cells—all in a single module package. As a result, users need not build such functions themselves or use an external signal-conditioning box. The next step beyond Wi-Fi might be cellular, and Delvizis said, “We keep our eye on all technologies, and we provide ways you can use LabVIEW to connect with a cellular network,” for example by using a hotspot card such as Verizon MiFi.

And in an online video,9 Agilent’s Forcier describes how a cellular router can be used to extend measurements over very long distances. In the video, he demonstrates an iPad running the free Agilent 34972A DAQ mobile app.

As for emerging hot applications areas, Schwartz at NI sees opportunities in machine condition monitoring. “MCM is quickly growing. You can watch signatures in the vibration data or voltage and power signatures and tell if, for example, your wind turbine is balanced,” he said.

Looking forward, vendors will be seeking ways to optimize speed. Delvizis noted that current 802.11 implementations might not be sufficient for an application involving eight accelerometers, so NI plans to take advantage of emerging 802.11ac technology with its gigabit-per-second and up data rates.

Concluded Schwartz, there are many new wireless protocols, and NI wants to make sure it can adapt each to its customers’ needs, whether for data throughput or very low power. Low-power wireless technology for remote monitoring will be a topic covered in next month’s EE-Evaluation Engineering.

References

1. Chalons, J-M., and Campagna, H., “Protecting the Neighborhood From Noise and Vibration With SAVE,” National Instruments Case Study.

2. Fasl, Jeremiah, “Wireless Data Acquisition for a Bridge Collapse Test,” National Instruments Case Study.

3. Tan, Rodney, “Using LabVIEW and Wireless DAQ to Develop a Solar Cell Efficiency Assessment System,” National Instruments Case Study.

4. Velasco, Francisco Jesús, “Creating a Web Wi-Fi Platform With NI LabVIEW for Remote Experimentation of an Autonomous Marine Vehicle,” National Instruments Case Study.

5. “Increase Data Acquisition Flexibility Using Wireless LAN,” Measurement Tips, Vol. 9, No. 4, Agilent Technologies.

6. “Access Your 34972A Wirelessly With a TRENDnet Travel Router,” Measurement Tips, Vol. 9, No. 4, Agilent Technologies.

7. Nelson, R., “Mobile Apps Support Communications Test, Data Acquisition,” EE-Evaluation Engineering, January 2012, p. 20.

8. Forcier, N., Programming Tools for Apple and Android Smart Devices to Control Instruments, Agilent Technologies YouTube Video.

9. Remote Data Acquisition Using a Cellular Router, Make Measurements Anywhere That Has Cellular Access, ­Agilent Technologies YouTube ­Video.

For More Information

Agilent Technologies

National Instruments

TRENDnet

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