Wireless data acquisition is an extension of PC-based data acquisition to measurement applications where cables are inconvenient or impractical. NI CompactDAQ combines IEEE 802.11 wireless technology and support for over 50 measurement modules with the flexibility of NI LabVIEW software for remote monitoring and control of electrical, physical, mechanical, and acoustic signals. The NI cDAQ-9191 chassis houses a single C Series module and delivers IEEE 802.11b/g and Ethernet connectivity back to a host PC, while the NI cDAQ-9181 provides Ethernet connectivity only. C Series modules offer direct sensor connections and built-in signal conditioning for a variety of measurements, including temperature, strain, high-voltage digital I/O, acceleration, current, and voltage. You can use C Series modules interchangeably for a variety of measurement and control applications across several platforms, including both NI CompactDAQ and CompactRIO.
Figure 1. A Wi-Fi NI CompactDAQ measurement system combines a one-slot chassis and an NI C Series module to provide wireless sensor measurements.
Unlike most wireless sensors or wireless sensor networks, wireless data acquisition devices are meant to stream data continuously back to a host PC or laptop. A wireless sensor node is typically a low-power, autonomous battery-operated device intended for long-term deployment in applications where measurements are needed only every few minutes, hours, or even days. Wi-Fi data acquisition devices, on the other hand, behave in much the same way as a USB data acquisition device – a host PC collects data continuously (in real time) as the device acquires it. The data acquisition device may be battery-operated, but the focus is on the measurement versus the battery life. Also, Wi-Fi Wi-Fi NI CompactDAQ chassis use the near-ubiquitous wireless networking standard, IEEE 802.11, instead of ZigBee or other IEEE 802.15.4 variants because of its higher bandwidth and broader applicability. Finally, because the NI CompactDAQ chassis uses the same NI-DAQmx driver software as other NI data acquisition devices, you can develop your applications using NI LabVIEW; LabWindows™/CVI; ANSI C/C++; or Microsoft C#, Visual Basic, or Visual Basic .NET.
Each NI Wi-Fi and Ethernet NI CompactDAQ device can hold one NI C Series measurement module. The measurements, features, and specifications are defined by the type of C Series module in the NI cDAQ-9181 or NI cDAQ-9191 chassis. A standard 802.11b/g radio or IEEE 802.3 10/100 Mbps Ethernet connection provides connectivity to a host PC. Additionally, LEDs on the top of the chassis provide users with key information regarding the strength of the wireless signal - one of the biggest factors in signal streaming bandwidth.
Figure 2. NI cDAQ-9191 chassis provides key user feedback through indicator LEDs located on the chassis
|1. Antenna and Antenna Connector||5. POWER, STATUS and ACTIVE LEDs|
|2. 9-30 VDC Power Connector||6. Wireless Signal Strength LEDs|
|3. Ethernet Connector||7. Chassis Grounding Screw|
|4. Reset Button||8. Module Slot|
The NI cDAQ-9181 and NI cDAQ-9191 support over 50 NI C Series modules with measurements including voltage, current, temperature, force, strain, acceleration and many more.
View all C Series modules »
Wi-Fi and Ethernet NI CompactDAQ chassis are DC-powered and are compatible with 9 to 30 VDC power supplies. You may use the 12 VDC power supply included in each shipping kit to power the device or you may wire any 9 to 30 VDC power to a device using the power supply screw terminal connector kit (part number 780702-01). The maximum required input power for a these chassis is 4.5 W, though typical continuous power requirements are lower. For example, with a 12 VDC power supply, the continuous current draw for a NI cDAQ-9191 device is typically between 250 and 350 mA, depending on which module you use with the carrier.
Many battery combinations are also possible with different capacities and voltage levels. For instance, a stack of eight 1.5 V AA 2400 mAh NiMH rechargeable batteries typically provides between 6.5 and 9.5 hours of continuous operation for the example above. Lithium Ion-based universal laptop batteries can provide longer run times. When using an off-the-shelf battery, you can order the power supply screw terminal connector kit (part number 780702-01) to connect the battery leads to the NI cDAQ-9181 or NI cDAQ-9191.
When setting up your Wi-Fi NI CompactDAQ chassis, you may choose to connect to an existing enterprise network through a wireless access point or set up your own network with a wireless router. For existing IT infrastructure, Wi-Fi NI CompactDAQ chassis support WPA Enterprise and WPA2 Enterprise (IEEE 802.11i). If you set up your own network, you may use WEP, WPA Personal (WPA-PSK), or WPA2 Personal (WPA2-PSK) security. Wi-Fi NI CompactDAQ chassis also support ad hoc or peer-to-peer networks, which do not require any routers or access points. However, ad hoc support is inconsistent across wireless network interface cards and is not secure. Communication through a wireless access point or wireless router is the preferred mode of operation.
Every shipping kit includes the following:
The rate at which you can acquire data is limited by two factors: the type of C Series module you use in your NI cDAQ-9181 or NI cDAQ-9191 chassis and your RF environment. Currently, the fastest supported C Series module is the NI 9223, which can acquire up to 1 MS/s simultaneously on each of its four channels, equating to 64 Mb/s of data. Because IEEE 802.11g can transmit data at 54 Mb/s and approximately 20 Mb/s in practice, the NI 9223 will quickly overflow the onboard buffer of the NI cDAQ-9191 if transmitting over Wi-Fi. A NI cDAQ-9181 or NI cDAQ-9191 can still transmit data at full rate over the 100 Mb/s Ethernet port but to use the NI 9223 module over Wi-Fi, you should slow down your acquisition or use only one channel.
The quality of your RF environment can also impact your maximum data rate. Possible sources of signal interference include other Wi-Fi access points, laptops, cordless phones, and microwaves. IEEE 802.11 defines up to 14 different channels (depending on your region of the world) to avoid network interference. Choosing an open 802.11 channel can dramatically improve performance.
The number of devices you may use in an Wi-Fi NI CompactDAQ system is ultimately limited by the IEEE Standard 802.11g specification and the bandwidth available in your wireless network/environment. Consider the following four factors when determining how many devices you can place in your system: acquisition rate, measurement type, number of channels, and the RF environment. The faster you acquire data, the more TCP/IP packets your device must transfer back to a wireless access point or host PC. The same is true of a higher-resolution measurement or more measurement channels – some C Series modules provide 16 bits of resolution while others offer up to 24 bits. Finally, the theoretical bandwidth of 802.11g is 54 Mbps, though there are some practical limitations that keep this specification closer to 24 Mbps. For example, streaming data from four NI 9234 24-bit measurement devices on all four channels at the full 51.2 kS/s rate requires approximately 19.5 Mbps. One clear IEEE 802.11 channel can accommodate this traffic in a clean RF environment. By lowering the sample rate or adding another access point on a different 802.11 channel, you can add more devices.
The range and performance of wireless data acquisition devices is derived from the IEEE Standard 802.11 specifications. Typically, you can expect a 30 m range in an office-like environment, where obstructions such as walls and equipment can degrade RF transmissions. With line-of-sight or outdoor environments, a 100 m transmission is possible. Note that at longer distances, your maximum sustainable acquisition rate may decrease. These ranges are guidelines and can vary significantly depending on your wireless router, antenna, and physical obstructions. To extend the range of your wireless network, you may use additional access points, routers with high-gain antennae, or wireless repeaters. Some vendors certify their routers and access points for use with high-gain or directional antennae. Wireless emitters and antennae must be certified together to comply with FCC Rules, Part 15. Many off-the-shelf wireless routers can also function as repeaters to effectively double the range of your Wi-Fi network.
Most C Series modules (including those that work with Ethernet and Wi-Fi NI CompactDAQ hardware) offer isolation as a means of improving the quality and safety of your measurements.
Isolation electrically and physically separates sensor signals, which can be exposed to high-voltage transients and noise, from the measurement system’s low-voltage backplane. Isolation offers many benefits include the following:
For more information on isolation, refer to the NI Developer Zone Tutorial: Isolation Technologies for Reliable Industrial Measurements.
NI Wi-Fi devices implement the highest commercially available wireless network security standard, IEEE 802.11i (commonly known as WPA2 Enterprise), including network authentication and data encryption. Authentication ensures that only authorized devices have network access, and encryption prevents data packets from being intercepted. IEEE 802.11 security standards build on more than 10 years of use in the IT sector, and are widely adopted worldwide. By using standard security protocols, Wi-Fi NI CompactDAQ devices make it easy to add wireless measurements to existing IT networks safely.
The Advanced Encryption Standard (AES) was chosen by the IEEE 802.11i task group as the preferred encryption algorithm for securing data transmissions over Wi-Fi networks. AES uses a 128-bit cipher that is significantly more difficult to crack than the RC4 algorithm used by older Temporal Key Integrity Protocol (TKIP) and Wired Equivalent Privacy (WEP) encryption standards. In fact, the National Institute of Standards and Technology (NIST) chose AES as the encryption standard recommended for all U.S. government agencies. (FIPS publication 197 describes these requirements in detail.) Any wireless data acquisition application for the government or military likely has to use AES to transmit data.
Network authentication is essentially client access control. Before a client (such as an Wi-Fi NI CompactDAQ device) can communicate with a wireless access point it must authenticate with the network. There are two basic forms of authentication: server-based and preshared key-based. Most enterprise networks have at least one authentication server, usually running Remote Authentication Dial-In User Service (RADIUS). IEEE 802.11i (WPA2) networks make use of the IEEE 802.1X port-based authentication standard and the Extensible Authentication Protocol (EAP) to control access. Wi-Fi NI CompactDAQ devices support several EAP methods, including LEAP, PEAP, EAP-TLS, and EAP-TTLS. You can also use a pre-shared key if you do not have an authentication server on your network.
All Wi-Fi and Ethernet NI CompactDAQ devices use the same NI-DAQmx measurement services and driver software as other National Instruments PCI, PXI, and USB DAQ devices. NI-DAQmx measurement services software controls every aspect of your data acquisition system from configuration to programming. With NI-DAQmx software, you can quickly configure and acquire measurements using the DAQ Assistant and automatically generate code to get your application started quickly. NI-DAQmx also features virtual channels that automatically scale raw data into engineering units. Because you can use the same driver API to program new Wi-Fi NI CompactDAQ devices, incorporating wireless connectivity into your existing applications is easy.
In addition to NI-DAQmx driver software, all Wi-Fi and Ethernet NI CompactDAQ devices include Measurement & Automation Explorer (MAX) configuration software and LabVIEW SignalExpress LE data-logging software. You can use MAX to quickly configure and test your Wi-Fi and Ethernet devices without developing any code. LabVIEW SignalExpress is an interactive, measurement software tool for quickly acquiring, analyzing, and presenting data from hundreds of data acquisition devices and instruments, with no programming required. To learn more about LabVIEW SignalExpress LE, visit ni.com/labview/signalexpress.
Wi-Fi and Ethernet NI CompactDAQ devices work with development environments compatible with NI-DAQmx, including the following:
1Wi-Fi and Ethernet NI CompactDAQ devices are not supported by LabVIEW Real-Time Module software.
5. Services and Support
NI offers extensive support options through ni.com/support. You can call, e-mail, or troubleshoot problems online with NI engineers. In addition, ni.com provides a wealth of resources for every customer – from users getting started with NI CompactDAQ to experts looking for tips from the designers. Online resources include the following:
All Wi-Fi and Ethernet NI CompactDAQ devices have a one-year warranty that covers defects in workmanship and material from the date of product shipment. You can use NI extended warranty options to fix your maintenance costs over two or more years. Contact your NI sales representative for more information.
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