Wireless Sensor Network Frequently Asked Questions

Publish Date: Oct 06, 2011 | 7 Ratings | 3.00 out of 5 |  PDF

Table of Contents

General

1. What is a wireless sensor network?

A wireless sensor network consists of three main components:  gateways, nodes, and software.  The NI WSN platform provides options in each of these categories so that you can customize your WSN to meet the unique needs of your application.

Wireless measurement systems can overcome power and network infrastructure limitations and meet new and previously difficult application challenges. They deliver reduced costs and increased flexibility compared to traditional wired measurement systems, and they offer the ability to achieve long-term deployments with reliable, battery-powered devices.  

2. What is the difference between NI Wireless ComapctDAQ and NI WSN devices?

NI Wireless ComapctDAQ devices combine IEEE 802.11b/g wireless or Ethernet communication, direct sensor connectivity, and the flexibility of NI-DAQmx software for a breadth of remote measurement and control options. Externally powered, NI Wi-Fi DAQ devices can stream continuous waveform data on each channel at more than 50 kS/s and offer the highest commercially available network security (WPA2 Enterprise). These devices are intended for shorter term, high throughput/streaming applications, in which you have a single host connected to your wireless client devices.

NI WSNs deliver 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 wireless measurement nodes communicate with a central gateway using a protocol based on IEEE 802.15.4 to offer mesh routing capabilities that extend network distance and reliability. NI WSN systems support lower data rates to preserve power, are easily programmed using I/O variables.  These devices are intended for longer term, slower speed applications in which you might be interested in monitoring your assets or environment once per minute, hour, or day.  NI WSN supports multiple data consumers per client, meaning multiple people can access data from your WSN monitoring system any where, any time.

3. What WSN products are available from NI?

Consult the NI WSN Product and Configuration Guide to get up to date information on the different node, gateway, and software options available from NI.

4. What are the features of these products?

The measurement nodes each offer four analog input channels and two to four digital channels that you can configure on a per-channel basis for input, sinking output, or sourcing output. Four AA alkaline or lithium batteries can deliver up to a three-year node lifetime. The measurement nodes deliver -40 to 70 °C temperature ranges and industrial shock and vibration ratings, and they communicate via 2.4 GHz IEEE 802.15.4 radios that provide up to 300 m outdoor range with line of sight. The 9 to 30 V externally-powered gateways provides flexible connectivity to Windows or real-time OS controllers. 

5. Will NI offer more measurement options in the future?

Yes, NI plans to continue investment in WSN technology and provide a breadth of measurement node I/O options that are compatible with the current product offering.

6. Which network protocol does the NI WSN devices use?

The proprietary NI WSN protocol is based on IEEE 802.15.4 and ZigBee technology. The IEEE 802.15.4 communication standard defines the Physical and Medium Access Control layers in the networking model, providing communication in three frequency bands including the 2.4 GHz ISM band. ZigBee builds on the 802.15.4 standard with the network and application layers, offering features such as device coordination, reliability through mesh networking topologies, and the functionality to create user-defined profiles that allow for customization and flexibility within the protocol. NI-WSN sits on top of the ZigBee layer and closes the protocol to third-party devices, ensuring network and data reliability.

7. How is the network configured?

With NI-WSN software, which is included with the NI WSN gateways (or downloaded here), you can easily configure your network in the Measurement & Automation Explorer (MAX) utility. MAX provides an intuitive user interface to add and remove measurement nodes and configure wireless settings. To set up your NI WSN, add your gateway under Remote Systems in MAX and assign measurement nodes to a gateway by entering the node serial number. Upon power-up or reset, the nodes automatically reconnect to the assigned gateway. 

You can also use MAX to view all of the nodes in your WSN and their last communication time, battery status, and link quality. In addition, MAX provides an interface to set the ZigBee communication channel, configure the Gateway IP address, wirelessly update firmware on the measurement nodes, and configure a node to act as an end device or mesh router.

If you are using the NI 9792 Programmable WSN Gateway, these operations can also be performed from a web browser.

8. How do I extract measurement data from the WSN?

NI-WSN software provides seamless LabVIEW integration so that you can quickly and easily extract measurement data from your WSN. After adding aNI WSN gateway to a LabVIEW Project, the nodes configured with the gateway in MAX automatically populate in the LabVIEW Project, giving you instant access to their I/O and properties. Simply drag and drop I/O variables from the LabVIEW Project to a LabVIEW Block Diagram for data extraction, analysis, and presentation.

9. What are the power requirements for NI WSN devices?

The measurement nodes can operate on four 1.5 V, primary AA alkaline or Lithium cells or an external supply. Some NI WSN nodes support battery back-up, meaning the node will automatically switch over to battery power if external power is lost.  

When nodes are configured as routers, they must remain on to send and receive data across the network, and should be powered with an external source. 

You can use sources other than wall power, such as solar or vibration energy harvesting, to provide external power.  To learn more about using energy harvesting to power NI WSN nodes, read the corresponding whitepaper.

The WSN-9791 and NI 9792 gateways requires an external 9 to 30 V power supply. 

10. How do I know which products are certified for my country?

View the Wireless Product Certifications document to determine which products are certified for use in your geographical region.

Performance

11. How long does a node operate on battery power?

Measurement node power consumption depends on a variety of factors including sampling interval, temperature, network topology, RF environment, and whether or not the node behavior has been customized with the NI LabVIEW WSN Module.  National Instruments has found that with a one-minute sample interval at 25 C, typical battery lifetime is greater than 2 years.  

See below for more information on how to use the LabVIEW WSN Module to maximize power efficiency.

12. How many nodes can connect to a single gateway?

Creating a reliable network topology is a very important aspect in building your WSN system.  You should carefully consider network topologies and data communication paths when setting up a WSN system.  

To ensure maximum network reliability, National Instruments suggest that you adhere to the following criteria:

  • Without the use of router nodes, no more than 8 end nodes can connect directly to a single gateway
  • Using router nodes, each gateway can connect to a maximum of 36 total nodes (routers + end nodes combined)
  • No more than 8 end nodes can connect to a single router node
  • Each end node should be no more than 3 hops away from the gateway

To achieve the greatest amount of end nodes, NI suggests a topology consisting of one gateway, four router nodes, and 32 end nodes (eight end nodes for each router).   To achieve the greatest coverage distance, NI suggests a topology consisting of one gateway, eight router nodes, and 28 end nodes (seven end nodes for each second-tier router).  

The NI WSN protocol is built on a self-healing network, meaning that the network will automatically re-configure if necessary.  Because of this, it is important to analyze all network possibilities and maintain the 8:1 child-to-parent ratio for all network possibilities when designing your WSN topology.  

To learn more about creating a reliable network topology, read the WSN Topologies and Mesh Networking tutorial.

13. What is the range of the wireless communication?

The NI WSN Gateways and Measurement Nodes utilize a 2.4GHz IEEE 802.15.4 radio.  The Americas versions of these devices can maintain reliable network communication at an outdoor range of 300 m with line of sight.  Exact device-to-device range will vary based on geographic model, network traffic, network topology, and RF environment.  

14. How fast can I acquire using NI WSN devices?

Using default firmware/device personality, in which inputs are sampled and immediately transmitted to the gateway, the measurement nodes can sample on the order of 30-60 samples per minute.  This rate is user-defined and can be programatically assigned in NI LabVIEW.

Using the programmable nodes and the LabVIEW WSN Module, you can sample faster locally and store or process the data for transmission at a later time.  Because of this, you can sample faster than the default rates. View the LabVIEW WSN Benchmarks document for information on sampling faster with NI WSN measurement nodes. 

Applications

15. Can I use the measurement nodes outdoors?

Yes. NI offers an IP65 outdoor enclosure for the WSN measurement nodes. The NI WSN-3291 outdoor enclosure has two I/O glands for routing power or sensor cables, and is shipped with four I/O gland inserts so that you can custom-tailor the glands for your application. The enclosure has an external antenna that connects to the node through an internal SMB connector as well as an internal mounting plate with locking mechanism to secure the node inside.

NI also offers an IP65 outdoor enclosure for the NI WSN-9791 Ethernet Gateway.  An outdoor enclosure for the NI 9792 Programmable WSN Gateway will be offered soon.

View the online catalog to learn more about ingress protection and view NI WSN accessories.

16. What are the host controller options?

Each WSN gateway provides different connectivity and host controller options.  With the NI 9792 Programmable WSN Gateway, no additional host controller is necessary, as the device is a LabVIEW Real-Time target and can run independent of a host.  A LabVIEW Real-Time application can be deployed to the NI 9792 to aggregate data from measurement nodes and perform processing and analysis.  Even though no host controller is necessary, you can still connect the NI 9792 to other devices, such as a windows PC, database, or third party WSN gateways.  The NI 9792 offers dual ethernet ports and an RS-232 serial port to connect to these types of devices.  Furthermore, the NI 9792 has a built-in web server so that you can remotely visualize WSN measurement data in a web browser.

The NI WSN-9791 Ethernet gateway, however, does require the use of a host controller.  The flexibility of ethernet allows you to choose either a Windows or real-time host controller. The Windows controller can be a PC, industrial controller, laptop, or embedded device running a Windows OS, including embedded OSs such as XP Embedded, and LabVIEW for Windows. The real-time controller can be an NI CompactRIO or other programmable automation controller (PAC) running a real-time OS and LabVIEW Real-Time. 

17. Can I interface with other WSNs?

NI offers LabVIEW drivers for third-party WSN nodes, such as those from Crossbow, Accsense, and Microstrain, so you can integrate NI WSN measurements with third-party WSN measurements in your LabVIEW code. To communicate with these devices you must use their gateway.  You cannot use third-party WSN (or other ZigBee) devices to communicate directly with NI WSN gateways due to the proprietary NI WSN communication protocol.

18. Which sensors work with the nodes?

Visit the NI Wireless Sensor Network Sensor Partner page for more information on sensors that have been tested with the measurement nodes

Software

19. Can I program the node itself?

With the LabVIEW Wireless Sensor Network Module you can use graphical programming to customize node behavior by adding intelligence to extend battery life, increase analog and digital input performance, and interface with custom sensors. You can also use the module to embed local intelligence, respond to digital value change events, and modify behavior based on measurement inputs.

The default behavior of an NI measurement node is to transmit every sample acquired to the gateway; however, this is not a requirement for many applications and the LabVIEW WSN Module can be used to average samples over time and provide threshold or dead-band logic, allowing you to extend battery life by transmitting only meaningful data. Additionally, acquisition rates on the node can be increased by not incurring the overhead of transmitting each sample after acquisition. Using the LabVIEW WSN Module, you can then perform processing and data reduction on the node. LabVIEW WSN applications are downloaded over the air to NI WSN measurement nodes, allowing seamless updates to deployed nodes.

Only the programmable versions of the measurement nodes can be targeted by the LabVIEW WSN Module Pioneer.  To learn more about the LabVIEW WSN Module, view the whitepaper.

20. Which ADEs work with WSN?

NI wireless sensor networks currently only work with NI LabVIEW version 8.6.1 and later.

Support

21. How do I get technical support for NI WSN devices?

You can take advantage of the NI WSN Setup and Services page to find tutorials, drivers, discussion forums and more.

NI also 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 WSNs to experts looking for tips from the designers. Online resources include the following:

  • Downloadable drivers and updates for NI-DAQmx and other measurement products
  • More than 3,000 KnowledgeBase entries
  • Online product manuals (downloadable help files and PDFs)
  • More than 3,000 example programs
  • Tutorials and application notes

22. What warranty is provided with NI WSN devices?

All NI WSN devices have a one-year warranty that covers defects in workmanship and material from the date of product shipment. Extended warranty options are available that can help you fix your maintenance costs over two or more years. Contact your NI sales representative for more information.

23. Where can I get more information?

Visit the NI WSN homepage for the latest product and technology information, including whitepapers, tutorials, and pricing.  

You can also visit the Wireless Community to discuss wireless applications with other users, view and share example code, and determine the best wireless topology for your application.  

Or, purchase a WSN Starter Kit to get started with monitoring your assets or environment!

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