Logging Data Wirelessly

September 30th, 2007

From the 9/26/07 issue of Monitor, the email newsletter of Windmill Software.

Monitoring instruments and sensors wirelessly is becoming more and more common. A wireless network saves cabling costs and installation time. It is useful in electrically noisy or hostile environments. It lets you move your measuring device from place to place and remotely monitor conditions. You can log data from your existing devices wirelessly by adding appropriate adaptors or routers.

There are several different methods of wireless communication. The standards for many of these methods are still being developed.

• Bluetooth. Bluetooth was designed as replacement for short-range cables. It allows up to seven devices to be monitored over short distances, typically about 10 meters. It is called a wireless Personal Area Network (PAN) and conforms to the IEEE 802.15 standard. It is suitable when devices are close to the computer and high bandwidth is not required. You can use Bluetooth to log data from RS232 instruments by plugging a Bluetooth radio adaptor into your PC’s COM port and one into your instrument. Further reading: http://www.bluetooth.com/
• Wibree. (Ultra Low Power (ULP) Bluetooth) Wibree is a new interoperable radio technology for small devices like sports sensors. It was designed by Nokia for applications where ultra low power consumption, small size and low cost were the critical requirements. Released in 2006, in June this year it was decided that Wibree would be included in the Bluetooth specifications and renamed Ultra Low Power (ULP) Bluetooth. Further reading: http://www.wibree.com/
• WiFi. Similar to a traditional Ethernet model, WiFi comprises a local area network (LAN). It uses the same radio frequency as Bluetooth, but with higher power consumption. WiFi is preferable to Bluetooth for operating medium-to- large networks because it allows for a faster connection speed, greater range, more devices to be monitored and higher security levels. For more on WiFi and data acquisition see Issue 82 of Monitor, http://www.windmill.co.uk/monitor82.html.
• ZigBee. ZigBee was designed specifically for remote monitoring and control. It comprises a personal area network based on the IEEE 8-2.15.4 standard. ZigBee can support thousands of nodes in a star or mesh network. In a star network all devices communicate with the controlling node, as is used by WiFi and Bluetooth. In a mesh network, messages can be passed from node to node such that if any of the nodes fail, the message can still reach the destination. Once associated with a network, a ZigBee node can wake up and communicate with other ZigBee devices then return to sleep. This and its low power means that a device’s battery can last a very long time. Further reading: http://www.zigbee.org/
• WirelessHART. Passed earlier this month, the HART 7 specification includes the wireless protocol dubbed WirelessHART. This sets out to create a wireless version of the Wired HART protocol in order to ensure backward compatibility with wired devices. HART Communication is used to communicate between intelligent field instruments and host systems. Further reading: http://www.hartcomm.org/
• WiMax. WiMax, the Worldwide Interoperability for Microwave Access, aims to provide wireless data over long distances in a variety of ways. It is based on the IEEE 802.16 standard, which is also called WirelessMAN. Typically it has a range with a radius of 3 to 10 km. The WiMAX Forum expects the technology to allow city- wide wireless broadband access. In the data acquisition field, WiMax is envisaged as most useful for monitoring offshore facilities. Further reading: http://www.wimaxforum.org/
• GPRS and GSM. GSM (2G) networks are used for voice calls from mobile (cell) phones. They are limited when it comes to sending or receiving data as it can take up to 30 seconds to make a connection to the network. GPRS is a method of enhancing GSM. GPRS (General Packet Radio Service) devices can transfer data immediately and at higher speeds. GPRS uses the existing GSM network to transmit and receive TCP/IP based data to and from GPRS mobile devices. GPRS devices are always on, as opposed to dial-up modems. You can connect Ethernet devices to a GPRS network by adding a suitable GPRS router.

More Wireless Resources:

• IEEE Wireless Standards Zone. The IEEE is developing open, consensus standards for wireless networks.
• ISA-SP100. The ISA-SP100 group formed in 2004 with the charter to establish standards and recommended practices for implementing wireless systems in the automation and control environment, with a focus on the field level.
• ISA: Users fear wireless networks for control

Entry Filed under: Data Acquisition