Wirelessly monitoring instruments and sensors 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.
But what if your existing devices are not enabled for wireless measurements? In many cases you can make them so 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 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. You can then use software like Windmill's COMIML to collect data (https://www.windmillsoft.com/daqshop/rs232-modbus.html). Bluetooth is named after a Danish king who unified Denmark and Norway. 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. 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/
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.
WiFi networks conform to the IEEE 802.11 specifications. The first 802.11 specifications were introduced in 1997 and these have been regularly amended. Each new version of the specification has a different letter at the end - IEEE 802.11a and IEEE 802.11g for example. The differences between the versions include the frequency at which they operate and the speed of data transfer
It is very easy to enable your PC for WiFi communications: just plug an adaptor into the USB port. Many new computers come with a WiFi card built-in.
You can use instruments with RS232 ports over WiFi. To do this you need a serial device server. This will usually come with driver software which makes your instrument appear as if it were connected to the COM port. You can therefore use any data acquisition software which reads RS232 instruments to log data from your device. We of course recommend the Windmill COMIML software to automatically collect data from whatever instrument you have connected.
For more on WiFi and data acquisition see Issue 82 of Monitor, http://www.windmill.co.uk/monitor82.html
- 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/
- Passed in September this year, 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, 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.
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