Wireless Connectivity in Control


Over time, many different wireless technologies have evolved to support flexible links for industrial networking and process control applications with a range of capabilities from hardware-based real- time solutions to low cost. In the past, concern about security and reliability of wireless communication technologies in the industrial arena has limited its deployment. But more and more, the latest technology can support robust, reliable and secure industrial wireless systems including Ethernet-based wireless LAN solutions.

The use of industrial wireless communication is now opening up many new possibilities for highly flexible and efficient automation solutions. The benefits are many not least of which are the savings in the installation cost of cabling up a wired network – especially over long distances. In addition to which there are economies of scale with the easier addition of nodes, operational savings with better and faster monitoring, plus potentially much safer operation in hazardous environments that previously may have required an operator to take a reading or activate a valve for example.

The range of wireless frequencies and protocols available for process automation, coupled with the different performance requirements down to hard real-time responses, has created a fragmented industry. There is a range of unlicensed frequencies available, varying from the sub-1GHz variants in different parts of the world – the 915MHz band for the Americas, 868MHz in Europe and 920MHz in Japan – up to the unified 2.4GHz ISM (Industrial, Scientific and Medical) band.




Industrial Wireless LAN

In response to requirements for significantly higher levels of data and greater networking capabilities, Industrial Wireless LAN (IWLAN) technology is growing fast in the industrial automation arena. The technology is also especially suitable for demanding industrial applications that require end-to-end reliable and secure radio communications. IWLAN is an extension of the IEEE 802.11a/b/g and n standards offering from 54-Mbit/s upward to potentially hundreds of Mbit/s. In addition to higher data rates than other wireless systems, allowing applications such as video streaming for example, it also allows data transmission with other mobile devices leading to significantly improved process efficiency. The technology is also especially suitable for demanding industrial applications that require end-to-end reliable and secure radio communications. Existing Ethernet networks can be upgraded by up to 96 access points without requiring any changes to the network infrastructure, which opens up completely new options, such as the use of Voice-over-IP, video or Internet access in one single wireless network. Various services, security requirements and access criteria can thus be managed reliably so that all can use the same wireless network.

A leading player in IWLAN wireless communications is Siemens, which also offers a range of equipment for wireless remote networks or WirelessHART based solutions. All of its offerings are suitable for indoor and outdoor use under extremely harsh conditions and also provide reliability, robustness and security. The company’s SCALANCE W range of industrial Ethernet networking components includes access points, client modules and various accessories such as antennas and power supplies. For example, the SCALANCE W786-2RR access point device enables the establishment of very reliable wireless networks with approval in the license- free ISM bands at either 2.4GHz or 5GHz.

Siemens has numerous industrial applications in the IWLAN area, including crane control (see Figure 1) and automated guided vehicle systems in a container terminal (see Figure 2).


Figure 1 – Automated crane control using SCALANCE W devices



Bluetooth is of course very well known as a wireless data technology in consumer markets, but it is also gaining excellent traction in industrial. Offering multiple megabit-per-second data transmission capability, like IWLAN it operates in the 2.4GHz ISM band and delivers reliable wireless communication with automation components and also quick and easy implementation. Several advantages of the technology include: easy and safe installation, thanks to largely automatic configuration; extremely reliable and rugged data transmission, due to redundant transmission channels and integrated error correction; interference- free parallel operation of multiple Bluetooth wireless paths or Bluetooth wireless paths and WLAN systems, due to the efficient use of frequency gaps; and finally a transmission range of potentially up to several hundred meters. A major player in Bluetooth- based devices for industrial is Pheonix Contact, which offers products such as its PSI line of Bluetooth converters that convert the RS-232, RS-422 and RS-485 serial interfaces to Bluetooth making possible a point-to-point or multipoint connection, or for use as an access point for Bluetooth-capable devices such as notebooks or other smart portable devices to query operating status or carry out programming or diagnosis.


Figure 2 – Controller-based IWLAN applications with a large number of access points, such as in a container terminal



Low-latency solutions can be vital for those applications that require a hard real-time capability such as monitoring critical processes. Wireless versions of fieldbus-based protocols such as WirelessHART – which is a wireless sensor peer-to-peer networking technology adding wireless capabilities to the Highway Addressable Remote Transducer Protocol (HART) – provide a way to deliver real-time performance in a more flexible manner with wireless links. While it is based on the popular unlicensed band at 2.4GHz used by other technologies – such as WiFi or Bluetooth and also ZigBee – it also includes security and interference protection to ensure that every packet of information is delivered within a certain time. The protocol enables users to quickly and easily gain the benefits of wireless technology while maintaining compatibility with existing HART devices, tools and systems.

The WirelessHART protocol is an open standard designed for devices such as sensors connected over the 4-20mA analogue loop and offers a data rate of 250kbps. It uses a time- synchronised, self-organising and self-healing mesh architecture and includes several features to provide built-in 99.9% end-to-end reliability in all industrial environments, such as channel hopping to avoid interference and provide coexistence with other wireless networks. Clear Channel Assessments test for available channels, while blacklisting avoids frequently used channels, optimising bandwidth and radio time. Time synchronisation provides on-time messaging for the time-critical links to the interface, and the self-healing network topology means any breaks or failures do not impact the data transfer. Each device in the mesh network can serve as a router for messages from other devices. This means that a device does not have to communicate directly with a gateway, but can forward its message to the next closest device, thereby greatly extending the range of the network and providing redundant communication routes for increased reliability.

Security is also a key consideration for an industrial network. In this, WirelessHART employs the security techniques to provide the highest levels of protection available via 128bit AES encryption and a unique encryption key for each message, as well as device authentication.



Extensive Wireless Range

And finally, also available via RS are a range of wireless products including pushbuttons from Schneider Electric, wireless switches from companies such as Honeywell and Steute, and wireless LAN access point products from Pheonix Contact. In addition, brand new wireless industrial sensor products now include those from JUMO such as its Wtrans transmitter RTD (Resistance Temperature Detector) temperature probe. The Wtrans transmitter is designed to be used with a Wtrans receiver for stationary or mobile detection of temperatures within the operating range of –30 to +260°C or –200 to +600°C. The transmission electronics of the probe are vibration- proof and the case is both oil resistant and acid proof. The radio frequencies of the Wtrans measuring system (868.4MHz for Europe or 915MHz in the US) are largely impervious to external interference and allow transmission even in a harsh industrial environment.

For more information visit: www.rs-components.com/ wireless-automation


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