Towards the end of 2003, IMS Research reported that 42.7percent of respondents to its survey of automation product users were expecting to be utilising wireless networks for industrial applications within three years.
Almost exactly one year later, Frost and Sullivan’s research into the industrial wireless market predicted revenues for European wireless technologies would quadruple between 2003 and 2006, though the analysts did warn that user concerns over security and reliability had to be overcome if this level of take-up was to be achieved. The lack of standards at that time was also felt to be a constraint.
Jump forward to December 2005, and Venture Development Corporation (VDC) of the USA reported that its own study showed that a large per centage of those in industry actually using wireless technology were applying it to control applications, or for both control and monitoring. However, further analysis revealed that the identified control applications were largely in setup and maintenance and that reliability concerns were still inhibiting adoption for operational real-time use.
Looking at the survey results in more detail reveals some interesting points. The two most commonly identified problems encountered by users of both RF (radio frequency) and microwave wireless industrial monitoring and control were signal reception drop-outs/blockage and RF interference. Understandably, with these concerns, users are often reluctant to embrace wireless technology for operational real-time control where a slight delay in – or corruption of – data communication could have costly results.
Nonetheless, industrial wireless operational real-time control is being utilised in applications with slowly changing variables, such as temperature control or flow control in slowly fluctuating processes, or in those where the control is via man-made decisions (such as with cranes or hoists).
Controlling slow processes also requires less bandwidth than, say, high-speed automated machinery control systems, as data rate requirements are lower. So many of the wireless industrial operational real-time control applications operate in the available RF spectrum bands in the 400MHz, 800MHz and 900MHz bands where there is adequate channel bandwidth for these applications.
However, because higher speed applications can require more bandwidth, this tends to necessitate operating in higher microwave frequency bands such as 2.4GHz or 5GHz. The drawback here lies in the fact that, in general, moving to higher frequency bands makes the problem of signal drop-outs/blockage worse.
One of the most widely used communications technologies used for smart process instrumentation is Hart (Highway Addressable Remote Transducer), which was originally developed by Rosemount in the 1980s. This open protocol is now managed by the independent Hart Communication Foundation (HCF). As might be expected, pressure from within the process industries has led the HCF to develop technical standards for wireless Hart communications, and the Wireless Hart Working Group is hoping to publish draft specifications in spring 2006. If all goes to plan, wireless Hart products could be available by the end of 2006.
ABB is one of the companies involved in the wireless Hart project, but ABB has already developed its own range of wireless sensors for use on high-speed machinery. These wireless sensors were launched on the market in 2005, described as a reliable and cost-effective alternative to conventional proximity sensors for machine control applications. More than 60percent of sensors used in production machinery are estimated to be proximity sensors that are wired into place. ABB’s wireless proximity switch eliminates the need for cabling in sensor applications, thereby cutting the time and cost of installation by up to two-thirds.
Data is relayed from the switch to the machine control system using ABB’s WISA (wireless interface for sensors and actuators) protocol, specifically designed for industrial applications. WISA links signals from sensors and actuators to an input module via radio antennas that then relay sensor signals to the machine control system. The input module is can receive signals from up to 120 switches at a time. Note also that by using ABB’s Fieldbusplug (FBP) concept, the input node can also be connected to fieldbus systems such as Profibus, AS-I or Devicenet.
To eliminate the need for power cables, ABB has developed a system that uses an electromagnetic field created by an alternating current running through primary power loops. The wireless sensor is equipped with small secondary coils that pick up energy from the magnetic field. This provides the wireless switch with a constant, uninterrupted supply of power, avoiding the problems associated with batteries that have a finite life.
The first family of proximity switches on the market is available in four different sensor head sizes and covers switching distances ranging from 1.5mm to 15mm. Switches are available in flush- or non-flush-mounted design, have an IP67 protection rating and can operate in environments ranging from -25to55°C.
A further area in which ABB has been undertaking development of wireless systems is machine diagnostics, set-up and alarm response. Known as the wireless pocket portal, the system allows plant operators to patrol a factory and still be connected to operational data and controls. The absence of wires lowers manufacturing and engineering costs, allows for simpler components, and system users are no longer tied to fixed points.
Many factories, machines and processes are managed from a central control room. If operators leave the control room they must return as fast as possible to deal with an emergency. However, with ABB’s wireless pocket portal display, operators are free to roam the plant without ever losing access to control room information and controls. In an emergency, the operator retains full access to control data and intranet connections while outside the control room.
Apart from the wireless Hart project, ABB’s wireless developments have been largely proprietary. For those who prefer to use standardised products and systems, industrial Ethernet is a popular choice.
Westermo Data Communications is active in the wireless field and, at the end of 2005, released a standalone industrial radio modem that provides long-range transmission/reception and high reliability when connecting 10/100baseT Ethernet networks wirelessly. The Elpro 805U-E is designed for industrial Ethernet connections in process control and factory automation applications such as PLCs (programmable logic controllers), DCS (distributed control systems), Scada (supervisory control and data acquisition), data acquisition and wireless video. The module uses 869MHz license-free radio technology and provides a data rate of up to 77kbit/s for congested industrial environments, with a range of over 500m through buildings, factory walls and steelwork. It is suitable for long- and short-range applications, with a maximum range of 5km, or a repeater function can increase this distance further if required.
Wireless Ethernet clearly has benefits for industrial users but, at the device level, similar advantages are available. As an example of the type of products that are now on the market, Omron has released an additional version of its wireless Devicenet modems, the WD30-01, to extend the units’ application potential. A detachable antenna enables the modem to be mounted in a cabinet, while the antenna is mounted externally to increase the installation flexibility and improve the covered communication distance (Fig.1). These modems enable users to connect any Devicenet-compatible product on a truly wireless fieldbus. WD30 products are not just 1:1 devices for extending a network; a single WD30 master modem can address multiple slave modems – and placing multiple wireless masters on a single Devicenet network provides multiple, flexible topologies on the same system.
Omron’s wireless Devicenet modems combine two wireless communication technologies: spread spectrum and antenna diversity. The wireless communication relies on direct sequence spread spectrum (DSSS) technology, divided into 34 distinct channels at 2.4GHz (the ISM industrial, scientific and medical frequency); the spread spectrum technology minimises signal interference, thereby helping to ensure that the message gets through the first time. Each wireless Devicenet transceiver uses a dual antenna system. The transceiver samples the output signal of a device by discriminating between signal and reflections, then automatically selects the antenna with the better quality signal to minimise interference. Omron’s transceivers were said to be the first in the industry to combine these two technologies.
A further option for linking machine inputs and outputs (I/O) wirelessly is available from Cirronet. This company offers Hopnet wireless I/O modems, including the HNIO-091R and HNIO-241R relay modems, which operate at 900MHz and 2.4GHz, respectively, and the 900MHzNHIO-091A and 2.4GHzHNIO-241A analogue/digital modems.
Cirronet’s wireless I/O modems feature bidirectional transmission and use frequency hopping spread spectrum (FHSS) technology that is claimed to have a superior ability to deliver critical data regardless of the environment or conditions.
Unlike wireless data transceivers, which Cirronet also manufactures, wireless I/O modems transmit voltage or digital signals rather than serial data streams. Analogue/digital models are typically used to relay key levels of sensor data, while relay units control the state of equipment such as light fixtures, alarms and locks. Line-of-sight range extends beyond 32km for the 900MHz I/O modems and up to 11km for the 2.4GHz units, depending upon the antenna used. The modems can operate over an input voltage range of +9Vdc to +30Vdc, making them suitable for battery and solar power sources.
Hazardous areas can benefit from wireless communications even more than non-hazardous areas because the cost of installing cabling – both the purchase price of the hardware and the labour – is so much greater.
Phoenix Contact’s RAD-ISM-2400-SET-UD-ANT unidirectional wireless transmission system is designed for high-reliability applications in process industries. It transmits one 4–20mA analogue and two digital signals over ranges of up to 3000m to one or more receivers.
For harsh areas that are not designated hazardous, Aerocomm has introduced the ACE family of heavy-duty RF modems. The ACE6490 and ACE6790 are housed in rugged Nema-4x enclosures, designed to withstand the rigours of extreme weather or other severe surroundings (Fig.2). Each product delivers variable output power of up to one watt at 900MHz, thereby maximising the range in even the toughest environmental conditions.
ACE products embed two distinct protocols to offer exceptional flexibility for rugged applications. The ACE6790 utilises a dynamic peer-to-peer protocol for enabling a mesh topology, while the ACE6490 employs Aerocomm’s own server/client networking architecture. Both products instil the reliability that results from frequency hopping spread spectrum technology, plus they incorporate data encryption.
Aerocomm has also announced an 868MHz spread spectrum transceiver specifically for products to be used in Europe. Built to provide OEMs (original equipment manufacturers) with license-free RF communications over distances of up to 15km, the AC4868 is described as an alternative to products operating in the saturated 433MHz band (Fig.3).
Underlining its suitability for industrial applications, both static and mobile, the AC4868 module operates in temperatures ranging from -40 to 85°C. The transceiver modules are aimed at designers and manufacturers of industrial or commercial products that currently use alternative methods of communication, such as infrared, serial/wired, memory card download, or other less sophisticated wireless means.
For wireless transmission of RS-232, 422 and 485 serial signals over distances of up to 100m, B&B Electronics has launched the Vlinx wireless serial servers (Fig.4). These might be suitable if, for example, an item of plant needs to be moved unexpectedly. Instead of running expensive cabling, the machine’s serial ports can simply be connected to an Ethernet Lan. The advanced 802.11/g technology in the ESR wireless serial servers allows up to four machines to be connected to one transceiver and run at data speeds up to 54Mbps.
Built specifically for industrial applications, the units feature metal Din-rail mounting cases and operate in temperatures from 0 to 60°C. An external connector allows optional antennas to be used for greater range.
Bluetooth and Zigbee
Two wireless technologies that are starting to emerge in the industrial sector are Bluetooth and Zigbee. Bluetooth has been used in industrial applications, the first large-scale project being ABB’s implementation of Bluetooth technology at 179 pumping stations owned and operated by the municipal water utility in Oslo, Norway.
This will enable the utility’s service engineers to use a standard Bluetooth-enabled laptop computer or PDA (personal digital assistant) to instantly establish a wireless connection with any pump station and monitor the status of the equipment, access stored data and make any adjustments necessary. Service engineers will also be able to link up with the municipality’s wireless area network (Wan) and communicate simultaneously with the utility’s central control system.
The overall system was custom-designed for Oslo Municipality by ABB and Connectblue, a Swedish Bluetooth developer, and is incorporated within ABB’s Control IT AC 800C control system, which replaced the utility’s existing Scada system.
Bluetooth has been available for longer than Zigbee (IEEE802.15.4), but it has to be remembered that this technology only supports seven nodes. In contrast, Zigbee supports 264 nodes, enabling mesh networks of an almost unlimited size to be established. In fact Zigbee’s addressing scheme is capable of supporting over 64000nodes per ‘network co-ordinator’, and multiple network co-ordinators can be linked together to support extremely large networks. Ultimately the size of a Zigbee network depends on which frequency band is selected, how often each device on the network needs to communicate, and how much data loss or retransmissions can be tolerated by the application.
Of particular interest to industrial users is the fact that Zigbee is designed for the hostile RF environments found in mainstream commercial and industrial applications. The protocol uses direct sequence spread spectrum (DSSS) technology with features including collision avoidance, receiver energy detection, link quality indication, clear channel assessment, acknowledgement, security, support for guaranteed time slots and packet freshness.
While it is still early days in terms of Zigbee-enabled product availability, the automotive, food processing and petrochemical industries are predicted to be the first to make profitable use of the protocol.
At its quarterly Zigbee Alliance Open House and Exposition in Mongkok, Hong Kong, there were more than 21 live demonstrations of Zigbee products from Alliance members. Ember Corporation, for example, has developed Embernet embedded networking software and development tools for use with a low-frequency, self-organising, self-healing wireless embedded networking platform that supports the Zigbee standard (Fig.5).
At the beginning of 2006, The Zigbee Alliance announced it will begin certifying products as ‘Zigbee Certified’. Member companies can therefore test their Zigbee-ready products that are already on the market so they can be branded as Zigbee Certified for industrial, commercial or home market use.