RFID technology in industrial applications
21 October 2009
In any industrial process, as well as in public buildings such as hospitals, a wide variety of items of equipment come under particular scrutiny and have to be monitored continuously to ensure that they are fulfilling the demands and requirements made on them.
RFID helps to manage rail logistics operations by providing identification of a slag wagon travelling between the smelter and the weighing station at a copper plant.
For example, in the food and animal-feed industry, stainless steel containers are cleaned regularly in order to meet the hygiene standards required by European regulations for the protection of humans and animals. Only if data are stored and updated on an ongoing basis is it possible to prove that containers have been cleaned after each use as per requirements and thereby achieve high process safety.
Another example might be a cleaning-agent pump that conveys liquids under high pressure and at high temperatures. Such items are subject to hygiene regulations, and also have to undergo regular preventive maintenance in order to avoid process downtime.
In the retail and logistics sectors, one approach to the process of product identification and monitoring is the use of bar codes. However, in industrial applications, factors such as high mechanical demands, dirt and frequent position changes make the use of barcodes impracticable.
In many areas of industry, radio frequency identification (RFID) is seen as a solution to capturing the data that enable such process monitoring to be achieved. However, in typical industrial environments RFID transponders have often failed because of the basic underlying conditions.
For example, the transponders can be surrounded by materials that absorb the RF signals. In addition, until fairly recently there have been no uniform standards for the transponder-reader interface, and consequently the systems available on the market were neither compatible with one another nor interchangeable.
This situation has led to users adopting isolated ‘one off’ solutions with very high development costs, which meant that they were not profitable for individual companies working alone.
Recent developments in RFID system technology, however, have made implementation in the manufacturing and process sectors a much more attractive proposition. Transponders are now available that are designed for direct mounting on metallic surfaces and on containers filled with liquid, along with readers that are sealed to IP 65 standards and offer a number of interfaces for stationary and mobile use.
RFID tags are normally used behind a metal barrier for protection against industrial environments, and transmit their data via small slots in the objects they are attached to.
The key to these developments is the use of MID (moulded interconnect device) technology, which allows the implementation of 3-dimensional directional antenna structures that, as passive transponders in the UHF (868 MHz) range, attain a ‘read’ range of over five metres.
Two other important developments are the availability of software to integrate RFID based data-acquisition into the industrial environment, and the emergence of communications standards—usually based on industrial Ethernet—so that the data can be transferred via a networking infrastructure and linked in with the overall plant information system.
Product life cycle
In a typical industrial application, the products to be monitored are fitted with a writable transponder in the form of an RFID data chip. Using a mobile reader/writer, product data can be read, updated and maintained quickly and reliably. The RFID transponder stores a variety of information which can be read via a stationary or mobile terminal prior to storing and transferring to a database.
In a manufacturing operation, the software can be used to organise data preparation, interpretation and documentation of individual product histories. This might be a product lifecycle which starts in prefabrication and continues until recycling. The user of the lifecycle software determines when to perform data tracking. At the same time, the software platform has open interfaces to ERP systems in order to guarantee a seamless link with the user’s business processes.
As checks are automatically carried out to ensure that defined processes are being observed, RFID technology also increases process safety and makes it possible to prove certified processes in areas of relevance to safety—in, for example, the chemical or pharmaceutical industries.
The software also features access control with various user levels and passwords in order to prevent misuse, such as unauthorised writing or deletion. In addition, data can be encrypted so that certain information can only be read by a pre-defined group of people.
The HARTING RFID reader captures and stores data from tags mounted on components or equipment, and uses industrial Ethernet communications to forward the information for further processing.
A further benefit of the integrated software approach to RFID is the ability to compare centralised stored data and decentralised information stored on the individual products RFID identity ‘label.’ In this way, it is possible to establish on-site whether all processes have been carried out and completed correctly.
Industrial transport applications
Today’s UHF RFID transponders are tough enough to be used under the most demanding conditions. One recent development has been their use for identifying and tracking rail freight wagons containing special cargoes including hot slag. Using this technique, passing trains and their contents can be accurately identified and tracked—even at high speeds.
A protocol known as EPC Gen2 has become an established standard in the RFID world, and this has boosted the efforts of manufacturers of RFID equipment to develop long-range transponders for mounting on metal surfaces.
One area where this technology is seen as particularly attractive is the rail-freight industry. With modern transponders, the data rate between the transponders and the read/write units is so high on EPC Gen2 that the ID numbers can be read from trains that are passing at speeds of 80 to 100 km/h.
Depending on the data volume, write operations take more time, but even that is not a problem if sufficient time is available at the loading terminals or freight yards.
For in-motion identification, rugged, weather-resistant read/write units can be placed on masts that are already installed alongside railway tracks, and data can be read from and written to the transponders on rolling stock from a distance of two metres. In order to reduce installation costs, two transponders can be mounted on each wagon, so that only one reader is needed to acquire information from trains travelling in either direction. To track shipments, it is sufficient to place readers at strategic locations such as stations or junctions and link them together in a network using industrial Ethernet.
Almost completely covered with dust, but still supplying data, the transponder mounted on a freight wagon.
One of the first—and most challenging—rail-freight tracking systems harnessing RFID technology involves high-temperature transponders for a copper smelter. The system integrator, Marie-Bentz, mounts the transponders on wagons carrying hot slag (photo). The transponders contain stored information originating from an automatic weighing operation which provides information about the residual concentration of copper in the slag.
Based on this information, the plant operator has been able to significantly improve the copper recovery rate. The tracking system also helps to improve wagon utilisation and ensures that sufficient capacity is always available. The deployment of RFID technology is tailored to customer requirements, with the ‘write’ capability of the transponders used when needed.
In another application involving harsh conditions, RFID transponders have been used as part of a data acquisition system to monitor slag tapping at a copper blast furnace in Bulgaria. A rugged, hermetically sealed housing and the use of plastics with an extremely high melting point ensure that the transponders survive the harsh conditions without failure.
The data-acquisition system carries out automatic weighing and identification of the wagons including product tracking, statistics, and wagon transit time.
A particular challenge was provided by the fact that the wagons overflow during loading, and therefore the mounting location has to be protected from above and from the sides. The transponders are wrapped in asbestos to protect them from uncontrolled splashing of the slag during unloading.
To ensure that the wagons can be accurately identified, the horizontal distance between the transponders and the readers is 5 m, and the minimum distance between two transponders is 1 m. The transponders mounted on the locomotives and the slag wagons have continued to work flawlessly since they went into operation.
—Kevin Canham, Harting
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