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RFID on the Production Line

01 February 2006

Engineers are using radio-frequency identification (RFID) in plant-floor applications, often with help from databases and software.

RFID is mostly used for identification, material handling, and other forms of documentation. Nevertheless it
has attracted interest for manufacturing applications, because of its ability to record data throughout the
production process.

Barcodes are used extensively in manufacturing, but these labels only offer 14 to16 digits of static data; the
smallest RFID tag allows 96 to 256 digits on each tag, which enough to identify products down to the shift, machine, and operator that produced them. Siemens A&D recently introduced a tag that stores 32KB.

RFID tags come in a variety of memories: some can be read-only, or write-once-read-many (WORM), or readwrite, or passively read by an antenna/reader, or actively send signals, usually aided by a battery.

RFID is essentially an automatic data collection technology. It can be integrated into control systems because it can read and write to those systems. A barcode tracks an item, while RFID tracks and records events, parameters, and measurements. This ability to store data, survive harsh conditions, and be written to make RFID more powerful than barcodes and less costly than a radio transmitter. This means users can make decisions and effect changes more quickly, such as finding an item faster if it doesn’t pass certain test criteria.

Closed loop to open loop
Similar to traditional radio transmitters, RFID tags were historically bricksized devices that cost about 100
euros, usually monitored work in progress (WIP) in harsh industrial applications, and were more capable,
such as having longer ranges. Data stored on RFID tags retained the recipes and other process data, but with Ethernet and client/server systems users started running applications with smaller memory tags which were linked to central databases and enterprise systems.

Though they’ve shrunk in size to a few centimetres and their cost dropped to a few euros or less over the years, these tags are still reused hundreds of times in closed-loop applications, amortising initial implementation costs. They’re typically used to track more expensive items, such as automobile chassis and components, which also helps make them economically worthwhile.

‘Traditional RFID tags work almost like an extended hard drive, and users can read and write onto them all the data on the quality measures that need to be achieved,’ says Alec Stuebler of Siemens. ‘For example, an RFID tag can help confirm that tools measuring torque during automotive assembly meet predefined
measurements, and then allow components being assembled to move to the next step. Or a heat-resistant tag can help start a paint process, and then verify quality when it comes out of the 250ºC oven.’

Read ranges for RFID tags can vary from 2 mm for flush-mounted tags in tooling applications to 2.4 GHz tags that can read several metres away. Memory sizes can range from 96-112 bytes up to multiple kilobytes, though more memory may require added power, such as a battery, to keep that memory active and accessible. RFID systems usually operate at three main frequencies: low frequency, which is below 1 MHz; high frequency, which is the 13.56-MHz universal frequency required worldwide for scientific instrumentation; and ultrahigh frequency (UHF), which is over 800 Mhz. UHF allows longer range and is less
costly, though it reportedly has some interference issues.

Siemens Automation and Drives (A&D) introduced its Simatic RF300 RFID product (photo) a few months ago; it is intended to be used as an identification system for use in production. The 13.56 MHz systems include new readers and tags which have been specially designed for high-speed identification applications
in assembly lines, conveyor systems and production lines.

The RF310R reader with its integrated antenna can be operated with various Simatic S7-300 communication modules and Profibus, with data transfer rates of more than 3,000 bytes per second. Tags
with a storage capacity of 8 KB, for example, can be read or written in approximately two seconds. In the
automotive industry this allows for short cycle times during motor production.

The IP67 or IP68 tags have an 8 or 32 KB storage capacity which is sufficient for the data needed in the course of production. All RF300 tags have a unique, unchangeable serial number and the capability of writing up to 20 bytes once (One Time Programmable Function). In this way, the user can protect his own workpiece tag information from being overwritten, independently of the serial number. Integrated diagnostic functions facilitate commissioning and service and improve plant availability. The user can, for example, query and evaluate field strength values for checking the correct configuration and error counters for
evaluating the quality of the communication.

Small size, price
Recent technological advances have reduced RFID tags to almost semiconductor chip-size, which is small
enough to be inserted into barcodes, other labels, or directly into products. They’re usually attached to increasingly smaller cases and packages, and are meant to be disposable, which is referred to as an ‘open-loop’ application.

Despite these advances, passive RFID tags typically cost 0.30 - 0.40 euros in large quantities, 0.60 - 0.65 euros in small quantities, or up to 0.70 euros and more for active RFID tags with more reading, writing, data storage, range, and other performance capabilities. Unfortunately, this remains higher than the 0.10 euro
threshold that RFID tags reportedly would have to achieve to make them economically viable in most mainstream, disposable, open-loop applications.

Passive tags are powered by the small amount of RF energy that excites them when they enter the electromagnetic field surrounding the RFID system’s antenna or reader. For example, 13.56 Mhz tags allow readings at up to 1 m. Once the tag is charged, the reader can interact with it, and pass the tag’s data to a linked controller, PLC, PC, or on up to higher-level enterprise systems.

Future evolution
By itself, RFID appears to have little to do with traditional control and automation. However, aided by
databases and other existing information sources, RFID can genuinely aid control and automation,
if indirectly.

Upcoming technical advances, such as energy-harvesting, active RFID tags, will likely settle any present arguments by letting the tags serve as wireless transmitters of analogue, digital, Ethernet, and/or Internet-based data.

In the next two or three years RFID tags will likely be combined with temperatures sensors that will be able
to continuously write to the tags for constant temperature indications.

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