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RFID for industrial applications

RFID for industrial applications Choosing the proper RFID system for use in industrial applications can be a confusing task. Mark Sippel of Balluff guides us through the options and looks at which systems work best in given environments.

With so much information floating around about RFID systems these days, it may seem as though any technology can be used just about anywhere. However, RFID is designed for many environments besides industrial, which can make it confusing as to what systems work the best.The three most widely available RFID systems are low frequency (LF), high frequency (HF), and ultra high frequency (UHF). Each of these frequency ranges provide advantages or disadvantages based on their characteristics, principles of operation, and application usage.

Low frequency systems generally operate between 70kHz to 500kHz, and are typically station based. This means the tags have data read and/or written to them at a specific 'check' point in a process. The systems are commonly used as 'read only' systems for the purpose of data tracking only. A read-only system typically uses an individual serial number normally no more than 40 bits in data capacity. This data is used by a control system to track a transportation device such as a pallet. Most read/write versions of LF tags are limited to less then 200 bytes in data capacity, but allow you to write data to and from the tags when required.

Most LF systems are based on inductively coupled technology. Inductive coupling (based on Faraday's Law) powers the tag using energy generated from a coil in the read/write head to induce a voltage in the coil. Data transmission is typically done by changing one characteristic of the alternating field used to power the tag. This makes the tags' data less susceptible to interference from other frequencies or simple magnetic forces.

LF systems can provide greater range performance, as much as 70-150mm on non-alloy surfaces, and as much as 50mm mounted on or in metal. An LF system typically has the longest transmission time for a given block of data compared to HF or UHF systems - a read process can take 180 milliseconds to read a block of 4 bytes of data. To write the same 4 bytes of data can take 300 milliseconds or more. LF systems are typically not used in applications that require moving read/write or 'on-the-fly' operation.

High frequency systems typically operate at 13.56MHz. These systems are usually based on either the ISO 14443 (also known as the Mifare standard) or the ISO 15693 standard. The benefits to these standards are that they can allow interoperability between several manufacturers of tags and read/write hardware. As a result, HF based systems can mean lower cost for the user, comparable in cost to LF tags. HF systems are also generally station based like LF systems.

Unlike the LF based tags, HF tags typically see significant read/write signal degradation when mounted in a metal alloy, thus limiting range unless designed specifically for this purpose. HF read/write ranges can also be degraded by having metal in or near the field created by the head. There are exceptions where some manufacturers have created special tag and head antenna designs allowing minimal effects from metal. These special tags and heads can use techniques like 'rod' style antennas instead of coil antennas.

HF systems also have good range, as much as 150mm or more when mounted on non-metal alloy surfaces. The range for HF tags mounted on or in metal is usually manufacturer specific. HF systems can read/write tag data considerably faster then LF systems. For example, to read a block of 16 bytes or  128 bits of data, a read process can be completed in 30ms or less. To write the same 16 bytes of data can typically be completed in 60ms or less.

Because of their higher read/write speeds, HF systems can be used for applications that require continuous movement at speeds of 3m/s or more, depending on the amount of data being transferred. Like LF systems, HF systems operate on the principle of inductive coupling, so are less susceptible to interference from other adjacent systems, with minimal distances are required between read/write heads compared to other RFID system types.

Ultra high frequency systems typically operate between 865MHz and 960MHz. Unlike LF or HF based systems, UHF systems are based on an operating principal known as 'backscatter coupling', where the reader uses a dipole antenna that transmits electromagnetic waves, creating mostly magnetic power, which is modulated and reflected from the dipole antenna of the tag (or transponder). This electromagnetic wave propagation is used for data transmission and powering the tags, thus making them passive. Unlike inductive based systems, the signal can create a 'dead zone' where a tag may not be powered or detected. Most UHF systems today are based on 'Gen 2' hardware which provides multiple frequency capability, making these systems very flexible in complying with international radio spectrum frequency usage restrictions.

Some of the advantages of UHF over its LF or HF counterparts are that it can be used for much longer read/write distances, as far as 4-5m reliably and sometimes farther depending on antenna and tag designs. Because of the nature of the propagating wave transmission method, UHF can also be reflected off conductive or partially conductive surfaces such as metal, water or concrete. This reflection property can be helpful by causing the waves to be redirected around objects allowing greater flexibility. But this can also be a disadvantage when trying to isolate a specific tag when a large quantity of tags are present in the field. Newer 'near field' forms of UHF are entering the market that may help resolve this condition.

Read and write speeds with UHF can vary greatly and many vendors claim reads of 20 to 1000 per second can be achieved. But be careful because many factors can significantly reduce the reliability of such claims. Often the only way to determine a reliable read rate is to perform a site survey and actually test the system's performance.

We can see, then, that choosing an RFID system can seem a daunting task. With each passing year, more options become available. Due to the nature of the infrastructure required to implement even a small RFID installation, choosing the wrong technology will have expensive and unreliable data collection consequences. The best recommendation is to not buy looking at cost alone. After all, the most important part of an RFID system is its ability to move and store data reliably. Without reliable data, everything else is inconsequential.
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