RFID: Trends and Considerations.
There is little doubt that the RFID initiative started by Wal-Mart several years ago has given this technology a level of visibility it did not previously possess. While much is written about radio frequency identification and how it will change the face of distribution, it is time to address several misconceptions about the technology and discuss the effects that recent developments have had on the discrete manufacturing sector.
RFID is a mature technology that is an absolute requirement in many fields of automation for the purpose of error tracking and prevention. Those who considered using RFID a few years ago, but decided against it should give it another look. The technology has further matured, prices have come down and connections to PLCs have improved.
But the visibility that RFID enjoys today is not without problems, as it has created significant hype and unreasonable expectations. Possibly more problematic is the fact that many potential users avoid taking advantage of RFID, perhaps hoping that the Wal-Mart initiative will result in a low-cost super-solution. This attitude only deprives the U.S. manufacturing base of a powerful method to compete in the global market.
RFID tags: The real cost
RFID tags - the memory-holding element attached to packaging and products - are now available for less than $1, but users must realize what they can expect from a tag at that price. For example, tags used by Wal-Mart are operating in the UHF band and offer only 12 bytes of memory. These tags are designed for open systems associated with logistics tracking. This means that they have to offer a reasonable level of readability and reliability - 99% is considered very good - at the lowest price possible.
For a tag to be useful in the manufacturing environment it must be housed in such a way to withstand harsh conditions. These tags are also expected to operate for many years. And is 99% read reliability good enough for industry?
With this in mind, it is doubtful that an effective industrial tag will ever be available for, say, 25 cents. While the cost of the chips used in those tags will continue to drop, most of the cost is tied to the construction and housing material, and it is unlikely that those prices will experience significant reductions.
EPC, UHF and HF
It's important to differentiate between EPC (electronic product code) and RFID. EPC is a number that uniquely identifies a product and/or group of products. A manufacturer of consumer items, for example, must purchase the code from EPCglobal. This is a U.K.-based organization created by industry to support the EPCglobal Network as the global standard for real-time, automatic identification of supply-chain information. The group has done a good job pushing for a standardized data format and RFID solutions.
As of this writing, EPC is virtually synonymous with RFID tags operating in the UHF (ultra high frequency) band. UHF was selected because it allows RFID tag inlays to be produced cheaply. UHF technology also allows tags to be read relatively far away from an antenna. This is an advantage when tracking pallets moving through a doorway, but can be a problem in automation where items located close to each other must be read individually. On most conveyor-based production lines, for example, tagged items move with accuracy, and a read/write range between 1 in. and 8 in. is suitable. This allows two items to be placed near each other without them being read simultaneously.
EPCglobal has identified this inherent limitation, and now HF (high frequency) systems are evaluated as a suitable EPC alternative.
While tag cost is often the primary issue discussed in RFID literature (both UHF and HF tagging technologies offer similarly priced tags), the cost of the read/write electronics is often forgotten. UHF readers are still expensive, though these readers are likely to drop below the $1,000 mark.
This cost needs to be contrasted with the cost of read/write electronics for other technologies. For example, the $1,000 price threshold is well above that of devices designed to operate in the HF and 125 kHz band. In this arena, complete solutions, including communication interfaces, are priced below $1,000 and are dropping. Consequently, operators of closed-loop systems where tags remain attached to carriers (and never leave the plant) should be less concerned with using a cheap tag and focus more on the total cost of ownership.
PLCs continue to dominate automation control in plants and manufacturing systems. Therefore, any suitable RFID solution for the plant floor must offer a reliable and easy way to connect to the dominant networks supported by those PLCs. DeviceNet, PROFIBUS and EtherNet are the most important industrial networks used with RFID technology today. Even though there is no direct connection between tag technologies and the networking solutions, there is a direct connection between applications for which UHF tags are suitable and the fact that they are not driven by PLCs. Today, typical UHF tags are not suitable for tough automation applications. Consequently, reader connections to PLCs are not required. Exchanging data with an ERP system is more important, and the providers of these solutions have realized and addressed this need.
Among the network solutions used for factory-automation RFID, EtherNet is clearly the most popular. RFID controllers are now available that simultaneously support the various EtherNet flavors introduced by companies such as Schneider Automation, Siemens and others.
With Modbus/TCP, Profinet I/O and EtherNet/IP implemented on the same hardware, users, machine builders and integrators can now take the "learn it once" approach - and at the same time, help RFID better meet a wide range of today's industrial needs.