Radio frequency identification (RFID) represents a variety of technologies with different characteristics. See how Siemens’ work with ultra high frequency RFID is easing the application of this technology on the plant floor.
Go back 70 years. An allied fighter pilot in the last year of World War II can see another plane off in the distance. In the failing light of dusk, he wonders if it is friend or foe and hopes he can tell the difference before it’s too late. Fortunately, a new device in his plane identifies the plane as a friend. That technology was RFID, and it helped him determine who’s who by using radio to read an identifier in the other plane.
From these beginnings, RFID has developed into an increasingly ubiquitous technology. Today we see it in one form or another virtually every day. From tollway pass transponders to pet tracking chips to the millions of little tags inserted into all sorts of products at retailers, the technology is at work all around us. RFID takes advantage of the fact that a device can gather energy sent by a radio transmitter and use it to send a return transmission encoded with some simple information.
Typically the information is a number or some other unique identifier that a tag can transmit on behalf of the thing that carries it. The tag may carry an identifier that is permanently embedded in it, and a larger system may need to look up more detailed information associated with the tag. Or, the tag itself may have information written to it that can be changed multiple times over its lifetime.
While people typically talk about RFID like it’s a specific thing, it represents a variety of technologies, each with its own characteristics. The biggest differentiator is frequency. Given the three main frequency classes, the selection of one for a given application should be driven by its specific needs. In large facilities, it is not uncommon to find more than one deployed in ways that uses those characteristics to its best advantage.
Low frequency (LF) systems use 125 KHz or 134.2 KHz bands that are well below AM radio. LF has limited distance range capabilities and the amount of data it can transfer is relatively small. For industrial applications, its best use is for products that move around on a conveyor or reusable pallets on a track, such as assembling a machine on a transporter. The device can pass close to the reader at a consistent distance and transmit a very reliable signal. Tags can be made indestructible and work for many years.
High Frequency (HF) systems use 13.56 MHz worldwide. This frequency is the most standardized, both from a country-to-country standpoint as well as vendor interoperability. Like LF systems, the reading distance is relatively short, but HF tags are able to carry the largest amount of information in a way that can be read quickly.
Both LF and HF systems work very well in situations where the reading distance can be kept uniform. The propagation of the signal is well behaved and predictable, so it can work reliably, year after year, with little interference from liquids, people, or metal objects in the vicinity.
The third class, ultra high frequency (UHF), operates around 915 MHz. The RF mechanism of this system is different than the other two in that the tag causes encoded backscatter of the transmission rather than inducing a return transmission from the tag. Like LF tags, UHF has a limited amount of information it can send, but it can cover much longer distances. UHF can handle more complex applications than the lower frequencies. Here’s an example: A forklift carries a pallet of boxes of pharmaceutical products. There are 16 cartons on the skid, and each carton has its own RFID tag to identify the product, lot number, and so forth. The driver passes a UHF reader and it detects, scans, and collects data from all 16 tags in one pass, even though they are in different positions on the skid.
A well-tuned system can perform this kind of operation easily and reliably. However, if some element changes, say the guard on the forklift behind the skid changes from a bar to a plate, that new metallic element may reflect the signal in a different way and cause the system to miss some tags or read them incorrectly. Consequently, UHF requires the most finesse when setting up the reader and antenna configuration, along with the transmitter power and sensitivity of the receiver. When settings are off, the system may read nothing, or it might detect tags on the other side of the warehouse that you are not interested in.
New Diagnostics for Setting Up UHF
With older UHF systems, setup was a tedious process with extensive trial-and-error to establish critical parameters:
- Transmitter signal strength
- Antenna size, placement, and orientation
- Receiver sensitivity
- Tag reading algorithm configuration
However, Siemens has introduced a variety of diagnostic capabilities into its SIMATIC RF650R/680R/685R product family. There are the usual capabilities to assist with integrating the system into the larger automation system using TIA Portal (more on those later), but it includes some unique diagnostics to help determine how the signal is propagating and how tags are being read.
For example, when evaluating the ability for the system to read over a given distance, it is a simple matter to scatter target tags at various distances from the reader. The system can be set to raise transmitter power slowly, automatically recording which tags it detects at each power level. Target tag positions can help determine both overall distance and how signals might be reflecting off large items within the reader’s range. Adjusting transmitter power and receiver sensitivity while watching this diagnostic capability makes it possible to read the specific area you want, no more and no less. In some areas where too many items are crowded into a small space, some undesirable tags may always be detected. Those can be filtered out manually by telling the system to ignore them. Fine-tuning signal strength by adjusting antenna position is also simplified by using a sensor at the critical distance. It’s possible to watch the strength measurement on a laptop screen while physically moving the antenna. The signal strength value is even displayed as a large number on the screen so it’s easy to see from a distance.
Simplified Engineering, Easy Configuration with the TIA Portal
Each Siemens UHF RFID unit has a built-in web browser so it can be configured without needing any special software. This makes it easy to set up in any environment; but the greatest benefits can be realized in situations where it can work with other Siemens products using the TIA Portal.
Over the years, Siemens has developed a variety of tag reading algorithms from experiences in many difficult environments. One example is a Mercedes auto body plant, as few situations have more complicated reading environments than an auto plant with a variety of odd metal shapes, constantly moving, that cause RF signals to bounce from one surface to another. As challenging as such a location might be, Siemens engineers have used lessons learned there to simplify more typical applications, and this kind of know-how is available through the TIA Portal.
Since an RFID system is only a small element of a larger manufacturing environment, the TIA Portal makes it a simple matter to use these tools to configure setup parameters and communication to PLCs and networks. Integrated tools and diagnostics in an environment with familiar look-and-feel characteristics make setup and commissioning as easy as possible. Interfacing with an HMI and collecting historical data is a simple matter because software editors for all devices within the TIA Portal use the same tools.
With all these elements working together, configuring a UHF RFID system is not nearly as difficult as it can be when working with less sophisticated equipment. Siemens may not be able to eliminate the tendency for signals to bounce off some surfaces or be absorbed by others, but it can make quantifying and working with those characteristics much simpler.Have an Inquiry for Siemens about this article? Click Here >>