Our last article talked about the two different kinds of chips that you might see in RFID. The question though is how the chip actually gets read by the computer and used for timing. There are 3 components that are required for RFID chip timing. One is the computer to make use of the chip read. The computer is usually a laptop but could be any computer. It has specialized software that knows how to interprete the chip data and turn it into an actual time that can be used for race timing and scoring. Then there is a RFID reader which is attached to the computer either through USB, Serial, or Ethernet. The reader's purpose is to generate the signal that is used to read the chip and then use the returned data and pass it along to the computer. The reader does the heavy lifting to communicate with the chip. The final piece is the antenna. Each reader has one or more antennas that are used to communicate between the reader and the chip. The signal strength and placement of the antennas is critical in defining how well the chip gets read.
When a timer sets up a system to capture chip reads at a race, it is critical that the antenna be placed in such a way as to maximize the number of reads. There are several configurations that you might see at a race. An older technology that most are familiar with and still refer to is mats. These looked like carpets that were thrown down across the timing point. This technology worked well with shoe tags but not so much with the newer chips on bibs. The reason is that the signal strength of the mat is not high enough to generate enough activity between the chip at the increased height and the mat. A shoe chip was within 1 foot of that mat while a bib chip is at 4 feet or more. This difference creates a huge problem for mats. An improved configuration for bib tags is antennas that are placed overhead. These antennas generate a high signal strength that can read chips at several feet. By placing the antennas overhead, the antennas are also more accurate as that their placement can be optimized to determine the exact point that the chip passed within a few inches. Mats had a problem in that their read zone was a foot in front and behind the mat so the actual read zone could be 4 to 6 feet.
One disadvantage of overhead antennas is that it requires a stable truss or other structure. This causes problems if using an inflatable arch so some timers will attempt to put antennas on the side. These antennas must have a very high signal strength and be placed closer together in order to ensure that all participants get read. The issue is that chips closest to the antennas will get read but chips out in the middle or in tightly packed groups can be missed. In order to compensate for this issue, the antennas must be placed in a linear configuration to help with read rates. This objective of this configuration is to get a read. Accuracy of the chip read is diminished but that is usually not a big deal except in tight races.
Another configuration is very much like mats but is a ground ramp. These are usually stronger antennas and are evenly spaced in a foldable type ground ramp. Here again the antenna strength must be strong enough to get a good read for the height of the runner. The read zone is narrower but the read rate is also lower. Timers get around this by putting multiple ramps in succession with the hope that if one doesn't get the read, then another will. The problem with this is that accuracy for missed reads is lower as the second ramp time is adjusted to compensate for the extra distance.
At Athlete Guild, we primarily used overhead antennas as we have learned over the last 12 years that they are the strongest and most accurate way to get a read. It allows us to use a single set of antennas so we are guaranteed of accuracy in chip reads. It's not always ideal though for this configuration so we will use side mount antennas when accuracy is not absolute or when unable to use a stable structure.
Take a look at the next race you attend and see if you can spot the configuration.
See you at the race!
