Read Probabilities are is defined as the fast and accurate identification of the tag. In the tracking of livestock, this rate should be greater than 99%. To maintain this level of reliability several aspects of the process and the system being used, must be considered.
It has become a common practice to specify the operation of a given RFID reader/tag combination as the maximum distance at which the tag can be identified. Usually these specifications do not consider application related variables such as the size, orientation, and speed (or timing) relationships of the tags and those of the readers. Another common variable is the type of reader/antenna. This can vary from fixed position to hand-held readers as applications demand.
Specifications are usually defined by tests made under optimum conditions -- -- proper tag/reader orientation and interference free environment. RFID commonly refers to a passive tag technology. Some manufacturers, such as those using "Charge pump" technology will specify "read range," only after an internal tag capacitor has been fully charged. The process of charging (pumping) may require several presentations of the tag to the reader at shorter than specified distances, or holding the tag in the field for an extended period of time. This process is repeated until it will operate at the maximum distance that is then specified as the read range.
In reality the intent of proximity readers should be to identify the tag quickly, the first time it is presented to the read field. This is true whether the use is to control access to doors, identify objects, track personnel or products, and especially when used to identify livestock.
When using RFID to identify livestock, do not be too concerned with the specified read range. The most important criteria should be that the RFID system is designed so that it is nearly impossible to not obtain a valid read of the tag. Numerous presentations, extended time in the read field, tag/reader orientation concerns and excessive environmental interference are some of the problems that should not be tolerated.
This system design often will incorporate tag/reader combinations that may appear to have a short read range. In reality this type system when properly engineered will give read probabilities that will approach 100%. The "long" read range system probabilities can be as low as 50 - 60% This low read probability can be the result of numerous shortcomings in any system accuracy.
The major factors affecting system accuracy deal with issues affecting the interface between the tag itself and the reader/antenna. These factors are distance, orientation and time. In summary we need to know howfar away can we read a tag, how long will it take to detect that tag and what orientation must the tag have to the reader in order to be detected.
These considerations are the most important aspects of RFID technology as it applies to livestock.
For more information on this issue or any of the other
TECHNOTES from AGRI SIGNAL Inc. technical staff please
contact us at
1530 Old Oakland Road Suite 100,
Tel. 408-451-2526 or FAX 408-441-0309