Appendix A - Radio Frequency Identification Defined Wireless Communication and Air Interface
Page A-8 MDE-3664B TRIND® Start-up, Service, and Parts Manual · June 2013
Powering Tags
Tags require power in order to work, even though the levels are invariably very small
(microwatts to milliwatts). Tags are either passive or active, the designation being determined
entirely by the manner in which the device derives its power.
Active tags are powered by an internal battery and
are typically read/write devices. They
usually contain a cell that exhibits a high power-to-weight ratio and are usually capable of
operating over a temperature range of -58 °F (-50 °C) to 158 °F (+70 °C). The use of a battery
means that a sealed active transponder has a finite lifetime. However, a suitable cell coupled to
suitable low power circuitry can ensure functionality for as long as ten or more years,
depending upon the operating temperatures, read/write cycles and usage. The trade-off is
greater size and greater cost compared with passive tags.
In general terms, active transponders allow greater communication range than can be expected
for passive devices, better noise immunity, and higher data transmissions rates when used to
power a higher frequency response mode.
Passive tags operate without an internal battery source, deriving the power to operate from the
field generated by the reader. Passive tags are consequently much lighter than active tags, less
expensive, and offer a virtually unlimited operational lifetime. The trade-off is that they have
shorter read ranges than active tags and require a higher-powered reader. Passive tags are also
constrained in their capacity to store data and the ability to perform well in
electromagnetically noisy environments. Sensitivity and orientation performance may also be
constrained by the limitation on available power. Despite these limitations, passive
transponders offer advantages in terms of cost and longevity. They have an almost indefinite
lifetime and are generally lower on price than active transponders.
Data Carrying Options
Data stored in data carriers invariable require some organization and additions, such as data
identifiers and error detection bits, to satisfy recovery needs. This process is often referred to
as source encoding. Standard numbering systems, such as Uniform Code Council
(UCC)/European Article Numbering (EAN) and assoc
iated data defining elements may also
be applied to data stored in tags. The amount of data will of course depend on application and
require an appropriate tag to meet the need. Basically, tags may be used to carry:
• Identifiers, in which a numeric or alphanumeric string
is stored for identification purposes
or as an access key to data stored elsewhere in a computer or information management
system, or
• Portable data files, in which
information can be organized, for communication or as a
means of initiating actions without recourse to, or in combination with, data stored
elsewhere.
In terms of data capacity tags can be obtained that
satisfy needs from single bit to kilobits. The
single bit devices are essentially for surveillance purposes. Retail EAS is the typical
application for such devices, being used to activate an alarm when detected in the interrogating
field. They may also be used in counting applications.
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General