Appendix A - Radio Frequency Identification Defined
Wireless Communication and Air Interface
Page A-10 MDE-3664B TRIND® Start-up, Service, and Parts Manual · June 2013
Costs
The cost of tags obviously depends upon the type and quantities that are purchased. For large
quantities (tens of thousands), the price can range from less than a few tens of pence for
extremely simple tags to tens of pounds for the larger and more sophisticated devices.
Increasing complexity of circuit function, construction, and memory capacity will influence
cost of both transponders and reader/programmers.
The manner in which the transponder is packaged to form a unit will also have a bearing on
cost. Some applications where harsh environments may be expected, such as steel mills,
mines, and car body paint shops, will require mechanically robust, chemical and temperature
tolerant packaging. Such packaging will undoubtedly represent a significant proportion of the
total transponder cost. Generally, low frequency transponders are cheaper than HF devices;
passive transponders are usually cheaper than active transponders.
Reader/Interrogator
The reader/interrogators can differ quite considerably in complexity, depending upon the type
of tags being supported and the functions to be fulfilled. However, the overall function is to
provide the means of communicating with the tags and facilitating data transfer. Functions
performed by the reader may include quite sophisticated signal conditioning, parity error
checking and correction. After the signal from a transponder has been correctly received and
decoded, algorithms may be applied to decide whether the signal is a repeat transmission, and
may then instruct the transponder to cease transmitting. This is known as the “Command
Response Protocol” and is used to circumvent the problem of reading multiple tags in a short
space of time. Using interrogators in this way is sometimes referred to as “Hands Down
Polling”.
An alternative, more secure, but slower tag polling technique is called “Hands Up Polling”
which involves the interrogator looking for tags with specific identities, and interrogating
them in turn. This is contention management, and a variety of techniques have been developed
to improve the process of batch reading. A further approach may use multiple readers,
multiplexed into one interrogator, but with attendant increases in costs.
RF Transponder Programmers
Transponder programmers are the means by which data is delivered to WORM and read/write
tags. Programming is generally carried out off-line, at the beginning of a batch production run,
for example.
For some systems, reprogramming may be carried out on-line, particularly if it is being used as
an interactive portable data file within a production environment. For example, Data may need
to be recorded during each process. Removing the transponder at the end of each process to
read the previous process data, and to program the new data would naturally increase process
time and would detract substantially from the intended flexibility of the application. By
combining the functions of a reader/interrogator and a programmer, data may be appended or
altered in the transponder as required, without compromising the production line.
The range over which the programming can be achieved is generally less than the read range
and in some systems near contact positioning is required. Programmers are also generally
designed to handle a single tag at a time. However, developments are now satisfying the need
for selective programming of a number of tags present within the range of the programmer.