Keri Systems SB-293 - Manual (Page 16)

Technical Reference Manual – PXL-250 and SB-293 Keri Systems, Inc.
Page 16 P/N: 01836-004 Revision 5.5
2.0 Proximity - Principle of Operation
Proximity, also known as Radio Frequency Identification (RFID), is a method of
reading a card or tag without requiring any physical contact between the card/tag and
the reading device. With proximity readers there is no physical wear and tear on the
card/tag or the reading device. No inserting of a card/tag into a reader slot or swiping
of a card/tag through a reader slot is required. The card/tag is simply held up to a
reader, within the reader's detection range. Refer to Figure 2-1 for a diagram of this
process.
In a proximity reader application, a continuous 125 kHz electromagnetic field is
radiated from a coil inside the reader. This field is called the "excitation signal." When
a card/tag is presented to a reader, a coil inside the card/tag picks up the excitation
signal from the reader generating a small current in the card/tag's coil. This current
powers a small integrated circuit (IC) within the card/tag that holds a unique
identification number.
The coil in the card/tag transmits this identification number using a 62.5 kHz
electromagnetic field, one-half the value of the excitation signal. This 62.5 kHz signal
acts as an analog RF carrier for the digital ID number and is called the "receive signal"
as the coil in the reader receives this signal.
The reader passes the signal on to the RF receiver in the controller for decoding where
it is processed, error checked, and converted to a digital signal. The receiver then
sends the digital signal with the ID number to the microprocessor in the controller
where an access decision is made.
The read range for a key tag is approximately one-half that of a card. This is due to the
size of the coil in the tag compared to the coil in the card. Since the coil in the tag is
smaller, it needs to be closer to the excitation signal to activate the IC within the tag.
The bigger the coil in the card, tag, or reader, the greater the read range is likely to be.
Figure 2-1: Proximity - Principle of Operation