Proximity Card
Proximity reader with keypad |
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| Developed by | Elko International |
|---|---|
| Usage | access control |
A proximity reader radiates a 1" to 20" electrical field around itself. Cards use a simple LC circuit. When a card is presented to the reader, the reader's electrical field excites a coil in the card. The coil charges a capacitor and in turn powers an integrated circuit. The integrated circuit outputs the card number to the coil, which transmits it to the reader.
A common proximity format is 26-bit Wiegand. This format uses a facility code, sometimes also called a site code. The facility code is a unique number common to all of the cards in a particular set. The idea is that an organization will have their own facility code and a set of numbered cards incrementing from 1. Another organization has a different facility code and their card set also increments from 1. Thus different organizations can have card sets with the same card numbers but since the facility codes differ, the cards only work at one organization. This idea worked early in the technology, but as there is no governing body controlling card numbers, different manufacturers can supply cards with identical facility codes and identical card numbers to different organizations. Thus there may be duplicate cards that allow access to multiple facilities in one area. To counteract this problem some manufacturers have created formats beyond 26-bit Wiegand that they control and issue to organizations.
In the 26-bit Wiegand format, bit 1 is an even parity bit. Bits 2–9 are a facility code. Bits 10–25 are the card number. Bit 26 is an odd parity bit. 1/8/16/1. Other formats have a similar structure of a leading facility code followed by the card number and including parity bits for error checking, such as the 1/12/12/1 format used by some American access control companies.
1/8/16/1 gives as facility code limit of 255 and 65535 card number
1/12/12/1 gives a facility code limit of 4095 and 4095 card number.
Wiegand was also stretched to 34 bits, 56 bits and many others.
Read more about this topic: Card Reader, Access Control Card Reader
Famous quotes containing the words proximity and/or card:
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—Blaise Pascal (1623–1662)
“In the game of “Whist for two,” usually called “Correspondence,” the lady plays what card she likes: the gentleman simply follows suit. If she leads with “Queen of Diamonds,” however, he may, if he likes, offer the “Ace of Hearts”: and, if she plays “Queen of Hearts,” and he happens to have no Heart left, he usually plays “Knave of Clubs.””
—Lewis Carroll [Charles Lutwidge Dodgson] (1832–1898)