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RS232 is typically used to connect a PC to a peripheral, for example, a printer. RS 485 is commonly used to connect all the access controllers together.
Clock & Data is how magstripe readers communicate with access controllers.
Wiegand is the standard interface between card readers and controllers. The term Wiegand originally applied to the technologies incorporated into a device called a Wiegand Reader and the credentials used with it. The Wiegand card was plastic, and had many tiny pairs of wires imbedded into it which formed a pattern which represented the encoded data on the credential. Although you couldn't see the wires with the naked eye, it wasn't difficult to figure out the pattern of the wires, and therefore possibly duplicate a card surreptitiously.
The Wiegand card was used in what was referred to as a turnstile reader. This reader had a slot in it, and the user dragged the card through he slot for it to be read. The Wiegand Card reader connected to the access controller using a data transmission protocol also called Wiegand. Although Wiegand cards and readers are no longer ‘technology du jour,' Wiegand protocol survives and is the most commonly used interface between readers, keypads and alarm controllers. The Wiegand interface requires three conductors; DATA-1; DATA-0; and DATA RTN. You'll usually see an additional wire or two for audible (beeper) and visual (LED) signals on the reader.
Proximity readers do not have slots or other apertures. The credential does not have to make physical contract with the reader. Additionally, proximity readers are frequently encapsulated modules with a short piece of cable for connection to the access controller, or housed in waterproof lexan cases. For particularly harsh environments, the reader may be further protected with non-metallic shields. Proximity technology uses low power 125 Kilocycle Radio Frequency transmission, which is attenuated by metal and distance between the credential and the reader.
Proximity readers are versatile and robust. There are many package styles from which to choose. Many commercial applications involve storefront type structure, and there are numerous mullion mount type proximity readers available. Single-gang electrical boxes are also a favorite home for proximity readers which blend into the aesthetics of any environment.
Perhaps someday you will be able to really impress a client if you remember that a proximity reader can read through plate glass and non-metallic wall material.
Mounting options might be partially dictated by the read range of your proximity reader. For example, for parking control applications, you would need to mount the reader on a pedestal, and an extended range would also be beneficial to assure convenience to the end-user and maximum through-put. In situations where the reader cannot be mounted in close proximity to the door being controlled, an enhanced read range might be a benefit.
On a recent project where we were installing access control onto the computer room door, we installed an extended range reader at the client's request. The idea was to maintain an aesthetic continuity throughout the structure where we already had a couple of dozen of the enhanced range readers in service. However, shortly after the access control system went into service, we got a hysterical phone call from the security department for us to hurry over. Seems that the computer room door was in a narrow hallway, and individuals merely passing by the reader were being picked up and producing unauthorized cardholder reports, or unlocking the door for those with authorization even if they didn't want to enter the computer room. We replaced the reader with one with a more appropriate read range.
A technology primer for locksmiths entering this access control market.