Timing is an important element in access control systems. When a valid credential or code is entered into the reader or keypad, the door unlocks for a predetermined period of time, then relocks. Frequently the door which is being controlled is also monitored as part of the premises' perimeter alarm...
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The handicapped exit switch is a normally open (N.O.) dry switch closure. The door operator to which we're sending our signal requires a momentary dry closure to trigger the door operator. The word 'momentary' is a very unscientific term, because it is not a precise measurement of time. We needed to present our door operators a contact closure of more than one second in order to achieve consistent operation. We tried a one second pulse and got inconsistent results from different door operators. So we used one of the 6062's built in features, a "Pulse Stretcher."
If you review the programming instructions for the 6062 (download them from the Altronix website, or they come packed with the timer module) and examine the circuit diagram, you can understand how it accomplishes what it does.
The sequence of operation is as follows:
The handicapped button is pressed which triggers Timer #1. Timer #1 actuate Relay #1 (Altronix RBUL) which in turn applies a switch closure across the access controller REX terminals, which tells the system the door opening is authorized and releases the electromagnetic lock on the door.
After Timer #1 cycles, the relay on Timer #1 turns off and the pulse this creates on the trigger terminal on Timer #2 causes Timer #2 to actuate. This presents a switch closure across the input terminals on the door operator, causing the door operator to open the doors. Timer #1 was set to a very short relay activation time because the REX input on the access controller only needed a short pulse to trigger reliably.
Go Forth and Multiply
While we're discussing circuits that solve design problems in the field, here is another quick solution for a common problem. You are installing a REX device on a door which is controlled by an access control system and locked with an electromagnetic locking device. The REX device is equipped with an S.P.D.T relay. The REX terminals on the access controller are isolated; that is, neither of them is common with the electromagnetic lock power supply, so a dedicated pair of wires must be connected to the REX terminals in order for the access controller to operate properly.
Hopefully you have already identified the dilemma in this situation. In order to safely control the door, you should directly cut power to the maglock. To suppress Forced Door alarms, you need to send a signal to the REX terminals. But because of the isolated REX terminals, you need two separate sets of contacts switching when the REX is actuated.
Again Altronix Alchemy is employed by wiring in a RBSN relay. The relay is wired in a fail-safe configuration so that if power is lost or if a wire is broken to the REX device, the electromagnetic lock will unlock.
For more information, contact Altronix, 140 58th Street, Bldg. A, 3 W, Brooklyn, NY 11220. Telephone: 888-258-7669. Web site: www.altronix.com.
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THE CRITICAL SAFETY COMPONENT IN ACCESS CONTROL