What is open and closed?
Before we get too far we need to explain what is “open”
and “closed”. With electricity “closed” means the circuit is connected and electricity
is flowing. “Open” means the opposite. The electrical current is open and no
electricity is flowing.
Normally?
The idea that something is “normal” means that it is a constant unless
a force changes it. Relays will need to be energized and switches such as Door
contacts need to be disconnected.
Normally Open and Normally Closed
Normally Closed
- This is when there
is a constant current of electricity
in its normal state. Energizing or
changing the state will open the
contact and disrupt the current.
Normally Open
- This is when there is
no current of electricity in its normal
state. Energizing or changing the
state will close the contact and allow
the current to flow.
Do not over think the concept. It is as easy as it sounds. Now lets see how this is
interpreted on the Access Control Board.
Below is a description of a Normally Closed device connected to the Access Control board. When
power is given through the relay and the relay is not energized it stays in a Normally Closed state. The
Normally Open port stays with no current. When the Access control board energizes the relay (From
a Reader asking to open the door) the relay switches the current to Normally Open and the Normally
Closed port looses current. So it is safe to say that the Access control boards are Normally Closed
devices by default.
S1
GRD
COM
NO
NC
S1
GRD
COM
NO
NC
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