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9.0 Zone Latching
“Latching” and “non-latching” refer to the behavior of an input. When a non-latching input
initiates an alarm, the alarm stays active until the input goes back to normal status. In contrast,
when a latching input initiates an alarm, the alarm stays active until the system is reset.
With advanced logic, you can latch normally non-latching zones such as monitor, trouble, and
non-latching supervisory zones. A latched zone maintains outputs or timers even if the original
input is no longer active.
For example, you can use zone latching to delay a strobe for a period of time after a page has
occurred. The page active status is the input that initially activates the zone. This zone is
correlated to the output strobes that become active when the zone becomes active. You make
the zone into a latching zone with advanced logic, so that the zone remains active even after
the page active status has become inactive.
9.1 Zone Latching Sequence
The order of events in a zone latching sequence is as follows:
1. A switch or input becomes active.
2. This activates the latching zone, which activates the output.
3. The zone remains active until the system is reset, so that the output also remains active.
The equation for the latching zone must have more than one input, separated by OR. One of
the inputs must be the latching zone itself.
For example, the following equation for the zone 01-00-**-IZ-011 tells the zone to become
active either by the input 01-00-00-IN-007, or by itself. As a result, the zone initiates itself.
01-00-00-IN-007:A OR 01-00-**-IZ-011
01-00-00-IN-007 – Initiating device
01-00-**-IZ-011 – Zone
When the initiating device becomes active, the latching zone becomes active, because the
advanced logic equation is true. If the initiating device becomes inactive or is restored, the
latching zone remains active, because the equation is still true. Therefore, the zone is latched.
In order to unlatch the zone, you must reset the system. This is similar to a normally latching
zone such as an alarm zone.
Note: The zone is referenced in its own advanced logic equation. This allows the zone
to latch itself.
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