DPS Telecom D-PK-NG216, User Manual

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17
Discrete Alarms 5.7
Contact to Ground
– Batt.
Alarm
Dry Contact
– Batt.
GND
Alarm
NetGuardian case
NetGuardian case
Note: Make sure that grounds have a common reference—
this is usually done by tying grounds together.
GND
Fig. 5.10 Discrete alarm points can connect as a dry contact or a contact to ground
This device features 16 discrete alarm inputs — also called digital inputs or contact closures. Discrete
alarms are either active or inactive, so they're typically used to monitor on/off conditions like power
outages, equipment failures, door alarms and so on.
The NetGuardian's discrete alarm points are single-lead signals referenced to ground. The ground side
of each alarm point is internally wired to ground, so alarm points can connect either as a dry contact or
a contact to ground.
In a dry contact alarm: The alarm lead brings a contact to the ground lead, activating the alarm.
In a contact to ground alarm: A single wire brings a contact to an external ground, activating the alarm.
You can reverse the polarity of each individual discrete alarm point, so that the alarm is activated when
the contact is open. This is done with a software configuration change.