Discrete Alarms - DPS Telecom NetGuardian 216 G4 User Manual

5.7

Discrete Alarms

Dry Contact
NetGuardian case
– Batt.
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.
GND
Alarm
Contact to Ground
NetGuardian case
– Batt.
Note: Make sure that grounds have a common reference —
this is usually done by tying grounds together.
GND
Alarm
17