Definition of Open and Closed Sensor Alerts
Author: Article Reference #:AA-00261 Views:23756 Date Added:2010-10-22 12:00 AM Last Updated:2011-08-25 10:07 AM 4.55 Rating/ 104 Voters

Definition of Open and Closed Sensor Alerts
SPOT HUG provides 4 dry contacts for external sensors. Two of the sensors are normally "Open" and the other two are normally "Closed". The open sensors are in alert state when the circuits are closed, while the closed sensors are in alert state when the circuits are open. Typical applications for open sensors are low battery voltage, bilge pump, high water mark, smoke detector, etc. Applications for closed sensors include on doors or engine theft for example. When an alert is triggered, SPOT HUG sends out notification via email or SMS to the designated contact.
Normally Open
Sensor Alert 1 - violet and violet/white wires
Sensor Alert 3 - orange and orange/white wires (wires with white are grounds)
These sensors are normally open and do not have an electrical current passing through. If the contacts are closed, it will generate a current, the High Alarm is activated, and the notification to contacts commences.
There will be a 30 second delay before sending the closed contact message. Here are some examples of applications where this can be used:

  • High Water monitoring
  • Low battery voltage
Normally Closed
Sensor Alert 2 - green and green/white wires (wires with white are grounds)
Sensor Alert 4 - blue and blue/white wired
These sensors are normally closed with an electrical current passing through.  When the circuit is broken, the notification to contacts commences. Below are application examples:

  • Cabin door monitoring. When door opens, the circuit is broken
  • Anti-motor theft
  • Power Monitoring. When power to cabin is off, the circuit breaks
If you configure your sensors incorrectly, (e.g. using a normally closed Sensor Alert contact for an application that works only in a normally open state) then it might not work properly, as normally closed sensors generate a Sensor Alert immediately. On a door for example, you need to know about someone opening the door immediately. 
In contrast, normally open sensors have to be triggered for a certain time to generate a Sensor Alert. This is to avoid unnecessary Sensor Alerts. Some sensors, like the bilge, could be coming on and off quite often but a Sensor Alert is only generated after it remains triggered for a certain period. 
Tracker and FOB Behavior in an Alert State
When the Tracker gets an alert trigger and if there is no authenticated FOB in range, it sends out a Sensor Alert message. It also sends out a Cancel Alert message when the alerted sensor returns to its normal state or when a FOB comes into range.
The FOB acts as a remote "key" for Sensor Alerts in the same fashion as in Unauthorized Movement detection. When a FOB comes into range of the Tracker, Sensor Alert monitoring is turned off automatically.

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