In equipment monitoring systems, sensors are used to detect the operational status of equipment, indicating whether it is functioning correctly or in an alarm state. The terms "Normally Open" (NO) and "Normally Closed" (NC) refer to the default state of the sensor's electrical circuit when the equipment is in its normal operating condition.

Definitions

• Normally Open (NO): In a Normally Open configuration, the sensor's circuit is open (not conducting) when the equipment is in its normal, non-alarm state. The sensor outputs a 0 to indicate this state. When an alarm condition occurs (e.g., equipment failure or abnormal operation), the circuit closes, and the sensor outputs a 1.

• Normally Closed (NC): In a Normally Closed configuration, the sensor's circuit is closed (conducting) when the equipment is in its normal, non-alarm state, outputting a 1. When an alarm condition is detected, the circuit opens, and the sensor outputs a 0.

Note: By default, our hardware outputs a 0 when not connected to any equipment, which means that, for equipment that only provides a NO output, it is not possible to obtain an alarm in the event of disconnection or poor connection between the sensor and the equipment being monitored.

Equipment Output and Status Labeling

The equipment provides a binary output based on its configuration:

• For Normally Open equipments:

  • 0: Normal operation (ViGIE Label OK)

  • 1: Alarm condition (ViGIE Label Alarm)
    
    

• For Normally Closed equipments:

  • 0: Alarm condition (ViGIE Label Alarm) 

  • 1: Normal operation (ViGIE Label OK) 

These outputs are processed by the monitoring system to assign appropriate labels, such as "OK" for normal operation or "Alarm" for fault conditions, ensuring clear communication of equipment status.

Application in Equipment Monitoring

• Choosing NO vs NC: The choice between NO and NC depends on the system's design and safety requirements. For example:

  • NO is often used when power loss or sensor failure should not trigger an alarm unless an actual fault occurs.

  • NC is preferred in fail-safe systems where a loss of power or sensor failure should trigger an alarm to ensure safety.