Alarm Tags

Alarm tags are used to establish rules for when an alarm should be triggered, and what behavior should occur.

The alarm tag type monitors the value of another tag and triggers an alarm when that tag’s value reaches or passes a given setpoint.

The Setpoint property can be a user-defined number or it can be supplied by another tag’s value. The two values are compared using an operation such as greater than, equal to, or less than. If the result of this comparison is determined to be true, then the alarm tag will be triggered.

When the alarm tag is triggered and while the trigger condition remains true, the value of the alarm tag itself becomes 1; otherwise, the value of the alarm tag is 0.

The alarm tag itself can also serve as a setpoint object since its value is 1 when the alarm condition exists or 0 when an alarm condition does not exist.

The urgency of the alarm (from Event to Critical) is defined by the Alarm Priority tag selected in the alarm tag’s properties.

 

Alarm tags can be configured as either “Trip” or “Level”.  Trip alarms are intended to watch for a trigger changing between 0 and 1 (in either direction, as you configure it).  A tag from the Digitals group should always be used as the trigger for a trip alarm.

A trip alarm will never be displayed in the list of Active alarms.  They are primarily used in situations where the momentary existence of an alarm condition should “trip” the alarm, after which the state of the trigger tag is irrelevant.  As an example, consider an intrusion detection system:  When an unauthorized person opens a door, the alarm is triggered. When the door closes, the condition that triggered the alarm may no longer exist, but the alarm should remain set.

While the value of the alarm tag itself will return to 0 when the trigger condition is no longer true, a trip alarm will not be cleared until the operator acknowledges it.

A level alarm by contrast, will show up in the active list as long as the underlying trigger condition remains true, and will be cleared and removed from the active list when that condition returns to a normal state

Both trip and level alarms must be acknowledged by an operator before their audible and visual warnings will stop.

 

Alarm Tag Type Characteristics

Tag Browser Name: Alarm

Database Table Name: AlarmPoint

Type: Attribute

Tag Group Memberships: Digitals, Numeric

Log Enabled Variables: Value

Native Drawing Methods: Alarm Tag Drawing Methods