Digital alarms activate in response to the state of one or two digital variables.

When you define the variable tags for a digital alarm, you can precede a tag name with the logical operator "NOT". This specifies that the OFF state (0) is the triggering condition for the variable tag.

Example

A digital alarm is configured to activate in response to the following variable tags:

Variable Tag A = RFP3_TOL

Variable Tag B = NOT MCOL3043

In this scenario, the alarm is triggered when the state of both variables changes to the active state:

• RFP3_TOL changes to ON (1)
• MCOL304 changes to OFF (0).

You can specify a delay for a digital alarm, which means the alarm only becomes active when the triggering condition spans the duration of the specified delay period.

See Add a Digital Alarm.

Time stamped alarms are similar to digital alarms, except that a counter variable is used to provide an external time stamp of when a triggering condition occurs, rather than the poll time. Time stamped alarms can only be associated with a single digital variable.

See Add a Time Stamped Alarm.

Analog alarms are triggered when an analog variable changes beyond one or more specified limits. Each alarm can be configured as any combination of the following types:

• High and high high alarms - where the value reaches an atypical high
• Low and low low alarms - where the value reaches an atypical low
• Deviation alarm - where the values moves away from a predefined set point
• Rate of change alarm - where a dramatic value change occurs within a specified period of time.

See Add an Analog Alarm.

An advanced alarm activates when the result of an associated expression changes to true.

See Add an Advanced Alarm.

Multi-digital alarms use the output for up to three digital variables to define eight states. These states represent different combination of true and false values. You can specify which of these states will trigger an alarm.

The following eight states represent the possible tag value combinations. The tags are represented in the order tag C, tag B, tag A.

• State 000 - all 3 tags are false.
• State 00A - tags C and B are false, tag A is true.
• State 0B0 - tags C and A are false, tag B is true.
• State 0BA - tag C is false, tags B and A are true.
• State C00 - tag C is true, and tags B and A are false.
• State C0A - tags C and A are true, tag B is false.
• State CB0 - tags C and B are true, tag A is false.
• State CBA - all 3 tags are true.

You can indicate whether a particular state will trigger an alarm by applying a value of 1 (indicates an alarm state) or 0 (indicates no alarm will be triggered).

See Add a Multi-digital Alarm.

Time stamped digital alarms operate via a process where the alarm server is notified if a value changes to a specified digital variable using the Cicode function AlarmNotifyVarChange.

The alarm server uses this information to update alarms that monitor the variable, allowing an accurate time stamp to be associated with an alarm condition.

Time stamped digital alarms activate in response to the state of one or two digital variable tags. When you specify the variable tags, you can precede a tag name with the logical operator "NOT". This specifies that the OFF state (0) is the triggering condition.

Events trends can be used in conjunction with time stamped digital alarms to provide millisecond accuracy for both trend and alarm data. See the TrnEventSetTable and TrnEventSetTableMS Cicode functions.

See Add a Time Stamped Digital Alarm.

Note: When a time stamped alarm is used in conjunction with some protocols (such as OFS, OFSOPC and DNP3), a time stamp will be pushed from a tag into an alarm without the need to use AlarmNotifyVarChange.