About alarms

An alarm occurs when something goes wrong or is about to go wrong. Alarms can signal that a device or process has ceased operating within acceptable, predefined limits, and can indicate breakdown, wear, or process malfunctions. Alarms are also used to indicate the approach of a dangerous condition.
Alarms are an important part of most plant control applications because an operator must know the instant something goes wrong. It is often equally important to have a record of the alarm and whether the alarm was acknowledged.
Use alarms to notify the operator when a situation requiring immediate attention occurs. When an alarm condition occurs, the application can open an alarm graphic display, set off an audible signal, send a message to a printer or a display, send the alarm trigger value to the data source, or do any combination of these. All triggered alarms in the application are logged in the alarm history.
Alarm display
Alarms can be shown in the following graphic objects:
  • Alarm list
  • Alarm banner
  • Alarm status list
Generating alarms
In the Alarm Setup editor, define a tag as a trigger and give it a trigger value, and define a message to be shown when the trigger value is set.
Configure the data source so that when a particular event occurs, the value in the tag changes to the trigger value.
For example, you might set up a tag to be an alarm message trigger with the trigger value 10, for the alarm message
Tank about to overflow
. Configure the data source to monitor the tank level. When the level is higher than 99 percent of the tank’s capacity, the data source sets the alarm trigger connection to 10, and the message is sent to the operator.
Retaining alarm messages
As soon as the project starts running, the application begins monitoring the trigger connections for alarm conditions. When an alarm occurs, the application adds the associated message to the alarm list. The list is saved (logged to the alarm history) 30 seconds after an alarm is triggered or acknowledged. The alarm list is retained when an application is restarted due to a shutdown or power loss. However, alarms that were triggered or acknowledged less than 30 seconds before power loss will not be included in the alarm history. When a newer version of the application is run on the runtime computer, the alarm list for the older version is deleted.
If the alarm list object is configured to show unacknowledged alarms only, acknowledged alarms are not shown, although they are retained in memory.
TIP:
  • For a permanent record of alarms, configure alarm messages to print to a printer on the
    Messages
     tab of the
    Alarm Setup
     editor.
  • You can delete the alarm log file from the runtime computer at project startup.
Setting up alarms
Use the following editors to set up alarms:
  • Alarm Setup
     - set up alarm triggers (the tags to monitor), define the alarm messages and their trigger values, and specify the alarm window to show.
  • Startup
     - to turn on alarm monitoring, select the
    Alarms
    check box.
  • Graphics Display
     (optional) - modify the default [ALARM] display or create your own graphic display to use for alarms. For example, if you won’t be using audible alarm signals, edit the default display to remove the
    Silence Alarms
     button.
Acknowledging alarms
When the operator presses the
Acknowledge Alarm
 button, the
Enter
 button, or the
Enter
 key on an external keyboard or keypad, the selected alarm is acknowledged and the audio indicator for the alarm, if any, is silenced.
When the alarm is acknowledged:
  • If assigned, the Ack connection is set to the alarm trigger value at the data source. The value is held as long as the operator presses the button, or for the notification hold time, whichever is longer. Assign the Ack connection and specify the hold time in the
    Alarm Setup
     editor.
    If the hold time is still in effect and the operator acknowledges a new instance of the same alarm, the new acknowledgment is ignored.
  • When an alarm is acknowledged, it will be removed from the list only if the alarm no longer meets the selected Alarm conditions for the list, as defined on the
    Display
    tab or on the
    Connections
     tab (if assigned). This means that an alarm that is no longer in alarm, but has not been acknowledged, will be removed from the list when the alarm is acknowledged, only if the alarm conditions for the list at that time are Inactive and acknowledged.
  • If the highlight bar is on an acknowledged alarm when the operator presses the
    Acknowledge Alarm
     button, the button press will be ignored.
  • If you have chosen to show the
    Acknowledged symbol
    column, and have selected a symbol (on the
    Alarm
     tab), the symbol will appear beside an alarm when it is acknowledged.
  • Acknowledging messages does not remove the alarms or the messages from the alarm history.
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