13.1 Creating a New Alarm tag
Remember that alarm tags monitor the value of other tags and trigger an alarm based upon the value of that tag. This operation is accomplished using a "setpoint". The value of the tag being monitored is compared with the setpoint value using a function such as "greater than", "equal to", or "less than". If the defined condition is met, an alarm will be triggered.
In this exercise, the alarm tag you will create will monitor "AI20_1 Booster Tank Level".
1. Open the Tag Browser tool in the Configuration Toolbox.
2. Select "Alarm" from the Types drop-down list.
The tag list is currently empty, as there are currently no alarm tags configured.
3. Click the New button. A new alarm tag properties folder opens.
4. Enter "Alm20_1_1" in the Name field.
5. Ensure "Tank" is selected from the Area drop-down list.
6. Enter "Booster Tank Low Level Alarm" in the Description field.
The completed properties of the ID tab should appear similar to Figure 172.
Figure 172
7. Click the Trigger tab. The Trigger tab's properties are displayed.
The properties of the Trigger tab define the process conditions at which the alarm will be triggered. In this case, we want a low level alarm when the booster tank level ("AI20_1") drops below 30 inches.
8. Click the tag button to the right of the Triggered By field.
The Tag Browser opens and displays the available numeric tags.
9. Select "AI20_1 Booster Tank Level" from the tag list.
10. Click the Select button.
The "AI20_1 Booster Tank Level" tag appears in the Triggered By field.
11. Select "Less Than <" from the Function drop-down list.
This will be the function used to compare the value of the tag being monitored against the user-defined setpoint.
12. Enter "30" into the Setpoint field. The completed panel should look like
Figure 173
13. Click the Actions tab to open it.
Figure 174
Most of the default settings happen to be correct for the configuration of this tag. The Disable Alarm field has a value of "0", indicating that the alarm is not disabled and no custom sound file is specified for this alarm. Detailed information on the properties for alarm tags can be found in the VTS Developer's Guide.
Note the "Disable Alarm" field. This feature can be very handy to prevent configured alarms from being triggered during maintenance operations.
14. Select "2 – High" from the Priority drop-down list.
This alarm will now be a high level alarm, rather than a critical level alarm.
15. Click the OK button.
Now that you have successfully configured your first alarm tag, and the virtual Modicon PLC simulator is constantly feeding values to the application, the alarm tag is fully functional. Because the booster pump is regulating the value of the booster tank between 60 and 80 inches, and the alarm setpoint is 30 inches, no alarm will be triggered at this point.