Alarm Limits

Alarm limits indicate when a process variable will trigger an alarm in the system. The Situational Awareness support in Plant SCADA allows these limits to be visualized using the Meter Composite Genie library object and its associated faceplates.

The Meter Composite Genie and faceplates that display meters support:

• Analog alarm tag limits (a single analog alarm defining all the limits) and

• PLC tag-based alarm limits (separate I/O tags to define each limit).

Tag-based alarm limits are particularly useful if you want dynamic control of the limits and/or if you want to specify a different category for each limit.

Note: Up to 14 limits may be defined, but the Meter object supports display of only 4 limits. However, you can build your own meter object with 6 limits for example.

By default, all analog equipment and your project are configured to use analog alarm limits. In most situations, a meter will be displaying the ".PV" item for your equipment. The meter objects will automatically source your HighHigh, High, Low and LowLow values from a matching PV analog alarm tag.

When using Situational Awareness-based projects, this behavior can be changed in the following ways:

1. Use analog alarm limits for all equipment

2. Use analog alarm limits for most equipment, and override with PLC-based limits on a per equipment basis

3. Use PLC-based alarm limits for all equipment

4. Use PLC-based alarm limits for most equipment, and override with analog alarm limits on a per equipment basis

The default you choose will depend upon:

• The number of analog equipment in your system that will use one or the other method

• The importance of the limits in your system. Analog Alarm Limits in Plant SCADA all share the same category. If you want a different category for HH as opposed to LL, PLC-based alarm limits should be used.

See Also

Associate an Alarm with Equipment

Configure PLC Limits with Equipment