TagEnableAlarms Function Block

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The TagEnableAlarms Function Block enables the alarms associated with an Alarm Tag.

The function block enables the alarms by sending an EnableAlarms Tag Command to the tag. The function block provides status information to:

Functions and Function Blocks

The TagEnableAlarms Function Block is intended for use in a Program Tag that runs on the Fernhill SCADA Server. A Program Tag uses a continuous execution model, where the program code runs at a fixed interval. A program uses the function block to sample the state of the tag command as it executes.

If you want to enable alarms from an Operator Action, use the TagEnableAlarms Function.


The TagEnableAlarms Function Block has this syntax:

        ERRORMSG=>Variable-Reference );

Note: All parameters are optional.


The TagEnableAlarms Function Block has these parameters:

Parameter Type Direction Description
REQ BOOL R_EDGE Input A rising edge starts the EnableAlarms Tag Command.
TAGNAME STRING Input The name of the tag to send the EnableAlarms Tag Command to.
BUSY BOOL Output Set to TRUE while the EnableAlarms Tag Command is in progress.
DONE BOOL Output Set to TRUE for 1 execution after the EnableAlarms Tag Command has completed.
ERROR BOOL Output Set to TRUE if the EnableAlarms Tag Command failed.
ERRORMSG WSTRING Output If ERROR is TRUE, the reason why the EnableAlarms Tag Command failed.


Once the EnableAlarms Tag Command begins, additional requests from the input signal REQ are ignored until the tag command completes.

These timing diagrams show the relationship of the REQ, BUSY, DONE, and ERROR signals processing two requests. The first request completes with an error, the second request completes normally:

        +--------+     +-+ +------+
  REQ   |        |     | | |      |
      --+        +-----+ +-+      +------

        +------+       +------+
 BUSY   |      |       |      |
      --+      +-------+      +----------

               ++             ++
 DONE          ||             ||

ERROR          |       |
      ---------+       +-----------------

The BUSY signal is TRUE while the tag command is in progress. The DONE signal is TRUE for 1 execution after the completion of the tag command.

Example Program

The following IEC 61131-3 Program shows:

  1. A FALSE to TRUE transition of a digital data point tag used to trigger a function block.
  2. A function block enabling alarms on another tag.
  3. Example logic to check the status of the function block.
Program MAIN
        (* The function block declaration *)
        EnableFB : TagEnableAlarms;

        (* The tag used to trigger the automatic alarm enable 
           Note: Uses a relative tag reference to 'Digital Trigger Tag' 
                 located in the same folder as this program *)
        TriggerTag AT %".Digital Trigger Tag" : BOOL;

    (* Call the TagEnableAlarms function block *)
        TAGNAME:="Tag to Enable Alarms on" );

    (* The DONE output is active for one cycle when the function block completes *)

        (* Was there an error ? *)
        IF EnableFB.ERROR THEN
            (* Handle any error *)
            (* Any additional work on successful completion *)


Further Information

EnableAlarms Tag Command

To learn about the EnableAlarms Tag Command.

Tag Command Function Blocks

To learn about other tag command function blocks.

IEC 61131-3 Expressions

To learn about the different types of expression to use as function parameters.

Elementary Data Types

To learn about the different types supported by Fernhill SCADA.

Common Elements

To learn about other IEC 61131-3 Common Elements.


For the meaning of terms used in Fernhill SCADA.