Applies To:
  • CitectSCADA 5.41, 5.41 Service Pack A, 5.41 Service Pack B, 5.42, 5.42 Service Pack A, 5.50, 5.50 Service Pack A, 5.50 Service Pack B, 5.50 Service Pack C, 6.00
  • CitectHMI 5.41, 5.41 Service Pack A, 5.41 Service Pack B, 5.42, 5.42 Service Pack A, 5.50, 5.50 Service Pack A, 5.50 Service Pack B, 5.50 Service Pack C, 6.00
Summary:
What could cause me a situation where:

1. Tags are not being updated.
2. Tags display wrong values.
3. Tags can be written to but when read from they display 0.
 

Solution:
Citect has become aware of a problem in the way Allen Bradley allocate handle numbers for its tags in the ControlLogix PLC. The symptoms described above could be due to two or more tags in the PLC having the same handle reference number.

The handle is generated and assigned to a tag when it is created in the PLC. The handle is supposed to be unique, however we have seen several instances whereby the same handle number is being used numerous times.

The way to confirm whether this is the cause of the symptoms is to do the following:

Step 1: Take note of the tag you are having difficulty with. Ensure you know the PLC tag name (not the Citect tag name).
Step 2: Set the parameter [ABCLX] LogTagInfo=1 in citect.ini file.
Step 3: Start CitectSCADA runtime and wait for the ABCLX device to come online (this is viewable in the kernel).
Step 4: Shutdown CitectSCADA.
Step 5: Navigate to the files that have just been generated by the LogTagInfo parameter (defaults c:\).
Step 6: Open the text file "<IOServer>_<Port>_taglist.txt" in a text editor.
Step 7: Search the contents of the file for the PLC tag name that you identified in Step 1.
Step 8: Take note of the handle number of the PLC tag name that you searched for and search the entire file for any other instance of that handle number being used.
Step 9: If you find another tag using the same handle number, you need to delete the other tags in the PLC with the duplicate handle and recreate it in the PLC.
Step 10: Remove the parameter [ABCLX] LogTagInfo so that it returns to its default value (i.e: 0)

Repeat process for further instances of tags exhibiting these problems.

If you do not find duplicate handles, please forward your files to Citect Support for analysis quoting this KB article number and the PLC tag that is causing concern.

Please note:
This issue may not be limited to Allen Bradley's ControlLogix as it may also be encountered with AB's CompactLogix and FlexLogix.

Citect has confirmed this to be a problem in CitectHMI/SCADA ABCLX version 3.2.3.0. We are researching this problem and will post new information here as it becomes available.
 
Keywords:
ABCLX, handle, handles, displaying, zero, 0 incorrect, value, Allen Bradley  

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