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Are 8 byte unsigned integers (UI8) supported in Vista OPC client?


Are 8 byte unsigned integers (UI8) supported in Vista OPC client?


TAC Vista 5.1.X

Vista OPC tool


Not all OPC data types (canonical data types) are supported by  OPC server. UI8 variables show a question in OPC tool. If the Canonical Type column shows a question mark for the variable (or tag) then this means that Vista has been unable to identify or does not support the data type. 


If possible divide the OPC tag/variable into 2 x 4 byte registers. It could also be worth checking what the expected maximum value is for that register and seeing if that value will fit in a UI4 (unsigned integer 4 byte).

An alternative solution, although the functionality must be checked by the engineer is to create the variable object manually and use the canonical type "string". To do this follow the steps below:

1. Note the name of the OPC variable to be added to Vista in the OPC tool browser window.

2. Under the OPC server object in Vista create a 'Value - String' and give it the same name as the OPC variable.

3. Hold down shift and ctrl and right-click the string value -  select properties.

4. Locate the Property RA and fill in the name of the folder, variable name and the data type in the following format: folder name.variable name|data type

Example of OPC naming convention including data type, in TAC Vista.

5. Click on OK and the variable should start updating after refreshing the folder.

More information on OPC data  types can be found here.

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‎2018-09-10 01:04 PM
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