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HK_95691137-Bedrock
7-Bedrock
December 24, 2023
Solved

PLC Tag Read Pass through without Tag in Kepware Database - C#, VB, or Python

  • December 24, 2023
  • 1 reply
  • 2257 views

Trying to pull data from an AB Plc using Kepware without having a TAG in the Kepware Database.  Looking for a way to just pass-through the READ request.  I know the below code snippet works just fine, however, the tag "YourPLCTag" needs to be in Kepware DB.  I just want to access "YourPLCTag" without the tag being in Kepware.

 

var serverUrl = new Uri("opc.tcp://localhost:4840");
// Connect to the OPC server
using (var client = new OpcClient(serverUrl))
{
client.Connect();
// Read PLC value
var nodeId = "ns=2;s=YourPLCTag"; // Replace with your PLC tag
var value = client.ReadNode(nodeId);
// Do something with the value...
client.Disconnect();
}

Best answer by HK_9569113

I stated earlier this did not work because the TAG 'TAG_ADDRESS1' was already created/defined in the Tagname Dictionary of the KepWare server (which it is).  I also stated I can easily poll tags that have already been created in the TagName dictionary.  I tried several times to get the above sample to work to no avail when a tag is NOT created in the TagName dictionary and thought the above solution was not helpful.

 

What I failed to try is fully qualifying the TagName in the request -- which solved my problem.  IE: when polling STRING data directly, the following was required.  ns=2;s=ABCLX.Device1.THIS_IS_A_STRING_TAG.DATA/82@String.  Please note the ....DATA/82@String at the end of the fully qualified TagName.  This was the trick.

 

Thanks

1 reply

C
cmorehead13-Aquamarine
13-Aquamarine
December 29, 2023

@HK_9569113 

 

Please take a look at the Kepware knowledge base article in the following link which covers Dynamic Addressing in Allen-Bradley ControlLogix devices:

 

Article - CS401609 - Dynamic Addressing in Allen-Bradley ControlLogix Ethernet driver of PTC Kepware Products

 

Thanks,

 

*Chris

    H
    HK_95691137-BedrockAuthorAnswer
    7-Bedrock
    December 29, 2023

    I stated earlier this did not work because the TAG 'TAG_ADDRESS1' was already created/defined in the Tagname Dictionary of the KepWare server (which it is).  I also stated I can easily poll tags that have already been created in the TagName dictionary.  I tried several times to get the above sample to work to no avail when a tag is NOT created in the TagName dictionary and thought the above solution was not helpful.

     

    What I failed to try is fully qualifying the TagName in the request -- which solved my problem.  IE: when polling STRING data directly, the following was required.  ns=2;s=ABCLX.Device1.THIS_IS_A_STRING_TAG.DATA/82@String.  Please note the ....DATA/82@String at the end of the fully qualified TagName.  This was the trick.

     

    Thanks

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