[Questions] Trying to understand the S7-1500 OPC tags (such as the www.siemens.com in the OPC Item Path)

Ignition v8.1.5
I created an OPC tag from the OPC server on an S7-1500 CPU. The OPC item path to the tag I’m reading is below. I can’t find anything in the forums or manuals that describe why the item path has a internet address to siemens.com. Can someone explain this please?

nsu=http://www.siemens.com/simatic-s7-opcua;s=“gdb_AdjMtx”.“tmpElecUnits”.“amps”

Some curiosities…

  1. In the gateway I only have the CPU OPC server configured, the gateway does not have a device connection to the CPU. I thought you needed both but it seems that isn’t necessary. Any thoughts?
  2. The manual states the gateway can’t read optimized data blocks yet the global data blocks in my PLC are optimized. Any thoughts?
  3. The manual states the you have to provide direct addressing for PLC tags based on memory area and offset…this is a VERY OLD method…I’m able to look at the tags in the data blocks just like I do when working in TIA Portal. Any thoughts?

Responses are very much appreciated!
Kind regards,
Ted.

  1. Perfectly normal. An OPC connection directly to processors that support such is entirely separate from a driver connection through Ignition’s native OPC server.

  2. Ignition’s driver has this limitation, among others, as it only uses the public techniques for communicating with Siemens processors. Optimized block access requires a more modern, and unpublished, protocol.

  3. Siemens’ own OPC server(s) use Siemens’ restricted protocols and access methods, so this is no surprise.

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The OPC Item Path of an OPC tag from an OPC UA server (as opposed to OPC Classic) corresponds to its NodeId. NodeIds are namespaced in every server, and part of what you’re seeing is the URI of that namespace. The server maintains a table of namespaces and any Node with a NodeId from a namespace at index 2 or greater will, when brought into Ignition, be identified using its absolute NodeId with URI rather than its relative NodeId with numeric index.

The rest of your curiosities, as Phil mentioned, are all due to the fact that everything you’re reading in the manual is about our S7 driver and none if it applies when using a newer model PLC that has a built in OPC UA server you can make a direct connection to.

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Hello Phil, Hello Kevin.
Thank you for your explanations, it is all very clear now, very much appreciated!
Regards,
Ted.