OPC Item Path contains ns=1;s=[PLC]

Starting work on a project developed by someone else - many tags have leading syntax in the OPC item path that are unfamiliar to me. here is an example:

ns=1; s=[PLC]B3:3.6

My question is, what is the ‘ns=1; s=’ part of this doing?

This system has AB Micrologix and ControlLogix PLC’s.


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When the tag is from an OPC-UA server, the OPC Item Path is really just the Node Id of the node in that server. The ns=X; prefix is part of the Node Id syntax that specifies the namespace the node belongs to.

Older versions of Ignition would omit the prefix if the namespace was 1, but starting in 7.8 it always specifies the namespace explicitly when a tag is dragged in. Using no prefix still works and defaults to ns=1, however, it’s just not the default behavior to rely on that any more.

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I posted my question on the wrong thread…can I parameterize an SLC PLC OPC Item Path directly from Ignition’s OPC-UA?