Can Tag metadata be transmitted via MQTT?


I try to evaluate the MQTT solution for one of my projects.
I would like to know if all the metadata (engUnits, Scaled mode, alarm definition, …) of a tag defined on Edge will be transmitted to the MQTT Distributor / Engine ?

Best regards.

Hi Amarth,

It doesn’t seem like that is the case - the tag appears on the MQTT Engine missing most properties (e.g. History, probably Alarming) from the MQTT Transmitter. I alleviated this problem by sending additional metadata tags in with it in a UDT that contains relevant values or attributes.

It also seems problematic to edit the MQTT Engine tags directly as edits may be unstable (you might be trying this out as well). It’s better to use OPC tags that read the MQTT Engine tags and make edits to those generated OPC tags instead. You can do this by exposing tag providers in the OPC-UA Server settings in the gateway.


Hey Team, i am also trying something similar but unable to update the metadata tags.
Please find the details of the issue.

  1. i am writing tags in ignition via a simple mqtt client with a plain JSON (non spark-plug) and i am able create tags.
  2. i wanted to add values of the metadata tag for these tags but i could not find any json structure by which i can do that.

Any help would be appreciated . Thanks