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In general, the Edge is the source of truth for tag timestamps although there are several events that will cause the timestamps to differ across the system:

In a BIRTH message

  • The BIRTH message for each Edge Node and Device will set the timestamp associated with each tag to the current time of the publishing client server's OS.
  • This means that the timestamp at the Edge will show the last known timestamp and the receiving application will display the timestamp included in the BIRTH message.

OPC Tag Disabled

  • When an OPC tag is disabled, the timestamp at Edge will reflect the time the tag was disabled.
  • The associated DDATA message will reflect the timestamp of the disabled tag change.

OPC Tag Enabled

  • When an OPC tag is enabled, the timestamp at Edge will reflect the last known change timestamp from the PLC.
  • The associated DDATA message will reflect the timestamp of the enabled tag change.

OPC Restart Tag

  • When an OPC tag is restarted, the timestamp at Edge will reflect the last known change timestamp from the PLC.
  • The associated DDATA message will reflect the timestamp of the tag restart. 



The timestamp for an Edge tag read from a PLC will be the timestamp assigned by the PLC and associated Ignition driver. 

The timestamp for any other Edge tag will be the Ignition server OS time for change in Qualified Value (Value, Quality or Timestamp).

All timestamps published on the wire are in UTC and displayed converted to local time at the receiving application.



If times are not synchronized across the system components, for example by using an NTP server, its possible that the time at the PLC is older than other system components. If using MQTT engine, this can result in tag change events being ignored as the new event time is before current time for the tag at MQTT Engine.



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