Timeline of a timestamp through the MQTT modules

PLC > Edge > MQTT Server > Engine

The timestamp for a tag read from a PLC will be the timestamp assigned by the PLC.

Events causing timestamps to differ across the system

On a Transmission refresh

• The BIRTH message for each Edge Node and Device will set the timestamp associated with each tag to the current time of the host server's OS.
• The timestamp at the Edge will show the last known timestamp from the PLC and Engine will display the timestamp included in the BIRTH message

OPC Tag Disabled

• When an OPC tag is disabled, the timestamp at Edge and Engine will reflect the time the tag was disabled.

OPC Tag Enabled

• When an OPC tag is enabled, the timestamp at Edge will reflect the last known change timestamp from the PLC whilst Engine will reflect the timestamp of the enabled change.

OPC Restart Tag

• When an OPC tag is restarted, the timestamp at Edge will reflect the last known change timestamp from the PLC whilst Engine will reflect the timestamp of the restart.