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1. Set up a tag on the Transmission side with an alarm. 

   Note
   The Ack Mode must be set to Manual or Auto The alarm properties that are currently propagated are: Name, Priority and Notes

   
   Below is an example that will generate an event if the value of the tag goes above 100:
   

2. Trigger the alarm.
   In this example, we set the value of the memory tag to 101. This resulted in an alarm event at the Edge as shown below in the Alarm Status Table:
   
   
   
   
3. Because the alarm event was published via MQTT, we can also see it on the Central Gateway running MQTT Engine:
   
   
   
   

4. At this point, we can acknowledge the alarm at either the Edge or the MQTT Engine side via the Alarm Status Table by clicking the 'Acknowledge' button as shown below. Once acknowledged, it will be reflected as so on both the Edge and the MQTT Engine sides.

   
   

   Note

   Warning In order for the alarm acknowledgement or clearing at the Edge to be published to MQTT Engine, the Edge must be in an active Sparkplug session with MQTT Engine or have determined that the connection is unavailable such that the event changes are stored to the Disk Backed History Store for publication on reconnect. MQTT Transmission can take upto 1.5 times the configured keep alive time to determine that there is a connection failure and any alarm acknowledgements or clearings can be lost during this time leaving alarms 'stranded' at MQTT Engine. How to remove stranded alarms from the MQTT Engine Alarm Status Table. The recommended approach to mitigate this issue is to configure a Rolling History Buffer for the Disk Backed History Store which will cover data loss during a keep alive timeout scenario While testing the alarm acknowledgements whilst the Edge is disconnected, you can confirm that the connection status via the MQTT Transmission Servers view in the UI or through the MQTT Client Online tag

   
   

   Note
   In order for the alarm to be acknowledged from MQTT Engine, the Edge must be in an active Sparkplug session with MQTT Engine If the Edge node is offline, the following will be displayed in the Alarm Status Table and Ignition logs at MQTT Engine:  Once the Edge node comes online, any new alarm acknowledgement will be successful from MQTT Engine.

   
   

After doing so, you can see the acknowledged alarm on the Central Gateway (MQTT Engine side) :

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and the Edge (MQTT Transmission side) :

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Removing stranded alarms from the MQTT Engine Status Table

If alarms have been 'stranded' in the MQTT Engine Alarm Status Table, they can be remove through the MQTT Engine Python Scripting API scripting using the readAlarms and clearAlarms calls.

MQTT Modules v4.0.16 to v4.0.22

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