How to combine multiple streams in an Activator rule

This article shows you how to:

Monitor data from multiple eventstreams and automate actions by defining an Activator rule
Set up multiple advanced conditions, such as average, maximum, or minimum value of a data property, by using Activator modeling capabilities.

Scenario

In this example, you can track the health of your water pumps (machines) by monitoring the FlowRate and Vibration of the machine. The goal is to automatically take action, such as sending an alert or starting a business process, if Vibration is abnormal while the machine is running and moving significant amount of water (FlowRate). High water pump vibration might signal underlying issues, however it's expected as long as FlowRate is insignificant.

Machines monitoring data flows into two eventstreams:

MachineHeartbeat eventstream contains MachineId column identifying a machine and MachineRunning column that indicates if machine is running (1) or not (0). An event is emitted every time a machine state changes.
MachineSensorsReadings eventstream contains a MachineId column together with FlowRate and Vibration columns. Every machine emits sensors readings every few seconds.

In this scenario, you want to raise an alert when all these conditions are true:

Maximum Vibration in the last 1 hour increases above 18.
Average FlowRate in the last 10 minutes is above 185.
Machine is running.

Activator rules support complex conditions based on multiple eventstreams. You can create computed properties based on event columns and combine them in the rule condition.

In this scenario, you bring two eventstreams together by creating an object that feeds from both streams. When you add an eventstream to the object, you specify which column in the events uniquely identifies the instance of an object.

Then, you create a property that computes average(FlowRate), another one for max(Vibration), and combine them with IsRunning property. When evaluating the rule, Activator computes property values according to their definitions and maintains the last computed value of every property. These values are used when evaluating the condition.

In Activator rules, you must set one Condition, such as max(Vibration) > 18, and add optional filters, such as avg(FlowRate) > 185 AND MachineRunning. The rule fires when the Condition is met, provided the filters are also true.

The condition drives the rule as illustrated in the following picture:

Solution

Add Activator destination to both eventstreams. Make sure both eventstreams use the same Activator instance.

Both eventstreams are configured with the same Activator destination:
Open Activator item. Now you can combine both eventstreams in an object and set up a rule.
To combine these two streams, select any stream and select New object.
Select the column name used to identify the instance of an object and columns that are needed for the rule, and then select Create. The value of MachineId column in each event is the key identifying the machine that emitted the event.
Select another eventstream, select New object, and then select Add to existing object in the Build object pane. Choose MachineId column as unique identifier. Select Assign. Now the two streams are combined in one object.
Now you can define the computed property. Create an attribute for computing average of FlowRate in the last 10 min. Select FlowRate attribute and select Edit details.
On the Definition pane, select Add summarization, choose Average, and set 10 minutes as window size. Select Save.
Select Vibration attribute and select Edit details. On the Definition pane, select Add summarization, choose Maximum, and set 1 hour as window size. Select Save.
Now create the rule. Select Vibration property and select New Rule.
In the Definition pane, set up Increases above condition with 18 as threshold.
Add a filter for FlowRate property and one for MachineRunning property.
Select an action of your choice like sending email or Teams messages, running business process like pipeline, notebook, or functions, or running no-code custom action with Power Automate. Select Save and start.