To create a virtual sensor, go through the following steps:

Step 1: In the main menu, on the left side, click on Settings.

Step 2: Choose the option Structure Setup.

Step 3: Click on the New Item button.

Step 4: In Item Type, select Monitoring Device. 

Step 5: In Configuration Type, select Virtual Sensor.

Step 6: Assign to the virtual sensor a Name, a Label (Name used for alerts) and a Parameter (Unit of measurement of the virtual sensor's output). If none of the displayed parameters match the unit of measure for the virtual sensor output, click Add New Parameter and add the properly parameter.

Step 7: Click Next.

Step 8: Enter the mathematical expression that will generate the virtual sensor output using sensor parameters and/or mathematical constants and operators.

Step 9: Click Test Formula to validate the mathematical expression.

Step 10: Click on Create new.

Step 11: Click on Back.

Step 12: You will see the created virtual sensor. Drag it to the structure of your organisation, placing it in the appropriate location.

Example of the procedure: