Virtual Variables are used to create new calculated variables that are a mathematical function of one or more sensor readings. Virtual Variables can be used as any other sensor in the system. Add it to a plot and configure for an alarm.
Open Virtual Variables (VV)
Go to Setup > Virtual Variable.
Click + button in the top right corner to create a new VV.
- Select the Site and Variable to include in the formula. Double click it to add it to the Equation window.
- It is possible to select Variables from different Sites into the same Equation
Here is a basic sensor calibration Equation. Notice the $1612$ which is the Variable ID. All variables in the equation will be listed in the Variable table.
It is possible to have different formula for different time period. This is useful if the sensor has been replaced or re-calibrated and a new formula is needed.
Check the Time Variable checkbox to activate the Time variable. A date picker appears above the equation to select the data when this formula starts.
To add a new time period click the + button below the first equation calculation example.
It is simple to add constants into the Equation to make it easier to manage and read.
Expand the Constant section and add a New constant. It is possible to add multiple constants.
Often there is a need to use a baseline reading in the equation. The Datum feature is useful for this purpose.
Expand the Datum Section and click Select.
Select Site, Variable and Timestamp for the Datum Reading. VDV will automatically select the oldest reading in the database. Click Select to select the Datum value.
Now we can change the baseline reading (8553.91) and simply type in datum. When the Datum reading is changed the formula is updated at once.
When a VV has been created it is a good practice to make sure it is working properly.
Expand the Calculation Example section.
Change the Value for each Variable in the equation and see how the result changes.