Vermont Energy Control Systems

Practical monitoring and control for the real world

Data Elements

In the Vesta system, 'Data Element' refers to any input, output, or variable that can be displayed, datalogged, or used in a rule. Almost all interaction with the system is through Data Elements. A Data Element has a user-defined name and may represent either a physical input, a physical output, or a variable.

One important difference between the Vantage/Pro and the Classic: Where the Classic one tab for managing data elements ('Data Elements') and another for rules, these tabs have been combined into a single tab ('Elements & Rules') on the Vantage and Pro.

A screenshot of the home page with a variety of data elements

Figure 3.1: Home Page showing a variety of Data Elements

IMPORTANT CONCEPT: Vesta rules can act only on data elements. There are only two types of data elements:

  1. Physical inputs and outputs. These allow the rules to act on and control the outside world.
  2. Variables. These contain numeric or logical values that can be used as part of any rule.

You can always see which physical channels are assigned to specific data elements - just click on the 'Configure I/O' tab ('Physical I/O' tab on the Classic).

Creating Data Elements

Data elements representing physical I/O are created using the 'Configure I/O' tab ('Physical I/O' tab on the Classic).

Data elements representing variables are created on the 'Elements & Rules' tab ('Data Elements' tab on the Classic).

The Vesta controller is programmed by creating rules that act on Data Elements. Rules cannot be created until the associated data elements exist.

One of the first tasks in setting up an Vesta system is to give each physical I/O channel a data element with a name that describes its function such as 'Wood Boiler Outlet Temp' or 'Second Floor Heat Demand'. This is covered in the user's manual, and is typically part of initial system setup.

Once data elements for physical I/O have been created, the next task is to create data elements for any variables that will be needed.

All available data elements are displayed on the 'Elements & Rules' tab ('Data Elements' tab on the Classic).

This tab allows the name of any data element to be changed. It allows the creation of new variables as well as setting the value for any variable.


There are three types of variables:

  1. Standard variables
  2. State variables
  3. Timer variables

Standard Variables

Standard (analog) variables are data elements that contain numeric values. They can get their values from the user interface, or can be set by rules. Values are stored as floating point numbers, but any variable can also be treated as a boolean (true/false) value.

State Variables

State variables are a special class of variable. State variables are treated as boolean values. If they are managed by the rule engine, they are automatically set to 'false' and will remain false unless a rule sets them to true. In the Classic, any variable with a tilde (~) as the first character in the name will be treated as a state variable.

Timer Variables

A timer variable is a standard variable that is named as the target of a timer rule. These variables will be decremented automatically by the rule engine. Their value at any time is the number of seconds remaining before they reach zero. See the section on timer rules for more details.

Variables as True/False Values

In the Vesta, any non-zero value is considered 'true'. For example, a variable used as a timer will have a numeric value representing the number of seconds remaining. If that value is non-zero, then the timer is 'true'. There are also predefined elements named TRUE and FALSE with values of 1 and 0.

The value of any variable may be set or changed via a rule, it may remain constant for all time, or it may be changed via the web interface.

Variables can be created as needed, and their values may be changed at any time via the web interface. All changes take effect immediately.

Creating Variables

To create a variable, enter the name and numeric value in the corresponding boxes on the Elements & Rules (or Data Elements) tab, and click the 'Create' button.

The view shown above contains the elements set up at initial delivery, These support the 'Front Panel' example that will be discussed in the next section.