The NFCS is programmed by creating rules that act on data.
In the NFCS, all data is represented by data elements. Data elements have user-defined names. They represent the physical inputs and outputs of the controller as well as any user-defined numeric values or user-defined system states. Rules operate ONLY on data elements. Rules do not contain numeric values.
Typically, the first task 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.
IMPORTANT CONCEPTS: NFCS rules can act only on data elements. There are only two types of data elements:
All available data elements are displayed on the 'Data Elements' tab of the web interface. 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.
Variables are data elements that contain numeric values that are needed for rules. For instance, suppose there was an alarm output to be turned on when the wood boiler outlet temperature exceeded 200 degrees. A data element would be needed to carry this number. It might be given a name such as 'Wood boiler overheat setpoint' and assigned a value of 200.
There is only one type of variable = a numeric value. That numeric value can be interpreted either as a number or logical (true/false) value. In the NFCS, 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 or 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.
To create a variable, enter the name and numeric value in the corresponding boxes on the Data Elements' tab, and click the 'Create' button.
The Data Elements view shown here contains the elements set up at initial delivery, These support the 'Front Panel' example that will be discussed in the next section.