An operand is the data or item in the expression that is operated on. All values are managed as floating point data. This includes parameters of function blocks that are floating point values.
The valid operands in an expression are:
Named set constants in the form 'SetName:ValueName'.
Inputs (references to inputs of a function block that are float with status data types).
Outputs (references to outputs of a function block that are float with status data types).
Input Device Signal Tags (DSTs) (references to input signals that are float with status data types.
The expression evaluator is stack oriented and allows a maximum of 32 operands and operators. The use of parentheses to organize the expression minimizes the stack usage. The equations are evaluated using RPN (Reverse Polish Notation).