Variables in expressions

Variables are only used in expressions for the Calc/Logic Function block. You can simplify complex calculations by using variables to temporarily store values. The following examples show how variables can be used in a Calc/Logic block.

• This expression defines the value of pi:

  pi := 3.14159;

• This expression assigns the value of input1 to the RADIUS variable:

  RADIUS := IN1;

• This expression assigns the value of 2 times the RADIUS to the DIAMETER variable:

  DIAMETER := 2.0 * RADIUS;

• This expression assigns the value of 2 times pi times the RADIUS to the CIRCUMFERENCE variable:

  CIRCUMFERENCE := 2.0 * pi * RADIUS;

• This expression assigns the value of pi times the RADIUS squared to the AREA variable:

  AREA := 3.14 *(RADIUS * * 2);

• These expressions assign the variables to outputs of the Calc/Logic function block:

  OUT1 := DIAMETER;
  OUT2 := CIRCUMFERENCE;
  OUT3 := AREA;
  

Some keywords are reserved for DeltaV expressions and cannot be used as local variable names.

From the above information, it is apparent that variables do not have to be declared. They are assumed to be variables because of the absence of quotation marks ("…","…") around their names. Variable names are not case sensitive.

All variables are floating point numbers. The value of a variable is retained from one scan to the next. The initial (first scan) value of a variable is zero.

The scope/visibility of variables is limited to the Calc/Logic function block in which they exist.

• VAR...END_VAR; – This structure is used to declare local variables in expressions in CALC function blocks. If the Option Explicit statement is used it must be followed by VAR...END_VAR to declare local variables. Any temporary variables that are not declared within the VAR...END_VAR structure (when using Option Explicit) will not be accepted by the structured text parser.

Option Explicit; (* This is optional.*)
VAR (* Used to declare local variables *)
    T63;
    T64;
    T17;
    T18;
END_VAR;
T63 := .5;
T64 := -15.803;
T17 := SIGN(T63);
T18 := SIGN(T64);
T62 := 88; (* This will give an error with the option explicit, since no T62 declared; otherwise no error is flagged. *)

• (* *) - This is a comment notation. Anything between (* and *) is treated as a comment, even if it spans lines. These comments do not nest. The first occurrence of *) will terminate the comment no matter how many instances of (* have occurred. The content of this comment has no effect on any processing.

• REM - This denotes that a remark is following. Text on the line following REM (note that a space after REM is required) is treated as a comment. The content of this statement has no effect on any processing.