PLC Programming

The Util.lib library
The input IN is of the type INT. All values are initialised anew when the BOOLean input RESET is
TRUE.
The output MN contains the minimum, MX of the maximum value from IN. AVG describes the
average, that is the expected value of IN. All three outputs are of the type INT.
Block in FBD:
STATISTICS_REAL
VARIANCE
This function block corresponds to STATISTICS_INT, except that the input IN is of the type REAL like
the outputs MN, MX, AVG.
VARIANCE calculates the variance of the entered values.
The input IN is of the type REAL, RESET is of the type BOOL and the output OUT is again of the type
REAL.
This block calculates the variance of the inputted values. VARIANCE can be reset with
RESET=TRUE.
The standard deviation can easily be calculated as the square root of the VARIANCE.
10.17.4 Controllers
PD
The PD controller function block:
ACTUAL (actual value) and DESIRED (desired or nominal value) as well as KP, the proportionality
coefficient, are all input values of the type REAL. TV is of the type DWORD and contains the
derivative action time in msec. Y_OFFSET, Y_MIN and Y_MAX are of type REAL and are used for the
transformation of the manipulated variable within a prescribed range. MANUAL, of type BOOL,
switches to manual operation. RESET is of the type BOOL and serves to reset the controller.
Y = KP ⋅ (∆ + TV δ∆/δt) + Y_OFFSET whereby ∆=SET_POINT-ACTUAL
Y is also limited to the allowed range between Y_MIN and Y_MAX. If Y exceeds this range,
LIMITS_ACTVE, a BOOLean output variable, becomes TRUE. If no limitation of the manipulated
variable is desired, Y_MIN and Y_MAX are set to 0.
If MANUAL is TRUE, then the regulator is suspended , that is Y is not altered (by the controller), until
MANUAL becomes FALSE, whereby the controller is re-initialized.
10-54 CoDeSys V2.3