lbessard@192:  FUNCTION_BLOCK DERIVATIVE
lbessard@192:    VAR_INPUT
lbessard@192:      RUN : BOOL ;          (* 0 = reset                  *)
lbessard@192:      XIN : REAL ;          (* Input to be differentiated *)
lbessard@192:      CYCLE : TIME ;        (* Sampling period            *)
lbessard@192:    END_VAR
lbessard@192:    VAR_OUTPUT
lbessard@192:      XOUT : REAL ;         (* Differentiated output      *)
lbessard@192:    END_VAR
lbessard@192:    VAR X1, X2, X3 : REAL ; END_VAR
lbessard@192:    IF RUN THEN
lbessard@192:       XOUT := (3.0 * (XIN - X3) + X1 - X2)
lbessard@192:               / (10.0 * TIME_TO_REAL(CYCLE)) ;
lbessard@192:       X3 := X2 ; X2 := X1 ; X1 := XIN ;
lbessard@192:    ELSE XOUT := 0.0; X1 := XIN ; X2 := XIN ; X3 := XIN ;
lbessard@192:    END_IF ;
lbessard@192:  END_FUNCTION_BLOCK
lbessard@192: