Lenze PLC Designer PLC Designer (R2-x) - Manual (Page 668)

L-force | PLC Designer
PLC Designer Libraries
666 DMS 3.2 EN 02/2011 TD29

Y_OFFSET, Y_MIN und Y_MAX are used for the transformation of the manipulated
variable within a prescribed range.
MANUAL can be used to switch on and off manual operation. RESET serves to reset the
controller.
In normal operation (MANUAL = RESET = LIMITS_ACTIVE = FALSE) the controller
calculates the controller error e as difference SET_POINT – ACTUAL, generates the
derivation with respect to time δe/ δt and stores these values internally.
The output, i.e. the manipulated variable Y is calculated as follows:
Y = KP ⋅ (Δ + TV δΔ/δt) + Y_OFFSET whereby Δ=SET_POINT-ACTUAL
So besides the P-part also the current change of the controller error (D-part) influences
the manipulated variable.
Additionally Y is limited on a range prescribed by Y_MIN and Y_MAX. If Y exceeds
these limits, LIMITS_ACTIVE will get TRUE. If no limitation of the manipulated variable
is desired, Y_MIN and Y_MAX have to be set to 0.
As long as MANUAL=TRUE, Y_MANUAL will be written to Y.
A P-controller can be easily created by setting TV=0.
PID
The library util.lib provides the following PID controller function block:
Unlike the PD controller, this function block contains a further REAL input TN for the
readjusting time in sec (e.g. "0.5" for 500 msec).