Burkert Type 8635 - Manual (Page 102)

100 - 8635
O
PERATING THE
P
ROCESS
C
ONTROLLER
(S/HART)
P.CO TUNE
Self-optimization of the process controller (process tune)
The control system SIDE Control is equipped with a positioner which if required can be supplemented
by a superimposed process controller (see chapter
Operation as a Process Controller).
The positioner controls the position of the process valve to the desired setpoint and is automatically
parametrized and optimized by the
X.TUNE function.
The superimposed process controller, which together with a sensor forms a process control loop,
controls any process variable. It has a PID structure whose components may be combined in various
ways (P, PI, PD, PID), and freely parametrized (KP, TN, TV).
In order to obtain good control behaviour, the structure of the controller must be adapted to the
characteristics of the process (controlled member). The parameters must be chosen to obtain a short
setting time, a small overshoot width and good damping.
Parametrization demands experience in control technique, measuring equipment and is time
consuming. For this reason, SIDE Control has a self-optimization function
P.TUNE. This function
provides an unique, direct determination of the parameters. The results may be read out as needed and
modified in any way desired.
METHOD OF OPERATION
During commissioning of the control system, the process is excited by a step in the setpoint in a closed
control loop. This step is carried out within the future working range of the process control system and
serves to determine characteristic variables of the process. Calculation of the PID controller parameters
is carried out on the basis of these characteristic variables by use of a modified Ziegler-Nichols
procedure.
SETPOINT MODULATOR
In addition to optimization of the PID parameters, a setpoint modulator (filter) is calculated for the
reduction of unwanted non-linear effects. Such effects may arise because of physical limitation of the
correcting variables and the floating time of the control valve.
The setpoint modulator further improves the control behaviour. It is activated as long as the P.TUNE
function is activated in the operating menu of the SIDE Control (P.TUN ACT). When the function P.TUNE
is deactivated in the operating menu (P.TUN D’ACT) after completion of self-optimization, the process is
controlled with the optimized PID parameters and the setpoint modulator is deactivated.
ATTENTION!
Be sure to comply with the sequence ... on setting up the process control system!