Siemens SIPART DR22 Manual page 223

Manual
-- Ratio-cascade control
When adapting the master controller in ratio cascades, the master process variable
should not fluctuate too greatly otherwise additional changes in this controlled variable
may occur at a constant ratio factor (v±∆v) due to the control dynamic of the ratio control-
ler (follow-up controller) and non-linearities between the ratio factor and the controlled
variable of the master controller. These additional changes in the controlled variable
would falsify the adaptation result because only changes by the ratio factor are to be
measured.
-- Override controls
When selecting the operating point in override controls (including the ∆y-step for the
adaptation) it must be ensured that the limiting setpoint is not exceeded in adaptation of
the limiting controller and the main controller.
If the desired operating point cannot be attained due to the operating state of the system,
the adaptation must be made at a level which comes closest to the later operating state.
In the example explained in chapter 1.5.4.9, page 77, (core temperature control with
casing temperature limiting) the maximum permissible casing temperature cannot be
reached in adaptation of the limiting controller if the cooling water flow is not interrupted.
Therefore adaptation must take place at a low level without exceeding the maximum
permissible core temperature. In the other case, if the cooling water is switched off or
fails, the maximum permissible casing temperature is exceeded, when adapted to the
normal core temperature. In this case adaptation must take place at a low core
temperature.
-- Non-linear controlled systems
In non-linear controlled systems several adaptations should be made at different load
states. The adaptation results and the (previously selected with S60) controlling variable
SG must be noted. The controlling variable is also read off in the parameterization mode
AdAP in the range from 0 to 100 %. The parameter sets determined in this way, related
to the controlling variable SG, are then entered in the structuring mode PASt (if
necessary with interpolation). In this way ideal controller results can be achieved even on
non-linear controlled systems.
D Notes on the adaptation results
-- D-part
In S-controllers and K-controllers on controlled systems of 1st order the D part brings no
noticeable advantages due to the finite actuating time ty or for reasons founded in the
control theory. The disadvantages in the form of wear on the positioning side dominate.
-- Range limits
If one of the determined parameters reaches its range limits, the other parameter should
be adjusted slightly in the opposite direction of action.
If systems of the 8th order are identified the determined Kp must be reduced for safety
reasons and if the control circuit is too slow (uncritical), then re-increased in manual opti-
mization.
SIPART DR22 6DR2210
C79000-G7476-C154-03
4 Commissioning
4.5 Automatic setting of control parameters
221