Notes On Operation With Cascaded Control - Siemens SIMATIC S5 Manual

The evaluation factor (byte 12) specifies how many percent of the correction factor of the master
controller should be added to the setpoint. Positive evaluation factors from 0 to 127 and negative
evaluation factors from 128 to 255 as a negative evaluation factor of 0 - 127% can be selected. The
master controller can therefore be weighted zone by zone. The evaluation is limited internally to
100%.
Main control bytes (message 15):
Bit 5 must be set to 1 (cascaded control on) in main control byte 1 (byte 27).
Following each complete machine cycle, bit 0 must be set to 1 in main control byte 3 (byte 29).
Setting this bit triggers the actual value averaging and the processing of the master controller. The
bit is automatically reset by the module.
Message 21 (cumulative setpoints SZn):
Bytes 0/1 contain the setpoint of the master controller. Bytes 2 to 25 contain the corrected setpoints
(cumulative setpoints) of the secondary zone controllers 1 to 12. If cascaded control is not being
used (switch S0 off), the setpoint is at the appropriate location (Fig. 3.2.6/5).

3.2.6 Notes on Operation with Cascaded Control

The master controller should only be switched on (S0 on) when the actual values of the secondary
controllers are within the first tolerance band (interrogation of the error bytes) and the extruder is
switched on. If the master controller is enabled too early, the integrator can cause a large overshoot
in the material temperature.
The gain of the master controller must not be selected too high, since the system oscillates easily.
If a limiter (B1 to B12) is activated, the integrator is slowed down. The correction of the material
temperature then requires more time. This should be taken into account when selecting the
limitation values.
The correction of the zone values is limited by the evaluation factor and the limitation value which
can be calculated as follows for each zone:
The two correction values K1 and K2 are calculated internally. The smaller of the two values
produces the correction setpoint SFn directly. The effective setpoint for the individual controllers
(cumulative setpoint SZn) is calculated as follows:
SZn – SFn + SBn
If the temperature of the material is not corrected after a longer period of time, you should check
whether the limit of correction has been reached.
IP244
C79000–B8576–C860–02
Special Functions for Plastic Machines
4–77