Cascaded Control; Introduction: Example Plastic Processing Machines; Description Of The Controller Structure - Siemens SIMATIC S5 Manual

Ip 244 temperature controller with function block fb 162
Hide thumbs Also See for SIMATIC S5:
Table of Contents

Advertisement

3.2 Cascaded Control

3.2.1 Introduction: Example Plastic Processing Machines

The conventional zone wall control with the extruders of plastic processing machines has the
disadvantage that the temperature of the mass of plastic discharged is only constant in one
operating status. Changes, for example in the screw speed, always mean changes in the
temperature of the material. To compensate for this, the setpoints of the control zones on the
extruder must be adjusted.
With cascaded control, this adjustment is made by measuring the temperature of the material
output by the extruder and by adjusting the setpoints of the individual zones if a deviation is
recognized.

3.2.2 Description of the Controller Structure

The controller structure for cascaded control is shown in Fig. 3.2.6/1. The extruder is divided into
individual heating zones. The temperature of these zones can be controlled by up to 12 zone
controllers, all subordinate to the master controller. The structure of the zone controllers is identical
to that of the previously described temperature controllers.
The temperature of the material is averaged over one machine cycle. This averaging is performed
since temperature fluctuations occur when the reservoir head is output (see Fig. 3.2.6/2). The
deviation of the actual value from the setpoint is fed back to a PI controller (master controller). The
calculation of the manipulated variable of this master controller is always made on completion of
a machine cycle. The master controller outputs its manipulated variable in degrees Celsius or in
degrees Fahrenheit. The master controller output can be disabled totally with switch S0 and for
each individual zone controller individually with switches S1 to S12 (control byte 1).
If the switch of a controller is set to "OFF", this controller can be used as an independent
temperature controller (S0 to S12).
The setpoint correction can be influenced by the evaluation factors F1 to F12 to set a correction
profile. The limiters B1 to B12 prevent a zone setpoint from being over-adjusted.
A temperature profile can be set with the individual zone setpoints.
3.2.3 Selecting Cascaded Control
Cascaded control is selected by setting bit 5 in main control byte 1. Once selected, a start-up must
be executed (set bit 2 in main control byte 4).
IP244
C79000–B8576–C860–02
Special Functions for Plastic Machines
4–75

Advertisement

Table of Contents
loading

This manual is also suitable for:

Simatic s7

Table of Contents