Special Functions For Plastic Machines; Hot Channel Control; Introduction; Approach Phase - Siemens SIMATIC S5 Manual

3 Special Functions for Plastic
Machines

3.1 Hot Channel Control

3.1.1 Introduction

The heating cartridges used in hot channel control are extremely sensitive to fast temperature
changes. To handle this characteristic, an "approach phase" was developed.
The system time constants involved when using these heating cartridges are small compared with
those encountered using heating collars. The sampling time must therefore be kept as short as
possible.

3.1.2 Approach Phase

Until the actual value (actual value = approach setpoint (SW
uniform manipulated variable S is set for all controllers, e.g. 25% (no closed-loop control).
Once the value reaches the approach zone, the approach time t
setpoint is used during this time. When the start-up time t
then becomes valid. If, during operation, the actual value sinks below the value = approach setpoint
(SW ) minus zone (Z ) the approach procedure is restarted.
A A
Fig. 3.1.2/1 Approach phase for hot channel control
IP244
C79000–B8576–C860–02

Special Functions for Plastic Machines

) – start-up zone (Z )) is reached, a
A A
is started and the approach
AZ
has elapsed, the temperature setpoint
AZ
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