Special Functions for Plastic Machines
4–73
IP244
C79000–B8576–C860–02
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
A
) – start-up zone (Z
A
)) is reached, a
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
AZ
is started and the approach
setpoint is used during this time. When the start-up time t
AZ
has elapsed, the temperature setpoint
then becomes valid. If, during operation, the actual value sinks below the value = approach setpoint
(SW
A
) minus zone (Z
A
) the approach procedure is restarted.
ClosedĆloop control with
SW
B
Operating setpoint
ClosedĆloop
control with
approach
setpoint SW
A
T
Actual
temperature
value
Approach zone Z
A
SW
B
Approach setpoint
Approach time
t
AZ
SW
A
From this point, the end of the
approach phase is indicated in
message 16, bytes 6 and 7.
OpenĆloop control
with approach
manipulated
variable S
Fig. 3.1.2/1 Approach phase for hot channel control
Hot channel controllers may only be configured as 2Ćstep controllers.
SelfĆtuning is not possible!
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