Controller functions
Page 58 RES-445
10.24.9 Preheating (with time control)
If time control is active, the preheating temperature
( section 10.11 ""PREHEAT" signal (preheating)" on
page 47 is only deactivated during the heating phase.
Preheating is active during the starting delay and the
cooling phase.
The ACTUAL temperature consequently cannot fall
below the set preheating temperature during the coo-
ling phase.
The temperature which is set for the end of the cooling
phase ( section 10.24.5 "Setting the cooling value"
on page 55) must always be higher than the preheating
temperature. If not, the end of the cooling phase is
never reached, i.e. the internal timeout does not
elapse.
If the cooling temperature is required to be lower than
the preheating temperature, the "PREHEAT" signal
must be deactivated until the end of the cooling phase
and then activated again.
10.24.10Example
The example below illustrates the basic design of a
pneumatically operated L-sealer with a solenoid valve.
The heatsealing process is started by means of a foot
switch.
The functional sequence is as follows:
1. The controller receives the "START" signal for
internal time control via the foot switch.
2. The heating process must begin immediately – wit-
hout a starting delay.
3. When the ACTUAL temperature reaches 95% of the
SET temperature (T = 180°C), the normally open
contact of relay K1 must close. The solenoid valve
is then energized and the sealing jaws are closed.
The heatsealing time (t
2
= 1s) begins simulta-
neously.
4. The heatsealing bands are not heated any further at
the end of the heatsealing phase (i.e. at the end of
the heatsealing time). The cooling phase begins.
5. The cooling phase must end when the ACTUAL
temperature of the heatsealing bands falls to
T
80°C. The sealing jaws are still closed (the nor-
mally open contact of relay K1 is also still closed).
6. The normally open contact of relay K1 opens again
at the end of the cooling phase. The sealing jaws
are also opened again.
7. End of the heatsealing process.
Controller Relay K1
Start
U
Film
Film
Heatsealing band
Heatsealing bar
Retainer
Cylinder
Solenoid valve
Foot contact
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