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conveying, melting, and metering) are fitted with air fan cooling, their controller output
ranges from -100 to 100 instead of [0
,
100] for heating only control.
Each temperature controller also supports RS-422 serial communication which is
then converted to RS-232 to be connected with computer. Several variables, such as set-
ting point, measured value, and controller outputs, can be directly read or write through
this communication. Therefore, by taking the controller outputs and their associated
heating and cooling power, their energy consumption can be easily calculated as
5
P
thermal
=
p
i
u
i
(3)
i
=1
p
i
=
p
heating
u
i
0
p
cooling
u
i
<
0
(4)
5) denotes the
i
th
heating or cooling power, and
u
i
represents the
i
th
controller output.
By using the proposed methods, it is also possible to monitor the energy consumption
at different heating zones. According to the recorded data, zone 1 consumes nearly half
of the total thermal energy. This can be caused by the plastic granules absorbing heat
energy when passing through zone 1. However, due to the high heat conduction of
metal, a significant amount of energy is wasted in cancelling the zone 1 heating and
feed area water cooling. The installation of heat isolation plate between zone 1 and feed
section should help to significantly reduce the overall thermal energy consumption.
where
p
i
,
(
i
=1
,
···
3.2
Monitoring of Motor Energy Consumption
The Killion KTS-100 extruder is fitted with Eurotherm 512C motor drive and a tacho
meter. The motor controller also utilizes PID control algorithm implemented through
PWM. For the ease of configuration, the 512C controller also provides several termi-
nals which can be used to read or write the motor status through analogue or digital
signals. These include the screw speed, setpoint ramp, tacho feedback, torque/current
limit, current meter output, start/stop, and so on.
For a DC motor, the rotational speed is known to be proportional to the motor arma-
ture voltage while the screw torque is proportional to the motor armature current. This
relationship can be summarised as
V
a
=
R
a
I
+
E
b
(5)
E
b
=
K
v
ω
(6)
T
=
K
m
I
(7)
V
a
=
R
a
I
+
K
v
ω
(8)
where
V
a
and
R
a
denote the armature voltage and current (or motor supply voltage
and current),
E
b
is known as back EMF (Electro Motive Force),
ω
represents the mo-
tor rotational speed, and
T
denotes the torque, finally,
K
v
and
K
m
are motor specific
parameters which can be identified through the measurements of
V
a
,
I
a
,
T
,and
ω
.
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