Douwe Egberts Cafitesse 100, Руководство по обслуживанию

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07.2004
5F - 12
Functions - Cooling System Service Manual Cafitesse 100
F.4 Electrical Diagrams
F.4.1 Cooling Circuit
Fig. 1
fuse
F04
trans-
formator
T01
mains
bridge
rectifier
conden-
sator
Peltier
measuring
resistor
0.1Ω
empty LED
high/low
temperature
LED
temperature
sensor
tran-
sistor
voltage
regulator
MP
11-13 V≈
• A transformator supplies the cooling circuit
with 11–13V AC (depending on the mains
voltage).
The Peltier element is supplied with dc
current by a condensator and a bridge
rectifier on the pc board.
The microprocessor requires the data of the
cooling compartment temperature and of
the Peltier current in order to control the
cooling and to check the circuit functions:
a) Measuring the cooling compartment
temperarture:
The sensor resistance increases when the
temperature increases (PTC). The
microprocessor switches the Peltier supply
via a transistor as follows:
ON when R > 853 Ohm
(correspondingly T > 5.7 °C)
OFF when R < 846 Ohm
(correspondingly T < 4.7 °C)
• The microprocessor activates flashing of the
temperature indicator LED when:
temperature high R > 905 Ohm
(correspondingly 12.7 °C)
temperature low R < 830 Ohm
(correspondingly 2.4 °C)
The temperatures mentioned above are
sensor temperatures.
The product temperature is almost by
3°C lower than the sensor
temperature.
The temperature of the cooling
compartment base is almost the same
as the product temperature.
The deviation of the PTC is +/- 5 Ohm,
corrspondingly +/- 0.7 °C
b) Measuring the Peltier current:
The microprocessor measures the current
via a measuring resistor and switches it via
a transistor as follows:
No effect when
I > 1 A and < 3.3 A
(normal function, transistor is switched due
to the cooling compartment temperature).
ON/OFF cycle when
I > 3.3 A and < 4 A.
The current is pulsed in order to guarantee
that 3.3 A (effectively) will not be exceeded.
The pulse duration depends on the
measured current values.
• OFF when
for more than 10 sec.
I < 1 A or > 4 A.
The microprocessor activates flashing of the
empty indicator LED.
• Immediate switch-off when I > 5 A.
The microprocessor activates flashing of the
empty indicator LED.