Douwe Egberts Cafitesse 100 Service Manual page 172

Service Manual Cafitesse 100
Temperature sensor
• The function of the temperature sensor in
combination with the microprocessor is
similar to that of a thermostat.
• Temperature deviations at the cooling
compartment wall are transferred to the
sensor by means of thermal conduction.
Increasing or decreasing temperatures
result in a corresponding increase or
decrease of the sensor resistance (PTC).
• This alteration results in a voltage change
in the control circuit which will be registered
by the microprocessor.
• The microprocessor compares the data to
switch the cooling circuit on or off.
• The correct function of the PTC sensor is
important for the correct function of the
cooling system.
• In the case of improper cooling, the sensor
must be checked.
Fig. 1 -25 -20 -15 -10
5F - 10
• Alternatively, one of the following
procedures can be applied:
a) Comparative measurement old - new, at
the same temperature
b) Resistance measurement and
comparison with the value from the
diagram.
Due to self-heating, the measuring
current must not exceed 1 mA.
• Formula for the resistance
R = 813 + (6.96xT) + (0.0208xTxT) Ohm
T = temperature of the sensor in °C
The formula is valid for -25 < T < 25 °C.
Resistance/temperature table
Normal R (Ohm)
1000
1050
• Sensor tolerances
at an indicated temperature : +/- 5 Ohm
at an indicated resistance : +/- 0.7 °C
Ω
1100
1000
900
800
700
600
0
-5 5 10 15
Functions - Cooling System
Normal T (°C)
652 -25.0
700 -17.1
750 -9.3
800 -1.9
813 0
850 5.2
900 12.1
950 18.6
25.0
31.2
°C
20 25 30 35
07.2004