January 2001
5A - 28
Functions - Water System
Service Manual Cafitesse 500
A.3.9 Function: Temperature Sensor
●
The sensor is of the NTC define type. Its
resistance is reduced when the temperature
increases. The electronic control applies a
constant voltage to the sensor.
●
The electric current which linearly depends
on the sensor resistance is monitored by
the electronic control. This signal is used
for the on/off regulation of the relais.
●
The NTC properties can be used to check
the boiler functions, e.g. both inputs of the
sensor to the electronic control could be
short circuited. In this case the heating is
switched off.
●
On the other hand the electronic control
switches the heating on if the plug
connection is removed from the sensor.
Checking the resistance of the temperature
sensor:
●
The two following methods can be used
alternatively:
a) Comparative measurement old-new,
at the same temperature
b) Resistance measurement and subsequent
comparison with the value from the chart.
Due to self-heating the measuring current
must not exceed 1 mA.
Resistance measurement
Temperature sensor - resistance in Ohm
Temperature sensor - temperature in °F
normal
normal
temp.
resistance
(°F)
(R) (Ohm)
122
1802
131
1495
140
1246
149
1044
158
878.5
167
742.8
176
630.7
185
537.9
194
460.6
203
395.9
212
341.6
0
500
1000
1500
2000
100
°
F
120
°
F
140
°
F
160
°
F
180
°
F
200
°
F
220
°
F
