Douwe Egberts Cafitesse 700, Back Office Manual

Page: 221 / 265

July 2004
5F - 19
Functions - cooling system
Temperature sensor (2)
• The sensor is an NTC-type sensor, i.e. the
resistance decreases with increasing tem-
perature.
• Constant voltage is applied to the sensor
by the control system. The control system
(module C) registers the electric current
which is linearly dependent on the sensor
resistance. This signal is used for the ON/
OFF control of the Peltier current.
• The "NTC" properties can be used to check
the cooling function, e.g. by short-circuiting
both inputs of the sensor on the control
system (module C). In this case, the elec-
tric current to the Peltier element must be
switched on. Conversely, when the plug-in
connection of the sensor is pulled off, the
control system must switch off the cooling
system.
Checking the sensor resistance:
• One of the two following methods can be
applied on an optional basis:
a) comparative old-new measurement, at
identical temperature
b) resistance measurement and comparison
with the value from the chart. Due to
intrinsic heating, the measuring current is
not allowed to exceed 1 mA.
Comparative measurement
Resistance measurement
Normal Normal Normal
temp. temp. resistance
(
°
F) (
°
C) (R) (ohm)
14 –10 27667
23 –5 21156
32 0 16322
41 5 12690
50 10 9946
59 15 7851
68 20 6243
77 25 4998
86 30 4027
95 35 3265
104 40 2663
113 45 2185
0
5000 10000 15000 20000 25000 30000
-10
0
10
20
30
40
50
Temperature sensor – resistance in ohm
Temperature
sensor
–
temperature
in
°
C
Cafitesse 700 - Functions - cooling system