Douwe Egberts Cafitesse 700, Back Office Manual

Page: 165 / 265

July 2004
5A - 23
Functions - water system
0 500 1000 1500 2000
40
60
80
100
Function: Temperature sensor
Resistance measurement
Normal Normal Normal
temp. temp. resistance
(
°
F)(
°
C)(R) (Ohm)
122 50 1802
131 55 1495
140 60 1246
149 65 1044
158 70 878.5
167 75 742.8
176 80 630.7
185 85 537.9
194 90 460.6
203 95 395.9
212 100 341.6
Temperature sensor –resistance in ohm
Temperature
sensor
–
temperature
in
°
C
• The sensor is an NTC-type sensor, i. e. the
resistance decreases with increasing tem-
perature. A constant voltage is applied to this
sensor by the control system.
• The electric current, which is linearly depen-
dent on the sensor resistance, is registered
by the control system. This signal is used for
the ON/OFF control of the relays.
• The NTC properties can be used to check
the boiler function, e.g. by short-circuiting
both inputs of the sensor on the control
system. In this case, the heating system is
switched off.
• Conversely, the control system switches on
the heating system whenever the plug con-
nector of the sensor is pulled off.
Checking the resistance of the temperature
sensor:
One of the two following methods can be ap-
plied on an optional basis:
a) comparative measurement old-new, at identi-
cal temperature
b) resistance measurement and comparison with
the value from the chart. Due to intrinsic
heating, the measuring current is not allowed
to drop below 1 mA.
Cafitesse 700 - Functions - water system