Douwe Egberts Cafitesse 50, Service Manual

Page: 51 / 106

Functions (water) - 11
Version 1.36
02/2004
Figure 5-a-10 NTC output data control
Boiler temperature control
The heater switches on when the temperature drops more than 2 °C/3.6°F under the set temperature.
(T
on
=T
set
-2 °C/3.6°F) The boiler temperature can be adjusted by means of the service device between
83 ~ 96 °C/205°F. (T
set
). The default boiler temperature is 92 °C/198°F.
Water is heated by a heating element located at the bottom of the boiler and is activated by a signal
from the temperature sensor. The power is supplied directly from the AC input voltage circuit and
switched by a relay.
Overheating prevention
If the temperature sensor detects a temperature exceeding the set boiler temperature by 4 °C/7.2°F,
the heating element is switched off by means of a relay.
The temperature sensor is an NTC-type sensor; The resistance of the sensor decreases when the
water temperature increases. The resistance is continuously measured and the resulting data is proc-
essed to control the heating element.
Water dosing
When the hot water button is pressed, the front outlet valve opens and the programmed amount of hot
water is delivered . When the coffee button (cup/pot) is pressed, the rear outlet valve opens.
Outlet valve open control
Delivery mode = portion control: Set cup volume [ml] / water flow [ml/s ]= open time (sec.)
Delivery mode = continuous flow: Valve opens as long as the specific button is pressed.
Boiler level control
The sensor is basically an electrode that connects to GND (= the water level). The presence of water
is checked by sending a pulse of 50 ms. every second. When the water level drops, the sensor does
not connect to GND (no pulses return) and a signal is sent to the main board. (T
lowlevel
> 1 sec.) In turn,
the main board sends a signal to the inlet valve and water is supplied.
B. The boiler
40/104
80/176
100/212
60/140
Temperature sensor (temperature in °C/°F)
0 500 1000 1500 2000
Temperature sensor (resistance in Ohm)
50/122
55/131
60/140
65/149
70/158
75/167
80/176
85/185
90/194
95/203
100/212
1802
1495
1246
1044
878.5
742.8
630.7
537.9
460.6
395.9
341.6
Normal
resistance (Ohm) Normal
temperature (°C/°F)
= out of measurement range