Asko DW90 Series Service Manual page 15

Service manual DW90
Component description
Pressure sensor
The pressure sensor is connected to the
pressure chamber in the bottom drain. It
measures the pressure, which corresponds to
the water level in the machine. If the water level
in the machine is too high (for five consecutive
seconds) the drain pump starts and all other
components are switched
level is reached, the program continues where
it left off. If the level sensor generates an output
signal of <1 VDC during the prewash (indicating
a blocked filter), an additional prewash is
activated with an SCS step.
The level sensor also controls the draining
time (can be extended from 20 seconds to a
maximum of 2 min). The sensor also checks the
need to refill (such as if a bowl fills with water).
Purpose: To prevent overflow, to detect
a 'blocked filter', to when necessary refill the
machine (such as if a bowl has filled with water)
and to control the draining time.
Overflow guard
The overflow guard is integrated with the bottom
drain. This overflow guard consists of a micro switch
activated by a float if water collects on the machine's
bottom plate. The micro switch is normally closed.
When it is activated, it breaks the circuit to the CU,
the drain pump starts, the program is interrupted
and the machine indicates an overflow.
Purpose: To provide protection from any water
leaks or flooding from the machine.
off. When the correct
Turbidity sensor
Machines with an auto program have a turbidity
sensor that measures how cloudy the water is. The
sensor comprises an LED and a phototransistor.
Between these two is the dishwater. The less light
that reaches the phototransistor, the cloudier the
water. The sensor is calibrated during the last rinse
of the auto program. At different points during the
auto program the output signal from the turbidity
sensor provides data used to determine how the
program will continue (number of prewashes,
temperature, program time, number of rinses and
so on). If the turbidity sensor fails, the machine
assumes the water is "very cloudy", which results in
a longer program time, with prewashes, additional
rinses and so on.
The turbidity sensor is located at the front edge of
the bottom drain and is replaced from the front of
the machine.
Purpose: To sense how dirty the dishes are and
to provide the control unit with information about
which program is best suited to the dishes.
15