15
The Control System
The electronic control, with input from various
sensors, has total operation of the dishwasher once
a wash cycle has been started. The electronic
control is mounted inside the console with its power
coming directly from the power junction box. Power
to operate the control can not be interrupted by
opening or closing the door. However, the control
does know when the door is opened. The black
power lead from the door switch is attached to the
control this line operates all of the components in the
dishwasher. Input to the control comes from the
following: the
keypad
is a membrane switch that
allows the user to select a specific wash cycle and
any available option for the dishwasher to perform, a
soil sensor
that determines the concentration of soil
in the water, a
thermistor
to measure the tempera-
ture of the water, a
Hall sensor
to track the speed of
the motor, an
optical sensor
reports the position of
the vent door, finally a
reed switch
in the rinse aid
dispenser to report the pressents of rinse aid in the
dispenser. This section will describe the sensors
how they operate followed by tests that can be
performed to test the control system and all of the
components in the dishwasher.
Soil Sensing
A soil sensor is used by the control to make adjust-
ments to length of wash cycles based on the soil
level found in the water. This sensor is located in the
base of the sump directly in front of the wash motor
intake. The soil sensor receives a voltage signal from
the control which it converts into a small beam of
light; the transmitter then directs this light beam to a
receiver through water that has been used to pre-
wash the load in the unit. As the light passes through
the water the density of the water can reduce the
strength of the light beam reaching the receiver. The
receiver turns the light back to a voltage this is then
returned to the control, which interprets this reading
and adjusts the cycle length accordingly. See Figure
29
The number of times the control checks the soil level
varies with cycle but in cycles it is used the pre-wash
water will always be checked. The control can
increase a cycle length or decrease as needed but
never longer then the longest cycle or shorter then
the shortest cycle available.
The control pauses the wash motor for 30 seconds
to allow time for the water to settle before checking
then the water is drained and any adjusts to the cycle
are made.
Temperature controls
The control is programmed with preset wash and
rinse temperatures for each cycle. The use of a
thermistor in the sump provides water temperature
information to the control to maintain these tempera-
tures. The control provides options for the user to
select a higher temperature wash as well as a
sanitize rinse.
The thermistor is located in the same housing as the
Soil Sensor. The post on the Soil Sensor that is taller
is the location of the Thermistor. With the sensor in
the water of the sump it gets a more accurate reading
of water temperature. See Figure 29
.
To insure the pre-programmed water temperature for
the wash cycle is reached the control can pause the
main wash cycle up to 10 minutes in a Temp assure
cycle. This Temp assure cycle is automatic and not
selected as an option. If the Hi-temp wash option is
selected, the control will delay the main wash section
once again for up to10 minutes to increase the water
temperature to a higher degree. Whether or not the
water temperature is reached in this10 minutes delay,
the cycle will continue without indication that it
reached or did not reach this temperature.
When the Sanitize option is chosen, the National
Sanitation Foundation requires in the final rinse cycle
that 155°F be reached and maintained for a certain
amount of time. During the final rinse, the control
pauses the time remaining for up to 30 minutes to
reach this 155°F temperature before proceeding to
the end of the cycle. Should the cycle meet the
requirements defined for the sanitize option, the
Sanitize light will come on and stay on until the door
is opened. If the requirements are not met the
sanitize light will not come on at the end of the cycle.
Figure 29
Soil sensor
Thermistor
