Turbidity Sensor - GE PDW9200 Series Technical Service Manual

Turbidity Sensor

The turbidity sensor is located on the side of the
sump.
Sump
Turbidity Sensor
The turbidity sensor measures the amount of
suspended particles in the wash water in the
sump. The control sends the turbidity sensor a
pulse width modulated 5 volt signal for calibration
and usage during operation.
The control then receives an analog signal of
the sensed turbidity, which is processed by the
microprocessor.
The base-line reading is taken during the fi rst
fi ll as the sump water level is between the
3
/ -in. gap between the LED transmitter and the
8
receptor. Successive tur bid i ty mea sure ments
are sup plied to the control module and used to
de ter mine whether any prewash or rinse cycles
can be skipped. The sensing LED is on during all
pre-wash cycles and during the fi nal rinse.
Decisions are based on a com par i son of clean
water mea sure ments at the beginning of the fi rst
fi ll, mea sure ments taken at selected fi lls, and
water tem per a ture. By measuring the turbidity
level, the control module can conserve energy
on lightly soiled loads by skipping un nec es sary
cycles.
Note: If the turbidity sensor circuit fails to open or
is shorted, the sensing LED on the control panel
will not light, and the unit will operate for the
maximum amount of time, using the maximum
number of wash and rinse fi lls for the selected
cycle.
The turbidity sensor also contains the thermistor
for automatic temperature control.
The thermistor's resistance has a negative
temperature coeffi cient. As the temperature
increases, the resistance goes down. At 75°F, the
resistance is approximately 9.9K Ω. At 140°F, the
resistance is approximately 2.8K Ω.
Turbidity Sensor Test
The
Service Mode
test the turbidity sensor circuit. The turbidity
sensor circuit con tains the control module, wiring,
and the tur bid i ty sensor.
1
/ - to
4
Note: When replacing the turbidity sensor, always
run the
Factory Test Mode
sensor to the control board.
When installing the turbidity sensor, align the key
on the sensor with the keyway on the sump.
– 15 –
is the most accurate way to
to calibrate the turbidity
Key