Temperature and Wash Arm Sensors
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Completing the suite of sensors in the WPS are a thermistor for measuring
temperature and a magnetoresistive sensor to
monitor wash arm rotation. Both are conventional technology.
Temperature is critical in determining the effectiveness of the detergent
cleansing and the state of dryness. The wash arm sensor is used to monitor
the rotation of the water-pressure-powered lower spray arm in the dishwasher.
It employs a magnetically-sensitive device manufactured by Micro Switch to sense
the passage of a magnet attached to the spray arm assembly. The processor in the
WPS monitors this device to calculate wash arm rpm. The controller combines the wash
arm sensor signal with observations from the current sensor monitoring the motor
current to provide diagnostic feedback to detect if the wash arm is blocked. If the
wash arm is obstructed, the dishwasher can alert the user.
Other external sensory inputs that help the fuzzy controller determine optimal
cycle times and settings include monitoring the time between loads so the appliance
can adjust for dried-on food, and counting the number of times the dishwasher door
is opened to estimate the number of dishes.
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