Introduction
Introduction
Basic washing machines are open loop control systems, especially the cold wash, top loading systems common in developing countries
More advanced washing machines are closed loop control systems with multiple forms of feedback various sensors controlling the outputs of a number of actuators.
Sensors
Washing Machine Sensors
Washing machines contain a number of analog to digital(ADC) input transducers to provide feedback on the washing process.
Weight sensor
Weight sensors are a type of transducer than can be used within a washing machine to detect the weight of the load and adjust the wash cycle settings (such as wash duration and required water levels
Float reed sensor
Float reed sensors are a type of reed sensor that is used to detect the volume of water within the drum as the drum fills up. They are also used to detect that that the drum has been completely drained by the drain pump before unlocking the drum door
Hall effect sensor
A hall effect sensor is used to detect the spin speed of the washing machine drum, so that the output of the drum motor can be maintained at the correct speed for the selected cycle.
Reed sensor
Reed sensors are also used to check that the washing machine has been placed on a flat level surface prior to beginning the wash cycle, as well as checking:
- The drum is not vibrating excessively
- The drum door & detergent door have been shut properly by the user
Actuators
Washing Machine Actuators
Washing machines make use of Digital to Analog output transducers to control the washing machine process.
Water Input Valve
The water input value is switched on/off as required in order to fill up the washing machine as necessary for the cycle.
Water Drain Pump
The water drain pump is used to empty water out of the drum during and at the end of the cycle as necessary.
Drum Motor
Drum motor is controlled in order to spin the drum at the required RPM.
Door Lock
A door locking actuator is used to ensure that the user can’t accidentally open the drum door whilst the wash is in progress.
Heating element
The heating element is used to heat up the water within the washing machine to the required temperature for the cycle ( usually around 30 to 40 degrees for clothes and 60+ for cotton linen)