All about position and level sensing in washing machines

Reed sensors and Hall Effect sensors are both very reliable and will operate over millions of cycles with long-term integrity when used with microprocessor electrical loads. Both reed and Hall Effect devices are operated by a magnetic field. Reed switches and sensors consume no power, while Hall Effect devices are semiconductors and will consume a small amount of current in both the activated and de-activated state.

Lid/door position sensing
In top-load washing machines, the wash cycle begins by pumping water into the drum. As a safety precaution, the wash cycle doesn’t begin the rotation of the drum unless the top lid is closed.

Typically, a micro switch can be used to detect when the lid is in the closed position. However, like many mechanical devices, micro switches tend to wear out over many close/open operations. Reed switches, on the other hand, are used as a longer-lasting alternative to micro switches. Reed switches offer the benefit of being contact-less sensors that can last for many close/open operations.

A magnet is placed onto the moveable lid and actuates a reed switch that is mounted to the frame of washing machine near where the lid rests when closed. When the reed switch is closed, the microprocessor in the washing machine’s electronics panel reads that the lid is closed and allows for the drum rotation to begin.

Similarly, in front-load washing machines, a reed switch can be used to detect whether or not the door is closed. A magnet is mounted to the swinging door and a reed switch is mounted to the frame of the washing machine near the door lock. When the door is closed, the microprocessor reads that the door is in the closed position and signals the lock mechanism to lock the door in place. The wash cycle can then begin or resume.

Not only can reed switches be used for lid and door position sensing, but reed sensors, provided in different housing types, can be used. Hall Effect sensors may also be used, especially in washing machines with microprocessor-controlled electronics.

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