Position and level sensing in refrigerators and freezers

Littelfuse’s magnetic sensor products help make these appliances as reliable as ever.

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.

Refrigerator and freezer door position sensing
Refrigerators equipped with a microprocessor control unit are compatible for the use of noncontact-type sensing technologies such as reed switches/sensors and Hall Effect sensors. These technologies are very compatible for the low DC voltage and current requirements of the microcontroller.

No longer is there a need for the traditional mechanical and plunger-type switches that have been previously used for directly switching 120VAC incandescent lights. Modern appliances that use the microcontroller have converted to an LED light for the interior. This is a huge advantage for energy saving.

When the door of a refrigerator, freezer, or wine cooler is opened, a light is turned on to illuminate the inside compartments. In order to accomplish this, a proximity sensor is needed to detect if the appliance door is open or closed.

A reed sensor or Hall Effect sensor can be used to detect the position of the door. For example, in refrigerators, a reed sensor is mounted to the frame of the appliance and a permanent magnet actuator is mounted to the door.

Each reed switch or Hall Effect sensor and magnet actuator is positioned such a way that the reed switch or Hall Effect sensor is activated when the door is closed, and the light will turn off. When the door is open, the magnet on the door is positioned outside the sensor’s activation range and the sensor is deactivated and the light will turn on in this mode. The controller uses reverse logic to control the light relative to the sensor activation.

The sensor units are not visible since these are mounted behind the panels of the frame or door, greatly improving the aesthetic appeal of the appliance. Unlike mechanical or plunger switches that have levers or buttons visible, these sensors are ‘non-contact’ and do not require physical contact to operate.

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