What is the working principle of the reed liquid level sensor?

The reed level sensors come in all different packages, but each sensor includes a housing that incorporates the reed switch and any circuitry along with wires to make the electrical connections to an external circuit. Also included is a float that contains a permanent magnet. The float can be part of the housing where it would ride up and down along the extension or stem of the housing. Floats can also be completely separate from the housing giving complete versatility to the sensor. When the float is in proximity to the reed switch, the contacts will sense the magnetic force closing the contacts.

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