Introduction to Three Types of Magnetic Reed Sensors

The reed switch sensor is a device that uses a magnet or electromagnet to create a magnetic field that opens or closes the reed switch inside the sensor. This seemingly simple device can reliably control circuits in various industrial and commercial products.

Working principle of reed switch sensors

The reed switch is a pair of electrical contacts that form a closed circuit when they touch and an open circuit when they separate. The reed switch forms the basis of the reed switch sensor. The reed switch sensor has a switch and a magnet that provides power for opening and closing the contacts. This system is contained within a sealed container.

Three types of reed switch sensors

There are three types of reed switch sensors: normally open, normally closed, and latching. All three types can use traditional magnets or electromagnets, and each type of magnet has a slightly different driving method.

Normally open reed switch sensor

As the name suggests, these reed switch sensors are normally in the open (disconnected) position. When the magnet in the sensor reaches the reed switch, it polarizes each connection into opposing electrical charges. The new attraction between the two connections forces them to close the circuit together. Equipment with normally open reed switch sensors is mostly in a power-off state unless the magnet is intentionally moving.

Normally closed reed switch sensor

Conversely, normally closed reed switch sensors create a closed circuit as their default position. The reed switch only opens and breaks the circuit connection when the magnet triggers a specific attraction force. Current flows through the normally closed reed switch until the magnet forces the two reed switch connectors to share the same magnetic pole, separating the two components.

Latching reed switch sensor

This type of reed switch sensor combines the functions of normally open and normally closed reed switch sensors. The latching reed switch sensor is not defaulted to being powered or unpowered, but rather held in the last position until forced to change. If the electromagnet forces the switch into an open circuit state, the switch will remain in an open circuit state until the electromagnet is powered and closes the circuit, and vice versa. The operation and release points of the switch will produce natural hysteresis, locking the reed switch in place.

The reed switch is a unique technology that can be used in almost any environment due to its fully sealed characteristics. Although the structure of the reed switch is simple, its production process includes multiple processes. Over the years, the size of the reed switch has evolved from approximately 50 mm (2 inches) to as small as 6 mm (0.24 inches), making it applicable to more fields, especially meeting the needs of radio frequency and fast time domain applications.