Reed Relays and
Electronics India Limited
Manufacturer of Reed Switches, Reed Sensors and Reed-based products
Reed Relays and Electronics India Limited Incorporated in 1971
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Actuating a Reed Switch

In all reed switch actuation applications, a magnet and a reed switch must be brought to within a specific proximity of each other. This distance will vary in accordance with the magnetic sensitivity of the reed switch and the strength and size of the magnet. When the magnet is close enough, the Normally Open contacts will close or operate. When the magnet is taken away, the contacts will open or release. The relative distance for an operate is always less than the distance for a release. There are various ways in which a reed switch is actuated with a magnet and some examples of magnet motion are shown below.

Perpendicular Motion

When the magnet is moved perpendicular to the Reed Switch, it provides only one closure with maximum magnet travel.

Reed Switch with magnet moving perpendicular (magnet parallel)
Reed Switch with magnet moving perpendicular

When the magnet is moving parallel to the reed switch, specifically to the center of the contact, it provides only one closure with maximum magnet travel.

Reed Switch with magnet moving perpendicular to it
Reed Switch with magnet moving perpendicular to contact center

Parallel Motion

When the magnet is moving parallel to the reed switch, it provides as many as three closures with maximum magnet travel and one closure with minimum magnet travel. It should be kept in mind that approaching a reed switch with a single pole of magnet is not advisable.

Reed Switch with magnet (perpendicular) moving parallel
Reed Switch with magnet (perpendicular) moving parallel
Reed Switch with ring magnet moving parallel
Reed Switch with ring magnet moving parallel

Pivoted Motion

When the magnet is moving pivoted, at an angle to the reed switch, it provides one switch closure. Large angular magnet travel may be necessary.

Reed Switch with magnet moving pivoted
Magnet moving pivoted to the reed switch

Rotary Motion

Rotating the magnet or reed switch, normal to their axes, reverses magnetic polarity resulting in two closures per revolution. When these axes are parallel, the switch closes. When the axes are perpendicular, the switch opens. Although the poles reverse, they still induce the opposite poles that close the reed switch. This is because a reed switch is an omni-polar device.

Reed Switch with magnet rotating near it
Magnet rotating near reed switch

Biased Actuation

A biasing effect is produced by placing a stationary magnet permanently near the reed switch, to keep it in a Normally Closed state. The approach of another magnet with reversed polarity cancels the magnetic lines of force, and the reed switch opens. Care should be taken not to bring the actuating magnet too close to the biased reed switch, as it could close again (re-closure). Form A type reed switches meant for this kind of application should be selected from a release AT group instead of from an Operate AT group.

Reed Switch with biasing magnet and actuating magnet
Biased Reed Switch being actuated with another magnet

Shielded Actuation

In this type of actuation, magnet and reed switch are permanently fixed in such a position that the reed switch contacts are closed. A piece of Ferro-magnetic material is passed between the magnet and the reed switch, to cause a drop out. The magnetic field that is keeping reed switch closed, is shunted by the external ferro-magnetic material, eliminating the attraction between the reeds. When the shield is removed, the reed switch closes once again.

Reed Switch the Ferromagnetic shield and actuating magnet
Magnet field being broken by shunt (shield)