REED SWITCH

A reed switch consist of two ferromagnetic contact tips (reeds) in a capsule filled with inert gas.

Reed switches are used for touchless switching. To trigger the contact, a permanent magnet approaches in such a way that one contract tip receives flux from the north pole and the other from the south pole, until they are sufficiently magnetised to attract and make contact. When the magnet is removed or turned so that the two contact tips have flux from the same pole, the switch opens again.

The figures illustrate the functional interaction between reed switches and magnets. The switching behaviour of a magnet-reed contact arrangement exhibits hysteresis, means, the closing position is different from the opening position. The dashed lines show the closing position when a magnet approaches. The dashed lines show the reed contact opening position.

Moving the magnet paralell, the outer lobe can also be approached as a magnetisation region.

Figure 1:

In the arrangement at the top of Fig. 1, the distance from magnet to reed switch ist he greatest. This results in a single throw switch. If the magnet moves closer to the reed contact (lower arrangement), or if a stronger magnet is used, the result is a triple throw switch.
In this arrangement, very tight switching point tolerances are achieved, if the magnet moves about in the region between the outer and inner lobes. This example illustrates the switching behaviour with a rectangular or disc magnet. The same behaviour can be achieved with a ring magnet slid over the reed contact.

Figure 2:

The magnet may approach in a path perpendicular to the reed contact, either centrally or in the region of the outer lobes.

Figure 3:

The approach of the magnet perpendicular to the reed contact can be either in the center of the reed contact or in the area of the outer lobes.

Figure 4:

When approaching the magnet perpendicular to the reed contact, the magnet can be moved in the reed contact plane (z=0) or shifted in the z-axis.

Figure 5:

In figures 5 and 6, the magnet is perpendicular to the reed contact. The switching arrangement in figure 5 results in a dual circuit, depending on the y-position, i.e. if the magnet is moved centrally over the reed contact (y=0), the contact is not closed.

Figure 6:

Depending on the x-position of the solenoid, the switching arrangement in Figure 6 results in a dual circuit, i.e. if the solenoid is moved centrally over the reed contact (x=0), the latter is not closed.

Figure 7:

Depending on the x-position of the solenoid, the switching arrangement in Figure 6 results in a dual circuit, i.e. if the solenoid is moved centrally over the reed contact (x=0), the latter is not closed.

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