Working Principle and Function of Magnetic Reed Switch

The working principle of a magnetic reed switch

The working principle of a magnetic reed switch is very simple. Two magnetizable spring pieces (usually made up of iron and nickel) overlapping at their endpoints are sealed in a glass tube. The two spring pieces are arranged in an overlapping manner with a small gap of only a few microns. The contact points on these two spring pieces are plated with a layer of hard metal, usually rhodium and ruthenium, which greatly enhances the switching frequency and product life. High-purity inert gas (such as nitrogen) is filled in the glass tube. For some dry reed switches, the inside is made into a vacuum state to improve their high-voltage performance.

The role of the spring piece is equivalent to a magnetic flux conductor. When not in operation, the two spring pieces do not touch each other. When a magnetic field generated by a permanent magnet or an electromagnetic coil passes, the external magnetic field causes different polarities to be generated near the endpoint positions of the two spring pieces. When the magnetic force exceeds the elastic force of the spring piece, the two spring pieces will attract and complete the electric circuit. When the magnetic field weakens or disappears, the dry reed switch will release due to its own elasticity, and the contact will separate to open the circuit.

The switchable spring piece is in contact with the normally closed piece when there is no magnetic field. When a strong enough magnetic field is generated, the spring piece moves toward the normally open piece, and the normally open and normally closed pieces are both fixed. Both the fixed pieces and the switchable spring piece are ferromagnetic pieces. The only difference is that the contact surface of the normally closed dry reed switch is welded with non-magnetic metal on the dry reed switch. When placed under a magnetic field, the fixed pieces on both sides of the normally open and normally closed have the same polarity, but opposite to the polarity of the swingable spring piece. The non-magnetic metal on the normally closed end will isolate the magnetic flux. Therefore, when the magnetic force between the normally open end and the swingable spring piece is large enough, the swingable spring piece will come into contact with the normally open piece to close the circuit.

The role of a magnetic reed switch

The magnetic reed switch has been widely used in household appliances, automotive, communications, industrial, medical, security and other fields. Let's briefly explain the application of magnetic reed switches in magnetic reed relays and dry reed sensors.

Magnetic reed relay

Placing a magnetic reed switch around a coil causes the current passing through the coil to generate a magnetic field similar to that of a permanent magnet. A coaxial shield is placed around the switch to switch high-frequency signals up to 20 GHz. Because dry reed switches have no susceptible parts, the contact can switch low-level signals.

Dry reed sensor

Using a magnetic reed switch, dry reed sensors can sense various movements using permanent magnets. Dry reed switches consume zero current when in the open state, making them an ideal choice for energy-saving devices. Even when air, plastic, and metal are separated, the magnets and dry reed switches can generally be separated by physical enclosures or other barriers. Dry reed sensors are used for motion detection, counting, detecting liquid levels, measuring liquid levels, switching in harsh environments, implanted devices, etc.