Modern electronics cannot be imagined without contact elements capable of switching significant currents for a long time. Magnetically operated reed switches were invented to extend the service life of switching devices operating at maximum load. These products with a long historical past are in demand in modern conditions. Due to their low cost and reliability in operation, they are actively used in many electronic circuits.
Types of reed switches
Like conventional contact products, according to their performance characteristics, reed switches are divided into:
- Two-position changeover switches with one reversible contact plate.
- Disconnecting devices, the design of which provides for a closed (in normal state) contact.
- Closing with one open contact.
By their design, switching elements of this class are divided into devices with dry switches and mercury samples. The former are among the simplest products with all their inherent disadvantages. One of them is the so-called "bounce" of contacts, which means their parasitic vibrations when closing and opening. As a result, a separate actuation of the switching element causes a whole series of irregular switching operations, which is very dangerous for the operation of electronic circuits. The second samples differ in that a drop of mercury is placed in the inner zone of the sealed flask. It wets the switching contacts when triggered, eliminating bounce and reducing contact resistance.
Reed switch design
The existing types of reed switches have a similar design, differing only in minor details. All of them are a sealed glass flask with a pair of permalloy contacts inside. To increase the reliability of actuation, they are coated with a thin layer of precious metals. Their external parts or leads are used to connect the device to the working circuit.
The inner space of the flask is filled with inert gas, or air is pumped out of it. This allows you to extend the service life of the switching product and increase the corrosion resistance of metals.
Operating principle
To operate the reed switch for a short circuit, you will need to create a magnetic field of the required strength around it. It does not matter at all what the source of the field structure is: an electromagnet or its permanent analogue. Under the action of this magnetic field, the contacts are magnetized and attracted to one another, overcoming their own elasticity.
Note: They are in this state until the moment when the action of the magnetic field stops.
Opening contacts act quite differently. The system of magnets in them is designed so that when a field appears, they are magnetized in the same way and begin to repel. In devices of the switching type, another normally closed contact of non-magnetic material is provided. Under the action of the field, the open contacts pass into the opposite state, and the non-magnetic one remains in the same position.