Reed switches were invented by Bell Telephone Laboratories. It is an electrical switch that operates with the help of applied magnetic field. It is composed of ferrous metal reeds that are hermetically sealed in a glass envelope. One of the most common applications of reed switch is in the burglar alarm.

How Does A Reed Switch Work

The metal reeds come together under the influence of magnetic field that is created with the help of permanent magnetic or an electromagnet, thus the electrical circuit is completed. When the circuit is open the magnetic field ceases so the metal reeds separate and in this condition the switch is considered to be open.

Configuration Of Reed Switches

Silver, ferrous, gold & mercury are the widely used metals. Sensitivity is an important quality of the red switches. It is measured in Ampere-turns that is the number of amperes of electricity flowing in the coil multiplied by the number or total turns of the coil. Thus smaller the size of reed switch, the more sensitive it is. In other words the size & sensitivity of reed switches are inversely proportional. The glass used in the reed switch must be free from volatile components like lead oxides & fluorides. It must also possess a high electrical resistance.

Uses Of Reed Switches

In the past century somewhere in 1970, telephone exchanges used millions of reed relays particularly by the British community. When the operating currents are low, reed relays provide a high speed; good perform ace & long life.

The most common use of reed switches is in sensors & alarms. When the lid of the modern laptops is closed, the system is put on sleep or hibernation mode with the help of these reed switches. The door & window sensors in burglar alarms make use of reed switches. In the automobile industry they are used to sense the temperature & rate of flow of coolant.

The dentist’s drill also has reed switches to check the pressure of the drill. The liquid in dishwashers & washing machines is dispensed with the help of reed switches.

In spite of the cutting edge technology, there are limitations of the reed switches as well. Cracking & chipping is common owing to the small size & glass casing. When the contacts are soldered or welded on circuit board, the contacts being fragile are often damaged. Reed switches are in great demand in the robotics & automation industry.