Reed Switches By V. G. Electric

Reed Switches consists of a pair of flexible reeds made of a magnetic material, and sealed in a glass tube filled with inert gas. The reeds are overlapped but separated by a small gap. The contact area of each reed is plated with a noble metal; such as Rhodium or Ruthenium, to provide the switch with stable characteristics and long life.

Application of magnetic field, generated by a permanent magnet or a coil, to the reed switch causes both reeds to be magnetized. This produces an N-pole at the contact area of the one reed, an S-pole at that of the other reed. If the magnetic attracting force overcomes the resistive force caused by elasticity of the reed, the reeds come in contact (Pull-In) i.e. the circuit is closed. Once the magnetic field is removed, the reeds are separated again by the effect of elasticity of the reed (Drop-Out) i.e. the circuit is opened.

The sensitivity of a reed switch is a measurement of the magnetic energy required to
Operate the switch. The unit of measurement is Ampere-Turn (AT), which is the current in a given coil, multiplied the number of turns on the coil.

There are 30 different types of reed that include: General application, high power, high insulation resistance, low thermal emf, form C and mercury wetted.

Reed Switches, find application in vast areas like position sensing in doors; cell phones; satellite dishes, radio transmitters; microphones, automatic test equipments; copiers; scanners; appliances; security sensors; electronic ener