Reed Switch

Operational Characteristic

The Reed Switch was first invented by Bell Labs in the late 1930s.  However, it was not until the 1940s when it began to find application widely as a sensor and a Reed Relay.  Here it was used in an assortment of stepping/switching applications, early electronic equipment and test equipment.  In the late 1940s Western Electric began using Reed Relays in their central office telephone switching stations, where they are still used in some areas today.

The Reed Switch greatly contributed to the development of telecommunications technology.
Over the years several manufacturers have come and gone, some staying longer than they should have,  tainting the marketplace with poor quality, and poor reliability. 
However, most of the manufacturers of Reed Switches today produce very high quality and very reliable switches.  This has given rise to unprecedented  growth.

Today Reed Switch technology is used in all market segments including: test and measurement equipment, medical electronics, Telecom, automotive, security, appliances, general purpose, etc. Its growth rate is stronger than ever, where the world output cannot stay abreast with demand.

As a technology, the Reed Switch is unique. Being hermetically sealed, it can exist or be used in almost any environment.  Very simple in its structure, it crosses many technologies in its manufacture.  Critical to its quality and reliability is its glass to metal hermetic seal, where the glass and metal used must have exact linear thermal coefficients of expansion.  Otherwise, cracking and poor seals will result. Whether sputtered or plated, the process of applying the contact material, usually Rhodium or Ruthenium, must be carried out precisely in ultra clean environments similar to semiconductor technology.  Like semiconductors, any foreign particles

present in the manufacture will give rise to losses, quality and reliability problems. 

Over the years, the Reed Switch has shrunk in size from approximately 50 mm (2 inches) to 6 mm (0.24 inches).  These smaller sizes have opened up many more applications particularly in RF and fast time domain requirements.

Form A = normally open contact (N. O.)
Form B = normally closed contact (N.C.)
Form C = change over contact (S.P.D.T.)
Form E = Bistable / Latching
AT = Ampere Turns; Parameter that describes magnetic sensitivity.