A Brief History of the Reed Switch

A reed switch is an electrical relay operated by an applied magnetic field. While it may just look like a piece of glass with leads protruding from it, it is an intensely engineered device that works in amazing ways with customization methods employed for their use in many applications. Nearly all reed switches work on the premise of an attractive force: an opposite polarity develops across a normally open contact. When the magnetism is sufficient, this force overcomes the stiffness of the reed blades, and the contact pulls together.

This idea was originally conceived in 1922 by a Russian professor, V. Kovalenkov. However, the reed switch was patented in 1936 by W. B. Ellwood at Bell Telephone Laboratories in America. The first production lot “Reed Switches” hit the market in 1940 and in the late 1950s, the creation of quasi-electronic exchanges with a speech channel based on reed switch technology was launched. In 1963 Bell Company released its own version – an ESS-1 type designed for intercity exchange. By 1977, about 1,000 electronic exchanges of this type were in operation across the U.S.A. Today, reed switch technology is used in everything from aeronautical sensors to automatic cabinetry lighting.

From industrial control recognition, all the way down to neighbor Mike just wanting a security light to come on at night to tell him when someone is too close to home, there are many ways to utilize these switches and sensors. All that’s needed is a spark of ingenuity to understand how the most common everyday tasks can be made better with a switch or sensing device.

The unique attributes of a reed switch makes them a unique solution for an array of challenges. Because there is no mechanical wear, operation speeds are higher and durability is optimized. Their potential sensitivity allows reed switch sensors to be embedded deeply within assembly while still being activated by a discreet magnet. There is no voltage required because it is magnetically activated. Moreover, the functional attributes of reed switches make them ideal for difficult atmospheres, such as shock and vibration environments. These attributes include non-contact activation, hermetically sealed contacts, simple circuitry, and that the activating magnetism moves right through non-ferrous materials. These advantages make reed switches perfect for dirty and difficult applications. This includes use in aerospace sensors and medical sensors that require highly sensitive technology.

In 2014, HSI Sensing developed the first new reed switch technology in over 50 years: a true form B switch. It is not a modified SPDT form C switch, and it is not a magnetically biased SPST form A switch. Through end-to-end engineering, it features uniquely designed reed blades that ingeniously develop a like polarity in the presence of an externally applied magnetic field. When the magnetic field is of sufficient strength the repelling force developed in the contact area pushes the two reed members away from each other, thus breaking the contact. With the removal of the magnetic field, their natural mechanical bias restores the normally closed contact. This is the first truly innovative development in reed switch technology in decades!

To date, HSI Sensing continues to be the industry experts in solving problems for customers in challenging reed switch design applications. HSI Sensing also provides precision manufacturing solutions to customers who demand consistent, unmatched quality.