IEN: How can manufacturers use existing technologies in new ways?
Lanphier: Reed switches, or magnetic proximity sensors, were originally developed for telephone relay applications. Today, they are ideal for supplying high-speed digital input into microprocessors like counters, PLCs, and position sensors. Reed switches have high speed switching capabilities up to 1,000 Hz. We are finding that customers are taking a new look at reed switch technology because of the high reliability, versatility, and low cost the technology offers.
How a reed switch operates: The operation of a reed switch consists of two low reluctance flexible contacts, referred to as "reeds," positioned so the ends align and overlap, but do not touch. The reeds are then hermetically sealed in an inert gas atmosphere within a glass tube. While the reed switch is exposed to an external magnetic field, poles of opposite polarity are created, and the contacts close when the magnetic force exceeds the spring rate of the reeds. As the magnetic field is reduced to a point where the force between the reeds is less than the spring rate, they open. When the magnetic field causes the contacts to open or close, an electrical circuit will be broken or completed.
Since a magnetic field operates the switch, the position and settings are held even during a power failure with no resetting necessary. Another unique characteristic of a reed switch, because it consumes no power, is that it controls the circuit without changing the circuit''s electrical characteristics.
Used as safety interlocks: Reed switches make products and equipment safer by providing safety interlocks, current indicators, flow control and position verification of an object. Have you ever been on a train and wondered, "How does the train know that all the doors are closed prior to leaving the station?" You have guessed it there is a magnetic actuator mounted on the train door and a reed switch mounted on the doorframe. When the door is closed the switch is closed by the magnetic field, completing the circuit, and the train knows it can leave the station.
Advantages of a reed switch: Everyone is looking to save time and money in designing, manufacturing and supporting their products. The advantages of reed switches are repeatable operation for millions of cycles with no adjustments or maintenance required, making them very consumer friendly, and OEMs like the versatility of one switch covering a wide range of voltages. The compact size, various mounting methods, and low cost make it easy for design engineers to design the switch into a whole host of products. Reed switches are used in a multitude of industries requiring open and closed circuits to control safety interlocks, counting devices, limit controls, and to monitor the position or speed of an object. Both simple and complex mechanisms can incorporate reed switches.