![]() With the window open-or if someone cuts the wire-an alarm will sound. A movable window or door houses a magnet, and the sensor resides on the base, passing a signal until the magnet’s removal. In fact, alarms are a nearly perfect application for this technology. You’ll find sensors in everyday items like cars and washing machines, but one of the most prominent places these switch/sensors operate is in burglar alarms. Sealing isolates the contacts, which prevents corrosion and any sparks that might result from contact movement.įigure 1: NO reed switch Reed Switch Applications in the Real World A glass envelope filled with inert gas-commonly nitrogen- seals the contacts at an internal pressure under one atmosphere. ![]() Some varieties even use mercury, which must be kept in the proper orientation to switch correctly. An approaching magnet will disconnect the contact and pull away from the switching contact.Ĭontacts are constructed from a variety of metals, including tungsten and rhodium. Some reed switches also contain a non-ferromagnetic contact, which forms a normally closed (NC) output. Once touching, the blades close the normally open (NO) contacts, allowing electricity to flow. When a magnet approaches these blades, the two blades pull toward one another. The switching mechanism is comprised of two ferromagnetic blades, separated by only a few microns. The switch looks like a small glass capsule with electrical leads poking out of each end. Ellwood at Bell Telephone Laboratories, and it earned its patent in 1941.
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