Reed Sensors


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Reed Sensors find widespread use in detecting proximity and movement, liquid flow and the presence of metals. They are used in burglar alarms to detect opening of a door, in laptops to trigger the sleep mode when the lid is closed, in tailpipes of automobiles to trigger a fuel mix adjustment when emission levels are high, to stop the motor of a washing machine if the lid is opened by accident, and in many other applications. This widespread acceptability is due to their inherent advantages, such as not requiring electrical power to operate, ability to switch extreme loads without requiring amplification circuits, immunity to electrostatic discharge, and the ability to sense a wide range of distance. The reed switch, the major component of the reed sensor, comes in a hermetically sealed glass enclosure, making it safe to use in all conditions, between -50C and 200C, even in very humid and explosive environments. The reed switch includes a pair of ferrous metal reeds with contacts. When a magnetic field is applied to the switch, the reeds come together, completing an electrical circuit. When the magnetic field decreases, the reeds separate and open the circuit. The quality of the reed sensor depends on the sensitivity of the reed switch, measured by the strength of the magnetic field necessary to actuate it. Generally, the lower the AT, the more sensitive the reed switch. Reed sensor models differ in terms of switching capacity, switching voltage, switching time and type of contact.