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A measurement is taken when the current passed through the coils is sufficient to actuate the switch providing the ampere-turns rating for each and every switch. As an electric current is passed through the coiled wire, it creates a magnetic field. When a reed switch is manufactured, it is placed within a test coil with a specific number of turns of wire. The sensitivity of a reed switch is rated based on the magnetomotive force measured in the ampere-turns (AT) required to pull in or release the contact points. Although you can’t see the lines of magnetism, it is known that they flow from north to south along the shortest route without ever crossing each other, as seen by the bar magnet representation below.Įach reed switch has a number of ‘active’ regions surrounding it, sometimes referred to as lobes, the size of which varies depending on the sensitivity of the switch. Understanding how a magnet will influence a reed switch requires an appreciation of how a magnet’s magnetic field is formed. When selecting a magnet for a reed switch application there are several main factors to consider shape of magnet, magnet strength, switch sensitivity, distance and angle between magnet and switch. However, ferrite magnets, although much weaker, are popular because of the deep magnetic field that they produce. Neodymium magnets are the strongest type of magnets commercially available, and therefore even tiny magnets can be effective. Any permanent magnet will work with a reed switch but it is important to remember that different materials have different strengths and different sized magnets produce different sized magnetic fields. The wider the distance between switch and magnet, the stronger the magnet will need to be to interact with the switch. Because a reed switch can be hidden or embedded within an assembly and still operated by a magnet, the distance between the magnet and the switch is all important. The size and type of magnet required depends entirely on the type of reed switch and how the reed switch is built into an assembly. Without a magnet, a reed switch is redundant but introduce a magnetic field to the reed switch and the switch will spring into action. What type of magnets are used with reed switches?
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There is a third configuration that has three contact points, rather than two. When a magnet is moved close to a switch, or the switch close to a magnet, the reeds repel one another and split apart, breaking the circuit.
#Switch orientation principle app full#
Remove the magnet and the reeds return to their original position breaking the circuit.Ī normally closed switch works in the opposite way, when no magnetic field is present the reeds are in full contact, the electric circuit is complete and the device is ‘on’. When a magnet is moved close to the switch, it pulls one of the reeds towards the other so that they are touching, and therefore completing the circuit. In a normally open switch, the two reeds, which are made from ferrous material such as a nickel-iron alloy are positioned so that they are not touching. There are two fundamental types, ‘normally open’ and ‘normally closed’. Unlike mechanical switches they do not require something or someone to physically flick them on or off, they are controlled completely by invisible magnetic fields! Types of reed switch The switch effectively works like a gate, or a bridge, in an electric circuit so when the two reeds are in contact, electricity can flow around the circuit operating a device. They are made from two or more ferrous reeds encased within a small glass tube-like envelope, which become magnetised and move together or separate when a magnetic field is moved towards the switch. A reed switch is an electromagnetic switch used to control the flow of electricity in a circuit.