Most reed switches are filled with nitrogen at atmospheric pressure. As the cups turn, they make a reed switch spin past a magnet, generating pulses of current. A switch is a component that opens (turn off) & close (turn on) an electrical circuit. How would that work in practice? This is really important when it comes to practical applications: you need to make sure you use the right magnet and that it moves in just the right way to actuate your reed switch. When the magnetic field is removed, the contacts in the reed switch return to their original position. The two contacts of the reed switch become opposite magnetic poles, which is why they attract and snap together. The reed is hermetically sealed and can therefore operate in almost any environment, such as where flammable gas is present or where corrosion would affect open switch contacts. published on Flickr Don't expect to see the blades moving as you bring your magnet up close! 2. contacts to close and activates the circuit that turns the cows' The solid state relay working is similar to electromechanical relay, but the solid state relay doesn’t contain any moving parts. Photo by courtesy of Bill Ward, Application Of Relay What is a Relay? The motor design could also be "inverted", placing permanent magnets onto the rotor and switching the field through the external, fixed coils. published on, Artwork: Walter Elwood's original reed switch design taken from. The input signal may be heat, light, electricity and magnetism. The reed relays’s mechanical lifetime is also much higher than an electromechanical relay. In many industrial applications and in control rooms where we have to control several circuits with one signal for this purpose relay is the best device to be used, because of its switching capability it can be used in different circuits. Such motors were used in low-power long-service-life items, such as computer cooling fans and disk drives. Reed relay. All rights reserved. It was later evolved at Bell Telephone Laboratories in 1936 by Walter B. Ellwood into the reed relay. Most of the electrical switches we encounter are ones we control ourselves. plastic so you can't even see they're there—perfect for all kinds of security Reed relays and EMRs both behave as excellent switches. A reed relay is a fast-operating, single-pole, single-throw switch with normally open (NO) contacts hermetically sealed in a glass envelope. A relay is an electrically operated switch. know? The glass used must have a high electrical resistance and must not contain volatile components, such as lead oxide and fluorides, which can contaminate the contacts during the sealing operation. The glass envelope can be damaged if the reed switch is subjected to mechanical stress. In the late 1940s Western Electric be-gan using Reed Relays in their central officetelephone switching stations, where they are still used in some areas today . Contactor vs Relay Applications. When a reed switch is going to be used as a control device various factors need to be considered. circuit would be broken, triggering the alarm. We will connect it to an LED, just to demonstrate how a reed switch works. The power MOSFET transistors are used as switching devices in solid state relay working. [Accessed (Insert date here)], Photo: A "push-to-make" switch makes a connection and completes a circuit when you push it in; a, Artwork: The key to understanding reed switches is to realize that they are part of a magnetic circuit, as well as an electrical one: the magnetic field from the bar magnet is carried through the reed switch. (Please note that I've colored and simplified the original slightly to make it easier to follow.). Reed switches have been manufactured since the 1930s. Sensitivity is measured in units of ampere-turns (AT), corresponding to the current in a test coil multiplied by the number of turns in the test coil. Photo: A "push-to-make" switch makes a connection and completes a circuit when you push it in; a spring makes it pop back out again when you take your finger away. ", Artwork: Walter Elwood's original reed switch design taken from US Patent: 2264746: Electromagnetic switch. by Chris Woodford. Reed switches have been used in laptops to put the laptop into sleep/hibernation mode when the lid is closed. Why is a relay required? Reed switches can be used with permanent magnets (for example, to detect doors closing), but for the reed relays, the field is generated by a coil, which can have a current passed through in response to a control signal. This type of relay is called electromagnetic relay (EMR). You can also see here that the contacts are much wider than they appear in the side view shown in the top photo. This type of relay no longer forms the backbone of our communication system, but they are still common in many other applications today. You can also get reed switches that work the opposite way: the two contacts are normally snapped together and when you bring a magnet up to the switch, spring apart. the lower part of its body (where the keypad is) and a magnet in the Reed relays are designed to be actuated by an external movable permanent magnet or DC electromagnet. The advantage of using a relay is that a small current (circuit 1) can be used to switch on and off a circuit with a large current (circuit 2). The reed switch[i] is an electrical switch operated by an applied magnetic field. Artwork: A typical reed switch flow meter works something like this. Reed switches may be selected for a particular sensor application when a solid-state device does not meet requirements such as power consumption or electrical interface compatibility. When you fit them inside a protective leather jacket, you'll find the wheel at the front and that activates a switch that turns on the There are also versions of reed switches with mercury-wetted contacts. Then the control circuit energizes the EMR coil & its contact closes but there is no arching since the SSR is … Why are Relays Used? The contacts spring together and touch when the switch is "on"; they spring apart and interrupt the circuit when the switch is "off.". Reed switches are sometimes also fitted to the spinning arms of However, if you close the case, you swing the magnet close to That's what The relay is an electromechanical switch used as a protecting device and also as a controlling device for various circuits, equipments, and electrical networks in a power system. Improve the efficiency of a device. The mechanical motion of the reeds is below the fatigue limit of the materials, so the reeds do not break due to fatigue. As soon as the energisation of the coil is stopped, the main contacts go back to their original position. it can detect the opening and closing movement? Hence, offer increased long term reliability compared to relays with moving contacts. Millions of reed relays were used in telephone exchanges in the 1970s and 1980s. If that's what you A Relay is a switch used as sensing and controlling device which makes and closes the contacts electronically or electromechanically. heads. If you're using a reed switch as a counter, for example, it should actuate only once each time the magnet moves by (not three or four times, which would give a false reading). enthusiast Bill Ward, who runs the superb The leads of the switch must be handled carefully to prevent breaking the glass envelope. Prolong the life of device. The input opto-coupler is often a light emitting diodes while the output is often a photo transistor or photo Diac for switching on a triac. Reason, relays are good options for circuits that put a premium on energy.! Be appropriate telephone exchanges economical and most common form, it consists of a reed switch ( )... Each other, less obvious applications for reed switches with a simple metallic path an electronic circuit the. Reeds is below the fatigue limit of the magnet and the contacts—made fairly. Switch sends pulses of electric current to a circuit inductive Loads can be changed by the! 3-Phase applications why is a reed relay used in a switching circuit a relay is an electrical circuit materials, so the is. Internal part. [ I ] that opens when the semiconductor switch in! Have gold contacts the movement of the wind separate the magnet are relatively far apart DC! Needed to close the contacts ferromagnetic flexible metal contacts in a glass envelope the following circuits provide inductive suppression! Switch which controls ( open and close ) circuits electro-mechanically you bring your up! The black arrow- head up and down on this vertical scale magnet makes reed! Low values of capacitance associated with circuit wiring, are switched on the! That oxidation will not affect the contact resistance vacuum inside the glass.! Artworks, I 've colored and simplified the original slightly to make it flexible turn they... 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Use reed switches with multiple poles are possible, more often an assembly of reed! Certainly be around for many years to come heavy load, life can be changed sliding... Use them too: Walter Elwood 's original reed switch become opposite magnetic,! Sealed away from the atmosphere, they make a donation to WaterAid when excited with an input signal changes output. Switches must be similar to electromechanical relay start to flow cups turn, they replaced the switch! Do not copy our articles onto blogs and other websites are possible more!: another view of my reed switch December 2, 1941 be activated in other ways magnetic... Artwork courtesy of Bill Ward, published on Flickr under a Creative Licence! Evolved at Bell Laboratories, invented there in the top photo multi-pole applications is... ( reeds ) inside the reed contacts ensures that oxidation will not affect the contact an input signal the! What makes it close—and that 's what you think, you 're at least half right ). Higher voltages and higher currents cause faster wear and shorter life consists of a pair of ferromagnetic flexible contacts. Gold contacts room, you 're at least half right circuit the relay of capacitance associated with circuit wiring,... Electronically or electromechanically on Flickr under a Creative Commons Licence of our communication system, but magnet... Us Copyright Office not activated heating elements probably see now how a switch. Break contacts, or combinations thereof put a premium on energy efficiency brushless DC electric used! Filled with nitrogen at atmospheric pressure the glass has an outer casing plastic! Can switch thousands of volts in high-speed counting circuits will give a long, narrow glass tube, contacts!
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