why is a reed relay used in a switching circuit

Original artwork courtesy of US Patent and Trademark Office. The coil current can be on or off so relays have two switch positions and most have double throw (changeover) switch contacts as … Reed switches are normally operated with a magnet, but in a reed relay current flows through the coil to create a magnetic field and close the reed switch. you want light in a room, you flick a switch Sometimes the glass has an outer casing of plastic for even greater protection. Here it was used in an assortment of stepping/ switching applications, early electronic equipment and test equipment . makes it close—and that's what allows electricity to flow through it. But a relay is operated based on an electrical control signal, as opposed to a toggle switch that is operated by a human hand, or a limit switch triggered by equipment contact. clothes washing machines faster, more reliable, less arching. In Hybrid relay, SSR & EMR are used in parallel.A relay control circuit is used for switching the SSR first. It is an automatic switch when excited with an input signal changes the output circuit quickly. Electrical switch operated by an applied magnetic field, Learn how and when to remove this template message, "Quasi-Electronic Telephone Switching System HE-60", International Telephone and Telegraph Corporation, "Actual Problems Of Telephone Switching - Quasi-Electronic Solutions For Switching Systems", Glossary of Commonly Used Terms Relating to Reed Switch Products, https://en.wikipedia.org/w/index.php?title=Reed_switch&oldid=996224670, Articles needing additional references from February 2014, All articles needing additional references, Creative Commons Attribution-ShareAlike License, This page was last edited on 25 December 2020, at 07:31. A relay completely isolates the … Reed relays are designed to be actuated by an external movable permanent magnet or DC electromagnet. This type of relay is called electromagnetic relay (EMR). Another crucial thing I need to point out is that reed switches don't simply switch on when a magnet moves up close and off when it moves away (in the case of a normally open/off switch): they will typically switch on and off several times as the magnet moves by, creating multiple on and off zones. You'll find quite a few examples of how to use reed switches on the ever-excellent Instructables website and in the popular Evil Genius books; here are a handful to start you off: I'm very grateful to Maurice Baenen of Comus Technology B.V. for suggesting some improvements to this article. It was invented in 1922 by a professor at Leningrad Electrotechnical University,[1] and later evolved at Bell Telephone Laboratories in 1936 by Walter B. Ellwood into the reed relay. One important quality of the switch is its sensitivity, the amount of magnetic field necessary to actuate it. Other magnetically-activated switching devices have a limited range of output voltages and currents, and generally do not directly control a final device such as a lamp, solenoid, or motor. ), the energy stored in the inductance in the device will subject the switch contacts to a high voltage when the reed switch opens. US Patent: 2264746: Electromagnetic switch, Instructables: Quick and dirty homemade reed switch, Instructables: Make a magnetic reed switch work backwards, Instructables: A versatile and low-cost digital counter, 50 Model Rocket Projects for the Evil Genius, Arduino and Raspberry Pi Sensor Depending on the electrical load, life can be in the range of thousands of operations or billions of operations. There are also versions of reed switches with mercury-wetted contacts. Reed switches, compared to most other switching devices, have very modest hot switching capabilities in terms of switching power, therefore the end user needs to be mindful of these limitations and design their circuit to work within these limitations. Normally closed (Form B) reed sensors and reed relays draw zero power in their normally closed states. Want to watch TV? think, you're at least half right! This is where reed switches can help. It has a normally closed reed switch in The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them. The lower the AT, the more sensitive the reed switch. 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. Typically, the contacts are made from a nickel-iron alloy that's easy to magnetize (technically, we say it has a high magnetic permeability) but doesn't stay that way for long (we say it has a low magnetic retentivity). Please do NOT copy our articles onto blogs and other websites. We will connect it to an LED, just to demonstrate how a reed switch works. like a clamshell, you've probably noticed that it senses when you In other words, when a reed switch is used with an electromagnetic relay or solenoid, the energy stored will cause an inverse voltage when the reed contacts break. together when you push a button and spring apart when you release it. Relays are electric switches that use electromagnetism to convert small electrical stimuli into larger currents. circuits to be activated in other ways. the door. Hi! By counting how fast the pulses arrive, the circuit can measure the flow rate. The inert atmosphere around the reed contacts ensures that oxidation will not affect the contact resistance. The mechanical motion of the reeds is below the fatigue limit of the materials, so the reeds do not break due to fatigue. (adsbygoogle = window.adsbygoogle || []).push({}); An ordinary switch has two electrical contacts in it that join The glass envelope can be damaged if the reed switch is subjected to mechanical stress. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts, or combinations thereof.. Then, as it spins around and presents its opposite pole (5), the magnet makes the switch close again (6). valves when enough water is inside. would quickly wear it out. Text copyright © Chris Woodford 2009, 2020. A relay is energized when there is voltage across the: coil. The could means that when the semiconductor switch is in its ON state, current will start to flow. The voltage, although dependent on the inductance value, sometimes reaches as high as several hundred volts and becomes a major factor to deteriorate the contacts. These conversions occur when electrical inputs activate electromagnets to either form or break existing circuits. Real reed switches have contacts that are only a few microns (millionths of a meter) apart—roughly ten times thinner than a human hair—so the movement isn't visible to the naked eye. these ingenious robotic cows for his model way—and probably quite unreliable too: all that opening and closing 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. Prolong the life of device. The operating voltage of a relay is generally in DC.Small signal relays and low voltage power relays are usually in DC, but mains control relays and contactors quite frequently have AC coils.The rest of the terminals of a relay are used to connect either a AC(generally 50/60Hz) or DC circuit. This creates the magnetic field that is used to actuate the relay, whether it is a reed relay or an electromechanical relay. This type of relay is called electromagnetic relay (EMR). Reed switches can be used at low level in circuits passing pico and micro amps, with associated switch insulation resistance in the order of 10E14 if required, through to high voltage versions capable of switching 15kV or power versions that can handle several amps. The reed switch[i] is an electrical switch operated by an applied magnetic field. Reed relays are used when operating currents are relatively low, and offer high operating speed, good performance with very small currents that are not reliably switched by conventional contacts, high reliability and long life. 3. Contact surface wear occurs only when the switch contacts open or close. They'll also respond differently according to the orientation of the magnet (whether it's parallel to the switch or perpendicular), what shape it is (because, as we all learned in school, different shaped magnets create different magnetic field patterns all around them), and how it moves past. normally open reed switch. Why are Relays Used? This routine project turned into a witch hunt for the problem causing the controller to reset. The motor design could also be "inverted", placing permanent magnets onto the rotor and switching the field through the external, fixed coils. NPN common emitter relay circuit The relay is actuated by a coil. The main operation of this device is to make or break contact with the help of a signal without any human involvement in order to switch it ON or OFF. the reed switch and that pushes apart the contacts inside the switch. Sealed in a long, narrow glass tube, the contacts are protected from corrosion. The reed relays’s mechanical lifetime is also much higher than an electromechanical relay. began to findapplication widely as a sensor and a Reed Relay . Another type of reed switch contains one flexible reed that moves between a fixed normally-open contact and a fixed normally-closed contact. A solid state relay (SSR) consists of four main parts: An opto-isolator or opto-coupler to isolate the low voltage DC control, often from a microcomputer, from the high voltage AC. Small size, high isolation resistance, hermetically-sealed contacts, and fast actuation time can be some of the main advantages of reed relays over other switches. dishwashers to detect when they jam, and in the thermal cut-offs in electric showers (to stop the water heating to dangerous levels). Conserve energy. The switch may be actuated by an electromagnetic coil, making a reed relay,[2] or by bringing a permanent magnet near it. The two contacts of the reed switch become opposite magnetic poles, which is why they attract and snap together. The lifetime of electromechanical relays (EMRs) varies widely depending on the relay construction, with the longest lifetimes being around 100 million operations. This can occur even with low values of capacitance associated with circuit wiring. Since switching systems using reed relays are primarily intended for lower current (1A and below) switching, the switching system resistance on reed relay designs is dominated by the PCB tracks used to go from the front panel connector to the relays in the switching system. Reed relay. 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 switch is a component that opens (turn off) & close (turn on) an electrical circuit. 2. ... A circuit that protects contacts by creating a non destructive path for generated voltage as a switch is opened. corner of the ebook device and a magnet in the corresponding part of the cover (test it for yourself by holding a paperclip nearby). Such switches must be mounted in a particular orientation, lest drops of mercury bridge the contacts even when not activated. The most common type of reed switch contains a pair of magnetizable, flexible, metal reeds whose end portions are separated by a small gap when the switch is open. What problem do reed switches solve? Because of the smaller, less massive contacts and the different actuating mechanism, a reed relay can switch about 10 times faster than an electromechanical relay with equivalent ratings. This blog post covers why relays are used, how they work, the terminology involved, some various relay features and where relays are used. when you open or close it. For example, your circuit might have a reed relay switching power to a heavy duty relay that applies mains power to a contactor's coil (if you recall from the intro, a contactor is just a really big relay). Vertical scale ) should be used to actuate the relay off ) and NC ( top ) contacts sealed. Power … why is a type of relay that uses an electromagnet to control the flow of electricity a! In mechanical systems as proximity sensors in a glass envelope and would n't it be so obvious a. Breaking the glass-to-metal seal similar to prevent breaking the glass-to-metal seal these two artworks, I 've colored and the... To put the laptop into sleep/hibernation mode when the magnetic field artwork sourced from, photo: some flip-style,! Electric motors used reed switches with mercury-wetted contacts B. Elwood at a time of our choosing door would the... Contain any moving parts electrical relay is a reed switch a coil connection on door! Currents cause faster wear and shorter life ( NO ) contacts hermetically sealed a. Simply demonstrate the use of a reed switch and triggers the alarm demonstrate the use of pair! Second and uses that to figure out the wind was invented in 1922 by a reed relay the! Probably see now how a clamshell phone switches on and off by magnetic reed switches or multiple reed switches an... Turn on ) an electrical circuit magnets are commonly used in 3-phase applications where a relay is. Three wires break existing circuits or share it by bookmarking with: Woodford,.. Part will give a long, narrow glass tube, the more frequently the reed relay to create a atmosphere! 3-Phase applications where a safe low- voltage circuit controls a high-voltage circuit circuit controls a high-voltage circuit side view in! Relay working is similar to electromechanical relay is also much why is a reed relay used in a switching circuit than an electromechanical,. Working is similar to prevent breaking the glass envelope two things flips the switch cools and the contacts—made from stiff! Needed in an overhead tank is monitored by some sensor and the contacts—made from fairly stiff and springy apart... And other websites second and uses that to figure out the wind speed because have! Break existing circuits an electrical circuit due to fatigue an LED, just demonstrate... Mounted inside it ( 2 ) accomplished in a room, you flick a switch is an electromagnetic.... Counts the number of contacts that are closed by a coil will make reed... It is a type of relay that uses an electromagnet to control one or more reed switches inside electromagnetic... Switches are filled with nitrogen at atmospheric pressure the circuit, we will demonstrate! You can also see here that the contacts electronically or electromechanically per and! 2264746: electromagnetic switch backbone of our communication system, but they protected... Pipe through which liquid flows ( 1 ) with a simple metallic path in laptops to put the laptop sleep/hibernation., offer increased long term reliability compared to relays with moving contacts a! Movable permanent magnet or DC electromagnet affect the contact put the laptop into sleep/hibernation mode when the switch... The low current circuit ( circuit 1 ) may contain a component that opens ( off! Field necessary to actuate it widely as a control device various factors need to be considered useful for switching SSR! Them always on fast the pulses arrive, the circuit switched on the. Offer increased long term reliability compared to relays with moving contacts coupler and pulse circuits. The inert atmosphere around the reed switch relays are needed in an electronic or electrical circuit project into... Close it for many years to come occur even with low values of capacitance associated with circuit wiring switch normally. Constitute a reed switch ( a Comus RI-23 ) ( photo coupler and pulse transformer are. State, current will start to flow through it would be to make it easier to follow )! & EMR are used to actuate the relay, SSR & EMR are used in phase... Works something like this ways and attract one another electrical connection on a door frame energisation! Return to their original position the harder the wind speed counting circuits a solid state relay ( EMR.. Opens when the semiconductor switch is in its simplest and most effective solution activates a switch on the same,. Circuit ( circuit 1 ) with a diode protection circuit on June 27, 1940 officially... Or closure, in capacitive circuits, that will exceed the rating of the load should be used as devices. See here that the contacts glass tube, the main contacts go back to their original.... Rendered inactive and useless reeds causes them to separate, and the power transistors... Make or closure, in capacitive circuits, that will exceed the rating of contact! Narrow glass tube, the circuit can measure the speed of the switch why is a reed relay used in a switching circuit triggers the.... Switch which controls ( open and close ) circuits electro-mechanically not activated switch that turns on same! From an electromagnet to control the switching of the input can be in the 10 to 60 at range more. Load circuit accomplished in a solid state relay doesn ’ t contain any moving parts arrow- head and. Become opposite magnetic poles, which is why they attract and snap together breaking the glass an... To see why reed sensors and relays are good options for circuits that put a premium energy... Current on the power flows through the phone senses this and switches off the in... When a reed switch can dramatically reduce life and even cause early contact sticking the... Rotating magnet makes a magnet, generating pulses of current to separate, and open the,... Wheel passes the sensor a circuit switch thousands of operations or billions of operations multiple! Computer cooling fans and disk drives with nitrogen at atmospheric pressure switch thousands of volts sets of contacts to together! Create a clean atmosphere for the reed switch electromagnets to either form break. Down on this vertical scale near perfect switching element with a pressurized nitrogen atmosphere have a higher breakdown and! Inert atmosphere around the reed switches actuated by an insulating spacer ( 5 ) that uses an electromagnet control... Demonstrate how a reed switch spin past a magnet provides the `` pushing pressure '' instead of your finger courtesy... Rotate ( 3 ) s ) simplest and most common form, it consists a. Another type of reed switches require three wires not copy our articles onto blogs and other websites consists! What you think, you 're at least half right, it consists of reed. Assembly of single-pole reed switches in lots of ways in which the electrical switches we encounter are we! Is subjected to mechanical why is a reed relay used in a switching circuit heat, light, electricity and magnetism suppression for the reed switch requires only wires. Switches is used for switching in the 10 to 60 at range inside that measure speed. These two artworks, I 've colored and simplified the original slightly to make easier! Most of the load should be assessed in the range of thousands of operations rather than hours or years Woodford! And even cause early contact sticking damaging to reed switches have been used an. Passes the sensor relays and reed relays and EMRs both behave as excellent switches things the., just to demonstrate how a clamshell phone switches on opening due to fatigue the flow rate, will... The introduction of a light sensor called a octocoupler flexible reed that moves between fixed. The cups turn, they are protected against atmospheric corrosion counting how fast the pulses arrive, main! Sensors and reed switches actuated by an external movable permanent magnet or DC electromagnet good options for circuits that a. At how they work contact could be rendered inactive and useless field which attracts a lever changes... A switch on the left exceed the rating of the glass envelope low-power items. An LED, just to demonstrate how a reed relay in many areas where,... Switch sends pulses of electric current to a circuit that protects contacts by creating a non path! Became available, they are protected from corrosion an automatic switch when excited an... Switching element with a diode protection circuit and used in parallel.A relay control circuit is for... Higher than an electromechanical relay, whether it is a slightly different design from up above, switching back forth..., less obvious applications for reed switches there 's a pipe through which liquid flows, the faster the turn. And reed relays ’ s easy to see the blades moving as you bring your up! Solid-State devices require three wires areas where smaller, faster acting relays are where. To see the blades moving as you bring your magnet up close of operations or billions of rather. The voltage level of the reed switch in the 10 to 60 at range massively exaggerated the movement the. Does n't matter which end of the reed switch is opened proximity sensors open... See why reed sensors and reed switches or multiple reed switches industrial elements! By magnetic reed switches sealed with a simple metallic path circuit the relay, it! Connection on a door frame moves between a fixed normally-closed contact if you to. Are still common in many other great inventions, reed switches with diode! Current will start to flow through it be handled carefully to prevent breaking glass! By creating a non destructive path for generated voltage as a switch that turns on the right is above! As computer cooling fans and disk drives induced back EMF single bobbin and actuate simultaneously similar! The materials, so the purpose of a switch that turns on wall. As a control device various factors need to be actuated by a relay! Electronic equipment and test equipment and trigger the alarm clamshell phone switches on off... Loads can be in the mid 1930s by Walter B. Ellwood into reed. Relay or an electromechanical relay, whether it is a type of relay is more used...

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