NPN common emitter relay circuit The relay is actuated by a coil. Reed relays are particularly effective for low voltage switching because their contacts are hermetically sealed in glass, and contaminating films cannot build up on the contacts. 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 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 is an electrical switch operated by an applied magnetic field was invented in 1922 by a professor at Leningrad Electrotechnical University . Reed relay-based switching systems are commonly used in test and measurement applications. Brickpile blog 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. (adsbygoogle = window.adsbygoogle || []).push({}); An ordinary switch has two electrical contacts in it that join ... A circuit that protects contacts by creating a non destructive path for generated voltage as a switch is opened. This was despite the fact that I used every relay with a diode protection circuit. Reed relay-based switching systems are commonly used in test and measurement applications. Contactor vs Relay Applications. The could means that when the semiconductor switch is in its ON state, current will start to flow. If you've got a laptop computer Since the contacts of the reed switch are sealed away from the atmosphere, they are protected against atmospheric corrosion. [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. Because of this, manufacturers rate life in number of operations rather than hours or years. Artwork: A typical reed switch flow meter works something like this. Where switch-off time is particularly critical, controlled avalanche MOSFETs might be appropriate. think, you're at least half right! Improve the efficiency of a device. The voltage level of the input can be changed by sliding the black arrow- head up and down on this vertical scale. A reed switch like this is normally open (NO) (normally off), unless a magnet is positioned right next to it, when it switches on, allowing a current to flow through it. Copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties. If the load is slightly inductive (such as a small relay, solenoid or contactor), or if long cable runs are to be used, consideration should be given to employing measures useless. This is a slightly different design from up above, switching back and forth between two different circuits with one of them always on. and How does a Relay works! They may also be used to control diving equipment, such as flashlights or cameras, which must be sealed to keep water out under high pressure. A Relay is a switch used as sensing and controlling device which makes and closes the contacts electronically or electromechanically. The circuit powering the coil is separate from the circuit switched on by the relay. the alarm. As the cups turn, they make a reed switch spin past a magnet, generating pulses of current. The rotating magnet makes a reed switch open (4). Reed switches like this are called normally closed (NC) (normally switched on), so electricity flows through them most of the time. Another configuration contains a non-ferromagnetic normally-closed contact that opens when the ferromagnetic normally-open contact closes. Applications of relays. As you bring a magnet up to the reed switch, the entire switch effectively becomes a part of a "magnetic circuit" that includes the magnet (the dotted line in the artwork shows part of the magnetic field). A reed switch phone senses this and switches off the power in an orderly way. Think about it more carefully and This was despite the fact that I used every relay with a diode protection circuit. Intruder alarms and The switch may be actuated by an electromagnetic coil, making a reed relay,[2] or by bringing a permanent magnet near it. If the current stops altogether or flows all the time, you know the fluid has stopped moving, possibly indicating a jam or a blockage. There's a pipe through which liquid flows (1) with a paddle wheel mounted inside it (2). Contactor vs Relay Applications. the wheel at the front and that activates a switch that turns on the Then, as it spins around and presents its opposite pole (5), the magnet makes the switch close again (6). Rocker switches on wall lights (like the one in the photo up above) push the two contacts together when 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. Apart from switching a circuit with heavy load, on & off, a relay is required to. Prolong the life of device. Reed relay. 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. This avoided the need for any rubbing contact to provide power to the rotor. contacts to close and activates the circuit that turns the cows' We will connect it to an LED, just to demonstrate how a reed switch works. ... A circuit that protects contacts by creating a non destructive path for generated voltage as a switch is opened. We will connect it to an LED, just to demonstrate how a reed switch works. In high voltage capacitive charging and discharging circuits a reed relay can be used provided that the switching voltage is not exceeded and the load RC time constant is kept to … Although most reed switches have two ferromagnetic contacts, some have one contact that's ferromagnetic and one that's non-magnetic, while some (like the original Elwood reed switch illustrated at the bottom of this article) have three. The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them. railroad. ... What is used in a reed relay to create a clean atmosphere for the contacts? In this circuit, we will simply demonstrate the use of a reed switch by placing it in a very basic circuit. So it eliminates the arching problem. The humidity controller was connected to external mechanical relays that controlled industrial heating elements. The contacts are usually normally open, closing when a magnetic field is present, or they may be normally closed and open when a magnetic field is applied. by Chris Woodford. Reed relays are designed to be actuated by an external movable permanent magnet or DC electromagnet. But think how tricky This type of relay is called electromagnetic relay (EMR). A switch is a component that opens (turn off) & close (turn on) an electrical circuit. A common example of a reed switch application is to detect the opening of a door or windows, when used as a proximity switch for a security alarm. faster, more reliable, less arching. ", Artwork: Walter Elwood's original reed switch design taken from US Patent: 2264746: Electromagnetic switch. Mercury-wetted reed relays are sometimes used, especially in high-speed counting circuits. Explain reed relay operation and applications. makes it close—and that's what allows electricity to flow through it. A reed relay in many ways is a near perfect switching element with a simple metallic path. One important quality of the switch is its sensitivity, the amount of magnetic field necessary to actuate it. In its simplest and most common form, it consists of a pair of ferromagnetic flexible metal contacts in a hermetically sealed glass envelope. 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 Reed relays will certainly be around for many years to come. When a reed switch or reed sensor is used to control an inductive device (relay coil, solenoid, transformer, small motor, etc. When the switch is closed, the "bridge" is down and electric current can Explain reed relay operation and applications. you'll see a standard switch would be quite tricky to wire up in that know? valves when enough water is inside. It is mainly used … It was later evolved at Bell Telephone Laboratories in 1936 by Walter B. Ellwood into the reed relay. 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. Why is a relay required? (Photo coupler and pulse transformer circuits are complicated.) the lower part of its body (where the keypad is) and a magnet in the Reed relays are small and fast acting; they require a much lower level of power to actuate them than other traditional types of relay and as a result they find many uses in various forms of electronic circuits. Reed relays and reed switches are used in many areas where smaller, faster acting relays are needed in an electronic or electrical circuit. A thin layer of non-ferromagnetic material is applied to the reed switch contact area to serve as an electrical contact switching (wear) surface and, for normally-open contacts, as a magnetic spacer whose thickness is important in controlling the magnetic field level at which the contact opens (the drop-out). In this circuit, normally open reed switches will be used so that the load powers on only when a magnet is in its vicinity. they switch off automatically when you close the cover—and switch on again Examples are door and window sensors in burglar alarm systems and tamperproofing methods. disadvantages of a reed relay. Although reed switches with multiple poles are possible, more often an assembly of single-pole reed switches is used for multi-pole applications. This type of relay no longer forms the backbone of our communication system, but they are still common in many other applications today. small electric motor that's connected to a circuit in which there's a together when you push a button and spring apart when you release it. Applications of relays. Depending on the electrical load, life can be in the range of thousands of operations or billions of operations. 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. listen to your iPod? Then the control circuit energizes the EMR coil & its contact closes but there is no arching since the SSR is … This routine project turned into a witch hunt for the problem causing the controller to reset. This can occur even with low values of capacitance associated with circuit wiring. Reed switch contacts are typically rhodium, ruthenium, iridium, or tungsten. Reading through Elwood's patent, it's very easy to recognize the reed switch that's still in common use today: "When an external magnetic force is applied to this unit the two magnetic members which form part of the magnetic circuit... are moved together... since the external magnetic force acts to diminish the air-gap between the two said magnetic elements. Figure 2: Reed switch with both NO (bottom) and NC (top) contacts. corner of the ebook device and a magnet in the corresponding part of the cover (test it for yourself by holding a paperclip nearby). 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. Original artwork courtesy of US Patent and Trademark Office. Relay is also used as a protective device which sense the fault signal and sends to the circuit breaker which make decision to make or break the circuit based on the provided information by the relay. the door. There's a magnet in one part of the case and a reed switch in the other. A magnetic field from an electromagnet or a permanent magnet will cause the reeds to attract each other, thus completing an electrical circuit. As the liquid flows, the paddle spins and makes a magnet rotate (3). They take some time to respond to changes in the magnetic field (we say they have quite a bit of hysteresis)—in other words, they move quite slowly and smoothly. nearby. under a Creative Commons Licence. For this reason, relays are used where a safe low- voltage circuit controls a high-voltage circuit. 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. The contacts spring together and touch when the switch is "on"; they spring apart and interrupt the circuit when the switch is "off.". advantages of A reed relay. A reed switch is an electromagnetic switch used to control the flow of electricity in a circuit. train track and a little magnet is fitted to the side of the train. The could means that when the semiconductor switch is in its ON state, current will start to flow. However, if you close the case, you swing the magnet close to Reed switches with a vacuum inside the glass envelope can switch thousands of volts. The "reed" is the metal part inside the reed switch envelope that is relatively thin and wide to make it flexible. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts, or combinations thereof.. Suppose you want to wire up a bank safe so it An electronic circuit counts the number of pulses per second and uses that to figure out the wind speed. current carrying capabilities of the reed relay are limited. Separating the two things flips the switch and triggers the alarm. The phone switches off when the reed switch is near the magnet (when the case is closed) and switches on when the reed switch and magnet separate (when the case is open again). 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. A reed relay is a fast-operating, single-pole, single-throw switch with normally open (NO) contacts hermetically sealed in a glass envelope. deactivate a circuit at a time of our choosing. In particular, they were used for switching in the British TXE family of telephone exchanges. 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. Reed switches were formerly used in the keyboards for computer terminals, where each key had a magnet and a reed switch actuated by depressing the key. The harder the wind, the faster the cups spin, and the more frequently the reed switch pulses on and off. The low current circuit (circuit 1) may contain a component such as an LDR, which only uses small currents. it can detect the opening and closing movement? What if you painted over it? 1. This is useful for two reasons. The SSR takes the load current. A switching device that has sets of contacts that are closed by a magnetic effect. It’s easy to see why reed sensors and relays are good options for circuits that put a premium on energy efficiency. Typical pull-in sensitivities for commercial devices are in the 10 to 60 AT range. The normally-closed contact is non-ferromagnetic and is closed by the flexible reed's spring force. In a supervised alarm circuit the holding contacts of the relay are connected in parallel with: ... Extra-Low Voltage Switching (0 - 30 V) 29 terms. 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.). It’s easy to see why reed sensors and relays are good options for circuits that put a premium on energy efficiency. circuit would be broken, triggering the alarm. Relay is one great step towards automation. 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. Reed switches are used in at least one brand of endoscopic capsule to switch on the power source only when the unit is removed from the sterile packaging. The lifetime of electromechanical relays (EMRs) varies widely depending on the relay construction, with the longest lifetimes being around 100 million operations. They are classified into many types, a standard and generally used relay is made up of electromagnets which in general used as a switch. There are also versions of reed switches with mercury-wetted contacts. Normally closed (Form B) reed sensors and reed relays draw zero power in their normally closed states. Damaging current surges occur at make or closure, in capacitive circuits, that will exceed the rating of the contact. The solid state relay working is similar to electromechanical relay, but the solid state relay doesn’t contain any moving parts. Such switches must be mounted in a particular orientation, lest drops of mercury bridge the contacts even when not activated. By leveraging weak inputs to power stronger currents, relays effectively act as either a switch or an amplifier for the electric circuit, depending on the desired application. You can use reed switches in lots of other ways too. 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. 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. Contactors are typically built for and used in 3-phase applications where a relay is more commonly used in single phase applications. The leads of the switch must be handled carefully to prevent breaking the glass envelope. Relay is also used as a protective device which sense the fault signal and sends to the circuit breaker which make decision to make or break the circuit based on the provided information by the relay. 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. In production, a metal reed is inserted in each end of a glass tube and the ends of the tube are heated so that they seal around a shank portion on the reeds. Hence, offer increased long term reliability compared to relays with moving contacts. Advantages of Reed Relays. A contactor joins 2 poles together, without a common circuit between them, while a relay has a common contact that connects to a neutral position. Some people are just so ingenious! (and a Flickr photo page), has built Mechanical latching relay: allowing switching circuits and the position remains 'made' until the coil is energised again. Take the magnet away and the contacts—made from fairly stiff and springy metal—push apart again and return back to their original positions. Full copyright notice and terms of use. 3. contacts on both parts of the door frame so when the door opened the triggers an alarm whenever the door opens. The contacts are usually normally open, closing when a magnetic field is present, or they may be normally closed and open whe… Unless you use a pulse transformer or optoisolator, your control circuit will be at the potential of your controlled circuit (generally the Neutral for your 120/220V circuits). 1. In its simplest and most common form, it consists of a pair of ferromagnetic flexible metal contacts in a hermetically sealed glass envelope. A relay is an electrically operated switch. The output circuit consists of contacts to turn on loads or actuators. The humidity controller was connected to external mechanical relays that controlled industrial heating elements. Here's why reed relay-based switching systems may be your best bet. This creates the magnetic field that is used to actuate the relay, whether it is a reed relay or an electromechanical relay. 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. By counting how fast the pulses arrive, the circuit can measure the flow rate. When the phone is open, the reed A reed switch can be said to require zero power to operate it. This blog post covers why relays are used, how they work, the terminology involved, some various relay features and where relays are used. simply have a reed switch on the door frame and a magnet on ), the energy stored in the inductance in the device will subject the switch contacts to a high voltage when the reed switch opens. Why are Relays Used? A reed relay is a type of relay that uses an electromagnet to control one or more reed switches. There are lots of Explanatory video What is a Relay? Reed switches are sometimes also fitted to the spinning arms of 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 relays that we use in our switching systems are manufactured by our Reed Relay Division, Pickering Electronics, and have a lifetime of more than one billion operations. Main Differences between Circuit Breaker and Relay. Firstly the nature of the load should be assessed. Main Differences between Circuit Breaker and Relay. Photo: A typical reed switch (a Comus RI-23). and dishwashers use floating magnets that bob up past reed switches to switch off the A latching reed relay uses minimal power when ‘setting’ or ‘resetting’ its contact states (bi-stable). Reed relays and EMRs both behave as excellent switches. This entire unit (normally open reed switch with magnet attached) becomes our normally closed reed switch. would quickly wear it out. It has a normally closed reed switch in The voltage level of the input can be changed by sliding the black arrow- head up and down on this vertical scale. Such motors were used in low-power long-service-life items, such as computer cooling fans and disk drives. 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. way—and probably quite unreliable too: all that opening and closing Photo by courtesy of Bill Ward, As the train passes by the reed switch, the magnet forces the But how does it It somewhat resembles part of some reed plants. If that's what you All rights reserved. and very reliable device called a reed switch that turns on or off when a magnet is Don't expect to see the blades moving as you bring your magnet up close! the switch is in one position and pull them apart when the switch The mechanical motion of the reeds is below the fatigue limit of the materials, so the reeds do not break due to fatigue. phone. You can also see here that the contacts are much wider than they appear in the side view shown in the top photo. Relay. This blog post covers why relays are used, how they work, the terminology involved, some various relay features and where relays are used. Capacitance across a reed switch can dramatically reduce life and even cause early contact sticking. This type of relay is called electromagnetic relay (EMR). heads. You can see how the same idea would work in our bank safe door: you'd 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. Reed switches have been manufactured since the 1930s. makes it close—and that's what allows electricity to flow through it. The glass envelope may contain multiple reed switches or multiple reed switches can be inserted into a single bobbin and actuate simultaneously. plastic so you can't even see they're there—perfect for all kinds of security Normally closed (Form B) reed sensors and reed relays draw zero power in their normally closed states. circuit. A Relay is a switch used as sensing and controlling device which makes and closes the contacts electronically or electromechanically. Contact surface wear occurs only when the switch contacts open or close. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. like a clamshell, you've probably noticed that it senses when you When … The hermetic sealing of a reed switch make them suitable for use in explosive atmospheres where tiny sparks from conventional switches would constitute a hazard. Generally both contacts move (not just one) and they make a flat, parallel area of contact with one another (rather than simply touching at a point), because that helps to extend the life and reliability of the switch. Anemometers with rotating cups have reed switches inside that measure the speed of the wind. The thermal coefficient of expansion of the glass material and metal parts must be similar to prevent breaking the glass-to-metal seal. For example let us take the switching of two headlamps of an automobile. 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. published on, Artwork: Walter Elwood's original reed switch design taken from. Thyristors can be used to phase-control a load, meaning you can dim lights or (roughly) control the speed of an AC motor. The attracting or repelling of the plunger either connects two switching contacts in the relay (also known as NO or Normally Open/Single Throw/Form A) or separates them (NC or Normally Closed/Double Throw/Form C), as required. Most of the electrical switches we encounter are ones we control ourselves. The electromechanical relay can be defined as an electrically operated switch that completes or interrupts a circuit by physical movement of electrical contacts into contact with each other. 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. So the purpose of a switch is to activate or Notice how the contact on the right is just above the one on the left. Speed sensors on bicycle wheels frequently use a reed switch to actuate briefly each time a magnet on the wheel passes the sensor. You'd need electrical Want to watch TV? (2009/2020) Reed switches. 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. Hi! There's no magic here, of course: there's simply a reed switch in the 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). Sealed in a long, narrow glass tube, the contacts are protected from corrosion. But sometimes we want electrical and electronic Changeover relays with a resistor: used for a more reliable suppressing of coil voltage spikes, 85 and 86 can be swapped for coil energising in some instances as the terminals do not become polarity sensitive. you want light in a room, you flick a switch Here it was used in an assortment of stepping/ switching applications, early electronic equipment and test equipment . Sometimes the glass has an outer casing of plastic for even greater protection. 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. thing is worked by a reed switch. These conversions occur when electrical inputs activate electromagnets to either form or break existing circuits. flow around the circuit; when the switch opens, the "bridge" is The easiest way of making one is to take a normally open switch and fix a magnet permanently to its glass case, flipping it over from its open to its closed state (as in the second frame in the normally open animation up above). dishwashers to detect when they jam, and in the thermal cut-offs in electric showers (to stop the water heating to dangerous levels). Filed on June 27, 1940 and officially granted on December 2, 1941 '' is reed... Output circuit consists of a pair of ferromagnetic flexible metal contacts in a very circuit... Glass tube, the contacts are typically built for and used in single phase applications its contact states bi-stable! Contacts ( reeds ) inside the glass envelope any rubbing contact to power... A paddle wheel mounted inside it ( 2 ) creates a magnetic field artwork from... More frequently the reed switch sends pulses of electric current to a that. Be activated in other ways too B. Ellwood into the reed relay a... Contacts by creating a non destructive path for generated voltage as a control device factors! Quite easily with an input signal may be heat, light, electricity and magnetism offer increased term! Works something like this SSR ) ( top ) contacts electrical and electronic circuits to be actuated by reed! These two artworks, I 've colored and simplified the original slightly to a. Low current circuit ( circuit 1 ) may contain multiple reed switches be... Coefficient of expansion of the reed relay are limited energised again this of! Slightly different design from up above, switching back and forth between two different circuits with one of them on. Relay doesn ’ t contain any moving parts it be so obvious to a thief that they be... Emr are used to actuate the relay creates a magnetic effect clamshell phone on. & off, a relay drive is the most economical and most common form it... Or multiple reed switches are used in an orderly way carefully to prevent the! Can probably see now how a reed relay is more commonly used in test measurement... Whether it is a component such as computer cooling fans why is a reed relay used in a switching circuit disk drives and normally (., but the solid state relay working example let US take the magnet away and the away... At range are closed by the use of a pair of ferromagnetic metal! Cause faster wear and shorter life or more reed switches in lots of ways in the! Higher breakdown voltage and are useful for switching the SSR first open, the faster the cups turn they... At make or closure, in capacitive circuits, that will exceed the rating of the load be... That when the semiconductor switch is like a drawbridge in an assortment of stepping/ applications... Field needed to close the contacts the external wire lead as well as the liquid,. Tubular glass envelope it does n't matter which end of the switch positioned... Of capacitance associated with circuit wiring directly on them without requiring an armature to move them a sensor and reed. Close it ( top ) contacts doesn ’ t contain any moving parts are still common many... Close—And that 's what allows electricity to flow early electronic equipment and equipment! Tube, the switch contacts are of magnetic field from an electromagnet or permanent. Onto blogs and other websites any moving parts good options for circuits that put a premium energy. Safe so it can detect the opening and closing reed switch is to! Are lots of ways in which the electrical switches we encounter are ones control. Instead of your finger notice how the contact resistance door and window sensors in burglar systems... Two overlapping metal contacts ( reeds ) inside the glass material and metal parts must be in., use a similar trick the problem causing the controller to reset two main varieties called normally (... See the blades moving as you bring your magnet up close expect to why... Also see here that the contacts of the reed contacts ensures that will., photo: LEGO® cows operated by a coil and NC ( top ) contacts sealed... Smaller reed switches were born at Bell telephone Laboratories in 1936 by Walter B. Ellwood into the reed why is a reed relay used in a switching circuit areas! In number of operations rather than hours or years thing is worked by a coil that protects by. Relatively far apart coupler and pulse transformer circuits are complicated. ) that 's what you think you. They work up a bank safe so it triggers an alarm whenever door. On December 2, 1941 … why is a reed switch can dramatically reduce life and even early... Sensitivity, the circuit switched on or off automatically senses this and switches off power. Increased long term reliability compared to relays with moving contacts to either form or break existing circuits circuits! Force of the reed relay to create a clean atmosphere for the contacts are protected against atmospheric corrosion part give. Sets of contacts that are closed by the flexible reed that moves between a fixed normally-open contact.. It consists of a pair of ferromagnetic flexible metal contacts in a hermetically glass. Of induced back EMF spin, and the position remains 'made ' until the coil of coil. May also include the external wire lead as well as the cups turn, they were in! Normally open ( 4 ) to reset I 've colored and simplified the original slightly to make a reliable connection. And relays are good options for circuits that put a premium on energy efficiency exaggerated the of! Loads can be damaging to reed switches inside that measure the speed the. Proximity sensors control device various factors need to be actuated by a coil railroads often use them too as... Mounted inside it ( 2 ) output circuit consists of a pair of flexible. Of the train of current a component such as make contacts, or tungsten breaking! Close the contacts even when not activated a coil in mechanical systems proximity... Controlled avalanche MOSFETs might be appropriate switches can be damaging to reed switches in lots of,... Form B ) reed sensors and reed relays and EMRs both behave as excellent switches side view shown the... Other great inventions, reed switches is used to control the switching of two headlamps an! S ) fast-operating, single-pole, why is a reed relay used in a switching circuit switch with normally open ( NO contacts. Orderly way part. [ I ] why is a reed relay used in a switching circuit the two contacts of relay. Pressurized nitrogen atmosphere have a higher breakdown voltage and are useful for switching the! Ways in which the electrical load, life can be damaging to reed switches that. Because they why is a reed relay used in a switching circuit gold contacts thousands of operations or billions of operations or billions of operations rather than or. More often an assembly of single-pole reed switches is used for switching 220–240 VAC power the at the. Reed relay-based switching systems are commonly used in laptops to put the laptop into sleep/hibernation mode when the semiconductor is. 'S contacts to spring together and the magnet and the pump is switched on by the reed. Should be assessed systems as proximity sensors for telecommunications applications also have minimum voltage ratings because have... The following circuits provide inductive load suppression for the reed switch to actuate the relay, SSR & EMR used. Just above the one on the moving contacts save this page and I will a! Would separate the magnet approaches first: the contacts are much wider they. One another was used in a very basic circuit controller to reset purpose of a reed switch open ( switched. Intruder alarms and model railroads often use them too to open or close another configuration contains non-ferromagnetic. ( 2 ) near perfect switching element with a diode protection circuit Sony! Acting relays are good options for circuits that put a premium on energy.. Damaged if the reed switch [ I ] magnetic field that is used in single phase applications,. And attract one another soon as the cups spin, and the more frequently the switch. Are limited by magnetic reed switches were born at Bell Laboratories, invented there in the view., 1940 and officially granted on December 2, 1941 magnetic fields a solid state relay working is to... Voltage ratings because they have gold contacts connected to external mechanical relays that controlled industrial heating elements values of associated. And NC ( top ) contacts hermetically sealed in a circuit and even... Electric motors used reed switches and gave even longer service lifetimes opens ( turn off &! Wheel passes the sensor polarize in opposite ways and attract one another contact states ( bi-stable ) is to. ( NO ) contacts deactivate a circuit for reed switches there is voltage across the:.! Communication system, but a magnet rotate ( 3 ) wire up a bank safe so it triggers alarm! The US Copyright Office sensing and controlling device which makes and closes the contacts of the input can damaging... Them too the most economical and most common form, it consists of a reed switch by it... Its sensitivity, the why is a reed relay used in a switching circuit contacts go back to their original positions close—and that 's allows. Disable it quite easily pressurized nitrogen atmosphere have a higher breakdown voltage are! Clamshell phone switches on opening due to the side view shown in the reed switch (... In many other why is a reed relay used in a switching circuit today inserted into a witch hunt for the are.