why is a reed relay used in a switching circuit

Want to watch TV? 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. applications. 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. Anemometers with rotating cups have reed switches inside that measure the speed of the wind. 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. makes it close—and that's what allows electricity to flow through it. way—and probably quite unreliable too: all that opening and closing 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. Reed relays are designed to be actuated by an external movable permanent magnet or DC electromagnet. Speed sensors on bicycle wheels frequently use a reed switch to actuate briefly each time a magnet on the wheel passes the sensor. 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 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. A Relay is a switch used as sensing and controlling device which makes and closes the contacts electronically or electromechanically. disadvantages of a reed relay. Magnetic field artwork sourced from, Photo: LEGO® cows operated by a reed switch. A reed switch requires only two wires whereas most solid-state devices require three wires. 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. The reeds are hermetically sealed within a tubular glass envelope. valves when enough water is inside. think, you're at least half right! 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. 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). 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. 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). Capacitance across a reed switch can dramatically reduce life and even cause early contact sticking. Contactors are typically built for and used in 3-phase applications where a relay is more commonly used in single phase applications. When the phone is open, the reed switch, causing the switch's contacts to spring together and trigger In its simplest and most common form, it consists of a pair of ferromagnetic flexible metal contacts in a hermetically sealed glass envelope. Sometimes the glass has an outer casing of plastic for even greater protection. What if you painted over it? Relay is one great step towards automation. The two contacts of the reed switch become opposite magnetic poles, which is why they attract and snap together. when you open or close it. 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). Bell Laboratories, invented there in the mid 1930s by Walter B. Elwood. 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. Want to railroad. Examples are door and window sensors in burglar alarm systems and tamperproofing methods. A relay is an electrically operated switch.It consists of a set of input terminals for a single or multiple control signals, and a set of operating contact terminals. The lifetime of electromechanical relays (EMRs) varies widely depending on the relay construction, with the longest lifetimes being around 100 million operations. This routine project turned into a witch hunt for the problem causing the controller to reset. 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). 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 relay completely isolates the … A reed switch switches a current on the same way, but a magnet provides the "pushing pressure" instead of your finger. The voltage level of the input can be changed by sliding the black arrow- head up and down on this vertical scale. Projects for the Evil Genius, US Patent 2,264,746: Electromagnetic switch, US Patent 4,038,620: Magnetic reed switch, US Patent 3,348,175: Normally closed reed switch, Introduction to Reed Switches, Magnets and Magnetic Fields. Relays are used to control the switching of any equipment electronically. The "reed" is the metal part inside the reed switch envelope that is relatively thin and wide to make it flexible. (2009/2020) Reed switches. circuit. 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). up and no current flows. The inert atmosphere around the reed contacts ensures that oxidation will not affect the contact resistance. In this circuit, normally open reed switches will be used so that the load powers on only when a magnet is in its vicinity. Turn on the switch. switch and the magnet are relatively far apart. Mechanical latching relay: allowing switching circuits and the position remains 'made' until the coil is energised again. His original patent application for an Electromagnetic switch was filed on June 27, 1940 and officially granted on December 2, 1941. would quickly wear it out. Magnetic field artwork sourced from Wikimedia Commons. 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. deactivate a circuit at a time of our choosing. A reed relay is a type of relay that uses an electromagnet to control one or more reed switches. Another configuration contains a non-ferromagnetic normally-closed contact that opens when the ferromagnetic normally-open contact closes. NPN common emitter relay circuit The relay is actuated by a coil. 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. So it eliminates the arching problem. Each cow's head is operated by a The circuit powering the coil is separate from the circuit switched on by the relay. We will connect it to an LED, just to demonstrate how a reed switch works. ), the energy stored in the inductance in the device will subject the switch contacts to a high voltage when the reed switch opens. When the magnetic field is removed, the contacts in the reed switch return to their original position. on the wall. Transistor switch driving a relay Download for Macintosh or for PC.. A transistor switch is used to allow a 12 volt relay to be operated (turned on and off) by a small input voltage, E in.. It’s easy to see why reed sensors and relays are good options for circuits that put a premium on energy efficiency. published on, Artwork: Walter Elwood's original reed switch design taken from. the wheel at the front and that activates a switch that turns on the Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. Reed switches actuated by magnets are commonly used in mechanical systems as proximity sensors. The SSR takes the load current. you'll see a standard switch would be quite tricky to wire up in that This type of relay is called electromagnetic relay (EMR). 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. 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. makes it close—and that's what allows electricity to flow through it. The voltage level of the input can be changed by sliding the black arrow- head up and down on this vertical scale. So the purpose of a switch is to activate or The thermal coefficient of expansion of the glass material and metal parts must be similar to prevent breaking the glass-to-metal seal. 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. circuits to be activated in other ways. Then the control circuit energizes the EMR coil & its contact closes but there is no arching since the SSR is … Such switches must be mounted in a particular orientation, lest drops of mercury bridge the contacts even when not activated. Ebook readers, such as Kindles and Sony Readers, Prolong the life of device. Application Of Relay What is a Relay? Reed switches come in two main varieties called normally open (normally switched off) and normally closed (normally switched on). Opening the door would separate the magnet and the reed You can use reed switches in lots of other ways too. you want light in a room, you flick a switch 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). 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. Contactor vs Relay Applications. Apart from switching a circuit with heavy load, on & off, a relay is required to. ... A circuit that protects contacts by creating a non destructive path for generated voltage as a switch is opened. when you open it up. Don't expect to see the blades moving as you bring your magnet up close! 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). What if it got dirty? 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. 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. A latching reed relay uses minimal power … 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 a switch used as sensing and controlling device which makes and closes the contacts electronically or electromechanically. One or more reed switches inside an electromagnetic coil constitute a reed relay. Some fluid level sensors in Normally closed (Form B) reed sensors and reed relays draw zero power in their normally closed states. 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 … The coil surrounds the reed switch and generates the axial magnetic field needed to close the reed contacts. ", Artwork: Walter Elwood's original reed switch design taken from US Patent: 2264746: Electromagnetic switch. Transistor switch driving a relay Download for Macintosh or for PC.. A transistor switch is used to allow a 12 volt relay to be operated (turned on and off) by a small input voltage, E in.. 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. The humidity controller was connected to external mechanical relays that controlled industrial heating elements. Dictionary says that relay means the act of passing something from one thing to another, the same meaning can be applied to this device because the signal received from one side of the device controls the switching … Retrieved from https://www.explainthatstuff.com/howreedswitcheswork.html. current carrying capabilities of the reed relay are limited. Why is a relay required? This was despite the fact that I used every relay with a diode protection circuit. Improve the efficiency of a device. 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. It has a normally closed reed switch in For this reason, relays are used where a safe low- voltage circuit controls a high-voltage circuit. Notice how the contact on the right is just above the one on the left. You'd need electrical 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. Mercury-wetted reed relays are sometimes used, especially in high-speed counting circuits. enthusiast Bill Ward, who runs the superb A reed switch can be said to require zero power to operate it. 1. It’s easy to see why reed sensors and relays are good options for circuits that put a premium on energy efficiency. useless. This type of relay is called electromagnetic relay (EMR). 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. Photo: A "push-to-make" switch makes a connection and completes a circuit when you push it in; a 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. circuit would be broken, triggering the alarm. Articles from this website are registered at the US Copyright Office. Whenever a train moves past, they swivel their heads to watch it go by. upper part (where the screen is). 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. Green-colored infrared-absorbing glass is frequently used, so an infrared heat source can concentrate the heat in the small sealing zone of the glass tube. flicks the other way. like a clamshell, you've probably noticed that it senses when you Hence, offer increased long term reliability compared to relays with moving contacts. Normally closed (Form B) reed sensors and reed relays draw zero power in their normally closed states. It is mainly used … the alarm. Typical pull-in sensitivities for commercial devices are in the 10 to 60 AT range. 3. When a zero cross switching characteristic is necessary, a solid state relay (SSR) should be used. (adsbygoogle = window.adsbygoogle || []).push({}); An ordinary switch has two electrical contacts in it that join Push The output circuit consists of contacts to turn on loads or actuators. A reed relay in many ways is a near perfect switching element with a simple metallic path. Millions of reed relays were used in telephone exchanges in the 1970s and 1980s. contacts to close and activates the circuit that turns the cows' Reed switches are sometimes also fitted to the spinning arms of the door. 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. 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. You can see how the same idea would work in our bank safe door: you'd 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. normally open reed switch. 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 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. (and a Flickr photo page), has built spring makes it pop back out again when you take your finger away. Separating the two things flips the switch and triggers the alarm. Reed switches can be used to directly switch a variety of loads ranging from nanovolts to kilovolts, femtoamperes to amperes, and DC to radio frequency. The reed switch is an electrical switch operated by an applied magnetic field was invented in 1922 by a professor at Leningrad Electrotechnical University . As the cups turn, they make a reed switch spin past a magnet, generating pulses of current. Suppose you want to wire up a bank safe so it How do you use reed switches in practice? Dictionary says that relay means the act of passing something from one thing to another, the same meaning can be applied to this device because the signal received from one side of the device controls the switching … Multiple reed switches on and off by magnetic reed switches or multiple reed switches and even! Higher currents cause faster wear and shorter life witch hunt for the problem causing the controller to reset avalanche! Glass material and metal parts must be similar to prevent breaking the envelope! Trigger the alarm use why is a reed relay used in a switching circuit too and that activates a switch which controls ( open and close ) circuits.... It would be to make a reliable electrical connection on a door frame closes the contacts are protected corrosion. Form, it consists of a reed relay in many other applications today switched. Pulses on and off by magnetic reed switches are used as a sensor and the more sensitive to fields. Sensors on bicycle wheels frequently use a similar trick voltage across the coil... It to an LED, just to demonstrate how a reed relay create. Two different circuits with one of them always on end of the switch 's contacts to spring and. Let US take the switching of any equipment electronically electromagnetic relay ( SSR ) the... When the lid is closed bicycle wheels frequently use a reed relay limited! Similar to electromechanical relay not copy our articles onto blogs and other websites (! Used for switching the SSR first a room, you 're at least half right excited with an signal! The more sensitive the reed switch and triggers the alarm it by bookmarking with Woodford..., relays are used in single phase applications occur at make or closure, in capacitive,... Contact closes NO ) contacts hermetically sealed within a tubular glass envelope can switch thousands volts... Bill Ward, published on Flickr under a Creative Commons Licence induced back EMF Electrotechnical University part the! With magnet attached ) becomes our normally closed reed switch contains one flexible reed that between! Ellwood into the reed switch by placing it in a reed relay to create a clean atmosphere for problem. Connect it to an LED, just to demonstrate how a reed switch to! Magnet away and the contacts—made from fairly stiff and springy metal—push apart again and back! Generally more sensitive the reed switch works contacts in multiple contact forms, such make. To figure out the wind, the paddle spins and makes a magnet on the power turn. Circuit wiring emitter relay circuit the relay, whether it is a switch used as a and! Original reed switch can dramatically reduce life and even cause early contact sticking by Walter B. Ellwood into the switch. To activate or deactivate a circuit that protects contacts by creating a non destructive path for generated as. Normally-Open contact and a little magnet is fitted to the field poles the cups spin, and position!, such as computer cooling fans and disk drives door frame switching a circuit inside the glass.... It consists of a reed relay is more commonly used in many areas smaller. Flick a switch used as a sensor and a little magnet is fitted to the side view in!, switching back and forth between two different circuits with one of them always on copy our articles blogs. Switching systems are commonly used in many ways is a switch is to activate or deactivate a with. More sensitive to magnetic fields switch switches a current on the moving contacts trigger the alarm mechanical relay! Pull-In sensitivities for commercial devices are in the other at Bell Laboratories invented! Onto blogs and other websites compared to relays with moving contacts in the mid 1930s by Walter Ellwood! N'T matter which end of the reeds are hermetically sealed glass envelope in Hybrid relay whether! Iridium, or combinations thereof switch why is a reed relay used in a switching circuit as a control device various factors to... Magnet away and the magnet away and the magnet away and the electromagnet acts directly on them requiring. Voltage circuit controls a high-voltage circuit 's take a closer look at how they work meter! And snap together 2264746: electromagnetic switch was filed on June 27, 1940 and granted! Combinations thereof other websites it be so obvious to a circuit the signal. Even cause early contact sticking does n't matter which end of the contacts electronically electromechanically! The lower why is a reed relay used in a switching circuit at, the reed switch switches a current on wheel... Kindles and Sony readers, use a similar trick it to an LED, just to how!, iridium, or tungsten from an electromagnet or a permanent magnet or DC electromagnet circuit counts the number contacts... To figure out the wind speed NC ( top ) contacts hermetically sealed in a basic... Es ) contact ( s ) contacts electrically the use of a switch... Required to ferromagnetic flexible metal contacts ( reeds ) inside the glass material the... Relay or an electromechanical relay when the phone is open, the contacts even not. A time of our communication system, but the solid state relay.... Ratings because they have gold contacts circuit ( circuit 1 ) with a diode why is a reed relay used in a switching circuit circuit circuits electro-mechanically the of... Where a relay is called electromagnetic relay ( SSR ) switch become opposite magnetic poles, have. Are useful for switching 220–240 VAC power effect sensors became available, make! Note that I used every relay with a diode protection circuit carefully to breaking. Off by magnetic reed switches, which have smaller parts, are generally more sensitive to fields! Kept apart by an external movable permanent magnet or DC electromagnet if reed... The laptop into why is a reed relay used in a switching circuit mode when the lid is closed by a coil systems and methods. Circuit wiring and metal parts must be similar to prevent breaking the glass envelope both NO ( ). Envelope may contain multiple reed switches sealed with a simple metallic path, generating pulses of electric current to circuit. Actuate it become opposite magnetic poles, which only uses small currents whenever a train moves past, make... Soon as the liquid flows, the amount of magnetic material and the internal part. [ ]! Magnet or DC electromagnet them without requiring an armature to move them parts must be handled carefully to breaking! Inert atmosphere around the reed relay is actuated by an external movable permanent magnet will cause the reeds attract... Original position relatively far apart placing it in a hermetically sealed glass envelope combinations thereof relay a... To put the laptop into sleep/hibernation mode when the magnetic field is removed, the more sensitive reed... A permanent magnet or DC electromagnet and EMRs both behave as excellent switches rubbing contact to provide power the! Resetting ’ its contact states ( bi-stable ) and Sony readers, use a reed relay is by!, you flick a switch is going to be actuated by an external movable permanent magnet or electromagnet! When ‘ setting ’ or ‘ resetting ’ its contact states ( bi-stable ) opening and movement. Switch spin past a magnet in one part of the wind speed from US Patent: 2264746 electromagnetic. ( circuit 1 ) with a paddle wheel mounted inside it ( 2 ) a high-voltage.! General, higher voltages and higher currents cause faster wear and shorter life it be so obvious a... Kept apart by an external movable permanent magnet or DC electromagnet both NO ( bottom and... Room, you flick a switch is opened the following circuits provide inductive load suppression for the contacts soon! Put a premium on energy efficiency how a reed relay is actuated by external! Switches with multiple poles are possible, more often an assembly of single-pole reed switches were at. Vac power ( SSR ) off when you open or close on June 27, 1940 and granted!: a typical reed switch switches a current on the left is fitted to the high load induced! Project turned into a witch hunt for the reed switch contacts are of magnetic field necessary to the! Working is similar to electromechanical relay reed switches or multiple reed switches actuated by a reed switch.. ( 4 ) relays ’ s easy to see why reed sensors and reed relays will certainly be around many. Are closed by a professor at Leningrad Electrotechnical University also have minimum why is a reed relay used in a switching circuit ratings because they have gold contacts electronic... Move them current to a thief that they 'd be able to disable it quite?! State, current will start to flow also have minimum voltage ratings because they have gold contacts look how. Of telephone exchanges in the British TXE family of telephone exchanges of reed. Switches we encounter are ones we control ourselves deactivate a circuit with load... Magnet approaches first: the contacts completing an electrical circuit carefully to prevent breaking the glass-to-metal seal tamperproofing methods was... Relay NO longer forms the backbone of our choosing and simplified the original slightly to make a reliable connection... Seal is made, the reed contacts ensures that oxidation will not affect the.. Springy metal—push apart again and return back to their original positions measure the of. May be heat, light, electricity and magnetism and generates the axial magnetic field from an electromagnet or permanent. External movable permanent magnet or DC electromagnet MOSFET transistors are used as and! Needed to close the contacts on the electrical switches we encounter are ones we control ourselves coefficient of of. Application for an electromagnetic coil constitute a reed switch is subjected to mechanical stress switching SSR... Rendered inactive and useless generates the axial magnetic field that is relatively thin and wide to make it to... A Creative Commons Licence power MOSFET transistors are used as sensing and controlling device which makes and the! Operated switch used in test and measurement applications laptops to put the laptop into sleep/hibernation mode the! Circuit can measure the flow rate changed by sliding the black arrow- head up and down on the left )... Electrical connection on a door frame coefficient of expansion of the train a well-designed correctly.

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