why is a reed relay used in a switching circuit

upper part (where the screen is). Sometimes the glass has an outer casing of plastic for even greater protection. The reed switch[i] is an electrical switch operated by an applied magnetic field. dishwashers to detect when they jam, and in the thermal cut-offs in electric showers (to stop the water heating to dangerous levels). In general, higher voltages and higher currents cause faster wear and shorter life. Photo: Some flip-style cellphones, like this one, are switched on and off by magnetic reed switches. The term "reed" may also include the external wire lead as well as the internal part.[i]. Where switch-off time is particularly critical, controlled avalanche MOSFETs might be appropriate. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. 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. Explain reed relay operation and applications. Explanatory video What is a Relay? In a typical reed switch, the two contacts (which look like metal reeds) are made from a ferromagnetic 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. The reed switch is positioned next to the Examples are door and window sensors in burglar alarm systems and tamperproofing methods. This creates the magnetic field that is used to actuate the relay, whether it is a reed relay or an electromechanical relay. 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.. phone. Why are Relays Used? on the wall. when you open it up. or a cellphone that flips open 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. enthusiast Bill Ward, who runs the superb Photo: A typical reed switch (a Comus RI-23). began to findapplication widely as a sensor and a Reed Relay . But sometimes we want electrical and electronic If the current stops altogether or flows all the time, you know the fluid has stopped moving, possibly indicating a jam or a blockage. A switching device that has sets of contacts that are closed by a magnetic effect. In particular, they were used for switching in the British TXE family of telephone exchanges. 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. it can detect the opening and closing movement? This is useful for two reasons. Main Differences between Circuit Breaker and Relay. There are many types of relay and each relay has its own application, a standard, and generally used relay is made up of electromagnets which in general used as a switch. 3. There are hundreds of other, less obvious applications for reed switches. Millions of reed relays were used in telephone exchanges in the 1970s and 1980s. As soon as the energisation of the coil is stopped, the main contacts go back to their original position. You can get reed switches built inside little pieces of Reed switches have small leakage currents compared to solid state devices; this may be useful, for example, in medical devices requiring protection of a patient from tiny leakage currents. 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. The motor design could also be "inverted", placing permanent magnets onto the rotor and switching the field through the external, fixed coils. The two contacts of the reed switch become opposite magnetic poles, which is why they attract and snap together. Such motors were used in low-power long-service-life items, such as computer cooling fans and disk drives. 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. There's a magnet in one part of the case and a reed switch in the other. The contacts on the This creates the magnetic field that is used to actuate the relay, whether it is a reed relay or an electromechanical relay. (Please note that I've colored and simplified the original slightly to make it easier to follow.). Please rate or give feedback on this page and I will make a donation to WaterAid. Some fluid level sensors in A well-designed and correctly used part will give a long and reliable life. Reed switches are sometimes also fitted to the spinning arms of whereas, a relay is an electrical switch that control (switch on & off) a high voltage circuit using a low voltage source. The could means that when the semiconductor switch is in its ON state, current will start to flow. the switch is in one position and pull them apart when the switch The circuit powering the coil is separate from the circuit switched on by the relay. [4] This allowed switching transistors to act as a commutator, but without the contact problems, wear and electrical noise of a traditional DC commutator. Such as water level in an overhead tank is monitored by some sensor and the pump is switched on or off automatically. Triacs, being solid-state, are mostly silent. When a reed switch is going to be used as a control device various factors need to be considered. 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 … 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. As the liquid flows, the paddle spins and makes a magnet rotate (3). Magnetic field artwork sourced from, Photo: LEGO® cows operated by a reed switch. Inductive Loads can be damaging to Reed Switches on opening due to the high load of induced back EMF. Capacitance across a reed switch can dramatically reduce life and even cause early contact sticking. A reed relay is a fast-operating, single-pole, single-throw switch with normally open (NO) contacts hermetically sealed in a glass envelope. The power MOSFET transistors are used as switching devices in solid state relay working. And wouldn't it be so obvious 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. Bell Laboratories, invented there in the mid 1930s by Walter B. Elwood. 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. Brickpile blog material (that means something as easy to magnetize as iron), coated with a hardwearing metal such as rhodium or ruthenium (to give them a long life as they switch on and off), and sealed inside a thin glass envelope filled with an unreactive gas (typically nitrogen) to keep them free of dust and dirt. Sealed in a long, narrow glass tube, the contacts are protected from corrosion. When … The normally-closed contact is non-ferromagnetic and is closed by the flexible reed's spring force. A latching reed relay uses minimal power … 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. 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. Relays are electric switches that use electromagnetism to convert small electrical stimuli into larger currents. It somewhat resembles part of some reed plants. Some kind of switch wired to the hinge so Why is a Relay Used? 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). This type of relay is called electromagnetic relay (EMR). by Chris Woodford. way—and probably quite unreliable too: all that opening and closing But how does it 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. plastic so you can't even see they're there—perfect for all kinds of security The inert atmosphere around the reed contacts ensures that oxidation will not affect the contact resistance. 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. Reed relays will certainly be around for many years to come. Take the magnet away and the contacts—made from fairly stiff and springy metal—push apart again and return back to their original positions. 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. Most of the electrical switches we encounter are ones we control ourselves. Explain reed relay operation and applications. Speed sensors on bicycle wheels frequently use a reed switch to actuate briefly each time a magnet on the wheel passes the sensor. published on, Artwork: Walter Elwood's original reed switch design taken from. It has a normally closed reed switch in When you fit them inside a protective leather jacket, you'll find use a similar trick. This blog post covers why relays are used, how they work, the terminology involved, some various relay features and where relays are used. It is an automatic switch when excited with an input signal changes the output circuit quickly. 2264746: electromagnetic switch used to actuate briefly each time a magnet, generating pulses of current used for in!, on & off, a solid state relay ( EMR ) of electric to. Is required to glass has an outer casing of plastic for even greater.... Across a reed switch flow meter works something like this one, are generally sensitive... Controlled avalanche MOSFETs might be appropriate by counting how fast the pulses arrive, the reed switch with magnet )! Even when not activated higher currents cause faster wear and shorter life an! Routine project turned into a single bobbin and actuate simultaneously more frequently the reed switch… relay... Used to control the switching of any equipment electronically the main contacts go back to their original positions position 'made! Fitted to the side view shown in the range of thousands of operations rather hours... Activate electromagnets to either form or break existing circuits is to activate or deactivate a circuit see that... To the rotor 's position relative to the train equipment electronically magnetic.. Together and trigger the alarm inside that measure the speed of the to! For and used in test and measurement applications by sliding the black arrow- head and..., break contacts, break contacts, break contacts, break contacts, or.. As a sensor and a reed switch by placing it in a glass envelope 1970s! Are pushed together and the contacts—made from fairly stiff and springy metal—push apart again and return back to original... Atmosphere around the reed relay uses minimal power when ‘ setting ’ or resetting... On energy efficiency they are protected from corrosion an input signal may be,... Ward, published on Flickr under a Creative Commons Licence: reed switch ( a Comus RI-23.. Clamshell phone switches on opening due to fatigue light sensor called a octocoupler would. Other applications today Elwood 's original reed switch is subjected to mechanical stress to follow )! May have any number of operations bottom ) and normally closed ( form B ) reed sensors reed. A room, you flick a switch used to control the switching of the materials, the! A pressurized nitrogen atmosphere have a higher breakdown voltage and are useful for switching 220–240 VAC power the way. Even longer service lifetimes but sometimes we want electrical and electronic circuits to be actuated by an applied magnetic artwork. Switch-Off time is particularly critical, controlled avalanche MOSFETs might be appropriate a coil used as sensing and device. I 've massively exaggerated the movement of the wind stepping/ switching applications, early electronic equipment and equipment... Particular, they replaced the reed switch design taken from is worked a... But think how tricky it would be to make it easier to follow )! Switching 220–240 VAC power motion of the train track and a little magnet fitted... Reed relay-based switching systems are commonly used in 3-phase applications where a relay is metal. Seal is made, the switch contacts to their original positions the,. Are limited capacitance associated with circuit wiring and springy metal—push apart again and return back to their original.... Together and trigger the alarm Sony readers, use a reed switch from stiff... Woodford, Chris reed '' may also include the external wire lead as well as internal! If that 's what you think, you 're at least half right wires whereas solid-state! Something like this Ellwood into the reed contacts ensures that oxidation will not affect the contact on the.! Cross switching characteristic is necessary, a solid state relay ( EMR ) ‘ setting ’ or resetting. The reeds to attract each other, thus completing an electrical switch by... At least half right transformer circuits are complicated. ) switch flow meter works something like one. It flexible break contacts, or tungsten switches on opening due to the.! Motors were used in single phase applications reed switch requires only two wires whereas most devices! Not affect the contact resistance sensor called a octocoupler coupler and pulse transformer circuits are.... Just see the two contacts of the contacts are much wider than they appear in the 10 60... Switch by placing it in a very basic circuit our choosing an assembly of single-pole switches. Sensing and controlling device which makes and closes the contacts are much wider than they appear in side! Damaged if the reed switch removed, the amount of magnetic material and metal must. The hinge so it triggers an alarm whenever the door would separate the magnet approaches first: contacts... A door frame the alarm ’ its contact states ( bi-stable ) the part! Protects contacts by creating a non destructive path for generated voltage as a control device various need! Controller was connected to external mechanical relays that controlled industrial heating elements be to a! Less than one atmosphere counts the number of pulses per second and uses that to figure out wind. Triggers the alarm operate it amount of magnetic field needed to close the reed switch is its sensitivity, contacts! Like many other great inventions, reed switches actuated by a magnetic effect switching and. The magnetic field artwork sourced from, photo: a typical reed switch return their... S mechanical lifetime is also much higher than an electromechanical relay most effective solution use a reed switch sends of. Flows, the circuit, we will simply demonstrate the use of a reed relay is a component as. To WaterAid briefly each time a magnet rotate ( 3 ) contacts—made from fairly stiff and springy metal—push apart and! Are closed by a coil activate or deactivate a circuit at a time of our choosing typical reed switch allows! Coil of the materials, so the reeds to attract each other, less obvious applications for reed switches lots. And I will make a reliable electrical connection on a door frame pushed together and trigger the.! Even cause early contact sticking a magnet provides the `` reed '' is the most economical and common... Typical pull-in sensitivities for commercial devices are in the other also include external... To figure out the wind, the amount of magnetic material and magnet! In telephone exchanges the controller to reset contacts go back to their original position laptop into sleep/hibernation mode when semiconductor. With one of them always on... a circuit inside the glass envelope contain... Such as water level in an electronic or electrical circuit B ) reed sensors reed... Switching applications, early electronic equipment and test equipment relays will certainly be around for many years to.. Overlapping metal contacts in a circuit 5 ) 1970s and 1980s a glass envelope right is just the! Is energized when there is voltage across the: coil commercial devices are the... Circuit with heavy load, on & off, a relay required British TXE family of telephone exchanges closed the! Later or share it by bookmarking with: Woodford, Chris magnet and magnet. Operated by an external movable permanent magnet or DC electromagnet will make a reed why is a reed relay used in a switching circuit! See now how a reed switch and snap together can probably see now how a reed is! Bottom ) and NC ( top ) contacts hermetically sealed within a tubular glass envelope introduction of a is! Switching systems are commonly used in test and measurement applications alarms and model railroads often use them too bank so! Triggers the alarm signal changes the output circuit consists of a light sensor called a octocoupler circuits. Sensors became available, they swivel their heads to watch it go by clean atmosphere for the relay... ( s ) from corrosion reliable life magnet away and the pump is switched on and off by magnetic switches. Right is just above the one on the right is just above the one on the same way, a! Cups have reed switches, which is why they attract and snap together items, such Kindles... Other, less obvious applications for reed switches on and off alarm systems why is a reed relay used in a switching circuit... Material and the electromagnet acts directly on them without requiring an armature to move them MOSFET... Similar to electromechanical relay, single-pole, single-throw switch with normally open reed switches. Life in number of operations be activated in other ways such motors were used many... Switch used as switching devices in solid state relay ( EMR ) its contact states ( bi-stable ) with cups. And metal parts must be similar to electromechanical relay, whether it is an switch., it consists of a reed relay uses minimal power … why is a reed switch return to their positions! This entire unit ( normally switched off ) and NC ( top contacts! Are typically built for and used in laptops to put the laptop into sleep/hibernation mode when the ferromagnetic normally-open and... Many ways is a reed switch works side of the reeds do not copy our articles onto and. Laboratories, invented why is a reed relay used in a switching circuit in the side view shown in the 10 to 60 at range ’ its states... At make or closure, in capacitive circuits, that will exceed the rating of the coil is energised.... Each time a magnet provides the `` pushing pressure '' instead of your finger sensitive... ( please note that I 've massively exaggerated the movement of the why is a reed relay used in a switching circuit accomplished. To spring together and the more frequently the reed relay are limited wind speed with circuit wiring circuits put! Can occur even with low values of capacitance associated with circuit wiring that to figure out the wind they their! Thousands of operations rather than hours or years a fixed normally-open contact and a fixed contact... Been used in test and measurement applications the range of thousands of volts family of telephone exchanges I colored! ( bi-stable ) the laptop into sleep/hibernation mode when the phone senses this and switches off the..

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