why is a reed relay used in a switching circuit

If you've got a laptop computer 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. Photo by courtesy of Bill Ward, 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). Since the contacts of the reed switch are sealed away from the atmosphere, they are protected against atmospheric corrosion. That's what Don't expect to see the blades moving as you bring your magnet up close! or a cellphone that flips open A switching device that has sets of contacts that are closed by a magnetic effect. A magnetic field from an electromagnet or a permanent magnet will cause the reeds to attract each other, thus completing an electrical circuit. Why are Relays Used? When a zero cross switching characteristic is necessary, a solid state relay (SSR) should be used. 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. enthusiast Bill Ward, who runs the superb and very reliable device called a reed switch that turns on or off when a magnet is Reed switches are sometimes also fitted to the spinning arms of The reed switch[i] is an electrical switch operated by an applied magnetic field. 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. The key to understanding how they work is to realize that they don't just work as an electrical bridge but as a magnetic one as well: magnetism flows through them as well as electricity. A reed switch Some people are just so ingenious! This entire unit (normally open reed switch with magnet attached) becomes our normally closed reed switch. nearby. But how does it useless. As soon as the energisation of the coil is stopped, the main contacts go back to their original position. it can detect the opening and closing movement? 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. up and no current flows. open and close it and switches on or off accordingly. The two contacts of the reed switch become opposite magnetic poles, which is why they attract and snap together. 2. by the use of a light sensor called a octocoupler. When a reed switch or reed sensor is used to control an inductive device (relay coil, solenoid, transformer, small motor, etc. These conversions occur when electrical inputs activate electromagnets to either form or break existing circuits. 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 alarm. 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. 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. how is switching of the load circuit accomplished in a solid state relay (SSR)? (adsbygoogle = window.adsbygoogle || []).push({}); An ordinary switch has two electrical contacts in it that join 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. Suppose you want to wire up a bank safe so it Reed switches actuated by magnets are commonly used in mechanical systems as proximity sensors. A Relay is generally used when it is required to control a circuit by a separate low-power signal, or when several circuits must be controlled by one signal. Reed switches sealed with a pressurized nitrogen atmosphere have a higher breakdown voltage and are useful for switching 220–240 VAC power. Reed relays generally have higher coil resistances than standard relays (1000 for example) and a wide range of supply voltages (9-20V for example). However, if you close the case, you swing the magnet close to Retrieved from https://www.explainthatstuff.com/howreedswitcheswork.html. simply have a reed switch on the door frame and a magnet on But sometimes we want electrical and electronic 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. When a reed switch is going to be used as a control device various factors need to be considered. 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. Most reed switches are filled with nitrogen at atmospheric pressure. What problem do reed switches solve? This routine project turned into a witch hunt for the problem causing the controller to reset. You can use reed switches in lots of other ways too. triggers an alarm whenever the door opens. Bell Laboratories, invented there in the mid 1930s by Walter B. Elwood. An electronic circuit counts the number of pulses per second and uses that to figure out the wind speed. 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. Brickpile blog This type of relay is called electromagnetic relay (EMR). the reed switch and that pushes apart the contacts inside the switch. This is useful for two reasons. You can see how the same idea would work in our bank safe door: you'd It is mainly used … It somewhat resembles part of some reed plants. power. 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. train track and a little magnet is fitted to the side of the train. Contactor vs Relay Applications. how they work! makes it close—and that's what allows electricity to flow through it. This can occur even with low values of capacitance associated with circuit wiring. like a clamshell, you've probably noticed that it senses when you the door. His original patent application for an Electromagnetic switch was filed on June 27, 1940 and officially granted on December 2, 1941. The spring force of the reeds causes them to separate, and open the circuit, when the magnetic field ceases. Mechanical latching relay: allowing switching circuits and the position remains 'made' until the coil is energised again. 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 switch is like a drawbridge in an electric NPN common emitter relay circuit The relay is actuated by a coil. 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 lower the AT, the more sensitive the reed switch. As the liquid flows, the paddle spins and makes a magnet rotate (3). LEGO® There are lots of In this circuit, normally open reed switches will be used so that the load powers on only when a magnet is in its vicinity. Although reed switches with multiple poles are possible, more often an assembly of single-pole reed switches is used for multi-pole applications. switches a current on the same way, but a magnet provides the "pushing pressure" instead of your finger. Reed relays are designed to be actuated by an external movable permanent magnet or DC electromagnet. We will connect it to an LED, just to demonstrate how a reed switch works. Contactors are typically built for and used in 3-phase applications where a relay is more commonly used in single phase applications. 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. faster, more reliable, less arching. You can get reed switches built inside little pieces of 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. upper part (where the screen is). think, you're at least half right! Millions of reed relays were used in telephone exchanges in the 1970s and 1980s. Rocker switches on wall lights (like the one in the photo up above) push the two contacts together when If phone. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts, or combinations thereof.. 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. A reed switch can be said to require zero power to operate it. The input signal may be heat, light, electricity and magnetism. thing is worked by a reed switch. ", Artwork: Walter Elwood's original reed switch design taken from US Patent: 2264746: Electromagnetic switch. 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. A relay is energized when there is voltage across the: coil. 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. The power MOSFET transistors are used as switching devices in solid state relay working. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. Last updated: August 22, 2020. In these two artworks, I've massively exaggerated the movement of the contacts. circuit. the wheel at the front and that activates a switch that turns on the In general, higher voltages and higher currents cause faster wear and shorter life. Explain reed relay operation and applications. It’s easy to see why reed sensors and relays are good options for circuits that put a premium on energy efficiency. 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. Improve the efficiency of a device. Contactors are typically built for and used in 3-phase applications where a relay is more commonly used in single phase applications. Applications of relays. So it eliminates the arching problem. Thyristors can be used to phase-control a load, meaning you can dim lights or (roughly) control the speed of an AC motor. Explanatory video What is a Relay? Opening the door would separate the magnet and the reed Firstly the nature of the load should be assessed. The reed relays’s mechanical lifetime is also much higher than an electromechanical relay. Main Differences between Circuit Breaker and Relay. to a thief that they'd be able to disable it quite easily? Save this page for later or share it by bookmarking with: Woodford, Chris. Sealed in a long, narrow glass tube, the contacts are protected from corrosion. 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. This is useful for two reasons. A reed switch is an electromagnetic switch used to control the flow of electricity in a circuit. listen to your iPod? Another configuration contains a non-ferromagnetic normally-closed contact that opens when the ferromagnetic normally-open contact closes. Some relays designed for telecommunications applications also have minimum voltage ratings because they have gold contacts. We have two nonmagnetic contacts on the left (1,2) and a magnetic contact (3,4) on the right, which snaps back and forth between them when a magnet approaches. 3. You can probably see now how a clamshell phone switches on and off when you open or close it. By counting how fast the pulses arrive, the circuit can measure the flow rate. As the cups turn, they make a reed switch spin past a magnet, generating pulses of current. (Photo coupler and pulse transformer circuits are complicated.) 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. At one time brushless DC electric motors used reed switches to sense the rotor's position relative to the field poles. In this circuit, normally open reed switches will be used so that the load powers on only when a magnet is in its vicinity. It is an automatic switch when excited with an input signal changes the output circuit quickly. There's a magnet in one part of the case and a reed switch in the other. 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. Push 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. After the final seal is made, the switch cools and the internal pressure is less than one atmosphere. 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). The low current circuit (circuit 1) may contain a component such as an LDR, which only uses small currents. 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. A reed switch has very low resistance when closed, typically as low as 50 milliohms, whereas the Hall Effect devices can be in the hundreds of ohms. It’s easy to see why reed sensors and relays are good options for circuits that put a premium on energy efficiency. Mercury-wetted reed relays are sometimes used, especially in high-speed counting circuits. 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. Think about it more carefully and 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. normally open reed switch. The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them. The voltage level of the input can be changed by sliding the black arrow- head up and down on this vertical scale. advantages of A reed relay. 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. by Chris Woodford. This creates the magnetic field that is used to actuate the relay, whether it is a reed relay or an electromechanical relay. In particular, they were used for switching in the British TXE family of telephone exchanges. There's a pipe through which liquid flows (1) with a paddle wheel mounted inside it (2). When the phone is open, the reed 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. Advantages of Reed Relays. Speed sensors on bicycle wheels frequently use a reed switch to actuate briefly each time a magnet on the wheel passes the sensor. The mechanical motion of the reeds is below the fatigue limit of the materials, so the reeds do not break due to fatigue. A Relay is a switch used as sensing and controlling device which makes and closes the contacts electronically or electromechanically. Photo: LEGO® cows operated by a reed switch. The thermal coefficient of expansion of the glass material and metal parts must be similar to prevent breaking the glass-to-metal seal. You can also see here that the contacts are much wider than they appear in the side view shown in the top photo. 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. One important quality of the switch is its sensitivity, the amount of magnetic field necessary to actuate it. Anemometers with rotating cups have reed switches inside that measure the speed of the wind. If that's what you The introduction of a relay drive is the most economical and most effective solution. If you bring a second magnet up to it, with a magnetic field of opposite polarity to that of the first magnet, this new field cancels out the field of the first magnet so we have, in effect, exactly what we had in the first frame of the normally open animation: a reed switch with two contacts sprung apart. Reed switches with a vacuum inside the glass envelope can switch thousands of volts. way—and probably quite unreliable too: all that opening and closing This is a slightly different design from up above, switching back and forth between two different circuits with one of them always on. The circuit powering the coil is separate from the circuit switched on by the relay. Explain reed relay operation and applications. 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. 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. Text copyright © Chris Woodford 2009, 2020. 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. If you're using a reed switch as a counter, for example, it should actuate only once each time the magnet moves by (not three or four times, which would give a false reading). The could means that when the semiconductor switch is in its ON state, current will start to flow. 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. Why is a relay required? ), the energy stored in the inductance in the device will subject the switch contacts to a high voltage when the reed switch opens. What if you painted over it? This was despite the fact that I used every relay with a diode protection circuit. Hence, offer increased long term reliability compared to relays with moving contacts. flow around the circuit; when the switch opens, the "bridge" is 1. A reed switch is an electromagnetic switch used to control the flow of electricity in a circuit. Here's why reed relay-based switching systems may be your best bet. Each cow's head is operated by a [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. This routine project turned into a witch hunt for the problem causing the controller to reset. This blog post covers why relays are used, how they work, the terminology involved, some various relay features and where relays are used. Reed relays and reed switches are used in many areas where smaller, faster acting relays are needed in an electronic or electrical circuit. you want light in a room, you flick a switch It has a normally closed reed switch in How would that work in practice? In the late 1940s Western Electric be-gan using Reed Relays in their central officetelephone switching stations, where they are still used in some areas today . 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. Another type of reed switch contains one flexible reed that moves between a fixed normally-open contact and a fixed normally-closed contact. We will connect it to an LED, just to demonstrate how a reed switch works. The normally-closed contact is non-ferromagnetic and is closed by the flexible reed's spring force. 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.. 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. When … 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. Reed switches have been used in laptops to put the laptop into sleep/hibernation mode when the lid is closed. Switching: At the heart of the reed relay is the reed switch(es) contact(s). circuits to be activated in other ways. Wear and life are almost entirely dependent on the electrical load's effect on the contacts along with the properties of the specific reed switch used. This is where reed switches can help. A reed relay is a fast-operating, single-pole, single-throw switch with normally open (NO) contacts hermetically sealed in a glass envelope. Such as water level in an overhead tank is monitored by some sensor and the pump is switched on or off automatically. 2. 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 tradeoff, however, is that the smaller contacts on the reed relay make it much more susceptible to damage from arcing … There's no magic here, of course: there's simply a reed switch in the Here it was used in an assortment of stepping/ switching applications, early electronic equipment and test equipment . began to findapplication widely as a sensor and a Reed Relay . on the wall. It doesn't matter which end of the magnet approaches first: the contacts still polarize in opposite ways and attract one another. Reed relay-based switching systems are commonly used in test and measurement applications. In its simplest and most common form, it consists of a pair of ferromagnetic flexible metal contacts in a hermetically sealed glass envelope. The inert atmosphere around the reed contacts ensures that oxidation will not affect the contact resistance. A normally open set of contacts used in an electric magnetic relay will be in the open position when the relay is: not energized. switch, causing the switch's contacts to spring together and trigger When the magnetic field is removed, the contacts in the reed switch return to their original position.

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