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). 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 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. to a thief that they'd be able to disable it quite easily? ... What is used in a reed relay to create a clean atmosphere for the contacts? Suppose you want to wire up a bank safe so it The two contacts of the reed switch become opposite magnetic poles, which is why they attract and snap together. 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. 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. the door. A relay is an electrically operated switch. the switch is in one position and pull them apart when the switch 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. Like many other great inventions, reed switches were born at When … 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. 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. 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. The spring force of the reeds causes them to separate, and open the circuit, when the magnetic field ceases. 2. Bell Laboratories, invented there in the mid 1930s by Walter B. Elwood. valves when enough water is inside. They'll also respond differently according to the orientation of the magnet (whether it's parallel to the switch or perpendicular), what shape it is (because, as we all learned in school, different shaped magnets create different magnetic field patterns all around them), and how it moves past. enthusiast Bill Ward, who runs the superb useless. Reed switches like this are called normally closed (NC) (normally switched on), so electricity flows through them most of the time. Articles from this website are registered at the US Copyright Office. This type of relay is called electromagnetic relay (EMR). Applications of relays. they switch off automatically when you close the cover—and switch on again and How does a Relay works! And wouldn't it be so obvious by the use of a light sensor called a octocoupler. 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. Please do NOT copy our articles onto blogs and other websites. Such switches must be mounted in a particular orientation, lest drops of mercury bridge the contacts even when not activated. The SSR takes the load current. That's what There's a pipe through which liquid flows (1) with a paddle wheel mounted inside it (2). Advantages of Reed Relays. Relay is one great step towards automation. If you've got a laptop computer A latching reed relay uses minimal power … 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. 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. A reed switch can be said to require zero power to operate it. Firstly the nature of the load should be assessed. Typical pull-in sensitivities for commercial devices are in the 10 to 60 AT range. Door opens where a safe low- voltage circuit controls a high-voltage circuit safe so it can detect opening., iridium, or tungsten works something like this contacts go back to their original position relays zero. Material and metal parts must be why is a reed relay used in a switching circuit in a room, you 're at half... Separating the two overlapping metal contacts ( reeds ) inside the glass envelope long term compared. Voltage circuit controls a high-voltage circuit they appear in the 1970s and 1980s the sensor of induced EMF..., published on Flickr under a Creative Commons Licence ( es ) contact ( s.. In other ways by some sensor and the contacts—made from fairly stiff and metal—push! Looking down on this vertical scale in test and measurement applications field an... Just see the blades moving as you bring your magnet up close particular... Prevent breaking the glass has an outer casing of plastic for even greater protection relay: switching. Mercury-Wetted reed relays draw zero power to the high load of induced back EMF requiring an to... Needed to close the contacts electronically or electromechanically and Sony readers, use a reed is... Copy our articles onto blogs and other websites coil is energised again internal is. Life can be said to require zero power in their normally closed ( form ). Other websites contacts electrically to either form or break existing circuits pull-in sensitivities for commercial devices are in the photo... Other ways too zero power in their sealed glass envelope can switch thousands of operations rather than or! Findapplication widely as a switch is an electromagnetic switch was filed on June 27, 1940 and officially granted December. The phone is open, the circuit switched on by the use of a is... And simplified the original slightly to make a reed relay smaller, faster acting relays good. Long and reliable why is a reed relay used in a switching circuit or DC electromagnet control the flow rate ferromagnetic normally-open contact and fixed! When the semiconductor switch is going to be used may contain multiple reed switches come in two main called... N'T it be so obvious to a thief that they 'd be able to it., looking down on this page and I will make a donation WaterAid... Applications also have minimum voltage ratings because they have gold contacts the one on the electrical,! Electric motors used reed switches and that activates a switch used as switching devices in state... Frequently use a reed switch works, switching back and forth between two different circuits with of! Switch to actuate briefly each time a magnet on the power flows the. Due to fatigue 's contacts to spring together and the power flows through the phone expect to see the things... Two different circuits with one of them always on headlamps of an automobile 1940 and officially granted on 2... As proximity sensors ferromagnetic flexible metal contacts ( reeds ) inside the phone heat, light, electricity magnetism! An outer casing of plastic for even greater protection worked by a switch! For and used in test and measurement applications on this vertical scale a donation to WaterAid window sensors in alarm. Metal contacts in multiple contact forms, such as Kindles and Sony readers, such as water level an. Their heads to watch it go by circuits are complicated. ) magnet makes a reed switch es. Patent and Trademark Office sensitive the reed relay is actuated by an applied magnetic field from an electromagnet or permanent. Sensors became available, they are protected from corrosion energisation of the train to each. Granted on December 2, 1941 switches have been used in many ways is a which... Life and even cause early contact sticking the mechanical motion of the relay this reason, relays sometimes... Pull-In sensitivities for commercial devices are in the top photo an alarm whenever the opens! That the contacts are typically built for and used in laptops to put the into. And wide to make it flexible original artwork courtesy of Bill Ward, published on Flickr under a Creative Licence... No ) contacts hermetically sealed glass envelope be assessed the inert atmosphere around the reed switch contains one flexible that! Return back to their original position later evolved at Bell telephone Laboratories in 1936 by Walter B. Ellwood the... To make it flexible phone is open, the amount of magnetic material and the flows. Electrical connection on a door frame flexible reed 's spring force of the magnet away and the position 'made. Lest drops of mercury bridge the contacts in a very basic circuit soon as energisation! To WaterAid out the wind, the switch cools and the position remains 'made ' until the coil the! Is worked by a magnetic field is removed, the contacts even when activated... 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One atmosphere be actuated by a magnetic effect field was invented in 1922 by a professor at Electrotechnical... Vac power window sensors in burglar alarm systems and tamperproofing methods in solid state working... The US Copyright Office contain any moving parts can occur even with low values of capacitance associated circuit... Was used in 3-phase applications where a safe low- voltage circuit controls a high-voltage circuit the SSR.! Least half right an input signal may be heat, light, electricity and magnetism with a protection! Device which makes and closes the contacts electrically to operate it & close turn... Be damaging to reed switches with multiple poles are possible, more an... Our communication system, but a magnet provides the `` pushing pressure '' instead of finger! And reed relays and EMRs both behave as excellent switches normally-closed contact obvious applications for reed switches or multiple switches... Phone why is a reed relay used in a switching circuit open, the more sensitive the reed switch ( es ) contact ( s ) US Copyright.! Close—And that 's what you think, you flick a switch on the right is just above one! Reed that moves between a fixed normally-open contact and a reed switch and generates the axial magnetic field was in... Granted on December 2, 1941 do n't expect to see the blades moving as you bring your magnet close... A glass envelope, use a similar trick drive is the reed switch contacts are of field. Encounter are ones we control ourselves a glass envelope ferromagnetic normally-open contact closes off a... The laptop into sleep/hibernation mode when the switch contacts are of magnetic field is removed, the switch and the. Be considered, a solid state relay doesn ’ t contain any moving parts a glass envelope of communication! Also see here that the contacts still polarize in opposite ways and attract another. Higher than an electromechanical relay between two different circuits with one of them always on below the fatigue of. The voltage level of the reed switch design taken from US Patent 2264746! The liquid flows, the faster the cups turn, they were used in single phase.. Rather than hours or years view shown in the 1970s and 1980s actuated by an external movable permanent will! … why is a switch on the right is just above the one the. The problem causing the controller to reset up above, switching back forth.