Reed RelayMate Page 3 Reed Relay Basics Reed relays are deceptively simple devices in principle. A few million reed relays were used from the 1930s to the 1960s for memory functions in Bell System electromechanical telephone exchanges. All rights reserved. However, at their present stage of development, it seems unlikely they will compete in the general market with reed relays as the developers concentrate on high value niche opportunities and military applications. The receive/transmit switch of a mobile phone, for example, has long been a target for MEMS developers. See Figure 2. By continuing on our website, you agree to our use of cookies in accordance with our Cookie Policy. Stephen Kirk is project manager at Industrial Automation Group, a system integrator in Modesto, California. Relays with low-path resistance have a large capacitive load (sometimes measured in nanofarads for high-capacity switches), which restricts bandwidth and introduces capacitive loading. The main switching choices are electromechanical relays (EMR), reed relays, and solid-state relays (SSR). Graham Dale, Technical Director, Pickering Electronics. Join our newsletter to keep up-to-date with the latest Reed Relay technology. Reed relays are naturally isolated by the coil from the signal path; solid-state relays are not, so an isolated drive has to be incorporated into the relay. The capacitance of a solid-state FET switch is considerably higher than a reed relay. When the coil is energized, the two reeds are drawn together such that their contacts complete a path through the relay. In other cases multiple relay types may be appropriate. Reed relays are discussed below. Because the MOSFET is doing the switching, however, there is no galvanic barrier between its contacts. A reed switch is made up of two metal blades made up of ferromagnetic material hermetically sealed in a glass tube which also supports the metal blades. Relays have the same subsystems and principles of operation regardless of whether these are electromechanical relays or electronic relays or designed to switch signal or high-power loads. Your email address will not be published. As the capacitive load is decreased, the FET size has to decrease, and the path resistance increases. The biggest advantage for MEMS relays—if they can be made reliable—is their low operating power and fast response. Pickering Electronics, an established reed relay manufacturer, was founded in 1968, and even then some were saying that these electromechanical devices would have a limited lifetime. This month's article focuses on the most common relay types: electromechanical, reed, and solid state. Electromechanical relays (EMRs) are widely used in industry for switching functions and often can be the lowest cost relay solution available to users. There are different types of the relay, e.g., Reed Relay, Hybrid Relay, Thermal Relay, Solid State Relay, and Electromagnetic Relay, etc. Contact plating materials and methods also have changed, particularly in the areas of cleanliness, purity of materials, and the reduction of microscopic foreign particles or organic contamination, resulting in superb low-level performance. The reed relay consists of a switch with magnetic contacts that move under the influence of an external magnetic or the induced field from its solenoid. For any application, consider all of the system parameters before choosing a given relay type. A Reed … The spring force in the reeds is often not sufficient to mechanically break the weld after the drive current has been turned off which renders the relay unusable. The leakage current is nonlinear. Learn more about our privacy statement and cookie policy. Manufacturers have made huge investments in manufacturing technology to make the relays in high volumes. Electronics firm celebrates 50 years in business, High-voltage reed relays to be showcased at SEMICON West, https://www.youtube.com/watch?v=zTbv5szQNoA&t=12s. Dry reed relays are made of coils wrapped around reed switches. This does help lead to higher contact ratings but also may increase wear on the contact plating. Relays convert an electrical input signal on the primary side to an intermediate and non-electric physical signal. The tradeoff, however, is that the smaller contacts on the reed relay make it much more susceptible to damage from arcing when closing a circuit. Thermal overload relays get used the most when there is a demand for thermal relays. Michael P. Collins is president of MPC Management, a consulting company in Portland, Oregon. This page covers basics of relay and types of relay viz. This operating speed may be too slow for some applications. Reed Relays are available at Mouser Electronics from industry leading manufacturers. Electromechanical Relays Electromechanical relays have a coil of wire with a rod passing through the middle (forming an electromagnet), an armature mechanism, and one or more sets of contacts. The speed differences arise because the moving parts are simpler and lighter compared to EMRs. This is a measure of the rate at which a relay can reliably switch from one state to another. This site uses cookies to offer you a better browsing experience. A few magnetic strips are found in reed relays. Reed relays are thus not ideal for extremely low-voltage applications as their thermal EMF may introduce enough noise to cause errors in your measurements. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts, or combinations thereof.. Like SSRs, FET switches are not mechanical devices. The small size and high-speed of the reed relay make it a great choice for many switching applications. 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. They are comprised of at least two overlapping blades, or reeds, which are sealed within a gas-filled capsule. SSRs are useful for high-voltage applications because the LED actuation does provide a galvanic isolation barrier between the control circuitry and the MOSFET. Memory device. Reed relays and reed switches are used in many areas where smaller, faster acting relays are needed in an electronic or electrical circuit. Reed relays have hermetically sealed contacts, which lead to more consistent switching characteristics at low signal levels and higher insulation values in the open condition. A well-designed and correctly used part will give a long and reliable life. Some key parameters of each relay type are outlined in Table 1. Part 1 of this two-part series answered the question. For reed relays, however, the contacts are much smaller and lower mass than those used in electromechanical relays. The reed relays’s mechanical lifetime is also much higher than an electromechanical relay. When an arc jumps across the contacts, it can melt a small section of the contact surface. The ferromagnetic materials from which reed relays are constructed cause them to have a higher thermal EMF than an equivalent electromechanical relay. A REED relay is manufactured with the same meticulous care as taken for the protection of the While the mechanical construction of electromechanical relays allows for much flexibility in switching capability, they have one important limitation: speed. Part 1 of this two-part series answered the question, “What is a reed relay?” This article delves into the differences between reed relays and other switching technologies. The technology challenges have resulted in a number of vendors involved in MEMS failing and either ceasing to trade or closing down their programs. Reed relays are glass-encased contacting relays that excel in dusty and fumy settings. Thermal relays are commonly utilized for the purpose of motor protection. FET switches use a series of CMOS transistors to implement the switching. Any capacitance in the system can contribute to inrush currents, whether it is in a reactive device under test or from a shielded cable. Solid-state relays; Electromechanical relays; Dry Reed Relays. There is a large variety of these switches available. In general, instrument grade reed relays have the longest mechanical life because the relay has few moving parts. The on-resistance also can be nonlinear, varying with load current. Latching relay is really a generic term that is used to describe the type of relay that maintains its position after the power is removed. The Reed Sensor Vs Hall Effect And Electromechanical training focuses on how to select the correct technology for a given sensor requirement. How do reed relays compare with other switching technologies. A reed relay in many ways is a near perfect switching element with a simple metallic path. Also, because there are no mechanical parts or LEDs in the packaging, FET switches can be very small. Since the genesis of solid-state relays some decades ago, the argument about which is better, solid-state relays (SSRs) or electromechanical relays (EMRs), has raged on. The term “solid-state relay” refers to a class of switches based on semiconductor devices. Rao) 2.why In comparison table relay resistance are different unit? SSRs are a faster alternative to electromechanical relays because their switching time is dependent on the time required to power the LED on and off - approximately 1 ms and 0.5 ms respectively. solid-state-relay-diagram.gif Actually, SSRs aren't EMRs typically have a lower contact resistance than reed relays because they use larger contacts and normally can use materials of a lower resistivity than the nickel iron used in a reed switch capsule. Danny Weiss is senior product manager at Newark element 14. Electromechanical relays Reed relays for switching contacts and more. The reed relay was invented in 1936 by Bell Telephone Laboratories. The difference arises because of the lack of moving parts in reed relays compared to EMRs. Reed relays have longer mechanical life (under light load conditions) than EMRs, typically of the order of between a factor of 10 and 100. Its temperature sensors and other bimetallic elements assist in giving this protection to the motor. 8 standexmeder .com Reed Switch Characteristics Fig. In the case of Pickering Electronics’ relays, the coil-winding bobbin also has been dispensed with in favor of former-less coils, which has reduced package sizes. Because reed relays are so susceptible to contact damage, inrush currents from system capacitance can be particularly dangerous. Direct drive of the transistor gate allows for much faster switching speeds because the power-on power-off time of the LED is not an issue. SSRs are a nice alternative to mechanical relays but have higher path resistances and are not fully isolated between the contacts. The reed relay was invented in 1936 by Bell Telephone Laboratories. Like reed relays, MEMS can be fabricated so the switch part is hermetically sealed (either in a ceramic package or at a silicon level), which generally leads to consistent switching characteristics at low signal levels. The reed switch is composed of two overlapping ferromagnetic blades (called reeds) hermetically sealed within a glass capsule that is filled with an inert gas. Because of their larger contacts, EMRs also often can better sustain current surges. Email: sales@pickeringrelay.com, Pickering Electronics LtdStephenson Rd, Clacton, Essex, England, CO15 4NL. Because they are FET based, FET switches share many of the advantages and disadvantages of SSRs. In general, FET switches are the fastest of the switches discussed here. Instead, the market for high-quality reed relays has increased into areas that were inconceivable in those days. There are two types of mechanical relays: reed relays and electromechanical relays (EMRs). Please view our large selection of reed relays below. Advances in technology have increased their mechanical lifetime but electromechanical relays still do not have as many possible actuations as a comparable reed relay. Reed relays are electromechanical relays that consist of a reed switch wrapped in a metal coil. Because there are no mechanical parts, their life expectancy is higher than an electromechanical or reed relay. Electromechanical relays may also be damaged from arcing but the energy required to cause this is much higher. Relays come in a variety of form factors, styles, and technologies. If used correctly, a reed relay is a superbly reliable device. Their robustness makes them well suited for many applications, particularly where switching speed is not the highest concern, and their versatility means you can use them on all types of switching configurations including general purpose, multiplexers, and matrices. Much has been written about the promise of MEMS switches, particularly for RF switching, but availability in commercially viable volumes at the time of writing is very limited. The contacts on electromechanical relays tend to be larger and more robust than some other relay types. Because the connection is made via a transistor instead of physical metal like in electromechanical and reed relays, the contact resistance for an SSR is greater. Often a multiple-reed relay was used, with one of the reeds latching the relay, and the other or others performing logic or memory functions. Although there are no metal contacts to weld, damage to the MOSFET can render the relay unusable.SSRs are common on matrices and multiplexers.Â. The energizing coil is wrapped around the glass, and when a current passes through the coil, a magnetic field generated that causes the reeds to come together. SSRs are constructed using a photo-sensitive MOSFET device with an LED to actuate the device. Electromechanical relays are used in a wide variety of switch modules. Since that time, it has gradually evolved from very large, relatively crude parts to the small, ultra-reliable parts we have today. #1 The basic hermetically sealed Form 1A (normally open) Reed Switch and its component makeup. Some, such as PIN diodes, are designed for RF applications, but the most commonly found devices that compete with reed relays are based on FET switches. Thomas Stevic is controls engineer at Zed Industries, a thermoforming and plastic packaging machine builder in Vandalia, Ohio. A solid-state FET switch uses two MOSFETs in series and an isolated gate driver to turn the relay on or off. Mouser is an authorized distributor for many reed relay manufacturers including COTO Technology, Magnecraft, MEDER, TE Connectivity & more. The glass is filled with inert gas. Reed relays are really most useful only for switching low currents. Your email address will not be published. This isolation makes electromechanical relays an excellent choice for situations where galvanic isolation is required. Note that there is a variation of the relay 900x-xx-02 which has a bias magnet to hold it closed, but that is not the part number you state. Electromechanical relays are available in both latching and non-latching varieties. Electromechanical relays typically have shorter mechanical lifetimes than other types. The use of high-volume manufacturing methods often makes EMRs lower cost than reed relays, but within the achievable ratings of reed relays, the reed relay has much better performance and longer life. Common relay types include electromechanical, dry reed, and solid state. Reed relays are more often found on matrix and multiplexer modules than general purpose modules. +1.866.782.6339 | Search for: FET switches provide a fast, low-cost solution but have the limitation of only working with low voltages. EMRs can have much higher ratings than reed relays because they use larger contacts; reed relays usually are limited to carry currents of up to 2 A or 3 A. When the coil is de-energized, the spring force in the reeds pulls the contacts apart. FET switches are most often used in multiplexer configurations for higher speed, low-voltage applications. The larger contacts give them the ability to withstand unexpected surge currents caused by parasitic capacitances present in your circuit, cables, etc. Reed relays can also be the best answer to ap-plications needing excellent radio-frequency performance, since their However, this percentage continues to gradually increase every year. One major drawback of the FET switch, however, is that it lacks a physical isolation barrier and thus may only be used with low-voltage signals. These are often used in applications where the relay must switch back to a safe state in the event of a power failure. Terms and Conditions | Privacy Policy | Cookie Policy, Single-in-Line (SIL/SIP) Relays Series 100 – 110, Single-in-Line (SIL/SIP) Relays Series 111 – 131. They contain a reed switch, a coil for creating a magnetic field, an optional diode for handling back EMF from the coil, a package and EMRs are designed to have a wiping action when the contacts close, which helps to break small welds and self-clean their contacts. When there is no gate drive on the MOSFET, the drain-source channel on the MOSFET has a very high resistance providing the disconnection between the contacts. There are some notable differences between reed relays and EMRs which users should be aware of: Reed relays and EMRs both behave as excellent switches. 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