Automotive style miniature relay

A relay is an electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered, in a broad sense, to be a form of an electrical amplifier. This is a scan of a relay as used in cars (cover removed). ... This is a scan of a relay as used in cars (cover removed). ... Electrical switches. ... An electrical network or electrical circuit is an interconnection of analog electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. ... Iron filings in a magnetic field generated by a bar magnet A magnet is material or object that produces a magnetic field. ... Joseph Henry Joseph Henry (December 17, 1797 – May 13, 1878) was a Scottish-American scientist. ... | Come and take it, slogan of the Texas Revolution 1835 was a common year starting on Thursday (see link for calendar). ... Generally, an amplifier is any device that uses a small amount of energy to control a larger amount of energy. ...

Operation

When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current to the coil is switched off, the armature is returned by a force approximately half as strong as the magnetic force to its relaxed position. Usually this is a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing. In electricity, current refers to electric current, which is the flow of electric charge. ... A coil is a series of loops. ... Magnetic field lines shown by iron filings In physics, a magnetic field is a solenoidal vector field in the space surrounding moving electric charges, such as those in electric currents and bar magnets. ... In electrical engineering, an armature is usually the rotating part of an electric motor or dynamo. ... Helical or coil springs designed for tension A spring is a flexible elastic object used to store mechanical energy. ... An electric arc can melt calcium oxide. ...

If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a spike of voltage and might cause damage to circuit components. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle.^[1]

By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a thyristor or other solid-state switching device. To achieve electrical isolation, a light-emitting diode (LED) is used with a photo transistor. Circuit symbol for a thyristor The thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. ... Blue, green and red LEDs. ...

Types of relay

Small relay as used in electronics

small relay scan, upload by MH 12:33, 2004 Dec 14 (UTC) This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... small relay scan, upload by MH 12:33, 2004 Dec 14 (UTC) This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ...

Latching relay

A latching relay has two relaxed states (bistable). These are also called 'keep' relays. When the current is switched off, the relay remains in its last state. This is achieved with a solenoid operating a ratchet and cam mechanism, or by having two opposing coils with an over-center spring or permanent magnet to hold the armature and contacts in position while the coil is relaxed, or with a remnant core. In the ratchet and cam example, the first pulse to the coil turns the relay on and the second pulse turns it off. In the two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the advantage that it consumes power only for an instant, while it is being switched, and it retains its last setting across a power outage.

Reed relay

A reed relay has a set of contacts inside a vacuum or inert gas filled glass tube, which protects the contacts against atmospheric corrosion. The contacts are closed by a magnetic field generated when current passes through a coil around the glass tube. Reed relays are capable of faster switching speeds than conventional relays. See also reed switch. It has been suggested that this article or section be merged into Reed switch. ... Look up Vacuum in Wiktionary, the free dictionary. ... An inert gas is any gas that is not reactive under normal circumstances. ... See corrosive for the hazard. ... A coil is a series of loops. ... It has been suggested that Reed relay be merged into this article or section. ...

Mercury-wetted relay

A mercury-wetted reed relay is a form of reed relay in which the contacts are wetted with mercury. Such relays are used to switch low-voltage signals (one volt or less) because of its low contact resistance, or for high-speed counting and timing applications where the mercury eliminates contact bounce. Mercury wetted relays are position-sensitive and must be mounted vertically to work properly. Because of the toxicity and expense of liquid mercury, these relays are rarely specified for new equipment. See also mercury switch. General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Standard atomic weight 200. ... A Single-Pole, Single-Throw (SPST) mercury switch A mercury switch is a switch whose purpose is to allow or interrupt the flow of electric current in an electrical circuit in a manner that is dependent on the switchs physical position or alignment relative to the direction of the...

Polarized relay

A Polarized Relay placed the armature between the poles of a permanent magnet to increase sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and correct telegraphic distortion. The poles were on screws, so a technician could first adjust them for maximum sensitivity and then apply a bias spring to set the critical current that would operate the relay. A crossbar switch is one of the principal architectures used to construct switches of many types. ...

Machine tool relay

A machine tool relay is a type standardized for industrial control of machine tools, transfer machines, and other sequential control. They are characterized by a large number of contacts (sometimes extendable in the field) which are easily converted from normally-open to normally-closed status, easily replaceable coils, and a form factor that allows compactly installing many relays in a control panel. Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller mostly displaced the machine tool relay from sequential control applications. PLC & input/output arrangements A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. ...

Contactor relay

A contactor is a very heavy-duty relay used for switching electric motors and lighting loads. With high current, the contacts are made with pure silver. The unavoidable arcing causes the contacts to oxidize and silver oxide is still a good conductor. Such devices are often used for motor starters. A motor starter is a contactor with overload protection devices attached. The overload sensing devices are a form of heat operated relay where a coil heats a bi-metal strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload senses excess current in the load, the coil is de-energized. Contactor relays can be extremely loud to operate, making them unfit for use where noise is a chief concern. A contactor previously fitted in an elevator control system. ... Rotating magnetic field as a sum of magnetic vectors from 3 phase coils An electric motor converts electrical energy into mechanical energy. ...

Solid state contactor relay

25 amp or 40 amp solid state contactors

A solid state contactor is a very heavy-duty solid state relay, including the necessary heat sink, used for switching electric heaters, small electric motors and lighting loads; where frequent on/off cycles are required. There are no moving parts to wear out and there is no contact bounce due to vibration. They are activated by AC control signals or DC control signals from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other microprocessor controls. Image File history File linksMetadata Size of this preview: 723 × 599 pixel Image in higher resolution (1726 × 1431 pixel, file size: 466 KB, MIME type: image/jpeg) I, the creator of this work, hereby release it into the public domain. ... Image File history File linksMetadata Size of this preview: 723 × 599 pixel Image in higher resolution (1726 × 1431 pixel, file size: 466 KB, MIME type: image/jpeg) I, the creator of this work, hereby release it into the public domain. ... A solid state relay (SSR) is an electronic switch, which unlike an electromechanical relay, contains no moving parts. ... Rotating magnetic field as a sum of magnetic vectors from 3 phase coils An electric motor converts electrical energy into mechanical energy. ... PLC & input/output arrangements A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. ... A Motorola 68000-based computer with various TTL chips. ...

Buchholz relay

A Buchholz relay is a safety device sensing the accumulation of gas in large oil-filled transformers, which will alarm on slow accumulation of gas or shut down the transformer if gas is produced rapidly in the transformer oil. A Buchholz relay, also called a gas relay or a sudden pressure relay, is a safety device mounted on some oil-filled power transformers and choke coils, equipped with an external overhead oil reservoir called a conservator. ... Three-phase pole-mounted step-down transformer. ...

Forced-guided contacts relay

A forced-guided contacts relay has relay contacts that are mechanically linked together, so that when the relay coil is energized or de-energized, all of the linked contacts move together. If one set of contacts in the relay becomes immobilized, no other contact of the same relay will be able to move. The function of forced-guided contacts is to enable the safety circuit to check the status of the relay. Forced-guided contacts are also known as "positive-guided contacts", "captive contacts", "locked contacts", or "safety relays".

A solid state relay, which has no moving parts

Image File history File links Download high resolution version (1582x1284, 232 KB) Summary Photograph of a Solid State Relay, supplied by RS. Ruler for scale. ... Image File history File links Download high resolution version (1582x1284, 232 KB) Summary Photograph of a Solid State Relay, supplied by RS. Ruler for scale. ... In electronics, solid state circuits are those that do not contain vacuum tubes. ...

Solid-state relay

A solid state relay (SSR) is a solid state electronic component that provides a similar function to an electromechanical relay but does not have any moving components, increasing long-term reliability. With early SSR's, the tradeoff came from the fact that every transistor has a small voltage drop across it. This collective voltage drop limited the amount of current a given SSR could handle. As transistors improved, higher current SSR's, able to handle 100 to 1,200 amps, have become commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients. A solid state relay (SSR) is an electronic switch, which unlike an electromechanical relay, contains no moving parts. ... In electronics, solid state circuits are those that do not contain vacuum tubes. ... In engineering, electromechanics combines electromagnetism and mechanics. ... Advanced Mobile Phone System or AMPS is the analog mobile phone system standard, introduced in the Americas during the early 1980s. ...

Overload protection relay

One type of electric motor overload protection relay is operated by a heating element in series with the electric motor . The heat generated by the motor current operates a bi-metal strip or melts solder, releasing a spring to operate contacts. Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient temperature is provided. Rotating magnetic field as a sum of magnetic vectors from 3 phase coils An electric motor converts electrical energy into mechanical energy. ... Rotating magnetic field as a sum of magnetic vectors from 3 phase coils An electric motor converts electrical energy into mechanical energy. ... A solder is a fusible metal alloy, with a melting point or melting range of 180-190°C (360-370 °F), which is melted to join metallic surfaces, especially in the fields of electronics and plumbing, in a process called soldering. ...

Pole & Throw

Circuit symbols of relays. "C" denotes the common terminal in SPDT and DPDT types.

Since relays are switches, the terminology applied to switches is also applied to relays. A relay will switch one or more poles, each of whose contacts can be thrown by energizing the coil in one of three ways: Image File history File links Relay_symbols. ... Image File history File links Relay_symbols. ... Electrical switches. ...

• Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called a Form A contact or "make" contact.
• Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called a Form B contact or "break" contact.
• Change-over, or double-throw, contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called a Form C contact or "transfer" contact.

The following types of relays are commonly encountered:

• SPST - Single Pole Single Throw. These have two terminals which can be connected or disconnected. Including two for the coil, such a relay has four terminals in total. It is ambiguous whether the pole is normally open or normally closed. The terminology "SPNO" and "SPNC" is sometimes used to resolve the ambiguity.
• SPDT - Single Pole Double Throw. A common terminal connects to either of two others. Including two for the coil, such a relay has five terminals in total.
• DPST - Double Pole Single Throw. These have two pairs of terminals. Equivalent to two SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has six terminals in total. It is ambiguous whether the poles are normally open, normally closed, or one of each.

The diagram on the package of a DPDT AC coil relay

• DPDT - Double Pole Double Throw. These have two rows of change-over terminals. Equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has eight terminals, including the coil.
• QPDT - Quadruple Pole Double Throw. Often referred to as Quad Pole Double Throw, or 4PDT. These have four rows of change-over terminals. Equivalent to four SPDT switches or relays actuated by a single coil, or two DPDT relays. In total, fourteen terminals including the coil.

Image File history File links Relaycov. ... Image File history File links Relaycov. ...

Applications

A DPDT AC coil relay with "ice cube" packaging

Relays are used: Image File history File links ACRelay. ... Image File history File links ACRelay. ...

• to control a high-voltage circuit with a low-voltage signal, as in some types of modems,
• to control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile,
• to detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays),
• to isolate the controlling circuit from the controlled circuit when the two are at different potentials, for example when controlling a mains-powered device from a low-voltage switch. The latter is often applied to control office lighting as the low voltage wires are easily installed in partitions, which may be often moved as needs change. They may also be controlled by room occupancy detectors in an effort to conserve energy,
• to perform logic functions. For example, the boolean AND function is realised by connecting NO relay contacts in series, the OR function by connecting NO contacts in parallel. The change-over or Form C contacts perform the XOR (exclusive or) function. Similar functions for NAND and NOR are accomplished using NC contacts. The Ladder programming language is often used for designing relay logic networks.
  • Early computing. Before vacuum tubes and transistors, relays were used as logical elements in digital computers. See ARRA relay computer, Harvard Mark II relay computer, Zuse Z2 relay computer, Zuse Z3 relay computer.
  • Safety-critical logic. Because relays are much more resistant than semiconductors to nuclear radiation, they are widely used in safety-critical logic, such as the control panels of radioactive waste-handling machinery.
• to perform time delay functions. Relays can be modified to delay opening or delay closing a set of contacts. A very short (a fraction of a second) delay would use a copper disk between the armature and moving blade assembly. Current flowing in the disk maintains magnetic field for a short time, lengthening release time. For a slightly longer (up to a minute) delay, a dashpot is used. A dashpot is a piston filled with fluid that is allowed to escape slowly. The time period can be varied by increasing or decreasing the flow rate. For longer time periods, a mechanical clockwork timer is installed.

A modem (from modulate and demodulate) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. ... In electricity, current refers to electric current, which is the flow of electric charge. ... In 1903, the first U.S. patent for an automobile electric self-starter was issued to Clyde J. Coleman of New York City (No. ... Various solenoid actuators from Trombetta Motion Technologies A solenoid is a loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electrical current is passed through it. ... Karl Benzs Velo model (1894) - entered into the first automobile race An automobile or motor car (usually shortened to just car) is a wheeled passenger vehicle that carries its own motor. ... A circuit breaker is a piece of equipment which is designed to protect an electrical apparatus from damage caused by overload or short circuit. ... Ladder programming language (also known as ladder logic, relay ladder logic or ladder diagrams) is a graphical language very popular for programming programmable logic controllers. ... ...

Relay application considerations

A large relay with two coils and many sets of contacts, used in an old telephone switching system.

Selection of an appropriate relay for a particular application requires evaluation of many different factors: This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ...

• Number and type of contacts - normally open, normally closed, changeover (double-throw)
• In the case of changeover, there are two types. This style of relay can be manufactured two different ways. "Make before Break" and "Break before Make". The old style telephone switch required Make-before-break so that the connection didn't get dropped while dialing the number. The railroad still uses them to control railroad crossings.
• Rating of contacts - small relays switch a few amperes, large contactors are rated for up to 3000 amperes, alternating or direct current
• Voltage rating of contacts - typical control relays rated 300 VAC or 600 VAC, automotive types to 50 VDC, special high-voltage relays to about 15,000 V
• Coil voltage - machine-tool relays usually 24 VAC or 120 VAC, relays for switchgear may have 125 V or 250 VDC coils, "sensitive" relays operate on a few milliamperes
• Package/enclosure - open, touch-safe, double-voltage for isolation between circuits, explosion proof, outdoor, oil-splashresistant
• Mounting - sockets, plug board, rail mount, panel mount, through-panel mount, enclosure for mounting on walls or equipment
• Switching time - where high speed is required
• "Dry" contacts - when switching very low level signals, special contact materials may be needed such as gold-plated contacts
• Contact protection - suppress arcing in very inductive circuits
• Coil protection - suppress the surge voltage produced when switching the coil current
• Isolation between coil circuit and contacts
• Aerospace or radiation-resistant testing, special quality assurance
• Expected mechanical loads due to acceleration - some relays used in aerospace applications are designed to function in shock loads of 50 g or more
• Accessories such as timers, auxiliary contacts, pilot lamps, test buttons
• Regulatory approvals
• Stray magnetic linkage between coils of adjacent relays on a printed circuit board.

Acceleration is the time rate of change of velocity, and at any point on a velocity-time graph, it is given by the slope of the tangent to that point basicly. ... Look up aerospace in Wiktionary, the free dictionary. ... In mechanics, a shock is a sudden acceleration or deceleration caused, for example, by impact or explosion. ... The term g force or gee force refers to the symbol g, the force of acceleration due to gravity at the earths surface. ...

Protective relay

A protective relay is a complex electromechanical apparatus, often with more than one coil, designed to calculate operating conditions on an electrical circuit and trip circuit breakers when a fault was found. Unlike switching type relays with fixed and usually ill-defined operating voltage thresholds and operating times, protective relays had well-established, selectable, time/current (or other operating parameter) curves. Such relays were very elaborate, using arrays of induction disks, shaded-pole magnets, operating and restraint coils, solenoid-type operators, telephone-relay style contacts, and phase-shifting networks to allow the relay to respond to such conditions as over-current, over-voltage, reverse power flow, over- and under- frequency, and even distance relays that would trip for faults up to a certain distance away from a substation but not beyond that point. An important transmission line or generator unit would have had cubicles dedicated to protection, with a score of individual electromechanical devices. Each of the protective functions available on a given relay are denoted by standard ANSI Device Numbers. For example, a relay including function 51 would be a timed overcurrent protective relay. To meet Wikipedias quality standards, this article or section may require cleanup. ... For delivered electrical power, see Electrical power industry. ... The ANSI Standard Device Numbers denote what features a protective device supports (such as a relay or circuit breaker). ...

Design and theory of these protective devices is an important part of the education of an electrical engineer who specializes in power systems. Today these devices are nearly entirely replaced (in new designs) with microprocessor-based instruments (numerical relays) that emulate their electromechanical ancestors with great precision and convenience in application. By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays. However, due to their very long life span, tens of thousands of these "silent sentinels" are still protecting transmission lines and electrical apparatus all over the world. This article or section does not cite its references or sources. ...

Top, middle: reed switches, bottom: reed relay

reed relay and reed switches scan, upload by MH 12:34, 2004 Dec 14 (UTC) This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... reed relay and reed switches scan, upload by MH 12:34, 2004 Dec 14 (UTC) This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ...

Overcurrent relay

An "Overcurrent Relay" is a type of protective relay. The ANSI Device Designation Number is 50 for an Instantaneous OverCurrent (IOC), 51 for a Time OverCurrent (TOC). In a typical application the overcurrent relay is used for overcurrent protection, connected to a current transformer and calibrated to operate at or above a specific current level. When the relay operates, one or more contacts will operate and energize a trip coil in a Circuit Breaker and trip (open) the Circuit Breaker.

See also

• Contactor
• Dry contact
• Wire spring relay

A contactor previously fitted in an elevator control system. ... There are very few or no other articles that link to this one. ... A wire spring relay had springs made from drawn wires of phosphor bronze, rather than from flat sheet metal as in the earlier flat spring relay. ...

References

1. Vladimir Gurevich "Electrical Relays: Principles and Applications", CRC Press (Taylor & Francis group), London - New York, 2005, 704 pp. 2. Westinghouse Corporation, Applied Protective Relaying, 1976, Westinghouse Corporation, no ISBN, Library of Congress card no. 76-8060 - a standard reference on electromechanical protection relays (out of print - current edition published by ABB)

3. Terrell Croft and Wilford Summers (ed), American Electricians' Handbook, Eleventh Edition, McGraw Hill, New York (1987) ISBN 0-07-013932-6

1. ^ Mason, C. R., Art & Science of Protective Relaying, Chapter 2, GE Consumer & Electrical [1],

External links

• Information about relays and the Latching Relay circuit
• Example of the circuitry within a solid state relay
• Solid state relay -- heat sink and thermal considerations
• "Harry Porter's Relay Computer", a computer made out of relays.