Relay is also the name of a series of medium-altitude satellites; the first of which was launched in 1962.
A relay is an electrical switch that opens and closes under control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or overload relay 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 electrical amplifier.
These contacts can be either normally-open, normally-closed, or change-over contacts.
- Normally-open contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive.
- Normally-closed contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive.
- Change-over contacts control two circuits: one normally-open contact and one normally-closed contact.
Operation
When a current flows through the coil, the gpib relay controller latching relay drive circuit resulting magnetic field attracts an hvac relay armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current is switched off, the armature is control relay usually returned by a spring to its resting position. Latching relays exist that require operation of a second coil to reset the contact kinetic relay watches position.
By analogy with the functions of the original remote relay control electromagnetic device, a solid-state relay operates a thyristor or other solid-state switching device with a transformer or light-emitting diode to trigger it.
Types of relay
- A latching relay is mechanically arranged so that the armature can rest in either of two positions. There are two coils that pull the armature in opposite protective relay directions, so the relay can be frame relay switched to one position or the other and then left in that state indefinitely. 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. Some internet relay chat common relay for life fundraising relays may be wired to electrically latch, which offers no electromechanical relay power saving but does ensure that the relay returns to a known state during and after a power outage.
- A reed relay has two, usually normally open, contacts inside a vacuum or inert gas filled glass tube. This protects the contacts relay against atmospheric corrosion. The two contacts are closed by magnetism from a coil around the glass tube, or a permanent magnet moved towards it. See also: reed switch.
- A mercury wetted relay is a form of reed relay sprint relay in which the contacts are wetted with mercury. Such relays are used to switch low-voltage signals (one volt or less), or for high-speed counting and timing applications where the mercury eliminated contact bounce. Mercury wetted relays are position-sensitive and must be mounted vertically applied protective relay to work properly. Because of the toxicity and sound activated relay expense of liquid mercury, these relays are rarely specified for new equipment. See also mercury switch.
- A machine tool relay is a type standardized for industrial control of machine tools, transfer machines, auto kinetic relay seiko watch and other seqential 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. relay races Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller mostly displaced relay games the machine tool relay from sequential control applications.
- A contactor is a very heavy-duty relay used for switching time delay relay electric motors and lighting loads. Such devices are often used for motor starters, and power relay may be built up with kinetic auto relay overload protection devices attached. The overload bosch relay sensing devices contact relay are a form of heat operated relay where a coil heats a bi-metal strip to open contacts, or where a solder pot melts, releasing a spring to operate contacts.
- A Buchholz relay is a safety device sensing the accumulation omron relay of gas in large oil-filled transformers, which will alarm on slow accumulation relay socket of gas or shut down the transformer if gas is produced rapidly in the transformer oil. relay manufacturers
- A Solid State Relay (SSR) is a solid state electronic component that provides a similar function to an electromechanical relay but does seiko kinetic auto relay not have any moving components, increasing long-term solid state relay reliability.
Applications
Relays seiko auto relay watch are used:
- 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 relay contacts in series, the OR function by connecting contacts in parallel. Due to the failure modes of a relay compared with a semiconductor, they are widely used in safety critical logic, such as the control panels of radioactive waste handling machinery.
- as oscillators, also called vibrators. The coil is wired in series with the normally-closed contacts. When a current is passed through the electrical relay relay coil, the relay operates and opens the contacts that carry the supply current. This stops the current and causes the contacts to close again. The digital relay geologix cycle repeats continuously, causing the relay to open and close rapidly. Vibrators are used to generate pulsed current.
- to generate sound. A vibrator, described above, creates a buzzing sound because of the rapid oscillation of the armature. This is the basis of the electric bell, which consists of a vibrator with a hammer attached to the armature so it can repeatedly strike a bell.
Relay application considerations
Selection of an appropriate relay for relay for life fundraiser relay snubber circuits a particular application auto relay watches requires evaluation of many different factors:
- Number and type of contacts - normally open, normally closed, changeover (double-throw)
- 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, 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
- 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.
Protection relay
A protection 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, protection relays relay for life 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, ip relay solenoid-type saturn relay 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 relay switch point. An important transmission line or generator unit would have had cubicles dedicated to protection, with a score of individual electromechanical devices.
Design and theory of these protective devices is an important part of the education safety relay of a electrical engineer who specializes in power systems. Today these devices are nearly entirely replaced (in new designs) with microprocessor-based instruments (numerical relays) frame relay network 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 auto relay watch from seiko relays. However, due to their very long life span, tens of thousands of these "silent sentinels" aromat relay are meter relay still protecting transmission lines and electrical apparatus automotive latching relay driver relay all over the world.
See also
- Ladder programming language
- Schweitzer Engineering Laboratories
References
Westinghouse Corporation, Applied Protective Relaying, 1976, Westinghouse interposing relay general purpose relay Corporation, no ISBN, Library of Congress card no. 76-8060 - a standard reference on electromechanical protection relays (out of print - current edition published by seiko kinetic relay watch ABB)
Terrell Croft and Wilford Summers (ed), American Electricans' Handbook, Eleventh Edition, McGraw Hill, New York (1987) ISBN 0070139326
External links
- Example of the circuitry within a solid state relay
Many manfacturers of relays exist. Some commonly used relays are made by relay racks the following companies:
- Schweitzer Engineering Laboratories, Inc.
- Omron, manufacturer of small control and electronics relays
- Potter and Brumfield
- Opto 22
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Electronics Topics
The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the fields of electronic engineering, and the hardware design side of computer engineering. The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.
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