1.7 Relay Terms and Definitions-Glossary

The following definitions do not include terms peculiar to mathematical formulae, statistical analysis, relay reliability studies, and the like. Such terms are defined in the appropriate chapter. When cross-references are made, the preferred terminology is the one under which the definition appears.

Race, relay. A deficient circuit condition wherein successful operation depends upon a sequence of two or more independent contacts and in which the sequence is not insured by electrical or mechanical interlocking restraints. Ratchet relay. See relay, stepping.
Rated power of an energizing circuit, rated burden of an energizing circuit. The power of burden (watts if dc,volt-amperes if ac) absorbed under the reference conditions by a given energizing circuit of a relay and determined under specified conditions. (IEC)
Rated value of an energizing quantity The value of an energizing quantity to which some of the specified characteristics are referred.(IEC)
Rating, contact. The electrical load-handling capability of relay contacts under specified conditions and for a prescribed number of operations.
Rating, short time. The value of current or voltage that the relay can stand, without injury, for specified short time intervals. (For ac circuits, the rms total value, including the dc component, should be used). The rating recognized the limitations imposed by both thermal and electromagnetic effects.
Ratio, armature lever. The distance through which the armature buffer moves divided by the armature travel (See travel armature). Also, the ratio of the distance from the armature bearing pin (or fulcrum) to the armature buffer in relation to the distance from the bearing pin (or fulcrum) to the center of the pole face.
Rebound, armature. (1) The return motion or bounce-back toward the unoperated position after the armature strikes the pole face during pickup, referred to as armature pickup rebound; (2) The forward motion or bounce in the direction of the operated position when the armature strikes its backstop on dropout, referred to as armature dropout rebound.
Relay. An electric device that is designed to interpret input conditions in a prescribed manner and after specified conditions are met to respond to cause contact operation or similar abrupt change in an associated electric control circuit. Notes: (a) Inputs are usually electric, but may be mechanical, thermal or other quantities. (b) A relay may consist of several units, when responsive to specified inputs, the combination providing the desired performance characteristic.
Relay, all-or-nothing. An electrical relay which is intended to be energized by a quantity, whose value is either: (1) higher than that at which it picks up; (2) or lower than that at which it drops out. (IEC) Note: The adjective "all-or-nothing" can be deleted when no ambiguity will occur.
Relay, alternating current(ac). A relay designed for operation from an alternating-current source.
Relay, annunciator. A relay that indicates the present or former state of a circuit or circuits.
Relay, antenna switching. A special RF relay used to switch antenna circuits.
Relay, automatic homing A stepping relay that returns to its home or starting position under certain prescribed conditions.
Relay, automatic-reset. See reset, automatic.
Relay, auxiliary. A relay that operates to assist another relay or device in the performance of a function.
Relay, bar. A relay so designed that a bar actuates several contact simultaneously. Not to be confused with a relay having bar-shaped contact.(See card, armature.)
Relay, bidirectional or add and subtract relay. A stepping relay in which the rotating wiper contacts may be driven in either direction.
Relay, bimetal. A form of thermal relay using a bimetallic element to activate contacts when heated electrically.
Relay, bistable. An electrical relay which, having responded to an input energizing quantity (or characteristic quantity) and having changed its condition remains in that condition after the quantity has been removed. Another appropriate further energization is required to make it change over. (IEC)
Relay, center-off. See relay, center stable.
Relay, center-stable. A relay that is operated in one of two energized positions and that returns to a third, off position when the operating winding is de-energized. Also referred to as center-off.
Relay, chopper. A relay designed to produce a modified square wave output of the same frequency and bearing a definite phase relationship to a driving sine wave.
Relay, close. differential-A relay having its dropout value specified close to its pickup value.
Relay, coaxial. A special RF relay that opens or closes a coaxial cable or line. It is generally a low impedance device.
Relay, continuous-duty. A relay that may be energized with rated input power and carry a rated load indefinitely without exceeding specified limitations.
Relay, crystal can. A term used to identify a relay housed in a hermetically sealed enclosure that was originally used to enclose a frequency-control type of quartz crystal.
Relay, current-balance. A relay that operates when the magnitude of one current exceeds the magnitude of another current by a predetermined degree.
Relay, current-sensing. A relay that functions as a predetermined value of current; an overcurrent or an undercurrent relay, or a combination of both.
Relay, dashpot. A relay employing the dashpot principle to effect a time delay.
Relay, dependent-time measuring. A specified time measuring relay for which times depend, in a specified manner, on the value of the characteristic quantity. (IEC)
Relay, differential. A relay with multiple windings that functions when the voltage, current, or power difference between the windings reaches a predetermined value.
Relay, direct current (dc). A relay designed for operation from a direct-current source.
Relay, double arm. A relay with two pileups, each actuated by a separate armature arm.
Relay, electrical. A device designed to produce sudden, predetermined changes in one or more electrical output circuits, when certain conditions are fulfilled in the electrical input circuits controlling the device.(IEC)
Note 1-The term relay shall be restricted to a relay unit having a single relaying function between its input circuits and its output circuits.
Note 2-The term relay includes all the components which are necessary for its specified operation.
Note 3-The adjective "electrical" can be deleted when no ambiguity may occur.
Relay, electrical interlock. See relay, interlock.
Relay, electromagnetic. A relay whose operation depends upon the electromagnetic effects of current flowing in an energizing winding.
Relay, electromechanical power controller (EMPC). An electromechanical relay which contains electronic circuitry that monitors electrical characteristics of its containing system and causes the EMPC to open or close based upon its specified parameters. An EMPC combines the traditional function of a relay and a circuit breaker or fuse.
Relay, electromagnetic time delay. A relay in which the actuation of the contacts is delayed by the inductive effect of a conducting sleeve or slug (usually nonmagnetic) or a short-circuited winding over the core.
Relay, electromechanical An electrical relay in which the designed response is developed by the relative movement of mechanical elements under the action of a current in the input circuits. (IEC)
Relay, electrostatic. A relay in which operation depends upon motion of two or more insulated conductors caused by electrostatic effects.
Relay, electrostrictive. A relay in which operation depends upon the dimensional changes of an electrostrictive dielectric.
Relay, enclosed.
(1)Hermetically sealed-A relay contained within an enclosure that is sealed by fusion or other comparable means to ensure a low rate of gas leakage.(Generally metal-to-metal or metal-to-glass sealing is employed.)
(2)Encapsulated-A relay embedded in a suitable potting compound.
(3)Sealed-A relay contained in an unsealed housing.
(4)Covered-A relay contained in an unsealed housing.
Note: The coil and contact assemblies may be separately enclosed and isolated from each other by various combinations of the above enclosures.
Relay, ferreed. Coined name for a special form of dry reed having a return magnetic path of high remanence material that provides a bistable contact.
Relay, flasher. A self-interrupting relay, usually by the thermal type.
Relay, frequency sensitive. A relay that operates when energized electrically at a particular frequency or within specific frequency bands; for example, a resonant reed relay.
Relay, homing. A self-interrupting relay, usually of the thermal type.
Relay, hot-wire. A stepping relay that returns to a specified starting position,(home) prior to each operating cycle.
Relay, hybrid electromechanical-(HEMR). A relay with isolated input and output in which electromechanical and electronic devices are combined to perform a switching function with an electromechanical relay specifications.
Relay, hybrid solid state-(HSSR) A relay with isolated input and output in which electromechanical an electronic devices are combined to perform a switching function with a solid state output.
Relay, impulse.
(1) A relay that follows and repeats pulses, as from a telephone dial;
(2) A relay that operates on the stored energy of a short pulses after the pulse ends;
(3) A relay that discriminates between length and strength of pulses, operating on long or strong pulses and not operating on short or weak ones;
(4) A relay that alternately assumes one of two positions as pulsed.
Relay, independent-timer measuring. A specified-time measuring relay the specified time for which can be considered as being independent, within specified limits, of the value of the characteristic quantity. (IEC)
Relay, inertia. A relay with added weights or other modifications that increase the moment of inertia of its moving parts, either to slow its operation or to cause it to continue in motion after the energizing force ends.
Relay, instruments. A sensitive relay in which the principle of operation is similar to that of instruments such as the electrodynamometer, iron vane, galvanometer, and moving magnet.
Relay, integrating. A relay that operates on the energy stored from a long pulse or a series of pulses of the same or varying magnitude, for example, a thermal relay.
Relay, interlock. A relay with two or more armatures having a mechanical lindage or an electrical interconnection, or both, whereby the position of one armature permits, prevents, or causes motion of another.
Relay, intermittent-duty. A relay which must be de-energized at intervals to avoid excessive temperature or a relay that is energized at intervals, as in pulsing.
Relay, latching. A relay that maintains its contacts in the last position assumed without the need of maintaining coil energization.
(1)Magnetic latching- A relay that remains operated, held either by remanent magnetism in the structure or by the influence of a permanent magnet, until reset. (See relay, bistable.)
(2)Mechanical latching- A relay in which the armature or contacts may be latched mechanically in the operated or unoperated position until reset manually or electrically.
Relay, lockup. See relay, latching.
Relay, magnetostrictive. A relay in which operation depends upon dimensional changes of a magnetic material in a magnetic field.
Relay, manual reset. A relay that may be restored manually to its unoperated position.
Relay, marginal. A relay that functions in response to predetermined changes in the value of coil current or voltage.
Relay, measuring. An electrical relay intended to switch when its characteristics quantity, under specified conditions and with a specified accuracy, attains its operating value. (IEC)
Relay, mechanical time delay. A relay in which operate or release action is delayed by a clockwork, escapement, bellows, dashpot, or other mechanical device.
Relay memory.
(1) A relay having two or more coils and a set of contacts that remain in a position determined by the coil last energized;
(2) Sometimes used for a latching relay.
Relay, mercury contact.
(1) Mercury-wetted contact-A form of reed relay in which the reeds and contacts are glass enclosed and are wetted by a film of mercury obtained by capillary action from a mercury pool in the base of a capsule vertically mounted.
(2) Mercury contact-A relay mechanism in which mercury establishes contact between electrodes in a sealed capsule.
Relay, meter. See relay, instrument.
Relay, monostable. An electrical relay which, having responded to an input energizing quantity (or characteristic quantity) and having changed its conditions, returns to its previous condition when the quantity is removed. (IEC)
Relay, motor-driven. A relay whose contacts are actuated by the rotation of a motor shaft.
Relay, moving coil. See relay, instrument.
Relay, multiposition. A relay that has more than one operate or nonoperate position; e.g., a stepping relay.
Relay, neutral. A relay whose operation is independent of the direction of the coil current, in contrast to a polarized relay.
Relay, non-specified-time. An electrical relay for which the times are not subject to any accuracy specification.(IEC) Relay, open An unenclosed relay.
Relay, over current. A relay that is specifically designed to operate when its coil voltage reaches or exceeds a predetermined value.
Relay, plunger. A relay operated by a movable core or plunger through solenoid action.
Relay, polarized. A relay whose operation is dependent upon the polarity of the energizing current.
(1)Bistable.(1) A tow-position relay that will remain in its last operated position keeping the operated contacts closed after the operating winding is de-energized.
(2)Center-stable. A polarized relay that is operated in one of two energized positions, depending on the polarity of the energizing current, and that returns to a third, off position, when the operating winding is de-energized.
(3)Double-biased. See bistable.
(4)Magnetic latching. See bistable.
(5)Monostable. A monostable polarized relay is a two-position relay that requires current of a pre-determined polarity for operation and returns to the off position when the operating winding is de-energized or is energized with reversed polarity.
(6)Single-biased. See monostable.
(7)Single-side-stable. See center-stable.
(8)Three-position center-off. See center-stable.
(9)Un-biased. See center-stable.
Relay, power. A relay with heavy-duty contacts; usually rated 25 amperes or higher. Sometimes called a contactor.
Relay, reed. A relay using glass-enclosed, magnetic reeds as the contact members.
Relay, RF switching. A relay designed to switch electrical ac energy with frequencies higher than audio range.
Relay, rotary. A relay whose armature is rotated to close the gap between two or more pole faces. (Usually has a balanced armature.)
Relay, rotary solenoid. A relay in which the plunger's or armature's linear motion is mechanically converted into rotary motion.
Relay, sensitive. A relay that operates on comparatively low input power.
Relay, solenoid. See relay plunger.
Relay, solid state (SSR). A relay with isolated input and output whose functions are achieved by means of electronic components and without moving parts.
Relay, solid state power controller (SSPC). A solid state relay which contains electronic circuitry that monitors electrical characteristics of its containing system and causes the SSPC to open or close based upon its specific parameters. A SSPC combines the traditional functions of a relay and a circuit breaker or fuse.
Relay, static. An electrical relay in which the designed response is developed by electronic, magnetic, optical or other components, without mechanical motion. (IEC) See relay, solid state.
Relay, static with output contact, static relay with output contact. A static relay having a contact in one or more of its output circuits. (IEC) See relay, hybrid electromechanical.
Relay, static without output contact, static relay without output contact. A static relay having no output contacts in its output circuits. (IEC) See relay, solid state.
Relay, specified time. An electrical relay in which one or more of the times which characterize it (e.g., operating time) are subject to specified requirements; in particular, accuracy. (IEC)
Relay, stepping. A relay having many rotary positions, ratchet actuated, moving from one step to the next in succesive operations, and usually operating its contacts by means of cams.
Relay, telephone-type. A term sometimes applied to relay with an end -on armature, an L-shaped heel piece, and contact springs mounted parallel to the long axis of the relay coil. Originally used in telephone systems.
Relay, thermal. A relay that is actuated by the heating effects of an electrical current.
Relay, three position. A relay in which operation or release is delayed internally (coil slugs or sleeves), mechanically, (clockwork, bellows, dashpot, etc.), or by an accompanying solid state timing circuit.
Relay, undercurrent. A relay specifically designed to function when its energizing current falls below a predetermined value. (See relay, current sensing.)
Relay, undervoltage. A relay specifically designed to function when its energizing voltage falls below a predetermined value.
Relay, vacuum. A relay whose contacts are sealed in a low pressure environment.
Relay, vibrating reed. See relay, frequency sensitive.
Relay, voltage sensing. A relay that functions as a predetermined voltage relay, an overvoltage or undervoltage relay, or combination of both.
Relay, wire spring. A relay whose contact springs are made of spring wire.
Relay, zero-voltage-turn-on. A relay with isolated input and output in which added control circuitry delays the output turn-on until a zero voltage transition of the ac sine wave is detected. Construction may be all solid state or hybrid with a solid state output.
Release, measured. See operating characteristics, dropout measured.
Release, overtravel. See overtravel armature dropout.
Release specified. See operating characteristics, dropout specified.
Release time. See contact, release time.
Release value. See operating characteristics, dropout value.
Reset. The return of contacts or a mechanism to the normal state (initial conditions).
Reset, automatic. A qualifying term applied to:
(1) A stepping relay that returns to its home position either when it reaches a predetermined contact position or when a pulsing circuit fails to energize the driving coil within a given time. May either pulse forward or be spring reset to the home position.
(2)An overload relay that restores the circuit as soon as an over-current situation is corrected.
Reset, electrical. A qualifying term applied to a relay to indicate the it may be reset electrically after operation.
Reset, manual. A qualifying term applied to a relay to indicate that it may be reset manually after operation.
Residual, armature. The protrusion from the armature or pole face that provides the residual gap ( see residual screw, pin, plate, stud or shim). Residual screw, pin, plate, stud or shim. Non-magnetic screw, pin, plate, stud or shim attached to either the armature or the pole face of a relay to prevent the armature from directly contacting the magnetic core.
Residual setting. See gap residual.
Resistance, contact. The electrical resistance of closed contacts measured at their associated contact terminals.
Resistance, dynamic contact. Variation in contact resistance due to changes in contact pressure during the period in which contacts are motion, before opening or after closing (See Figures 1.1 and 1.2).
Resistance, winding. The total terminal-to-terminal resistance of a winding at a specified temperature.
Resonant reed relay. See relay, frequency sensitive.
Restoring spring. See spring, return.
Retractile spring. See spring, return.
Return. A relay returns when sequentially: (1) it disengages; (2) it passes from an operated condition towards the prescribed initial condition;(3) and it resets. (IEC)
Returning ratio. The ratio of the returning value to the operating value.(IEC)
Ring, mechanical damping. A loose member mounted on a contact spring to reduce contact chatter and bounce.
Ring, shading. A shorted turn surrounding a portion of the pole of an alternating-current electromagnet that delays the change of the magnetic field in that part, thereby tending to prevent chatter and reduce hum.
Rotary stepping relay. See relay, stepping.
Rotary stepping switch. See switch, stepping.