R

R (symbol) Symbol used to denote resistance in ohms.

rack (hardware) A cabinet used to house components, which permits convenient removal of portions of the equipment for repair or examination. Original racks were standardized steel frames for 19-in. relay panels in telephone exchanges. Today, racks vary in size and shape to meet the specialized requirements of aircraft, computer, military electronics, and test equipment manufacturers. Racks accept equipment packages sometimes referred to as "bins," "modules," and "black boxes."

rack and panel connector (connector) Mating connectors of which one - usually the plug - is mounted inside a cabinet (rack). The receptacle is attached to the back of a sliding drawer, and mates with the plug when the drawer is fully inserted.

random-access memory (RAM) (circuit/system) See memory, random-access.

Rated Voltage - The maximum voltage at which an electrical component can operate for extended periods without undue degradation or safety hazard.

REA - Abbreviation for Rural Electrification Administration, which is part of the U.S. Dept. of Agriculture. REA establishes specifications and provides approval for telephone station wire and power cable.
receptacle (connector) In coaxial rf connectors the receptacle is usually the fixed or stationary one that is mounted on a panel. In shell type multiple-contact connectors the receptacle usually contains the pin contacts and is mounted on the "cold" side of the circuit such as in a drawer or "black box." Receptacles mate with plugs.

rectification (circuit) The process of converting alternating current into a unidirectional current, by removing or inverting that part of the wave laying on one side of the zero amplitude axis.

redundancy (circuit/system) Any deliberate duplication, or partial duplication, of circuitry or information to decrease the probability of a system or communication failure.

reflection (electrical) The backward transmission of electrical energy caused by a change in impedance.

reflection coefficient (fiber optic) The fraction of light power reflected backward at the fiber end face. This accounts for about a .2 to .3 dB loss, typically.

Reflection Loss--The part of a signal which is lost due to reflection of power at a line discontinuity.

refractive index (n) (fiber optic) The ratio of the speed of light in a vacuum (c) to the speed of light in an alternate medium(v). n=c/v

register mark (process/component) A mark used to establish the relative position of one or more printed wiring patterns, or portions thereof, with respect to their desired locations on one or both sides of a printed wiring base.

relay (device) General: An electrical device that is designed to interpret input conditions in a prescribed manner, and - when specified conditions are met - to respond by causing contacts to operate, or similar abrupt changes in associated electric control circuits. Inputs are normally electric, but may be thermal, mechanical, or other qualities. Limit switches and other such simple devices are not to be considered as relays. A relay is an electrically operated switch.  Electromechanical: An electromagnetic switch employing an armature to open or close contacts. A small current through the coil actuates the armature, and thus controls a heavy duty circuit at the contacts.

relay contact bounce (chatter) (device/circuit) Undesired intermittent closure of open contacts or opening of closed contacts. This may occur either when the relay is operated or released, or when the relay is subjected to external shock or vibration. The term "bounce" is normally associated with internal causes.

repeater (circuit) A device that receives, amplifies and otherwise reconditions, and retransmits a signal.

reset (circuit) The operation of returning an electronic, or electrical, device to its original or "start" point. Most AMP data terminals offer manual reset, automatic reset, or both.

residual forces (property) The elastic forces which remain after each contact member has been deformed or deflected to its final state.

resiliency (property) That property of a strained body which enables it to recover its size and shape as it is unloaded after some initial deformation.

resist (process/component) A material such as ink, paint, metallic plating, etc used to protect the desired portions of the conductive pattern from the action of the etchant, solder, or plating.

Resistance - A measure of the difficulty in moving electrical current through a medium when voltage is applied. It is measured in ohms.

resistor (component) A circuit component which offers resistance to the flow of electric current. Its electrical size is specified in ohms or megohms (1 megohm = 1,000,000 ohms). A resistor also has a power handling rating measured in watts, which indicates the amount of power which can safely be dissipated as heat by the resistor.

Resonance--A frequency at which captive reactance and inductive reactance are equal and therefore cancel one another's effects.

restricted entry (component feature) A design feature incorporated in a female contact to prevent the entry of an oversize pin or test probe.

retaining ring (hardware) A small circular steel ring, often resembling the letter "C," that is usually inserted into a slot in a pivot pin to hold the pin in a specified position.

retaining spring (connector/accessory) Used to balance contact pressure and increase board retention when a single-sided pc board is used in a connector designed for two-sided boards. A limited number of springs are used to replace the contacts in the unused side of the connector.

RETMA (organization) Abbreviation for Radio-Electronics-Television Manufacturers' Association. Now changed to Electronics Industries Association (EIA).

Retractable Cord - Cord having specially treated insulation or jacket so that it will retract like a spring.

Reverse Lay - Cable with more than one layer of conductors with each layer cabled in different direction.

RF--Abbreviation for radio frequency.

RFI - Abbreviation for radio frequency interference.
RG/U--Symbol used to designate coaxial cables that are made to Government Specification (e.g., RG-58U; in this designation the "R" means radio frequency, the "G" means Government, the "58" is the number assigned to the government approval, and the "U" means it is a universal specification).

rib (feature) Configuration designed into a plastic part to provide lateral, horizontal, or other structural support.

Ribbon Cable--A flat cable of individually insulated conductors lying parallel and held together by means of adhesive or woven textile yarn.

right-angle edge connector (connector) The plug is mounted to a chassis or back panel, and the receptacle is mounted along an edge of - and soldered to - the circuits of a printed circuit board. Pins of the receptacle are generally simple rod stock bent at right angles and molded into the receptacle insert. The board and receptacle assembly is mated with the plug to complete circuit wiring.

Ring--A Local Area Network topology in which data is sent from workstations via a loop or ring. One conductor of a pair (vs. tip).

ring network (network) A network topology in which nodes are connected as point-to-point links in an unbroken circular configuration.

Rise Time--The time required for a component or logic circuit to change from the quiescent to the transient state when an input is applied. (i.e. elapsed time between application of input and attainment of full output level).

RMS--Abbreviation for root mean square.

robotics (technology) The theory and application of robots, a completely self-contained electronic, electric, or mechanical device, to such activities as manufacturing.

roentgen (property) The amount of radiation that will produce one electrostatic unit of ions per cubic centimeter volume.

Root Mean Square--The effective value of an alternating current, corresponding to the direct current value that will produce the same heating effect.

Rope Strand - Conductor composed of groups of twisted strands.

rotary switch (component) A multi-position switch operated by rotating a control knob (attached to its shaft) either clockwise, counterclockwise, or both.

rotor (component/motor) The rotating member of a motor that includes a shaft. Commonly called the armature.

RS 232, 422, 449 (computer) A series of standards defining the physical link between units of data communication equipment.

rubber (material) An elastomer capable of rapid elastic recovery. Specifically, natural rubber, the standard of comparison for elastomers.

RZ data rates (data format) Return to zero. A data transmission format in which the circuit must switch from 0 to 1 and back to 0 in a single clock pulse each time a logical 1 is presented. RZ rates are generally half those of NRZ rates.

See also NRZ data rates.