R - Symbol for electrical resistance or resistor.
Raceway - A channel for holding electric wires or cables.
Rack - 1. Same as cabinet. 2. The vertical or horizontal open support usually made of aluminum or steel that is attached to a ceiling or wall. Cables are laid in and fastened to the rack.
Rack mount - Designed to be installed in a cabinet.
Radio frequency - The frequencies in the electromagnetic spectrum that are used for radio communications. A band of frequencies between 10 kilohertz and 100 gigahertz.
RADIUS (remote authentication dial-in user service) - A service to authenticate dial-in users on a LAN (RADIUS server).
RAID (redundant array of inexpensive disks) - A term used to describe a storage systems’ resilience to disk failure through the use of multiple disks and by the use of data distribution and correction techniques.
RAM (random access memory) - Volatile memory.
Random interlace - A scanning technique commonly used in CCTV systems in which there is no external control over the scanning process. There is no fixed relationship between adjacent lines and successive fields.
Random winding - A winding in rotating equipment wherein wires do not lie in an even pattern.
Range finder - Used to determine the focal length needed and what the picture will look like on the monitor. The user looks through the device and adjusts the range finder to the desired picture. Numbers on the outside of the range finder indicate the focal length needed.
Raster - The rectangular pattern of scanning lines upon which the picture is produced. The illuminated face of the TV monitor without the video information present.
RBOC - Regional Bell Operating Company.
REA (Rural Electrification Agency) - A federally supported program to provide electrical service to rural area. Now referred to as Rural Utilities Services (RUS).
REACH (REGISTRATION, EVALUATION AND AUTHORIZATION OF CHEMICALS) - A European community regulation on the safe use of chemicals. Companies selling into the European market are required to provide compliance information to their downstream users. Compliance requires the investigation of the supply chain for the presence of certain chemicals called SVHCs (substances of very high concern). REACH began in 2008. Chemicals will be added for a period of several years.
Reactance - The opposition offered an alternating electron flow by a capacitance or inductance. The amount of such opposition varies with the frequency of the current. The reactance of a capacitor decreases with an increase in frequency; the opposite occurs with an inductance. The imaginary part of impedance.
Real-time system - An online computer that generates output nearly simultaneously with the corresponding inputs. Often, a computer system whose outputs follow by only very short delay its inputs. Also called transaction processing.
Recovered diameter - Diameter of shrinkable products after heating has caused it to return to its extruded diameter.
Red plague - A powdery, brown-red growth sometimes found on silver-coated copper conductors and shield braids.
Redraw - The consecutive drawing of wire through a series of dies to reach a desired wire size.
Redundancy - The inclusion of extra assemblies of circuits within the UPS, with provision for automatic switchover from a failing assembly or circuit to its operational counterpart.
Reel - A revolving flanged device made of plastic, wood or metal, used for winding flexible cable. Also called a spool.
Reference edge - See INDEX EDGE.
Reference junction - The junction of a thermocouple that is at a known reference temperature. Also known as the “cold” junction, it is usually located at the EMF measuring device.
Reflected light - The scene brightness or the light being reflected from a scene. Usually it represents 5 to 95 percent of the incident light, and it is expressed in foot-lamberts.
Reflection loss - The part of a signal that is lost to reflection of power at a line discontinuity.
Reflection - The change in direction (or return) of waves striking a surface. For example, electromagnetic energy reflections can occur at an impedance mismatch in a transmission line, causing standing waves.
Reflow soldering - The process of connecting two solder-coated conductive surfaces by re-melting of the solder to cause fusion.
Refraction - The bending of light waves or rays as they go from one material to another due to the difference in velocities in the materials.
Reinforced sheath - The outer covering of a cable that has a reinforcing material, usually a braided fiber, molded in place between layers.
Reliability - The probability that a device will function without failure over a specified time period of amount of usage.
Remote alarms - Alarm indications or status displayed at the distant end of a foreign location to the transmission line.
Repeater - 1. A device used to extend the length, topology or interconnectivity of the physical network medium beyond the limits imposed by a single segment. Repeaters perform the basic actions of restoring signal amplitude, waveform and timing applied to normal data and collision signals. 2. In an ISN system, a module in every information interface carrier that synchronizes bus transmissions throughout the packet controller by repeating on each IIC the timing and transmission signals generated by the clock module in the control and interface unit.
Resin - A solid or semisolid organic substance, originally of plant origin but largely synthesized now. Resins are broadly classified as thermoplastic or thermoset according to whether they soften or harden with the application of heat.
Resistance - In DC circuits, the opposition a material offers to current, measured in ohms. In AC circuits, resistance is the real component of impedance, and may be higher than the value measured at DC.
Resistive conductor - A conductor with high electrical resistance.
Resistivity - A material characteristic opposing the flow of energy through the material – expressed as a constant for each material - is affected by temper, temperature, contamination, alloying, coating, etc. The ability to resist the flow of electrical current either through the bulk of the material or on its surface. The unit of volume resistivity is the ohm-cm. The unit of surface resistivity is ohms/m2.
Resistor color code - A method of indicating resistance value and tolerance. The first color represents the first significant figure of the value. A second color represents the second significant figure and the third is the multiplier or the number of zeros that follow two significant figures. When there is a fourth color band, it indicates the tolerance.
Resistor - An electronic component designed to have a specific value of resistance.
Resolution - A measure of the ability of a camera or television system to reproduce detail. That is the number of picture elements that can be reproduced with good definition. It is a factor of the pickup device or the TV CRT characteristics and the video signal bandwidth.
Resonance - An AC circuit condition in which inductive and capacitive reactance interact to cause minimum or maximum circuit impedance.
Retained image (image burn) - A change produced in or on the target of the pickup device that remains for a large number of frames after the removal of a previously stationary light image and that yields a spurious electrical signal that corresponds to that light image.
Retractile cord - A cord having specially treated insulation or jacket, so it will retract like a spring. Retract ability may be added to all or part of cord’s length.
Return loss - A measure of the degree of impedance mismatch between two impedances. It is the ratio, expressed in dB, of the amplitude of a reflected wave to the amplitude of the main wave at the junction of a transmission line and terminating impedance.
Return wire - A ground wire or the negative wire in a direct-current circuit.
Return - Inbound direction; toward the headend.
Reverse direction - The direction on the cable from the modem to the headend.
Rew - A 600 volt Canadian wire type covered by CSA standards. Made with thermoset insulation.
REX (request to exit) - Sometime referred to as RQE.
RF (radio frequency) - Uses electromagnetic waveforms used for transmission, usually in the megahertz (MHz) range. Electromagnetic waves are usually transmitted between 500 kHz and 300 GHz.
RF modem (radio frequency modem) - Device used to convert digital data signals to analog signals (and from analog to digital) then modulate/demodulate them to/from their assigned frequencies.
RFI (radio frequency interference) - The disruption of radio signal reception caused by any source that generates radio waves at the same frequency and along the same path as the desired wave.
RFID (radio frequency identification) - A type of wireless access control technology between a proximity card and a reader. The most common is the 125 kHz frequency used with proximity cards. There is also a 13.56 MHz version that is a contactless smart card credential.
RG (residential gateway) - A network interface device that provides a means to access a service delivered to the home.
RG-58U 50-ohm coaxial cable assembly - Used as Ethernet thinnet trunk cable and many other 50-ohm compatible systems. True Ethernet has a standard center conductor.
RG-59U 75-ohm coaxial cable assembly - Used as interconnect data equipment for the Wang system CATV, and all other compatible data, voice, baseband and broadband video systems.
RG-62U 93-ohm coaxial cable assembly - Used extensively on the IBM cabling system and all other compatible systems.
RG-U - RG is the military designation for coaxial cable, and U stands for general utility.
RHH - Rubber-insulated, heat-resistant wire, rated 90°C in dry and damp locations. A UL cable type.
RHW - Rubber-insulated building wire, heat and moisture-resistant, 75°C dry or wet. A UL cable type.
RHW-2 - Rubber-insulated building wire, heat and moisture-resistant, 90°C dry or wet. A UL cable type.
RI - Ring in.
Ribbon cable - A flat cable of individually insulated conductors lying parallel and held together by means of adhesive or an extruded polymer web.
Ribbon fiber cable - A cable that accommodates 1 to 12 ribbons, each ribbon having1 2 fibers for a cable size range of 12 to 144 fibers. Ribbon cables are designed for use in large distribution systems where small cable size and high pulling strength are important.
Ridge marker - One or more ridges running laterally along the outer surface of a plastic insulated wire for purposes of identification.
Rigid coaxial cable - Nonflexible coaxial cable, usually a metal tube armored coaxial cable. Sometimes called “hardline.”
Ring - 1. In LAN technology, a closed loop network topology; contrast with bus and star. 2. One of the two wires in a telephone circuit. The ring wire usually has a negative battery potential relative to the tip wire. 3. A network topology in which stations are connected to one another in a closed logical circle. Typically, access to the media passes sequentially from one station to the next by means of polling from a master station, or by passing an access token from one station to another.
Ring in - On an access unit, the transmit or output receptacle.
Ring tongue - A solder less terminal that connects wire to a stud.
Ring-down circuit - A tie line connecting phones in which picking up one phone automatically rings the other phone.
Ringing out - Locating or identifying specific conductive paths by passing current through selected conductors.
Rip cord - Two or more insulated conductors in a parallel configuration that may be separated to leave the insulation of each conductor intact.
RISC (reduced instruction set computer) - The IBM RISC System/6000 system units are a second generation of computers using the RISC architecture. They offer a full range of multiuser, multitasking, open-architecture workstations and servers.
Rise time - The time it takes the voltage to rise from 0.1 to 0.9 of its final value.
Riser cable - Cable that is UL Listed as having adequate fire resistance for installation without conduit in building riser applications such as elevator shafts. (Examples: CMR and OFNR rated.)
Riser - Main distribution cable segments that run between floors or sections of a building.
RIV - Radio influence voltage. The radio noise appearing on conductors of electric equipment or circuits.
RJ11 - A six-contact modular phone-type plug. It may have straight-through or crossover pinning depending on the application.
RJ45 - An eight contact modular AT&T phone-type plug that has 4-pair unshielded twisted-pair wire (eight wires twisted in pairs).
RML (restricted mode launch) - It simulates the launch conditions of a vertical cavity surface emitting laser (VCSEL) into a multimode fiber. Measuring RML bandwidth gives a better indicator of multimode fibers performance when used with a VCSEL.
RMS - Root-mean square.
RO (read only) - A teleprinter receiver without a transmitter.
RO - Ring out.
Rockwell hardness - A measure of hardness determined by resistance to indention by a small diamond or steel ball under pressure.
ROHS (Restriction of Hazardous Substances) - The RoHS is a European directive that restricts the use of certain hazardous substances in electrical and electronic equipment.
Roll - A loss of vertical sync which causes the picture to move up or down on the TV screen.
ROM (read-only memory) - Nonvolatile semiconductor storage device manufactured with predefined contents. Compare with EPROM, PROM, and RAM.
Romex - A type of nonmetallic sheathed (Type NM) cable. A trademark of the Southwire Company. Root mean square (rms) - The effective value of an alternating current or voltages.
Root-mean-square (rms) - In a periodic quantity, this is the square root of the average or mean of the squares of the quantity taken over a complete period.
Rope - See CONCENTRIC-LAY CONDUCTOR.
Rope concentric - A group of stranded conductors assembled in a concentric manner.
Rope strand - A conductor composed of a center group of twisted strands surrounded by layers of twisted strands.
Rope Unilay - A group of stranded conductors assembled in a Unilay manner.
Rope-lay conductor - A conductor constructed of a bunch-stranded or a concentric-stranded member or members, as a central wire, around which are laid one or more helical layers of such members.
Rope-lay conductor - See CONCENTRIC-LAY CONDUCTOR.
Rotating cable - A coil of cable whose inner end is attached to a member that rotates in relation to a member to which the outer end of the cable is fastened.
Round conductor flat cable - A cable made with parallel round conductors in the same plane.
Round wire shields - Shields constructed from bare, tinned or silver-plated copper wire that include braided, spiral and reverse spiral.
Route table - A database entered in the packet controller’s memory by the system manager, containing addressing information on all nodes in the network. The packet controller refers to the router table when establishing virtual circuits between endpoints.
Router - A station that uses upper level protocols to control network communication between other stations. A dedicated router, such as a DECnet router, offloads the host computer of the routing function.
Routine tests - Tests made on each high-voltage cable or upon a representative number of devices, or parts, during production for the purposes of quality control.
RS-232 - An EIA recommended standard (RS); most common standard for connecting data processing devices, RS- 232 defines the electrical characteristics of the signals in the cable that connect DTE with DCE; it specifies a 25-pin connector (the DB-25 connector is almost universally used in RS-232 applications) and it is functionally identical to CCITT V.24/V.28.
RS-232-C - A technical specification published by the EIA that specifies the mechanical and electrical characteristics of the interface for connecting DTE and DCE. It defines interface circuit functions and their corresponding connector pin assignments. The standard applies to both asynchronous and synchronous serial, binary data transmission at speeds up to 20 kbps, in full- or half-duplex mode. RS- 232-C defines 20 specific functions. The physical connection between DTE and DCE is made through plug-in, 25-pin connectors. RS-232-C is functionally compatible with the CCIT Recommendation V.24.
RS-232-C serial I/O port - A standard connection interface for computer peripheral equipment.
RS-422 - A standard operating in conjunction with RS-449 that specifies electrical characteristics for balanced circuits. An EIA recommended standard for cable lengths that extended the RS-232 50-foot limit. Although introduced as a companion standard with RS-449, RS-422 is most frequently implemented on unused pins of DB-25 (RS-232) connectors. Electrically compatible with CCITT recommendation V.11.
RS-423 - A standard operating in conjunction with RS-449 that specifies electrical characteristics for unbalanced circuits. An EIA recommended standard for cable lengths that extended the RSD-232 50-foot limit. Although introduced as a companion standard with RS-422, RS-423 is not widely used. Electrically compatible with CCITT recommendation V.10.
RS-449 - Another EIA standard for DTE/DCE connection which specifies interface requirements for expanded transmission speeds (up to 2 Mbps), longer cable lengths and 10 additional functions. RS-449 applies to binary, serial, synchronous or asynchronous communications. Half- and full-duplex modes are accommodated and transmission can be over 2- or 4-wire facilities such as point-to-point multipoint lines. The physical connection between DTE and DCE is made through a 37-contact connector; a separate 9-connector is specified to service secondary channel interchange circuits, when used.
RS-485 - An EIA recommended standard which specifies electrical characteristics of generators and receivers for use in balanced digital multiport systems. It allows for multiple generators and receivers to be attached to a common interconnecting cable. Overall shielded twisted-pair cable is the primary transmission medium.
RTD - Resistance temperature sensing device. Converts temperature to an electrical signal.
RTP (real-time transport protocol) - An IP protocol that supports real time transmission of voice and video. Real-time control protocol is a companion protocol that is used to maintain QoS.
RTS - Request-to-send. An RS-232 modem interface signal (sent from the DTE to the modem on pin 4) that indicates that the DTE has data to transmit.
RTSP - Real-time streaming protocol.
RTU - Remote terminal unit.
Rubber insulation - A general term used to describe wire insulations made of Elastomer such as natural or synthetic rubbers, neoprene, CSPE, EPR, CPE and others.
Rubber, ethylene propylene (EPR) - A synthetic rubber insulation having excellent electrical properties.
RUS - Rural Utilities Service. A federal agency formerly known as the REA.