Engineering Glossary: R

77 definitions in plain language.

77 terms beginning with R. Use the filter to narrow the list, or the letters to jump to another part of the glossary.

77 terms

Ra #: The arithmetic average roughness: the average height of the surface irregularities from the mean line. Materials, manufacturing and measurement
Race condition #: A fault in which the result depends on the unpredictable timing of events. Programming, data and computing
Rack and pinion #: A pair of a round gear and a straight toothed bar that turns rotation into straight motion. Mechanical design and mechanics
Radian #: The SI unit of angle: the angle at the center of a circle that subtends an arc equal to the radius. 180 degrees is π radians. Math, units, quality and workshop Read more: Angles Converter
Radiation #: Heat transfer by electromagnetic waves, which needs no medium. Fluids, heat and thermodynamics Read more: Emissivity of Common Surfaces
Radius of gyration #: The distance from an axis at which the area of a section could be concentrated to give the same second moment of area. Mechanical design and mechanics
Rake angle #: The angle of the cutting face of a tool relative to the workpiece; a positive rake cuts more easily. Materials, manufacturing and measurement
RAM #: Random-access memory: fast, volatile memory used for variables and the stack. Programming, data and computing
Random error #: Unpredictable variation in measurements that averages out with more readings. Math, units, quality and workshop
Rankine cycle #: The cycle of a steam power plant: boiler, turbine, condenser and pump. Fluids, heat and thermodynamics Read more: Steam Power Cycles: Rankine
Raspberry Pi #: A low-cost single-board computer that runs Linux. Programming, data and computing
R_DS(on) #: The on-resistance of a MOSFET; the lower it is, the less heat it makes when conducting. Electronics
Reach #: The maximum distance a robot arm can extend from its base. Automation, controls and robotics
Reactance #: The opposition to AC current by an inductor or capacitor, in ohms. Electrical power and machines Read more: Reactance and Resonance Calculator
Reactive power #: The power that swings back and forth between source and load without doing work, in var. Electrical power and machines
Real power #: The part of AC power that does useful work, in watts. Also called active power. Electrical power and machines
Real-time operating system #: An operating system that guarantees tasks complete within a fixed time. Also called an RTOS. Programming, data and computing
Reaming #: Enlarging a hole slightly to an accurate size and a smooth finish with a reamer. Materials, manufacturing and measurement
Recall #: The fraction of the real positives that a classifier finds. Also called sensitivity. Programming, data and computing
Receiver #: A tank that stores compressed air and smooths out pressure variations. Fluids, heat and thermodynamics
Rectifier #: A device that converts alternating current into direct current. Electrical power and machines
Rectifier bridge #: Four diodes that convert AC to pulsating DC. Electronics
Recursion #: A function that calls itself to solve a smaller version of the same problem. Programming, data and computing
Reflow soldering #: Soldering surface-mount parts by heating a board with solder paste until the paste melts and joins the pads. Electronics
Refrigerant #: The working fluid of a refrigeration or air-conditioning cycle. Fluids, heat and thermodynamics
Refrigeration cycle #: A cycle that moves heat from a cold space to a warmer one using a compressor, condenser, expansion valve and evaporator. Fluids, heat and thermodynamics
Regeneration #: Return of energy from a decelerating load to the drive, which must be absorbed or fed back. Automation, controls and robotics
Register #: A numbered 16-bit memory location in a device that can be read or written over a network. Automation, controls and robotics
Regression #: Finding the relationship between one quantity and others from data. Programming, data and computing
Relative humidity #: The water vapor in air as a percentage of the most it could hold at that temperature. Fluids, heat and thermodynamics
Relative roughness #: The pipe wall roughness divided by the pipe diameter. Fluids, heat and thermodynamics Read more: Pipe Roughness Values
Relay #: A switch operated by an electromagnet, used to control a circuit with a smaller one. Electrical power and machines Read more: Inductors, Transformers and Relays
Reliability #: The probability that a product performs its function for a stated time under stated conditions. Math, units, quality and workshop
Relief valve #: A valve that opens at a set pressure to protect a system from overpressure. Fluids, heat and thermodynamics
Remote I/O #: Input and output modules placed near the machine and connected to the PLC by a network. Automation, controls and robotics
Repeatability #: The variation when the same person measures the same thing with the same instrument under the same conditions. Materials, manufacturing and measurement
Repeatability (robot) #: How closely a robot returns to the same position, usually much better than its accuracy. Automation, controls and robotics
Reproducibility #: The variation when different people or instruments measure the same thing. Materials, manufacturing and measurement
Residual current device #: A device that cuts the supply when the current in the live and neutral conductors is not equal, which means current is leaking to earth. Also called RCD or GFCI. Electrical power and machines
Resistance #: Opposition to the flow of current, measured in ohms. Electrical power and machines Read more: Resistors
Resistivity #: A material's inherent resistance to current, independent of shape, in ohm meters. Electrical power and machines Read more: Resistivity of Metals and Alloys
Resistor #: A component that opposes current by a fixed amount, used to limit current and divide voltage. Electronics Read more: Resistors
Resolution #: The smallest change that an instrument can show. Materials, manufacturing and measurement
Resolution (ADC) #: The number of bits of an ADC, which sets the smallest voltage step it can resolve. Electronics
Resolver #: An analog rotary sensor that gives the shaft angle from the voltages on two windings. Automation, controls and robotics
Resonance #: Large vibration that occurs when a system is driven at its natural frequency. Mechanical design and mechanics
Resonance (electrical) #: The condition in a circuit with inductance and capacitance where the reactances cancel; it occurs at f = 1 ÷ (2π √(L C)). Electrical power and machines
Retraction #: Pulling filament back slightly in a 3D printer to stop oozing between moves. Materials, manufacturing and measurement
Rework #: Repairing or replacing parts on a finished circuit board. Electronics
Reynolds number #: A dimensionless number, density times velocity times diameter over viscosity, that tells whether flow is laminar or turbulent. Fluids, heat and thermodynamics
Ring buffer #: A fixed-size buffer in which new data overwrites the oldest when it is full. Also called a circular buffer. Programming, data and computing
Ringing #: A damped oscillation that follows a fast change of signal. Electronics
Ripple #: The small AC component left on a DC supply after rectification or switching. Electronics
Rise time #: The time for a signal to go from 10 percent to 90 percent of its final value. Electronics
Rise time (control) #: The time for the response to rise from 10 to 90 percent of its final value. Automation, controls and robotics
Risk #: The combination of how likely a hazard is to cause harm and how serious the harm would be. Math, units, quality and workshop
Risk assessment #: A method of identifying hazards, judging how likely and how serious they are, and deciding on controls. Math, units, quality and workshop Read more: Workshop Safety
Rivet #: A permanent fastener with a head and a shank that is deformed after insertion to hold parts together. Mechanical design and mechanics
RMS #: Root mean square: the effective value of an alternating signal, giving the same heating as a DC value. A sine wave's RMS is its peak divided by √2. Electrical power and machines
Robot #: A programmable machine that can carry out a series of actions automatically. Automation, controls and robotics Read more: Industrial Robotics
ROC curve #: A graph of the true positive rate against the false positive rate as a classifier's threshold changes. Programming, data and computing
Rocker #: A link that swings back and forth about a fixed pivot. Mechanical design and mechanics
RoHS #: A European directive that limits hazardous substances such as lead in electronic products. Math, units, quality and workshop
Roller bearing #: A bearing that uses cylinders, needles or tapered rollers, carrying more load than a ball bearing of the same size. Mechanical design and mechanics
Rolling #: Passing metal between rollers to reduce its thickness or shape it. Materials, manufacturing and measurement
Rolling resistance #: The force that resists a wheel or ball rolling, caused by deformation of the surfaces. Mechanical design and mechanics
Root cause analysis #: A method of finding the underlying reason for a problem, not just its symptoms. Math, units, quality and workshop
Root sum square #: A statistical stack-up method that combines tolerances as the square root of the sum of their squares. Also called RSS. Materials, manufacturing and measurement
Rotor #: The rotating part of a motor or generator. Electrical power and machines
Rounding error #: The small error caused by storing numbers with a limited number of digits. Programming, data and computing
Rpm #: Revolutions per minute: a common measure of rotation speed. Math, units, quality and workshop
RS-232 #: A serial standard for short point-to-point connections between two devices. Automation, controls and robotics
RS-485 #: A serial standard for long, multi-drop, noise-resistant connections, used by Modbus RTU. Automation, controls and robotics
RTD #: Resistance temperature detector: a temperature sensor, usually platinum, whose resistance rises with temperature. Automation, controls and robotics
Rung #: One line of a ladder program, with conditions on the left and an output on the right. Automation, controls and robotics
Runout #: A tolerance on how far a surface may wobble when the part is rotated about a datum axis. Materials, manufacturing and measurement Read more: Profile and Runout
R-value #: The thermal resistance of insulation per unit area; a higher R-value insulates better. Fluids, heat and thermodynamics

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