Engineering Glossary: S

159 definitions in plain language.

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

159 terms

Safety factor #: The ratio of the strength of a part to the stress it is expected to carry. A factor of 2 means it could carry twice the load. Also called factor of safety. Mechanical design and mechanics
Safety integrity level #: A measure of how much a safety function reduces risk, from SIL 1 to SIL 4. Automation, controls and robotics
Safety relay #: A relay designed to monitor safety devices and switch off power reliably. Automation, controls and robotics
Sample #: A subset of a population from which measurements are taken. Math, units, quality and workshop
Sampled-data system #: A control system that measures and updates at fixed time intervals. Automation, controls and robotics
Sampling interval #: The time between successive measurements in a data logger. Programming, data and computing
Sampling rate #: How many times per second a signal is measured. Electronics
Sand casting #: Casting in a mold made of sand, suitable for large parts and small quantities. Materials, manufacturing and measurement
Saturation (inductor) #: The condition when a core can hold no more magnetic flux and the inductance collapses. Electronics
Saturation temperature #: The temperature at which a liquid boils at a given pressure. Fluids, heat and thermodynamics
Saturation (transistor) #: The state of a transistor that is fully on, acting as a closed switch. Electronics
SCADA #: Supervisory control and data acquisition: software that monitors and controls a distributed industrial process. Automation, controls and robotics
Scalar #: A quantity with only a magnitude, such as mass or temperature. Math, units, quality and workshop
Scan cycle #: The repeating loop of a PLC: read inputs, run the program, write outputs. Automation, controls and robotics
Scan time #: The time a PLC takes to complete one scan cycle. Automation, controls and robotics
SCARA robot #: A robot with a horizontal arm that is rigid vertically and fast in a plane; used for assembly. Automation, controls and robotics
Schedule (pipe) #: A number that sets the wall thickness of pipe of a given nominal size; a higher number is thicker. Fluids, heat and thermodynamics
Scheduler #: The part of an operating system that decides which task runs next. Programming, data and computing
Schematic #: A drawing of a circuit using symbols for components and lines for connections. Electronics
Schmitt trigger #: A comparator with hysteresis, which gives a clean switching output from a noisy input. Electronics
Schottky diode #: A diode with a low forward voltage and fast switching. Electronics
Scientific notation #: Writing a number as a value between 1 and 10 times a power of ten, such as 3.2 × 10⁵. Math, units, quality and workshop
Scope creep #: The gradual growth of a project's requirements beyond the original plan. Math, units, quality and workshop
Screw #: A threaded fastener that screws into a tapped hole or makes its own thread. Mechanical design and mechanics
Seal #: A part that stops fluid from leaking between two surfaces. Math, units, quality and workshop Read more: Seals, O-Rings and Gaskets
Seal-in #: A ladder circuit in which an output's own contact holds it on after the start button is released. Also called a latch or holding circuit. Automation, controls and robotics
Secondary winding #: The transformer winding that supplies the load. Electrical power and machines
Second law of thermodynamics #: Heat cannot flow by itself from a cold body to a hot one, and no heat engine can be 100 percent efficient. Fluids, heat and thermodynamics
Second moment of area #: A property of a cross-section that measures its resistance to bending about an axis, in mm⁴ or in⁴. Often called the area moment of inertia. Mechanical design and mechanics Read more: European I-Beam and H-Beam Sections (IPE, HEA, HEB)
Section modulus #: The second moment of area divided by the distance to the outer fiber. Bending stress is moment divided by section modulus. Mechanical design and mechanics Read more: European I-Beam and H-Beam Sections (IPE, HEA, HEB)
Self-locking #: A screw or worm drive whose friction is high enough that the load cannot turn it backward. Mechanical design and mechanics
Semiconductor #: A material, such as silicon, whose conductivity lies between a conductor and an insulator and can be controlled. Electrical power and machines
Sensible heat #: Heat that changes the temperature of a substance without changing its phase. Fluids, heat and thermodynamics
Sensible heat ratio #: The sensible cooling load divided by the total cooling load of a space. Fluids, heat and thermodynamics
Sensor #: A device that detects a physical quantity and turns it into a signal. Automation, controls and robotics Read more: Sensors and Field Devices
Sequential function chart #: A PLC language that describes a process as steps and transitions. Automation, controls and robotics
Series circuit #: A circuit in which components are connected end to end so the same current passes through all. Electronics
Service factor #: A multiplier showing how much overload a motor can carry continuously without damage. Electrical power and machines
Servo #: A closed-loop motion system in which a motor is controlled for position, speed or torque. Automation, controls and robotics Read more: Motion Control and Actuators
Servo drive #: The electronic amplifier that powers a servo motor and runs its control loops. Automation, controls and robotics
Servo motor #: A motor with feedback and a controller that gives accurate control of position, speed or torque. Electrical power and machines Read more: Motion Control and Actuators
Servo valve #: A valve that gives precise control of flow in proportion to an electrical signal. Fluids, heat and thermodynamics
Setpoint #: The value that a control loop is trying to reach and hold. Automation, controls and robotics
Settling time #: The time for the response to stay within a small band of its final value. Automation, controls and robotics
Setup time #: The time a digital input must be stable before the clock edge. Electronics
Shaft #: A rotating bar that carries gears, pulleys or wheels and transmits torque. Mechanical design and mechanics Read more: Shafts, Keys and Couplings
Shear force #: The internal force in a beam acting across its cross-section, equal to the sum of the vertical loads on one side of a cut. Mechanical design and mechanics
Shear modulus #: The ratio of shear stress to shear strain in the elastic range, also called the modulus of rigidity (G). Mechanical design and mechanics
Shear plane #: The surface across which a fastener or part is sheared. Mechanical design and mechanics
Sheet metal #: Metal rolled into thin flat sheets, cut and bent into parts. Materials, manufacturing and measurement Read more: Sheet Metal Forming
Shielding #: Surrounding a circuit or cable with a conductor to block electric noise. Electronics
Shift register #: A chain of flip-flops that moves bits along one position each clock pulse. Electronics
Short-circuit current #: The very large current that flows when a fault connects conductors of different potential. Electrical power and machines Read more: Protection, Earthing and RCDs
Shrink fit #: A joint made by heating the outer part or cooling the inner part so they fit, then returning to normal temperature. Mechanical design and mechanics
Signal conditioning #: Amplifying, filtering and converting a sensor signal so a controller can read it. Automation, controls and robotics
Signal-to-noise ratio #: The ratio of signal power to noise power, usually in decibels. Electronics
Significant figures #: The digits of a number that carry meaning about its precision. Math, units, quality and workshop
Silkscreen #: The printed text and outlines on the surface of a PCB. Electronics
Similitude #: The rules that let results from a model be applied to a full-size system by matching dimensionless numbers. Math, units, quality and workshop
Simply supported beam #: A beam resting on supports at its ends that allow rotation but not vertical movement. Mechanical design and mechanics
Simulation #: Using a computer model to imitate how a system behaves over time. Programming, data and computing
Sine #: In a right triangle, the ratio of the side opposite an angle to the hypotenuse. Math, units, quality and workshop
Single-board computer #: A complete computer built on one circuit board. Programming, data and computing
Singularity #: A pose where a robot loses a degree of freedom and its joint speeds can become very large. Automation, controls and robotics
Sinking and sourcing #: Two ways of wiring DC I/O: a sourcing device supplies current to the load and a sinking device draws current from it. Automation, controls and robotics
Sink mark #: A shallow depression on the surface of a molded part where thick material shrinks as it cools. Materials, manufacturing and measurement
SI prefix #: A word that multiplies a unit by a power of ten, such as kilo (10³) or milli (10⁻³). Math, units, quality and workshop Read more: SI Prefixes (Quetta to Quecto)
Site acceptance test #: A test of a system at the customer's site after installation. Also called SAT. Automation, controls and robotics
SI units #: The International System of Units: the modern metric system built on the meter, kilogram, second, ampere, kelvin, mole and candela. Math, units, quality and workshop Read more: SI Prefixes (Quetta to Quecto)
Six Sigma #: A set of methods for reducing variation and defects in processes. Math, units, quality and workshop
SLA #: Stereolithography: 3D printing by curing liquid resin with a light source, layer by layer. Materials, manufacturing and measurement
Slenderness ratio #: The effective length of a column divided by its radius of gyration; large ratios buckle at low stress. Mechanical design and mechanics
Slew rate #: The fastest rate at which an amplifier's output voltage can change. Electronics
Slicer #: Software that cuts a 3D model into layers and creates the toolpath for a printer. Materials, manufacturing and measurement
Slider-crank #: A mechanism that converts rotation into straight-line motion, as in an engine piston. Mechanical design and mechanics
Slip #: The difference between the speed of the rotating field and the motor shaft speed, as a percentage of the field speed. Electrical power and machines
SLS #: Selective laser sintering: 3D printing by fusing powder with a laser. Materials, manufacturing and measurement
S-N curve #: A graph of stress amplitude against the number of cycles to failure, used for fatigue design. Mechanical design and mechanics
Soft starter #: A device that raises the voltage to a motor gradually at start, to reduce starting current and mechanical shock. Electrical power and machines
Solder #: A metal alloy with a low melting point used to join electronic parts. Electronics Read more: Soldering
Solder mask #: The coating over a PCB that covers the copper except at the pads, preventing solder bridges. Electronics
Solenoid #: A coil that pulls a plunger when energized; used to operate valves and latches. Automation, controls and robotics
Solid height #: The length of a compression spring when all its coils are touching. Mechanical design and mechanics
Sound pressure level #: A measure of the loudness of sound, in decibels relative to a reference pressure of 20 micropascals. Math, units, quality and workshop
Specification #: A document that states the requirements a product or material must meet. Math, units, quality and workshop
Specific gravity #: The density of a substance divided by the density of water (for liquids) or air (for gases). Fluids, heat and thermodynamics
Specific heat #: The energy needed to raise the temperature of a unit mass of a substance by one degree, in J/kg·K. Fluids, heat and thermodynamics Read more: Thermal Conductivity of Materials
Specific weight #: Weight per unit volume: density times gravitational acceleration, in N/m³. Fluids, heat and thermodynamics
Speed of sound #: The speed at which small pressure waves travel through a fluid, about 343 m/s in air at 20 C. Fluids, heat and thermodynamics Read more: Properties of Air vs Temperature
SPI #: Serial Peripheral Interface: a fast four-wire serial bus between a controller and peripherals. Programming, data and computing
Spindle speed #: The rotation speed of a machine spindle, in revolutions per minute. Materials, manufacturing and measurement Read more: CNC Feeds & Speeds Calculator
Spline #: A set of ridges on a shaft that mesh with grooves in a hub to transmit torque. Mechanical design and mechanics
Spring #: An elastic part that stores energy and exerts a force when deformed. Mechanical design and mechanics Read more: Springs: Design, Stress and Fatigue
Springback #: The partial return of a bent part toward its original shape when the bending force is removed. Materials, manufacturing and measurement
Spring index #: The mean coil diameter of a helical spring divided by its wire diameter. Mechanical design and mechanics
Spring rate #: The force a spring exerts per unit of deflection, in N/mm or lb/in. Also called spring constant or stiffness. Mechanical design and mechanics
Sprocket #: A toothed wheel that meshes with a chain. Mechanical design and mechanics
Spur gear #: A gear with straight teeth parallel to its axis, used between parallel shafts. Mechanical design and mechanics
SQL #: Structured Query Language: the standard language for asking questions of relational databases. Programming, data and computing
Stability #: The property that a system settles to a steady value instead of growing without limit. Automation, controls and robotics
Stack #: A region of memory used for function calls and local variables, or a data structure where the last item in is the first out. Programming, data and computing
Stack-up #: The arrangement of copper and insulating layers of a PCB. Electronics
Stainless steel #: Steel with at least 10.5 percent chromium, which forms a protective oxide film that resists rust. Materials, manufacturing and measurement Read more: Stainless Steel Grades
Stamping #: Cutting or forming sheet metal in a press with a die. Materials, manufacturing and measurement
Standard #: A published document that sets agreed requirements, such as those of ISO, ASTM, ASME or IEC. Math, units, quality and workshop
Standard cubic foot per minute #: A flow rate of gas measured at standard conditions of pressure and temperature, written scfm. Fluids, heat and thermodynamics
Standard deviation #: The square root of the variance; a measure of how widely values are spread around the mean. Math, units, quality and workshop
State machine #: A program structure in which a system moves between a defined set of states according to rules. Automation, controls and robotics Read more: PLC & Logic Control
State of charge #: The remaining capacity of a battery as a percentage of its full capacity. Electrical power and machines
State space #: A way of describing a system with a set of first-order equations in state variables. Automation, controls and robotics
Statically determinate #: A structure whose support forces can be found from equilibrium equations alone. Mechanical design and mechanics
Statically indeterminate #: A structure with more supports or members than equilibrium alone needs, so the deformations must also be used to solve it. Mechanical design and mechanics
Static friction #: The friction that holds two surfaces still relative to each other, up to a maximum value. Mechanical design and mechanics
Statics #: The branch of mechanics that deals with bodies at rest and the forces on them. Math, units, quality and workshop Read more: Engineering Fundamentals
Static seal #: A seal between parts that do not move relative to each other. Math, units, quality and workshop
Statistical process control #: Using control charts and statistics to monitor a process and keep it stable. Also called SPC. Materials, manufacturing and measurement
Statistics #: The science of collecting, analyzing and interpreting data. Math, units, quality and workshop Read more: Engineering Fundamentals
Stator #: The stationary part of a motor or generator. Electrical power and machines
Steady-state error #: The error that remains after the response has settled. Automation, controls and robotics
Steam trap #: A valve that lets condensate and air out of a steam line but holds the steam in. Fluids, heat and thermodynamics
Stefan-Boltzmann law #: A black body radiates energy proportional to the fourth power of its absolute temperature. Fluids, heat and thermodynamics
Step-down transformer #: A transformer whose output voltage is lower than its input. Electrical power and machines
STEP file #: A neutral file format for exchanging 3D CAD models between programs. Programming, data and computing
Stepper motor #: A motor that turns in fixed steps, driven by pulses, used for positioning without feedback. Electrical power and machines
Step-up transformer #: A transformer whose output voltage is higher than its input. Electrical power and machines
Stiffness #: The force needed to produce a unit deflection; the opposite of flexibility. Mechanical design and mechanics
STL file #: A file format for 3D models that describes a surface as triangles, used for 3D printing. Programming, data and computing
Stoichiometric #: The exact proportion of fuel and air that gives complete burning with no excess of either. Fluids, heat and thermodynamics
Straightness #: A tolerance on how far a line or axis may deviate from a straight line. Materials, manufacturing and measurement
Strain #: The deformation of a material divided by its original size. It has no units. Mechanical design and mechanics Read more: Stress, Strain and Safety Factors
Strain gauge #: A foil sensor whose resistance changes when it is stretched, used to measure strain and force. Automation, controls and robotics Read more: Force, Load Cells and Vibration
Streamline #: A line that is everywhere tangent to the fluid velocity. Fluids, heat and thermodynamics
Stress #: Force per unit area inside a material, in pascals or psi. Normal stress acts perpendicular to a surface and shear stress acts along it. Mechanical design and mechanics Read more: Stress, Strain and Safety Factors
Stress concentration #: A local rise in stress at a notch, hole or sharp corner. Mechanical design and mechanics Read more: Fatigue and Stress Concentration
Stress concentration factor #: The ratio of the peak stress at a notch to the nominal stress there, written K_t. Mechanical design and mechanics
Stress corrosion cracking #: Cracking caused by tensile stress and a corrosive environment acting together. Materials, manufacturing and measurement
Stress relaxation #: The gradual drop in stress in a part held at constant strain, for example the loss of bolt preload over time. Mechanical design and mechanics
Stress relieving #: Heating a part to a moderate temperature and cooling it slowly to reduce internal residual stress. Materials, manufacturing and measurement
Structured text #: A high-level text language for PLCs, similar to Pascal. Automation, controls and robotics
Stud #: A rod threaded at both ends, screwed into one part and fitted with a nut at the other. Mechanical design and mechanics
Subnet mask #: A number that shows which part of an IP address identifies the network and which the device. Automation, controls and robotics
Superalloy #: A nickel, cobalt or iron-based alloy that keeps its strength at very high temperatures, used in turbines. Materials, manufacturing and measurement
Superheated steam #: Steam heated above its saturation temperature at the same pressure. Fluids, heat and thermodynamics
Superposition (circuits) #: In a linear circuit, the response to several sources is the sum of the responses to each source acting alone. Electronics
Surface finish #: The overall texture of a surface, including roughness, waviness and lay. Materials, manufacturing and measurement
Surface mount #: A component soldered to pads on the surface of a board, without holes. Also called SMD or SMT. Electronics
Surface roughness #: The fine irregularities of a surface left by manufacturing, measured by Ra or Rz. Materials, manufacturing and measurement
Surface tension #: The force at the surface of a liquid that makes it behave like a stretched skin. Fluids, heat and thermodynamics
Surge protection #: Devices that limit voltage spikes on power lines to protect equipment. Electrical power and machines
Switch bounce #: The rapid on-off contact opening and closing of a mechanical switch as it changes state. Electronics
Switchgear #: The combination of switches, fuses and breakers used to control and protect electrical equipment. Electrical power and machines
Switching regulator #: A voltage regulator that switches current on and off at high frequency to convert voltage efficiently. Electronics
Switch (network) #: A device that forwards data between the devices connected to it. Automation, controls and robotics
Synchronous motor #: An AC motor whose rotor turns at exactly the speed of the rotating field. Electrical power and machines
Synchronous speed #: The speed of the rotating magnetic field of an AC motor: 120 × frequency ÷ number of poles, in rpm. Electrical power and machines
Systematic error #: A consistent offset in measurements, such as that from a miscalibrated instrument. Also called bias. Math, units, quality and workshop
System curve #: A graph of the head a piping system needs against the flow rate. Fluids, heat and thermodynamics
System integration #: Combining machines, controls, software and networks into a working system. Automation, controls and robotics Read more: System Integration
System (thermodynamic) #: The quantity of matter or region of space chosen for study. Fluids, heat and thermodynamics

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