Engineering Glossary: D

72 definitions in plain language.

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

72 terms

DAC #: Digital-to-analog converter: a circuit that turns a number into a voltage. Electronics
Damping #: The loss of vibration energy, usually as heat, that makes oscillations die away. Mechanical design and mechanics
Damping ratio #: The ratio of the actual damping to the critical damping, written ζ. Mechanical design and mechanics
Darcy-Weisbach equation #: The equation for the pressure drop in a pipe: friction factor times length over diameter times velocity head. Fluids, heat and thermodynamics
Dashboard #: A screen that shows key measurements and status at a glance. Programming, data and computing
Database #: An organized collection of data that can be searched and updated. Programming, data and computing
Data logger #: A device that records measurements over time, on its own, in memory. Programming, data and computing
Data logging #: Recording measurements over time, usually with a time stamp. Programming, data and computing Read more: Data Logging
Data quality #: How accurate, complete and consistent a set of data is. Programming, data and computing
Datasheet #: The manufacturer's document giving a component's ratings, characteristics and application notes. Electronics Read more: Reading Datasheets
Data type #: The kind of value a variable holds, such as an integer, floating-point number or string. Programming, data and computing
Datum #: A theoretical exact point, line or plane from which measurements and geometric tolerances are referenced. Materials, manufacturing and measurement Read more: Datums and Datum Reference Frames
DC motor #: A motor that runs on direct current, with speed controlled by the armature voltage. Electrical power and machines
Deadband #: A range around a value inside which changes are ignored, used to reduce the amount of data logged. Programming, data and computing
Dead time #: The delay between a change at the input of a process and the first response at the output. Also called transport delay or time delay. Automation, controls and robotics
Debouncing #: Removing switch bounce, in hardware with a filter or in software with a delay. Electronics
Debugging #: Finding and fixing faults in a program. Programming, data and computing Read more: Software Practice, Testing and Debugging
Decibel #: A logarithmic unit for ratios; 20 log₁₀ of a voltage ratio, or 10 log₁₀ of a power ratio. Electronics
Decibel (sound) #: A logarithmic unit of sound level; every 10 dB increase is about a doubling of perceived loudness. Math, units, quality and workshop
Decoupling capacitor #: A capacitor placed near an IC power pin to supply fast current and keep the supply voltage steady. Electronics Read more: Capacitors
Dedendum #: The depth of a gear tooth below the pitch circle. Mechanical design and mechanics
Deep learning #: Machine learning with neural networks that have many layers. Programming, data and computing
Deflection #: The displacement of a beam or structure under load. Mechanical design and mechanics
Degrees of freedom #: The number of independent coordinates needed to describe the position of a system. Mechanical design and mechanics
Delta connection #: A three-phase connection in which the windings form a triangle. Electrical power and machines
Delta robot #: A fast parallel-link robot with arms joined to a common base, used for picking and packing. Automation, controls and robotics
Demand #: The average power drawn over a short period, used for billing and for sizing equipment. Electrical power and machines
Density #: Mass per unit volume, in kg/m³. For water it is about 1 000 kg/m³. Fluids, heat and thermodynamics Read more: Water Properties vs Temperature
Depreciation #: The spreading of a machine's cost over its useful life. Math, units, quality and workshop
Depth of cut #: How deep the cutter goes into the workpiece in one pass. Materials, manufacturing and measurement
Derating #: Using a component below its rated limits to improve reliability. Electronics
Derivative #: The rate of change of a function; the slope of its graph. Math, units, quality and workshop
Derivative action #: The part of a PID output that responds to the rate of change of the error, damping the response. Automation, controls and robotics
Derived unit #: A unit formed by combining base units, such as the newton (kg·m/s²). Math, units, quality and workshop
Design for assembly #: Designing a product so that it is easy to put together. Also called DFA. Math, units, quality and workshop
Design for manufacturing #: Designing a product so that it is easy and cheap to make. Also called DFM. Math, units, quality and workshop
Design of experiments #: A method of planning tests that change several factors at once to learn their effects with few runs. Math, units, quality and workshop
Determinant #: A number calculated from a square matrix that shows whether the matrix can be inverted. Math, units, quality and workshop
Determinism #: The guarantee that something happens within a known, repeatable time, important for control networks. Automation, controls and robotics
Dew point #: The temperature at which air becomes saturated and water starts to condense. Fluids, heat and thermodynamics
Dial indicator #: A gauge with a dial that shows small movements of a plunger, used to check runout and flatness. Materials, manufacturing and measurement
Diametral pitch #: The number of teeth per inch of pitch diameter; the inch measure of gear tooth size. Mechanical design and mechanics
Die casting #: Forcing molten metal under high pressure into a steel die, used for large runs of zinc, aluminum and magnesium parts. Materials, manufacturing and measurement
Dielectric strength #: The highest electric field an insulator withstands before breaking down, in volts per meter. Electrical power and machines
Diesel cycle #: The idealized cycle of a compression-ignition engine. Fluids, heat and thermodynamics
Differential equation #: An equation that relates a function to its derivatives, used to model how things change in time. Math, units, quality and workshop
Digital twin #: A computer model of a real machine or system that is kept up to date with data from it. Programming, data and computing
Dimensional analysis #: Checking an equation by comparing the units of both sides, and finding relationships between quantities from their units. Math, units, quality and workshop
Dimensionless number #: A quantity with no units, formed as a ratio of similar quantities, such as the Reynolds number. Math, units, quality and workshop
Diode #: A component that conducts current in one direction only. Electronics Read more: Diodes and LEDs
Direct current #: Current that flows in one direction only; also called DC. Electrical power and machines
Directional control valve #: A valve that directs flow to different paths in a hydraulic or pneumatic circuit. Fluids, heat and thermodynamics
Discrete I/O #: Inputs and outputs with two states, on and off. Automation, controls and robotics
Diversity factor #: The ratio of the sum of the individual maximum loads to the maximum of the combined load. Electrical power and machines
Dot product #: A way of multiplying two vectors to give a scalar; the magnitudes times the cosine of the angle between them. Math, units, quality and workshop
Draft angle #: A slight taper on the walls of a molded or cast part so it releases from the mold. Materials, manufacturing and measurement
Drag #: The force that resists the motion of a body through a fluid. Fluids, heat and thermodynamics
Drag coefficient #: A dimensionless number that gives the drag force relative to the dynamic pressure and the frontal area. Fluids, heat and thermodynamics
Drawing #: Pulling metal through a die to make wire, tube or rod, or forming sheet into a cup shape. Materials, manufacturing and measurement
Drilling #: Making a round hole with a rotating drill bit. Materials, manufacturing and measurement
Dropout voltage #: The minimum difference between input and output voltages for a linear regulator to keep regulating. Electronics
Dry-bulb temperature #: The air temperature measured by an ordinary thermometer. Fluids, heat and thermodynamics
Ductile iron #: Cast iron with spheroidal graphite that gives it much more strength and ductility than gray iron. Materials, manufacturing and measurement
Ductility #: How much a material can stretch or deform plastically before it fractures, often measured as elongation. Mechanical design and mechanics
Duplex stainless steel #: A stainless steel with a mixed austenite and ferrite structure, giving high strength and resistance to chloride cracking. Materials, manufacturing and measurement
Duty cycle #: The fraction of a period for which a signal is on, as a percentage. Electronics
Duty cycling #: Switching a system on only briefly and often, to cut its average power use. Programming, data and computing
Dwell #: The part of a cam cycle during which the follower stays still. Mechanical design and mechanics
Dynamic load rating #: The constant load a bearing can carry for one million revolutions with 90 percent survival, written C. Mechanical design and mechanics
Dynamics #: The branch of mechanics that deals with bodies in motion and the forces that cause it. Math, units, quality and workshop
Dynamic seal #: A seal between parts that move relative to each other. Math, units, quality and workshop
Dynamic viscosity #: The ratio of shear stress to velocity gradient in a fluid, in pascal seconds or centipoise. Fluids, heat and thermodynamics

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