Engineering Glossary: P

97 definitions in plain language.

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

97 terms

Pad #: The exposed copper area on a PCB where a component lead or terminal is soldered. Electronics
Parallel circuit #: A circuit in which components are connected across the same two points so the voltage is the same across all. Electronics
Parallelism #: A tolerance on how closely a surface or axis must stay parallel to a datum. Materials, manufacturing and measurement
Parametric model #: A CAD model whose shape is controlled by dimensions and rules that can be changed. Programming, data and computing
Pareto chart #: A bar chart that ranks causes by how much they contribute, to show which to fix first. Math, units, quality and workshop
Parity bit #: An extra bit added to data so that the count of 1 bits is even or odd, to detect single-bit errors. Programming, data and computing
Parting line #: The line where the two halves of a mold meet, which leaves a mark on the part. Materials, manufacturing and measurement
Pascal #: The SI unit of pressure and stress: one newton per square meter. Math, units, quality and workshop
Pascal's law #: A pressure change applied to an enclosed fluid is passed on equally in all directions. Fluids, heat and thermodynamics
Passivation #: Treating stainless steel with acid to remove surface iron and let the protective oxide film form. Materials, manufacturing and measurement
Payload #: The weight that a robot can carry at its wrist, including the tool. Automation, controls and robotics
Pearlite #: A layered structure of ferrite and iron carbide formed when steel cools slowly. Materials, manufacturing and measurement
Performance level #: A rating of the reliability of a safety function in machinery safety, from PL a to PL e. Automation, controls and robotics
Period #: The time of one full cycle of a waveform; the reciprocal of the frequency. Electrical power and machines
Perpendicularity #: A tolerance on how closely a surface or axis must be at 90 degrees to a datum. Materials, manufacturing and measurement Read more: Orientation Tolerances
Personal protective equipment #: Clothing and gear worn for protection, such as safety glasses, gloves and hearing protection. Also called PPE. Math, units, quality and workshop Read more: Workshop Safety
Per-unit system #: A way of expressing electrical quantities as fractions of chosen base values, to simplify calculations. Electrical power and machines
Phase #: The position of a point on a waveform within its cycle, in degrees; the difference in phase between two waves is the phase angle. Electrical power and machines
Phase margin #: How much extra phase lag a feedback system can take at the crossover frequency before it becomes unstable. Automation, controls and robotics
Phase voltage #: The voltage between one phase conductor and neutral; the line voltage divided by √3. Electrical power and machines
Phasor #: A rotating vector that represents the amplitude and phase of a sinusoidal quantity. Electrical power and machines
Photoelectric sensor #: A sensor that detects objects by interruption or reflection of a light beam. Automation, controls and robotics Read more: Photoelectric and Vision Sensors
Photovoltaic #: Converting sunlight directly into electricity; a solar panel is a photovoltaic device. Electrical power and machines Read more: Solar PV, Batteries and Backup Power
P&ID #: Piping and instrumentation diagram: a drawing that shows the pipes, valves and instruments of a process. Automation, controls and robotics
PID controller #: A controller that combines proportional, integral and derivative action on the error. Automation, controls and robotics Read more: PID Tuner
Pinout #: The assignment of functions to the pins of a connector or chip. Electronics Read more: MCU Pinout & Peripheral Multiplexer
Pitch circle #: The imaginary circle on which two meshing gears roll without slipping. Mechanical design and mechanics
Pitch diameter #: The diameter of the pitch circle. Mechanical design and mechanics
Pitch (general) #: The distance between repeating features such as threads, teeth or grooves. Math, units, quality and workshop
Pitot tube #: A tube that measures fluid velocity from the stagnation pressure. Fluids, heat and thermodynamics
Pitting #: Local corrosion that forms small deep holes in a metal surface. Materials, manufacturing and measurement
Planetary gear #: A gear set where planet gears orbit a sun gear inside a ring gear, giving a compact high ratio. Mechanical design and mechanics
Plastic deformation #: Permanent change of shape that remains after the load is removed. Mechanical design and mechanics
PLC #: Programmable logic controller: a rugged industrial computer that reads inputs, runs a program and switches outputs. Automation, controls and robotics Read more: PLC & Logic Control
PLC safety #: The use of safety-rated controllers and devices to protect people from machine hazards. Automation, controls and robotics
Pneumatic actuator #: An actuator that uses compressed air to produce force and motion. Automation, controls and robotics Read more: Pneumatic and Hydraulic Actuators
Pneumatics #: The use of compressed air to transmit power and control. Fluids, heat and thermodynamics
Pointer #: A variable that holds the memory address of another variable. Programming, data and computing
Poisson's ratio #: The ratio of sideways strain to lengthwise strain when a material is stretched. It is about 0.3 for steel. Mechanical design and mechanics
Polar moment of inertia #: A property of a circular section that measures its resistance to twisting, written J. Mechanical design and mechanics
Pole #: A value of s at which a transfer function becomes infinite; the poles determine stability and speed of response. Automation, controls and robotics
Poles #: The number of magnetic poles in a motor, which sets its speed: a 4-pole motor runs at about 1 750 rpm on 60 Hz. Electrical power and machines
Polling #: Repeatedly checking an input to see whether it has changed, instead of waiting for an interrupt. Programming, data and computing
Polymer #: A material made of long chains of repeating molecules; plastics and rubbers are polymers. Materials, manufacturing and measurement
Polytropic process #: A process that follows P Vⁿ = constant. Fluids, heat and thermodynamics
Population #: The whole group about which conclusions are wanted. Math, units, quality and workshop
Position tolerance #: A tolerance zone that controls the location of a feature such as a hole, relative to datums. Materials, manufacturing and measurement Read more: Position and Location
Positive displacement pump #: A pump that traps a fixed volume of fluid and forces it out, such as a gear or piston pump. Fluids, heat and thermodynamics
Potential energy #: Stored energy due to position, such as m g h for a weight lifted a height h. Mechanical design and mechanics
Potentiometer #: A resistor with a movable contact that gives an adjustable voltage divider or variable resistance. Electronics
Powder coating #: A paint finish applied as dry powder and baked into a hard layer. Materials, manufacturing and measurement
Power #: The rate of doing work: energy per unit time, measured in watts. Mechanical design and mechanics
Power (electrical) #: The rate of using electrical energy: voltage times current, in watts. Electrical power and machines
Power factor #: The ratio of real power to apparent power in an AC circuit: the cosine of the phase angle for a sine wave. Electrical power and machines Read more: Power Factor, Harmonics and Energy
Power quality #: How closely the supply voltage matches its ideal steady, clean sine wave. Electrical power and machines
Prandtl number #: A dimensionless number that compares how fast momentum and heat diffuse in a fluid. Fluids, heat and thermodynamics
Precipitation hardening #: Strengthening a metal by heat treatments that form fine particles in its structure, used for 17-4 stainless and 6061 and 7075 aluminum. Materials, manufacturing and measurement
Precision #: How closely repeated measurements agree with one another, regardless of whether they are correct. Materials, manufacturing and measurement
Precision (classifier) #: The fraction of items predicted positive that really are positive. Programming, data and computing
Predictive maintenance #: Using sensor data and models to predict when equipment will fail, so repair can be done before it does. Programming, data and computing
Preferred values #: Standard series of component values such as E12 and E24, spaced so every value is covered. Electronics Read more: E-Series Preferred Values (E6, E12, E24, E96)
Preload #: A load applied to a bearing or bolt before service to remove clearance or keep parts clamped. Mechanical design and mechanics
Press fit #: A joint made by forcing a part into a slightly smaller hole so friction holds it. Mechanical design and mechanics Read more: Press, Shrink and Expansion Fits
Pressure #: Force per unit area, in pascals, bar or psi. Fluids, heat and thermodynamics Read more: Pressure Converter
Pressure angle #: For gears, the angle between the tooth force direction and the pitch circle tangent, usually 20 degrees; for cams, the angle between the follower motion and the force. Mechanical design and mechanics
Pressure drop #: The loss of pressure between two points of a pipe, caused by friction and fittings. Fluids, heat and thermodynamics Read more: Pipe Flow and Pressure Drop Calculator
Pressure transmitter #: A sensor that measures pressure and gives an electrical signal. Automation, controls and robotics
Primary winding #: The transformer winding connected to the supply. Electrical power and machines
Principle of superposition #: For linear systems, the effect of several loads together is the sum of the effects of each load alone. Mechanical design and mechanics
Printed circuit board #: A board with copper traces that connects electronic components. Also called PCB. Electronics Read more: PCB Design and Layout
Priority inversion #: A fault where a high-priority task is delayed by a low-priority task holding a shared resource. Programming, data and computing
Probability #: A number from 0 to 1 that states how likely an event is. Math, units, quality and workshop
Probe #: A lead that connects an instrument to the circuit under test; a 10:1 oscilloscope probe reduces loading. Electronics
Process capability #: A measure of how well a process keeps parts within their tolerances. Materials, manufacturing and measurement Read more: Process Capability Calculator
Process variable #: The measured quantity that a control loop is controlling. Automation, controls and robotics
Profile of a surface #: A tolerance zone that limits how far a surface may deviate from its ideal shape. Materials, manufacturing and measurement
Programmable automation controller #: A controller that combines PLC reliability with computer-like functions. Also called a PAC. Automation, controls and robotics
Projectile #: An object thrown or launched that moves under gravity alone. Math, units, quality and workshop
Project management #: Planning, organizing and controlling a project to meet its goals on time and within budget. Math, units, quality and workshop Read more: Prototyping Techniques
Proof load #: The load a bolt can carry without permanent stretch, the proof strength times the stress area. Mechanical design and mechanics Read more: Bolt Strength Grades and Property Classes
Proof of concept #: A small test to show that an idea is feasible. Math, units, quality and workshop
Proof stress #: The stress that causes a stated small permanent strain, usually 0.2 percent, used as the yield strength of materials without a clear yield point. Mechanical design and mechanics
Propagation delay #: The time a signal takes to pass through a gate or circuit. Electronics
Proportional gain #: The part of a PID output proportional to the present error. Automation, controls and robotics
Prototype #: An early version of a product used to test an idea. Math, units, quality and workshop Read more: Prototyping Techniques
Proximity sensor #: A sensor that detects a nearby object without touching it. Automation, controls and robotics Read more: Proximity Sensors
Psi #: Pounds per square inch, the US unit of pressure. 1 psi is about 6.895 kPa. Fluids, heat and thermodynamics
Psychrometrics #: The study of the properties of moist air. Fluids, heat and thermodynamics Read more: Psychrometric Calculator and Chart
Pull-down resistor #: A resistor that holds a digital input at a low level when nothing else drives it. Electronics
Pulley #: A wheel with a grooved rim that carries a belt or rope. Mechanical design and mechanics
Pull-up resistor #: A resistor that holds a digital input at a high level when nothing else drives it. Electronics
Pump #: A machine that moves liquid by adding energy to it. Fluids, heat and thermodynamics Read more: Pumps, Pump Curves and NPSH
Pump curve #: A graph of the head a pump produces against the flow rate. Fluids, heat and thermodynamics
p-value #: The probability of seeing a result at least as extreme as the one observed if the null hypothesis were true. Math, units, quality and workshop
PWM #: Pulse-width modulation: controlling average power by varying the duty cycle of a fast on-off signal. Electronics
Pythagorean theorem #: In a right triangle, the square of the hypotenuse equals the sum of the squares of the other two sides. Math, units, quality and workshop
Python #: A readable high-level programming language widely used for scripting, data analysis and automation. Programming, data and computing Read more: Python for Engineers

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