AN - Engineering Definitions: Updated Periodically

analogue Pertaining to data in the form of continuously variable physical quantities. Contrast with digital. A waveform is analogue if it is continuous and varies over an arbitrary range.

analogue back up An alternate method of process control by conventional analogue instrumentation in the event of a failure in the computer system.

analogue control Implementation of automatic control loops with analogue (pneumatic or electronic) equipment. analogue signal An analogue signal is a continuously variable representation of a physical quantity, property, or condition such as pressure, flow, temperature, etc.

analogue simulation The calculation of the time or frequency domain response of electrical circuits to input stimulus. It assembles and solves a set of simultaneous equations associated with circuit topology.

angle of repose A characteristic of bulk solids equal to the maximum angle with the horisontal at which an object on an inclined plane will retain its position without tending to slide; the tangent of the angle of repose equals the coefficient of static friction.

angle valve A valve design in which one port is colinear with the valve stem or actuator, and the other port is at right angles to the valve stem.

angstrom A unit of length defined as 1/643 8.4696 of the wavelength of the red line in the Cd spectrum; largely replaced by the SI unit nanometer, or 10 9 meters.

angular momentum The product of a body's moment of inertia and its angular velocity.

angular momentum flowmeter A device for determining mass flow rate in which an impeller turning at constant speed imparts angular momentum to a stream of fluid passing through the meter; a restrained turbine located just downstream of the impeller removes the angular momentum, and the reaction torque is taken as the meter output. Also called an "axial flowmeter."

angular velocity Rate of motion along a circular path, measured in terms of angle traversed per unit time.

anhydrous Describing a chemical or other solid substance whose water of crystallisation has been removed.

anisotropic Exhibiting different properties when characteristics are measured along different directions or axes.

annealing Treating metals, alloys or glass by heating and controlled slow cooling, primarily to soften them and remove residual internal stress.

annular nozzle A nozzle whose inlet opening is ring shaped rather than an open circle.

annunciator A device or group of devices that call attention to changes in process conditions that have occurred. Usually included are sequence logic circuits, labeled visual displays, audible devices, and manually operated acknowldege and reset push buttons.

antialias filter A low-pass filter designed to block frequencies greater than one-half the measuring rate.

anti cavitation trim A combination of plug and seat ring or plug and cage that by its geometry permits noncavitating operation or reduces the tendency to cavitate, thereby minimising damage to the valve parts, and the downstream piping.

anti noise trim A combination of plug and seat ring or plug and cage that by its geometry reduces the noise generated by fluid flowing through the valve.

anti reset windup Device or circuit that prevents the saturation of the integral mode of a controller that develops during times when control cannot be achieved. Helps to prevent the controlled variable from overshooting its set point when the obstacle to control is removed.

anti surge control Control by which the unstable operating mode of compressors known as "surge" is avoided.