accelerometer; A transducer used to measure linear or angular acceleration.
access time; The interval between a request for stored information and the delivery of the information; often used as a reference to the speed of memory.
accuracy; The ratio of the error to the full-scale output or the ratio of the error to the output, as specified, expressed in percent.
acidity; Represents the amount of free carbon dioxide mineral acids and salts which hydrolise to give hydrogen ions in water. pH is the measure of hydrogen ions concentration.
ACK; Transmission control character transmitted by a receiving device as an affirmative response to a sending device.
acoustical ohm; The unit of measure for acoustic resistance, reactance or impedance; it equals unity when a
sound; pressure of one microbar produces a volume velocity of one cubic centimetre per second.
acoustic compliance; The reciprocal of acoustic stiffness.
acoustic dispersion; Separation of a complex sound wave into its various frequency components, usually due to variation of wave velocity in the medium with sound frequency; usually expressed in terms of the rate of change of velocity with frequency.
acoustic impedance; The complex quotient obtained by dividing sound pressure on a surface by the flux through the surface.
acoustic inertance A property related to the kinetic energy of a sound medium which equals Za/2 7rf, where Za is the acoustic reactance and f is sound frequency; the usual units of measure are g/cm4. Also known as "acoustic mass."
acoustic radiometer; An instrument that measures sound intensity by determining unidirectional steady state pressure when the sound wave is reflected or absorbed at a boundary.
acoustic sensitivity; The output of a transducer (not due to rigid body motion) in response to a specified
acoustical environment; This is sometimes expressed as the acceleration in g rms sufficient to produce the same output as induced by a specified sound pressure level spectrum having an overall value of 140 dB referred to 0.0002 dyne per sq cm rms.
acoustic stiffness; A property related to the potential energy of a medium or its boundaries which equals, where Za is the acoustic reactance and is sound frequency; the usual units of measure are dyne/cm.
actuator; A device responsible for actuating a mechanical device such as a control valve.
actuator, double acting; An actuator in which the power supply acts both to extend and retract the actuator stem.
actuator, electric type A device which converts electrical energy into motion.
actuator, electrohydraulic type; A self-contained device which responds to an electrical signal, positioning an electrically operated hydraulic pilot valve to allow pressurised hydraulic fluid to move an actuating piston, bellows, diaphragm or fluid motor.
actuator, electromechanical type; A device which uses an electrically operated motor-driven gear train or screw to position the actuator stem. May operate in response to either analogue or digital electrical signals
actuator, fluid motor type; A fluid powered device which uses a rotary motor to the actuator stem actuator,
hydraulic type; A fluid device which converts the energy of an incompressible fluid into motion
actuator, piston type; A fluid powered device in which the fluid acts upon a movable cylindrical member, piston, to provide linear motion to the actuator stem
actuator, pneumatic; A device which converts the energy of a compressible fluid, usually air, into motion.
actuator, single acting; An actuator in which the power supply acts in only one direction. In a spring and diaphragm actuator, for example, the spring acts in a direction opposite to the diaphragm thrust.
actuator, vane type; A fluid-powered device in which the fluid acts upon a movable pivoted member, the vane, to provide rotary motion to the actuator stem.
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