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Absolute: A measure having as its zero point or base the complete absence of the entity being measured.

Absolute Pressure: the pressure above zero absolute i.e. the sum of atmospheric and gauge pressure. In vaccum related work it is usually expressed in millimeters of mercury (mm Hg)

Absolute Positioning: Refers to a motion control system employing position feedback devices (absolute encoders) to maintain a given mechanical location.

Absolute Programming: A positioning coordinate referenced wherein all positions are specified relative to some referance, or "Zero" position. This is different from incremental programming, where distance are specified relative to the current position.

Acceleration: A change in velocity as a function of time. Acceleration usually refers to increasing velocity, and declaration to decreasing velocity.

AC Servo: A general term referring to a motor drive that generates sinusoidal shaped motor currents in a brushless motor wound as to generate sinusoidal back EMF.

Acceleration: The change in velocity of time. Acceleration usually refers to increasing velocity and deceleration describes decreasing velocity.

Accuracy: A measure of the difference between expected position and actual position of a motor or mechanical system. Motor accuracy is usually specified as an angle representing the maximum deviation from expected position.

Actuator: Air in the hydraulic fluid. Excessive aeration causes the fluid to appear milky and components to operate erratically because of the compressibility of the air trapped in the fluid.

Alternating Current (AC): A continuously changing magnitude of current, produced by a power source (e.g. generator, alternator)

Ambient Temperature: The temperature of the cooling medium, usually air, immediately surrounding the motor or another device.

Amplifier: A device for amplifying either voltage or current.

Analog Signal: An AC or DC voltage or current signal that represents variable physical quantities (e.g. voltage, current, pressure, temperature or speed).

AND Logic Gate: A digital circuit in which the output state equals a binary 1 if and only if all of its input are a binary 1 at the same time.

Annular Area: A ring shaped area- often refers to the net effective area of the rod-side of a cylinder piston, i.e. the piston area minus the cross-sectional area of the rod.

ASCII: American Standard Code for Information Interchange. This code assigns a number series of electrical signals to each numeral and letter of the alphabet. In this manner, information can be transmitted between machines as a series of binary numbers.

Atmosphere (One): A pressure measure equal to 14.7 psi.

Atmospheric Pressure: Pressure exerted by the atmosphere at any specific location. (Sea level pressure is approximately 14.7 pounds per square inch absolute.)

Attenuator: A variable resistive device used to reduce the value of current or voltage.