Accuracy: Degree of conformity of a measured value to an accepted standard value; or closeness of a reading or indication of a sensor to the actual value of the quantity being measured.
Accuracy rating: A number that defines a limit that the measurement errors will not exceed under some reference operating conditions. It includes the combined effects of conformity, hysteresis, deadband and repeatability errors.
Accuracy, units: The maximum positive or negative deviation (inaccuracy) observed in testing a device. It can be expressed in terms of the measured variable (± 1°C), or as a percentage of the actual reading (%AR), of the full scale (%FS), of upper range value (%URL), of the span or of scale length.
Admittance: Admittance of an ac circuit is analogous to conductivity of a dc circuit; it is the reciprocal of the impedance of an ac circuit.
Air consumption: The maximum rate at which air is consumed by an instrument while operating within its operating range, usually expressed in units of standard cubic feet per minute.
Alphanumeric: A character set containing both letters and numbers.
Alternating current (ac): A flow of electric charge (electric current) that undergoes periodic reverses in direction. In North America, household current alternates at a frequency of 60 times per second.
Ambient pressure: The atmospheric pressure of the medium surrounding a particular sensor. When no specific information is available, it is assumed to be 14.7 psia.
Ambient temperature: The average or mean temperature of the atmospheric air which is surrounding a sensor or instrument. If the sensor is a heat generator, this term refers to the temperature of the surroundings when the sensor is in operation. The ambient temperature is usually stated under the assumption that the sensor is not exposed to the sun or other radiant energy sources.
Ambient temperature compensation: An automatic correction which prevents the reading of a sensor or instrument from being affected by variations in ambient temperature. The compensator specifications state the temperature range within which the compensation is effective.
American National Standards Institute (ANSI): A professional organization in the United States responsible for accepting and designating the standards developed by other organizations as national standards.
Ampere (A or amp): The unit of electric current flow, defined as the rate at which one coulomb of electric charge (6.25 x 1018 electrons) is transferred in a second.
Amplifier: A device that generates an output which is stronger than and bears some predetermined relationship (often linear) to its input. It generates the amplified output signal while drawing power from a source other than the signal itself.
Analog signal: A signal that continuously represents a variable or condition.
Analog-to-digital (A/D) conversion: A generic term referring to the conversion of an analog signal into a digital form.
Analog-to-digital converter (ADC): An electronic device that converts analog signals to an equivalent digital form.
Attenuation: The reciprocal of gain; a dimensionless ratio defining the decrease in magnitude of a signal as it passes between two points or two frequencies. Large values of attenuation are expressed in decibels (dB).
Backlash: The relative movement of interlocked mechanical parts that occurs when motion is reversed.
Baud rate: Serial communications data transmission rate expressed in bits per second (bps).
Bipolar: A signal range that includes both positive and negative values (i.e., -10 V to +10 V).
Bode diagram: A plot of log amplitude ratio and phase angle values used in describing transfer functions.
Breakdown voltage: Threshold voltage at which circuit components begin to be damaged.
Byte (B): Eight related bits of data or an eight-bit binary number. Also denotes the amount of memory required to store one byte of data.