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Control and Instrumentation Glossary

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Arithmetic Average Roughness Height
Method of determining surface roughness.
Further Reading
Flange Surface Finish Guide

Absolute Pressure
The measurement of pressure relative to the pressure in a vacuum.
It is equal to the sum of the pressure shown on a pressure gauge and atmospheric pressure.
Further Reading


The closeness of the agreement between the result of the measurement and the conventional true value of the quantity.

Further Reading


AF - Across the Flats
Measurement between 2 parallel faces on a nut. Indicates the size of spanner or socket required to tighten or loosen the nut.

Further Reading


AGA - American Gas Association
Promoters of gas use in the US and publishers of widely used calculations for gas density (AGA 8) and gas flow (AGA 3).

Further Reading


Ambient Pressure
The atmospheric pressure surrounding a sensor or instrument.

Further Reading


Ambient Temperature
The average temperature of the atmosphere surrounding an instrument.
Assumes that the instrument is not exposed to the sun or other radiant energy sources.
Further Reading


Analogue signal
A signal that continuously represents a variable or condition.
Typical annalogue signal is 4 to 20 mA
Further Reading


Analogue to Digital Converter
An electronic device that converts analogue signals to an equivalent digital form.

Further Reading


A device that uses Pitot tubes to measure the gas flow rate within a pipeline.

Further Reading


ANSI - American National Standards Institute
A private non-profit organization that administers and coordinates the U.S. voluntary standardisation and conformity assessment system.

Further Reading


American Petroleum Institute
A trade association founded in 1919 sponsored by the oil and gas industry to develop Recommended Practices for the industry.
Further Reading


American Standard Code for Information Interchange established to achieve compatibility between various types of data processing equipment.

Further Reading
ASCII Code Guide

American Society of Mechanical Engineers.
Professional organisation focused on technical; educational and research issues of the engineering and technology community.
Further Reading


American Society for Testing and Materials.

Further Reading


EU Directive 94/9/EC covering equipment and protective systems for use in potentially explosive atmospheres.

Further Reading

A dimensionless ratio defining the decrease in magnitude of a signal as it passes between two points or two frequencies.
Occasionally expressed in decibels (dB).
Further Reading


AWG - American Wire Gauge
A standarised method for specifying the properties - including diameter - of electrical and electronic wire.

Further Reading
Electrical and Electronic Wire

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