Glossary of Terms

Absolute Pressure

This is the pressure at standard sea level which is the pressure of the atmosphere around us and is approximately 14.7 pounds per square inch absolute (14.7 Abs. PSIA): this will vary with changes in altitude or weather conditions.

Absolute Zero

The temperature at which a system would undergo a reversible isothermal process without transfer of heat and at which the volume of an ideal gas would become zero, calculated to be -273.16°C (-459.7°F) or zero degree Kelvin.


The maximum deviation to be expected between a meter reading and the actual value being measured under specified operating conditions. Usually expressed in percent of full scale for analog instruments, percent of reading for digital instruments.

A/D Converter

Analog-to-digital converter. A circuit or device for producing a set of digital output signals representing the magnitude of a voltage applied to its input.


A process that takes place without gain or loss of heat.

Air Damped

A construction utilizing an air vane to achieve movement damping. This vane is usually housed in a closed chamber to increase the damping action

Alloy 11

An alloy of copper with addition of approximately 0.5% nickel. Used with pure copper as compensating lead wire for Platinum/Platinum-Rodium thermocouples types R & S.

Alloy, Thermocouple

Any of a number of metal alloys having standardized and controlled thermoelectric properties. Designated dissimilar pairs of these alloys are used together to realize measuring or extension portions of thermocouple circuits.


Temperature coefficient of resistance in units of ohms per ohm, per °C. Usually expressed over the fundamental interval of 0 to 100°C. EXAMPLE: Platinum per DIN 43760: 0.00385?/?/°C

Alternating Current

Current that reverses its direction of flow periodically (Hz).

Ambient Temperature

The encompassing atmosphere; environment; air surrounding the equipment and instruments in use.


A unit of measure for the rate of current flow. Current is measured in amperes (A), when 6.28 billion billion electrons move past a certain point in one second. This represents one ampere of current.


In electrical quantities having the property of varying in a continuous, rather than incremental or discrete-step manner. Analog Panel Meter A scale and pointer meter, capable of indicating a continuous range of values from zero to the rated full-scale value.

ANSI C39, 1

Standard American National Standards Institute, Inc. Standard C39.1. Applies to analog instruments, defining nomenclature, test conditions and procedures, general construction requirements, mounting dimensions, and performance requirements.

Apparent Power

Applied voltage multiplied by current in an AC circuit. This value would not take the power factor into account. Unit is voltamperes (VA).


(Data transmission) An adjustable device for reducing the amplitude of a wave without introducing distortion. An adjustable passive network that reduces the power level of a signal without introducing appreciable distortion.


In digital instruments, the ability to measure DC values of either polarity, and to display the polarity of the measurement without the need to interchange test lead connections.


In digital instruments, the automatic updating of an error integrating/memory circuit prior to each measurement, eliminating the effects of zero offset and drift, resistance tolerance and drift, and time-constant tolerance and drift in the instrument circuits.

Average Responding

The measurement of an AC voltage or current obtained using a DC instrument with a rectifying input circuit that converts AC energy to DC. The meter scale or readout is usually calibrated in terms of the corresponding RMSD values, but is accurate only for pure sine wave inputs.


American Wire Gauge - Code System for Standard Wire Sizes.