Definitions A -
A/D: Analog-to digital conversion.
Aberration: An optical phenomenon resulting from the failure of a lens or
mirror to produce a good image.
Absolute Pressure: Actual pressure on a confined gas, irrespective of the atmosphere
on the outside.
Temperature: The temperature measured from absolute zero as in the Kelvin
and Rankine scales.
Absolute Zero: The lowest temperature theoretically attainable (at which the
kinetic energy of atoms and molecules is minimal).
Absorption: (1) Loss of energy traveling through a medium. (2) Internal
taking up of one material by another. (3) Transformation of radiant energy into other forms of energy when
passing through a material substance.
Acceleration: Rate of change of velocity.
Accommodation: Changes in focus of the crystalline lens to adjust the eye of
various object distances.
Accuracy: (1) The closeness of agreement between a test result and the
accepted reference value (ISO 5725-1). (2) Closeness of agreement between the result of measurement and a
true value of the measurand. Accuracy is a qualitative concept (VIM:1993)
Adjustment (of a measuring instrument): The operation of bringing a measuring instrument into a state of
performance suitable for its use.
Adsorption: Adhesion of one substance to the surface of another.
Alpha: The current amplification factor when connected in a common base
(AC): Current which reverses polarity at a uniform
Altimeter: An instrument that measures the height above ground.
Ambient Temperature: Temperature of the air in the immediate vicinity.
Ammeter: A meter that measures the flow of electrical current in
Amperes: The basic unit of electric current adopted under the Systeme
Amplification: The process by which ionization effects are magnified to a degree
suitable for their measurement.
Apparent Power: The power value obtained in an alternating current circuit by
multiplying the effective values of voltage and current. The result is expressed in volt-amperes, and must
be multiplied by the power factor to secure the average or true power in watts.
Arc: A portion of the circumference of a circle.
Pressure: The force exerted on a unit area by the weight of the
Auditee: The organization being audited
Backlash: A form of mechanical hysterysis (lag) in which there is a lag
between the application of a driving force and the response of the driven object.
Barometer: An instrument that measures atmospheric pressure.
Baud Rate: A unit of measure for data transmission speed. It represents the
number of signal elements transmitted per second.
Best Fit Straight
Line: The equation of a straight line, calculated from a set of
measurement results, which attempts to minimize the differences between the line and the measurement
results. There is more than one statistical method used, each of which may place the straight li
Beta: The current amplification factor of a transistor when connected
in a common-emitter configuration.
B H Curve: A characteristic curve showing the relation between magnetic
induction (B) and magnetizing force (H) for a magnetic material. It shows the manner in which the
permeability of a material varies with flux density.
Bifilar Winding: A method of winding transformers in which the wires are placed
side by side and wound together.
Bimetallic Element: Two strips of dissimilar metal bonded together so that a change
in temperature will be reflected in the bending of the element, as a result of differential
Bleed Valve: A small valve to bleed off small amounts of water from container
vessel or bath.
Blowdown: Removal of liquids or solids from a process/storage vessel or a
line by the use of pressure.
British Thermal Unit
(BTU): A unit of heat equal to the amount of heat required to raise
one pound of water one degree Fahrenheit at one atmosphere pressure.
Buffer: A solution that maintains a set pH value regardless of added
acids or bases.
Buoyancy: The power to float or rise in a fluid.
Buoyant Force: The upward force which any fluid exerts on a body placed in
Byte: Eight related bits of information processed as a unit. Eight bits
equals one byte.
Calibrate: Check or adjust the graduations of a quantitative measuring
Calibration Point: One particular measurement in a sequence of measurements aimed at
Calibration: A set of operations that establish, under specified conditions,
the relationship between the values of quantities indicated by measuring instrument or measuring system and
the corresponding values realized by standards.
Capillarity: The characteristic of a liquid to be raised or depressed in a
tube of small bore. This action is caused by a combination of cohesive, adhesive, and surface tension
Cavitation: Process in which small bubbles are formed and implode violently.
This results in aggressive cleaning action in ultrasonic cleaners.
Scale: A temperature scale based on mercury in glass thermometer with
the freezing point of water defined at 0 degree C and the boiling point of water defined at 100 degree C,
both under conditions of normal atmospheric pressure.
Instrument: The intersect point of the vertical, horizontal, and optical
axis of a transit or similar instrument when perfectly calibrated.
Centripetal Force: The inward force on a body moving in a curved path around another
Material (CRM): Reference material, by a certificate, one or more of whose
property values are certified by a procedure which establishes its traceability to an accurate realization
of the unit in which the property values are expressed, and for which each certified valu
Certify: Provide evidence for or authorize officially.
CGS System: The common metric system of units
Characteristic: A property that helps to differentiate between items of a given
population. Note: The differentiation may be either quantitative (by variables) or qualitative (by
Clinometer: An instrument used by surveyors in order to measure an angle of
inclination or elevation.
Coefficient of Linear
Expansion: The change in unit length in a solid when its temperature is
changed 1 degree.
Coefficient of Volume
Expansion: The change in unit volume of a solid when its temperature is
changed 1 degree.
Cohesion: The intermolecular force that holds together the molecules in a
solid or liquid.
Collimation: The process of aligning the optical axis of optical systems to
the reference mechanical axes or surfaces of an instrument, or the adjustment of two or more optical axes
with respect to each other.
Collimator: An instrument designed to produce collimated (parallel) rays of
light usually equipped with displacement and tilt graticules.
Comparator: An instrument for comparing some measurement with a fixed
Complex Vibration: The combination of two or more sinusoidal vibrations existing
Compound: Two or more substances combined in definite proportions by weight
and united chemically.
Condensate: Steam which rises and cools to a liquid.
Conductivity: The transmission of heat or electricity or sound.
Conformity: Fulfillment of specified requirements.
Contacts: Elements used to mechanically make or break an electric
Continuous Duty: A device able to operate continuously with no off or rest
Contract Review: Systematic activities carried out by the supplier before signing
the contract to ensure that requirements for quality are adequately defined, free from ambiguity,
documented, and can be realized by the supplier.
Contractor: Supplier in a contractual situation
Convection: Transmission of energy or mass in a medium by movement of the
Conversion Chart: Must be used to convert a parts per million reading to micromho
or vice versa because the ppm scales are non linear and the micromho scales are linear. Because of the
curve, there is no set ratio so one must refer to the chart.
Correction: The value added algebraically to the uncorrected result of a
measurement to compensate for systematic error.
Corrective Action: Action taken to eliminate the causes of an existing nonconformity
defect or other undesirable situation in order to prevent recurrence.
Creep: The long term change in dimensional characteristics of a body
under load, in an elastic force measurement device. This term refers to the change in reading which occurs
when a constant load is applied for a period of time.
Critical Angle: The angle between and at which there is neither refraction or
Critical Size: For fissionable material, the minimum amount of a material which
will support a chain reaction.
Cryogenic: The science of refrigeration pertaining to the methods for
producing and measuring very low temperatures.
Damping: (1) The prevention of free swinging or vibration by some means,
usually friction or resistance. (2) The dissipation of energy with motion or time.
Decay Time: The time required for the trailing edge of a pulse to decrease
from 90 percent to 10 percent of its maximum amplitude.
Defect: Nonfulfillment of an intended usage requirement of reasonable
expectation, including one concerned with safety.
Documentation: Extent to which evidence is produced to provide confidence that
specified requirements are fulfilled.
Deionization: Removal of ionized minerals and salts from a solution by a two
phase ion exchange procedure.
Demineralization: Removal of mineral constituents from water.
Density: The mass per unit volume. CGS unit: gm/cm
DI Water: Deionized water.
Dial Indicator: This is a mechanical lever system used for amplifying small
displacements and measuring it be means of a pointer which transverses a graduated dial.
Dialysate Meter: Verifies the total concentration of ionized salts in dialysate
solutions used in hemodialysis or kidney equipment.
Voltmeter: A voltmeter that operates on the potentiometric principle. The
unknown voltage is compared to an adjustable calibrated voltage developed within the differential
Circuit: A circuit in which the output voltage is proportional to the rate
of change of the input voltage.
Diffraction: When light passes sharp edges or goes through narrow slits the
rays are deflected and produce fringes of light and dark bands.
Digital Voltmeter: An electronic voltmeter that gives readings in digits.
Diopter: A unit of measurement of the refractive power of a lens which is
equal to the reciprocal of the focal length measured in meters.
Direct Current (DC): A current with a constant polarity.
Nonconformity: Action to be taken to deal with an existing nonconforming entity
in order to resolve the nonconformity.
Distortion: Any deviation from the desired waveform.
Double Pole Double Throw
(DPDT): A term used to describe a switch or relay output contact form.
Two separate switches that operate simultaneously each with a normally open and normally closed contact and
a common connector.
Drift: Slow change of a metrological characteristic of a measuring
Dyne: The unit of force which, when acting upon a mass of 1 gm, will
produce an acceleration of 1 cm/sec/sec.