Instrument Calibration Services Glossary

Welcome to the calibration services glossary where you can find information on everything and anything to do with calibration.

Absolute Pressure
Actual pressure relative to a perfect vacuum. See pressure calibration services.

Absolute Temperature
The temperature measured from absolute zero as in the Kelvin and Rankine scales. See temperature calibration.

Absolute viscosity
Measure of resistance to shear, unit is dyne-second per square centimetre, or more commonly known as centi-Poise (cP).

Rate of change of velocity.

Closeness of agreement between the result of measurement and the true value of the measurand. (VIM:1993). This should include linearity, repeatability and calibration uncertainty.

Adjustment of an instrument
The operation of bringing a measuring instrument into a state of performance suitable for its use.

Air eliminator
A device for removing entrained gas from a fluid stream.

Air Velocity

The velocity of air at a measurement point or plane, measured using an anemometer laser Doppler or pitot tube. See air velocity calibration.

An instrument that measures the height above ground.

Ambient Temperature
The local temperature of air in the immediate vicinity.

Atmospheric Pressure
The local air pressure in the immediate vicinity, which measured with reference to absolute vacuum. The pressure varies upon location, altitude and local weather conditions.

A device for measuring wind speed or air velocity. Readings indicated from the device are generally at actual test conditions.

ASTM Standard Practice for cleaning methods and cleanliness levels for materials and equipment used in oxygen-enriched environments.

An instrument that measures atmospheric pressure.

Bell Prover
A gas calibrator that immerses a "bell" of known dimensions into a bath of liquid over a specified time. This is generally used a primary source for gas flowmeter calibrations.

Blowby Meter
A flowmeter used in the automotive industry for the measurement of engine blow-by gases, often utilising vortex or orifice type flowmeters.

Bubble Flowmeter
An instrument that uses a soap film across a known bore and times it passage of movement. Care must be taken with soap film meters due to issues with vapour pressure, permeability of the soap film, changing shape of the film and the build up of solution on the walls.

Relationship comparison of the instrument performance against a known standard. Note this does not mean adjustment to bring within specification, as is commonly misunderstood.

Clamp-on Flowmeter
Generally an ultra-sonic type flowmeter that is positioned on the outside of a pipe to measure the flow in the pipe using time of flight or doppler techniques.

An instrument to measure an angle of inclination or elevation.

An instrument for comparing some measurement with a fixed standard.

Critical Flow Nozzle
A flow nozzle where the gas in the throat of the nozzle is kept above sonic velocity whilst in use, sometimes known as a sonic nozzle.

Cup Anemometer
A type of wind speed indicator used mainly in weather stations.

The mass per unit volume.

Differential pressure
The difference between the two measurements of pressure in a system.

Electromagnetic Flowmeter
A non-intrusive style flowmeter for use on conductive liquids, mainly water. Often referred to as a Magmeter.

Error of measurement
The result of a measurement minus the true value of the measurand.

Flow Straightner
A device for conditioning flow profile, mainly used upstream of flowmeters.

Gauge Pressure (g)
A measurement of the force/area exerted by a gas or fluid, relative to atmospheric pressure.

Gas Meter
A generic term for a gas flow meter. Many types of meter exist.

Gear Meter
A flowmeter that uses the meshing of gears to meter small volumes of a liquid. Most meters will be supplied with a Meter Factor calibration constant.

Gravimetric Calibration Rig
A measurement system that utilises fluid mass and time for the calculation of flow rate.

The unit of frequency.

Hot Wire Anemometer
An anemometer type for measuring wind speed or air velocity meter. These meter types often state the velocity reading to standard conditions. These are also referred to as Thermal Anemometers.

A measuring instrument for determining the specific gravity of a liquid or solid.

Measuring instrument for measuring the relative humidity of the atmosphere.

International Organisation for Standardisation.

ISO/IEC 17025:2017

International standard for the General requirements for the competence of testing and calibration laboratories.

K factor

A calibration constant for a flowmeter, defined as; number of pulses per unit volume. Often referred to as Meter Factor.

Kinematic Viscosity
The ratio of absolute viscosity to density, usually expressed as centistokes cSt.

Laminar Flow
Type of flow where the fluid moves in a parallel manner along the conduit, and has Reynolds numbers below 2000.

Laminar Flowmeter
A type of flowmeter that generate laminar flow through its core, and so generates a linear output in terms of pressure drop across the meter.

Laser Doppler Anemometry
A high performance measurement system that provides gas or fluid velocity at the laser intersection. Reference device often used for the calibration of wind tunnels and anemometers.

Is the deviation from a nominal calibration 'K' factor normally expressed as a percentage.

Load Cell
An instrument for the measurement of load or weight.

Master Meter
Typically a highly accurate flowmeter used as a reference device for calibrating other meters.

Measurement Uncertainty
The estimated amount by which the measured quantity may depart from the true value.

Meter Factor
Defined as;number of pulses for per unit volume. Also referred to a 'K' factor.

A unit of force equal to the force that imparts an acceleration of 1 m/sec/sec to a mass of 1 kilogram.

Newtonian Fluid
A fluid whose absolute viscosity is the same for all values of shear stress.

Non-Newtonian Fluid
A fluid whose absolute viscosity varies with the rate of shear stress.

Nutating Disc Flowmeter
A type of positive displacement flowmeter that uses a disc with a slot in that "wobbles" rather than rotates. Often referred to as a Wobble Plate Meter.

Orifice Plate
A differential pressure type device consisting of a plate with a smaller hole in the centre. Flow through the hole causes a pressure drop. Orifice plates are often made to International standards and can be theoretically predicted for flow and pressure drop.

Peak Flowmeter
A meter used to measure the maximum flow rate for measuring the lung efficiency of asthmatics.

Pelton Wheel Flowmeter
A type of radial flow turbine meter.

A sensor used on a flowmeter to detect pulse measurements.

Pitot Tube Static
A differential pressure device for measuring point velocity.

Positive Displacement Flowmeter
A type of flowmeter that fills small volumes of space, i.e. in between gears as the fluid flows from inlet to outlet, whilst turning the gears and generally providing a signal proportional to the flow rate.

Force exerted per unit area.

Primary Standard
A unit directly defined and established against which all secondary standards are calibrated.

A measure of how likely it is that some event will occur.

An instrument for measuring relative humidity.

An instrument for measuring high temperatures.

Reynolds Number
A dimensionless number defining the ratio of dynamic and viscous forces of fluids in any condition.

A trade name associated with Variable Area Flowmeters that uses gravity to balance the force on a float in a tapered tube. The height of the float in the tube is indicative of the flow rate.

Full scale output divided by the rated capacity of a given transducer / load cell.

A term referring to the passing of fluid though a flowmeter without registration. High slippage rates often occur on low viscosity fluids and can cause large errors.

The ability of a measuring instrument to maintain constant meteorological characteristics with time.

Standard Temperature & Pressure (STP)
Standard conditions for experimental measurements, to allow comparisons to be made between different sets of data. Be careful, as different bodies and institutes use different reference conditions.

Standard Uncertainty
Uncertainty of the result of a measurement expressed as a standard deviation.

A semiconductor device made of materials whose resistance varies as a function of temperature.

Turbine Flowmeter
A type of flowmeter used in gas or fluid streams, where the movement of the fluid causes a turbine wheel to rotate. The rotation is sensed from a suitable pick up. These meters will be supplied with a calibration K Factor.

Turndown Ratio
Also referred to as rangeability. It is the ratio between the maximum and minimum flow rate of the meter, across its specified operating range. Turndown can often be increased at the expense of meter accuracy.

Turbulent Flow
A condition where the fluid is travelling in an apparently uniform stream but the individual particles within the fluid are travelling in a random manner in all directions.

Measurement of duration.

Cause of rotary motion. It is equal to the applied force multiplied by the distance from the centre of rotation.

1/760 of an atmosphere.

Ability to trace the history of an instrument measurement.

An instrument that provide a voltage output.

Standard used as in intermediary to compare standards.

An instrument that provide a current output.

United Kingdom Accreditation Service

Ultrasonic Flowmeter
A type of flowmeter that uses high frequency sound waves to measure flow by either time of flight or Doppler methods.

Universal Viscosity Correction (UVC)
A method of correcting a turbine meter performance when being used on oil at varying temperatures. The changing temperature and viscosity can be corrected for utilising Strouhal-Roshko equations.

Any pressure below atmospheric.

Vane Anemometer
A type of wind speed measuring device, where a vane rotates in a housing and the rotational speed is converted into an air speed. For more information on Anemometers please visit our Flow Meter Sales section.

Variable Area Flowmeter
A type of flowmeter often referred to as a Rotameter (which is a trade name). The meter uses gravity to balance the force on a float in a tapered tube. The height of the float in the tube is indicative of the flow rate.

Velocity meters
A type of flowmeter that simply measures the velocity of the fluid usually at a single point, i.e. a pitot tube.

An instrument for measuring fluid viscosity.

Viscous Flowmeter
A type of flowmeter often referred to as a laminar flow meter, where the flow through the meter is under laminar conditions.

Resistance of a liquid to sheer forces.

Viscosity Correction (Air)
Utilised when operating laminar flow meters away from standard calibration conditions. Different methods are used depending upon instrument manufacture.

The force of gravity acting on an object.

Wilson Flow Grid
A type of multiport differential measurement system for ducts and tunnels.