Absolute viscosity:
A measure of resistance to shear or angular displacement.The unit is dynes per second per square centimeter, or Poise, usually expressed as centi-Poise.

Accuracy:
Deviation from absolute truth.This number should include linearity, repeatability and calibration uncertainty.

Degasser:
A device for removing entrained gases from a fluid stream.

Anemometer:
Device for measuring wind speed.

Annubar:
Proprietary cantilever pitot tube.

Asymmetric flow:
This is when the flow through the liquid path does not have a symmetrical velocity distribution, which causes false readings on most flow meter types.

Axial flow
Flow meter: A flow meter consisting of a "propeller" in a tube.

Back pressure:
Flow meter downstream sidePressureMeasurement value.

Ballistic Calibrator:
A flow meter calibrator that uses piston displacement of known dimensions to calibrate a test meter.

B-ell prover:
A gas calibrator that immerses a "bell" of known size into a bath of liquid, thereby displacing gas at a known velocity and pressure through a flow meter under test.

Bernoulli:
His important formula basically stated that the amount of energy possessed by any point in a pipe is constant regardless of the cross-sectional area.

Bubble flow meter:
Also called a bubble burette or soap bubble meter.This measures the volumetric displacement of a gas by introducing a soap film over a known pore and timing its passage.

Bypass flow meter:
A flow meter that measures only a small portion of the flow, allowing most to bypass the measuring element, like a shunt on an ammeter.

Calibration:
Check instrument performance against known standards.

Cavitation:
When pressure in a system drops, some of the flowing liquid can turn to vapor or release gas from the solution, causing instrument damage or erroneous readings.

Clamping:
This usually refers to an ultrasonic flow meter, which can be positioned on the outside of a pipe to measure flow within the pipe.

Coanda effect:
This is the term used when a liquid stream adheres to a nearby solid surface.

Emission coefficient:
A mathematical function that defines the ratio between "true" flow and "indicated" flow primarily used in differential pressure devices.

Compressibility:
A change in volume or density due to a change in pressure.

Coriolis meter:
These meters are based on the Coriolis effect, meaning they use inertial forces within the fluid to react with a moving flow tube to provide very accurate mass flow readings.

Corner tapping:
Type of "pressure tapping" used with pressure differential devices, where the pressure point is located at the corner of adjacent flanges.

Critical nozzle:
A restriction in which the gas at the throat of the nozzle is a sound wave makes it easy to calculate the volumetric flow rate, so they are very useful as calibration devices.

Cross-correlation:
A data processing system used to identify identical patterns in two or more apparently random signals.

Cup anemometer:
A common wind speed indicator.

Dall tube:
Proprietary low loss differential pressure gauge.

density:
The ratio of mass to volume.

differential pressure:
The difference between pressure measurements at two points in a system.

Emission coefficient:
SeeEmission coefficient.

Distinguish:
The smallest unit that a meter can distinguish.

Doppler effect:
Obvious changes in the frequency of the moving body relative to the homage point.

Eddie:
Flowing Vortex.

Valid range:
M the linear portion of the performance curve.

electrode:
Sensor measurements in electromagnetic flow meter.

Electromagnetic:
A flow meter that uses the same principle as a generator, where a voltage is induced when a conductor moves in a magnetic field, the fluid is the conductor, and the body of the meter provides the magnetic field and electrodes.

Flow regulator:
A device used to "normalize" asymmetric or swirling flow upstream of the flow meter.

Fluid flow meter:
A device that measures fluid flow using fluid properties such as the Coanda effect.

Flumes:
Open channel flow equipment.

Gas meter:
AnyGas flow meterA common name for, usually a domestic unit.

gear flow meter:
One of several types of flow meters that use the meshing of circular or oval gears to meter discrete volumes of liquid.

Weight calibration:
Measuring systems that weigh the mass of fluid as the basis for calibration.

Head:
The height of the fluid column is equal to the pressure.

hotline:
Used as an anemometer or anemometer.

Inertia effect:
Error caused by the inertia of a moving fluid or mechanical components associated with it.

Reasoning instrument:
A flow meter that uses known fluid properties to calculate mass flow by measuring one or more key parameters, such as velocity and density.

Insert instrument:
A term used for flow meters that measure point velocity in a fluid stream.The results are often used to calculate the flow rate throughout the pipeline.

K coefficient:
Number of output pulses per unit volume from the flow meter, e.g. pulses per liter

Kinematic viscosity:
This is the ratio of absolute viscosity to density, usually expressed in centokes; Centimeters.

Laminar flow:
A flow in which fluid moves in a parallel manner along a conduit (not turbulent flow), typically with a Reynolds number below 2000 and with a velocity distribution through the conduit that resembles a parabola.

Laser anemometer:
High performance point fluid velocity device.

Linear:
This is the deviation from the ideal value over a specified flow range, with the nominal "K" factor usually expressed as a percentage.

Mach number:
The ratio of local flow velocity to the speed of sound.

pressure gauge:
An instrument that measures pressure using a column of fluid (usually water or mercury).

mass flow:
Also called true mass flow, where the measurement is a direct reading of the fluid mass, not just the volume or velocity.

Main instrument:
Typically a highly accurate flow meter used as a reference for calibration purposes

Average pipe speed:
This is the average velocity of the entire pipe, not just a single point.

Instrument error:
The deviation of the meter output from the absolute value.

Instrument coefficient:
The number of pulses per unit volume is shown in the "K" factor.

Instrument prover:
Similar to a ballistic prover, but usually portable.

Non-Newtonian fluids:
A fluid whose viscosity changes with shear strain rate.

Nozzle:
Various types of differential pressure devices.

Nutating disc:
A positive displacement gauge that uses a disc with grooves that allow it to "oscillate" rather than rotate on spherical bearings in a specially shaped chamber.

Open channel flow meter:
One of a variety of flow meters designed specifically for operation in culverts, flumes, streams, or rivers.

Orifice plate:
A differential pressure device consisting of plates that restrict flow, using Bernoulli's equation and the principle of conservation of energy to result in predictable pressure losses, and can be concentric, eccentric or chordal.

Oval gear flow meter:
A type of positive displacement transducer that uses two oval blades with meshing teeth to form the linkage and driver.See also Gear Meter.

Over range:
Operating the flow meter outside its designed flow range.

Peak flow meter:
A meter used to measure maximum flow, often used to measure lung capacity in people with asthma.

Pelton wheel:
A Radial Flow Turbine Flow Meter: A turbine used to extract energy from water.

Pickup:
A sensor used on flow meters.

Pipeline prover:
See ballistic prover

Pipe wall roughness:
The roughness of the tube hole.This is very important when using theoretical analysis to calculate fluid behavior, for example using orifice plate.

Pitot tube:
Differential pressure devices that utilize kinetic energy to convert into pressure energy can be used for point measurements and can be cantilevered or static.

Point speed:
Fluid velocity at one point.This does not necessarily represent the entire flow in the pipe.

Volumetric flow meter:
A flow meter that uses the principle of having a discrete pocket of fluid from inlet to outlet with almost no leakage.

Pressure tapping:
The point in the system where pressure is read, this location is critical for some types of differential pressure devices.

Pulsating flow:
The condition is the change in velocity of the fluid in the pipe.

Radial flow meter:
A series of flow meters that use the kinetic energy of a fluid hitting a rotating blade 90 degrees to the direction of flow, often called a Pelton wheel meter.

Scope:
Linear operating range of the flow meter.

Adjustable range:
Also called regulation, it is the ratio between the minimum and maximum flow rates of a linear flow range.

Radioactive tracers:
A method of calibration using the velocity or dilution rate of short-lived radioactive material.

Repeatability:
The ability of a flow meter to provide the same results when run repeatedly under the same operating conditions is not to be confused with accuracy or linearity. A flow meter cannot have good performance without excellent repeatability.

resolution:
The smallest unit that a meter can differentiate is more accurately called discrimination.

Response time:
The time required to obtain an accurate reading.

Reynolds number:
Dimensionless ratio of dynamic and viscous forces used to determine fluid behavior under any conditions.

rotameter:
A variable area flow meter that uses gravity to balance the force on a float in a tapered tube, with the height of the float indicating the flow rate.

Sharp Orifice plate:
An orifice flow meter.

Shunt meter:
A flow meter in which a small portion of the main flow is metered to determine the flow rate of the entire pipe.

Sight flow:
A flow indicator, rather than a flow meter, displays the flow rate.

Sliding vane flow meter:
A very accurate positive displacement flow meter.

Slug flow:
The term used to describe the condition is liquid in a pipe interspersed with pockets of vapor that do not mix but travel in the form of a "slug."

Soap film buret:
See foam flow meter.

specific gravity:
More accurately called density.

Square root method:
This applies to most types of differential pressure devices, orifice plate, pitot tubes, etc., where the flow rate is the square root of the pressure difference.

static pressure:
Pressure measurements are not affected by dynamic changes in fluid flow and are often used as a reference for determining differential pressure.

Target instrument:
An instrument that uses force or displacement of a "target" (usually a disk) to determine flow.

temperature compensation:
Basic density and viscosity correction for accurate mass flow measurements using inferential flow meters.

Thermal mass meter:
A mass flow meter that uses the movement of a heated fluid to accurately measure mass flow in a pipe, not to be confused with a "hot wire" device that only measures point velocity rather than mass.

Three-phase flow:
A highly undesirable situation when discreet "clumps" of solid liquids and gases flow in pipes.

Flight time:
Method used for several flow meters, but usually refers to ultrasonic flow meters.Sound waves are sent along with the flow, one sound wave is accelerated and the other is delayed by half the speed of the fluid flow.

Tracer flow meter:
Instruments that monitor fluid flow rates using "tags" can be radioactive, dye, or thermal.

Transfer Criteria: Passed
Calibrated metrology components that can be cross-checked in multiple calibration laboratories.

Shipping time:
A method of recording traffic using reference to the time it takes to travel between predetermined points.Usually ultrasound but can be tracers in, for example, river flow measurements.

turbine flow meter:
Mainly used in "propeller in tube" type flow meters, but can also be used in many other flow devices such as Pelton wheels.

Adjustment ratio:
Also called adjustable range, it is the ratio of the minimum and maximum flow rates of the linear flow range.

Turbulence:
A condition in which the entire fluid travels in an apparently uniform flow but individual particles in the fluid travel in a random manner in all directions.

Two-phase flow:
When two fluids travel in a pipe instead of mixing.

ultrasonic flow meter:
A flow meter that uses high-frequency sound waves to measure flow by the time-of-flight or Doppler method.

Variable area meter:
A term used for mass flow meters that use the movement of one element relative to another in a specially shaped chamber to indicate flow rate.

Speedometer:
A flow meter that usually measures the velocity of a fluid at only one point (such as a pitot tube).

Speed curve:
Graphical or numerical representation of various speeds on a catheter.

Vena contracta:
Just after the orifice plate of the flow tube, the flow forms its smallest diameter.

Venturi flow meter:
A differential pressure gauge used to control upstream and downstream pipe geometry to minimize total pressure loss.

viscosity:
Resistance to shear at a known rate.

Viscometer:
A device used to measure the viscosity of fluids.

Viscous flow:
When the flow in a conduit moves uniformly in the same direction, the velocity distribution forms a parabola because the fluid closer to the wall travels more slowly due to viscous drag.

Vortex shedding:
When a blunt fluid is introduced into a fluid flow, it causes vortices to shed from alternating sides at a frequency proportional to the fluid velocity. This phenomenon is used in Vortex flow meter.

Water flow meter:
For domestic useFlow meterGeneral term.