Characteristics of volumetric or mass flow rate measurement sensors

From ASHRAE 1997, with permission

Measurement means

Application

Range

Precision

Limitations

Orifice and differential pressure measurement system

Flow through pipes, ducts, and plenums for all fluids

Above Reynolds number of 5000

1 to 5%

Discharge coefficient and accuracy influenced by installation conditions

Nozzle and differential pressure measurement system

Flow through pipes, ducts, and plenums for all fluids

Above Reynolds number of 5000

0.5 to 2.0%

Discharge coefficient and accuracy influenced by installation conditions

Venturi tube and differential pressure measurement system

Flow through pipes, ducts, and plenums for all fluids

Above Reynolds number of 5000

0.5 to 2.0%

Discharge coefficient and accuracy influenced by installation conditions

Timing given mass or volumetric flow

Liquids or gases; used to calibrate other flowmeters

Any

0.1 to 0.5%

System is bulky and slow

Rotameters

Liquids or gases

Any

0.5 to 5.0%

Should be calibrated for fluid being metered

Displacement meter

Relatively small volumetric flow with high pressure loss

As high as 1000 cfm (500 L/s) depending on type

0.1 to 2.0% depending on type

Most types require calibration with fluid being metered

Measurement means

Application

Range

Precision

Limitations

Gasometer or volume displacement

Short-duration tests; used to calibrate other flowmeters

Total flow limited by available volume of containers

0.5 to 1.0%

 

Thomas meter (temperature rise of stream due to electrical heating)

Elaborate setup justified by need for good accuracy

Any

1%

Uniform velocity; usually used with gases

Element of resistance to flow and differential pressure measurement system

Used for check where system has calibrated resistance element

Lower limit set by readable pressure drop

1 to 5%

Secondary reading depends on accuracy of calibration

Turbine flowmeters

Liquids or gases

Any

0.25 to 2.0%

Uses electronic readout

Instrument for measuring velocity at point in flow

Primarily for installed systems with no special provision for flow measurement

Lower limit set by accuracy of velocity measurement

2 to 4%

Accuracy depends on uniformity of flow and completeness of traverse

Heat input and temperature changes with steam and water coil

Check value in heater or cooler tests

Any

1 to 3%

 

Measurement means

Application

Range

Precision

Limitations

Laminar flow element and differential pressure measurement system

Measure liquid or gas volumetric flow rate; nearly linear relationship with pressure drop; simple and easy to use

0.0001 to 2000 CFM
50 mm3/s to 1 m3/s

1%

Fluid must be free of dirt, oil, and other impurities that could plug meter or affect its calibration

Magnetohydrodynamic flowmeter (electromagnetic)

Measures electrically conductive fluids, slurries; meter does not obstruct flow; no moving parts

0.1 to 10,000 GPM
0.006 to 600 L/s

1%

At present state of the art, conductivity of fluid must be greater than 5 mmho/cm

Swirl flowmeter and vortex shedding meter

Measure liquid or gas flow in pipe; no moving parts

Above Reynolds number of 104

1%