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 |
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 |
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% |