Advantages of Ultrasonic Flow meters:

Unobstructed flow passage

No moving parts

No additional pressure drop

Favorable choice of materials for chemically aggressive liquids

Linear relationship between flow rate and measured variable

Low maintenance

Operates in both flow directions (forward and reverse)

Transit time meters unaffected by temperature, density and concentration

Later installation in existing pipe possible with individual elements, but onsite calibration required

Limitation:

Still problematic for liquid and gas measurements

Sound beam must traverse a representative cross section, therefore flow profile dependent. Long inlet and outlet sections required

Errors due to deposits

Transit time meters require clean liquids

Doppler meters only for slight contamination or few gas bubbles

Doppler meters affected by sound velocity changes due to temperature, density and concentration

Unsuitable for heavily contaminated liquids

Advantages of Electromagnetic flowmeters:

Unobstructed flow passage without projecting parts

No moving parts

No additional pressure drop

Essentially flow profile insensitive, only short inlet and outlet sections required

Unaffected by changes in temperature, density, viscosity, concentration and electrical conductivity

Favorable choice of materials for chemically aggressive or abrasive measuring media

Unaffected by contamination and deposits

Especially suitable for hydraulic solids transport

Linear relationship between flow rate and measured variable

Operates in both flow directions (forward and reverse)

Measuring range setting can be optimized

Low maintenance, but still easy to maintain

Limitations:

For liquids only

Lower conductivity limit 0.05 μS/cm

Gas inclusions cause errors

Advantages of Turbine Flowmeters:

No external power supply for Rotating vane and Woltman meters

Turbine type flow meter suitable for cryogenic liquids

Customized gas turbine flow meter usable at extreme temperatures and pressures

Disadvantages:

Limited choice of materials

Only for low viscosities

Moving parts, wear

Sensitive to contamination

Axial flow totalizers are flow profile sensitive

Inlet and outlet sections required (not for rotating vane meters)

Advantages of Thermal Mass Flowmeters:

Direct gas mass flow measurement

No pressure and temperature compensation required

Very low pressure drop

High measuring accuracy

Large span

No moving parts

Rugged construction

Short response time

Easily sterilized

Limitations:

For gases only

Inlet and outlet sections required