Advantages and Disadvantages of Flowmeters,

Electromagnetic flowmeters

Advantages:

  • 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

Ultrasonic Flowmeters

Advantages:

  • 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
  • Gas bubbles cause errors

Coriolis Mass Flowmeters

Advantages:

  • True mass flow measurement
  • Additional temperature and density measurements
  • Very high accuracy for mass flow measurements
  • Highly accurate density measurement
  • Unaffected by pressure, temperature and viscosity
  • No inlet and outlet sections required
  • Operates in both flow directions (forward and reverse)
  • Measuring range settings can be optimized for flow rate and density
  • Self-draining

Limitations:

  • Affected by gas inclusions
  • Vibration sensitive when improperly installed
  • Limited choice of materials
  • Nominal diameter limited at the top

Thermal Mass Flowmeters

Advantages:

  • 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

Differential Pressure Flowmeters

Advantages:

  • Universally suitable for liquids, gases and steam
  • Also usable in extreme situations, e.g. viscosity, due to variety of versions
  • Calculations possible for unusual situations
  • Suitable for extreme temperatures and pressures
  • Range changes possible
  • Low pressure drop for nozzles

Limitations:

  • Square root relationship between flow rate and differential pressure, therefore smaller span
  • Affected by pressure and density changes
  • Pressure drop for orifice plates
  • Edge sharpness for orifice plates must be assured, therefore no solids or contamination
  • Very long inlet and outlet sections
  • Expensive installation requiring differential pressure lines, fittings and sensors
  • Installation and maintenance experience advantageous
  • High maintenance requirements

Turbine Flowmeters

Advantages:

  • No external power supply for Rotating vane and Woltman meters
  • Turbine flowmeters suitable for cryogenic liquids
  • Turbine flowmeters 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)

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