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
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Favorable choice of materials for chemically aggressive or abrasive measuring media - Unaffected by contamination and deposits
- Especially suitable for hydraulic solids transport
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Linear relationship between flow rate andmeasured 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)
