Comparing Flowmeters

A comparison of fluid flow meters:

Electromagnetic 

Electromagnetic flow meters - or induction flow meters - function with conductive fluids by measuring flow across a controlled magnetic field.

• Suitable for: clean and dirty viscous conductive liquids and slurries with high level of solids, turbulent or laminar flow 
• Not suitable for: hydrocarbons and fluids with low conductivity, partly filled pipes, gas flow
• Accuracy: ± 0.5 - 1 % of rate
• Rangeabliity: typical 40:1
• Pressure drop: none
• Required upstream pipe (diameters): 5
• Relative cost: high
• Effect of viscosity: none
• Moving parts: none
• Pipe size: wide range
• Corrosion: can be made with liners suited for corrosive fluids

Mass - Coriolis

Mass flow meters based on the Coriolis effect.

• Suitable for: clean and dirty liquids, gases and slurries - can be used to monitor concentration and solids content. Suitable for applications where temperature and pressures fluctuate.
• Not suitable for:
• Accuracy: ± 0.05 - 0.5 % of rate
• Rangeabliity: typical 10:1
• Pressure drop: low
• Required upstream pipe (diameters): none
• Relative cost: high
• Effect of viscosity: none
• Moving parts: none
• Pipe size: limited range
• Corrosion:

Mass - Thermal

Mass flow meters based on the thermal cooling effect of the flowing fluid.

• Suitable for: clean and dirty liquids, even some slurries
• Not suitable for:
• Accuracy: ± 1 % of rate
• Rangeabliity: typical 10:1
• Pressure drop: low
• Required upstream pipe (diameters): none
• Relative cost: high
• Effect of viscosity: none
• Moving parts: none
• Pipe size: limited range
• Corrosion:

Orifice

With orifice flow meters the pressure difference over an orifice in the flow is measured. Measured pressure difference is proportional with flow velocity squared. 

• Suitable for: clean and dirty liquids and for some slurries
• Accuracy: ± 2 - 4 % of scale
• Rangeabliity: typical 4:1
• Pressure drop: medium - pressure drop required for measurement
• Required upstream pipe (diameters): 10 - 30
• Relative cost: low
• Effect of viscosity: sensible
• Moving parts: none
• Pipe size: wide range
• Corrosion: can be adapted for some corrosive liquids

Turbine

Turbine flow meters are made with bladed turbine rotors mounted axially in the meter. When fluid flows through the meter the rotor spins at a speed proportional to the velocity of the fluid. The spin is detected with a magnetic pick up with typically a pulse output.

• Suitable for: clean viscous liquids and gases, turbulent flow
• Not suitable for: corrosive fluids and liquids with solids
• Accuracy: ± 0.25 % of rate
• Rangeabliity: typical 20:1
• Pressure drop: higher, back pressure required to avoid cavitation, bubbles in the liquid will affect accuracy
• Required upstream pipe (diameters): 5 - 10
• Relative cost: medium
• Effect of viscosity: sensible
• Moving parts: rotor
• Pipe size: wide range
• Corrosion: moveable components not suited for corrosive fluids

Ultrasonic

Ultrasonic flow meters are non-invasive volume flow meters based on transit-time (Time of travel) or Doppler effect technology. A transit-time flow meter measures the frequency shift (difference) between upstream and downstream ultrasonic pulses projected into and across the pipe. The frequency shift is proportional to flow velocity. A Doppler flow meters measure the frequency shift when an ultrasonic signal is reflected by suspended particles or gas bubbles in motion. The frequency shift is proportional to flow velocity.

• Suitable for: clean (transmit-time) and dirty (Doppler) liquids
• Not suitable for: gases
• Accuracy: ± 1 - 5 % of full scale
• Rangeabliity: typical 10:1 (Doppler), 20:1 (transmit-time)
• Pressure drop: low
• Required upstream pipe (diameters): 5 - 30
• Relative cost: medium
• Effect of viscosity: none
• Moving parts: none
• Pipe size: wide range
• Corrosion: can be made with liners suited for corrosive fluids

Vortex

Vortex flow meters are made with an obstruction object mounted in flow. When fluid flows through the meter an alternating vortex is created downstream the object. The vortex frequency is proportional with the flow and is detected with a pressure sensor, thermistor or ultrasonic sensor.

• Suitable for: clean and dirty liquids and gases - including steam, turbulent flow
• Not suitable for: high viscosity fluids
• Accuracy: ± 1 % of rate
• Rangeabliity: typical 10:1
• Pressure drop: medium
• Required upstream pipe (diameters): 10 - 20
• Relative cost: medium
• Effect of viscosity: sensible for fluids with high viscosity
• Moving parts: none
• Pipe size: wide range
• Corrosion: no moving components - can be adapted for corrosive fluids

Wedge

Wedge is used as primary element in flow measurement of liquid, gas and steam according to the differential pressure principle.

• Suitable for: slurries and viscous liquids
• Accuracy: ± 0.5 - 5 % of scale
• Rangeabliity: typical 3:1
• Pressure drop: low to medium - pressure drop is required for measurement
• Required upstream pipe (diameters): 10 - 30
• Relative cost: medium
• Effect of viscosity: low
• Moving parts: none
• Pipe size: wide range

V-Cone

A V-cone flow meter a differential pressure instrument where the differential pressure is measured before and after a cone located in the flow.

• Suitable for pharmaceuticals, oil, gas, chemical, food and beverage, plastics, district HVAC, textile, power and water and wastewater applications
• Can be used for fluids with sand and dust
• Can be used in high pressure and temperature applications
• Accuracy: ± 0.5 %
• Repeatability: ± 0.1 %
• Low maintenance - no moving parts
• Long life time
• Require little space - suitable for retrofit