Introduction to Flow meter Selection-Advanced Part (1)

Introduction to Flow meter Selection-Advanced Part (1)

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Introduction to Flowmeter Selection-Advanced Part (1)

Types of fluid flow meters

Introduced different types of liquid flow meters-Orifice, Venturies, Nozzle, Rotameter, Pitot Tube, Calorimetrics, Turbine, Vortex, Electromagnetic, Doppler, Ultrasonic, Thermal Mass, Mass, Coriolis

The most common calibration fluid flow measurement is:

  • Differential pressure flow meter
  • Speed flow meter
  • Volumetric flowmeter
  • Mass flowmeter
  • Open channel flowmeter

Differential pressure flow meter

The method of calculating the differential pressure flow of the drop device is to measure the pressure drop beyond the insertion flow of an obstacle.

The differential pressure flowmeter is based on the Bernoullis equation, where the pressure drops, and the further measured signal is a function of the square of the flow velocity.

The most common types of differential pressure flow meters are:

  • Orifice
  • Flow nozzle
  • Venturi tube
  • Variable Area-Rotameter


With the orifice, the fluid flow rate is measured by different pressures from the upstream to the downstream side of a partial blockage of the pipeline.

.The precise measurement of the spoiler provides a kind of pipe blockage, shrinkage and force contraction of the flowing liquid.

The orifice plate is simple, inexpensive, and can be used in almost any application with any material.

The accuracy conversion efficiency of the orifice plate is less than 5:1. Its accuracy is poor at low flow rates.

High accuracy depends on the orifice plate in good condition, with sharp edges on the upstream side.

Reduce the accuracy of wear.

  • Orifice, nozzle and venturi gauge

Venturi tube

Due to simplicity and reliability, venturi flowmeters are often used in applications where high range rates or reduced pressure drops are required, than orifice plates can provide.

In the venturi tube, the interception area where the fluid flow is reduced, and the pressure difference is generated in the flow path.

In the post-contraction zone, the fluid passes through a pressure recovery outlet section, and as much as 80% of the pressure difference is generated in the contraction zone and is recovered.

With proper instrumentation and flow calibration, the venturi flow can be reduced by approximately 10% of full scale with proper accuracy.


This provides a precision conversion efficiency of 10:1.

  • Orifice, nozzle and venturi gauge

Flow nozzle

Flow nozzles are often used in industrial applications as measuring elements for air and gas flow.

The flow of the nozzle is relatively simple and cheap, and can be used in many applications in many materials.

The conversion efficiency and accuracy can be compared with the orifice plate.

  • Orifice, nozzle and venturi gauge

In the sonic nozzle-severe (choke) flow nozzle

As the gas accelerates through the nozzle, the velocity increases, and the pressure and gas density decrease.

The maximum speed is reached in the throat, the smallest area, where the rest is Mach 1 or sound waves.

At this point it is impossible to increase the flow rate and reduce the downstream pressure.

Flow is choking.

This situation is used in many control systems to maintain a fixed, accurate, and repeatable gas flow regardless of downstream pressure.

Recover pressure drop orifice, nozzle and venturi gauge

The differential pressure flowmeter that has been generated after the pressure difference, the fluid passes through the pressure to restore the outlet section, and the pressure difference generated therein is partially restored in the contraction zone.

As we have seen, the pressure drop of the orifice is significantly higher than that of the venturi.

Variable area flowmeter or rotameter

The rotameter consists of a vertical glass (or plastic) tube with a larger end on the top, which is a freely moving tube within the measurement floating range.

The fluid flow causes the rising pressure difference of the floating riser pipe and the buoyant fluid overcomes the influence of gravity.

The float rises to the area between the annular tube and the float rises enough to allow a dynamic equilibrium state between the pressure difference and the buoyancy factor upward and downward gravity factor.

The height fluctuation is the displayed flow rate.

The tube can be properly calibrated and graduated in flow units.

Common float flow meters have a turndown ratio of up to 12:1.

The accuracy may not be as good as the 1% full scale rating.

Magnetic floats can be used for alarm and signal transmission functions.

Speed flow meter

The flow calculation method of the velocity flow meter is to measure the flow at one or more points of velocity, the flow velocity and the integrated flow area.

Pitot tube

.Pitot tube is one of the most commonly used (and cheapest) method to measure the flow of fluids, especially in air applications, ventilation and air conditioning systems, even when used on airplanes

Pitot tubes measure the flow rate of a fluid by converting kinetic energy into potential energy.

Use Pitot tube to limit point measurement.

With "Aniu", or a multi-port Pitot probe, you can measure dynamic pressure across the entire velocity profile, and Aniu can get an average effect.

Calorimetric flowmeter

The principle of calorimetric fluid flow measurement is based on the close contact of two temperature sensors with the thermal insulation of the fluid, but each other.

.In a fixed (no flow) oil state there is a constant temperature difference between two temperature sensors.

As the fluid flow increases, the thermal energy from the heating temperature sensor and the difference between the sensor decrease.

This reduction is proportional to the flow rate of the fluid.


Response time will vary due to heat transfer fluid.

Generally lower thermal conductivity requires higher speed for proper measurement.

The calorimetric flowmeter can achieve high accuracy and low flow rate.

Turbine flowmeter

There are many different designs and manufactures of turbine flow meters, but in general, they are all based on the same simple principle:

If the fluid moves through the pipe and acts on the turbine blades, the turbine starts to spin and spin.

The rate of rotation is measured to calculate the flow rate.

The turndown ratio may exceed 100:1, if the turbine flowmeter is calibrated for single flow and fixed conditions are used.

The accuracy may be better than +/-0,1%.

Vortex Flowmeter

Obstacle fluid flow produces vortex downstream flow.

Every time a critical fluid blocks the flow rate, a vortex street occurs.

An example of vortex shedding, where the alternating low pressure zone is downstream.

These AC low-pressure areas cause obstruction to the low-pressure area.

The intensity of the eddy current can be measured with the sensor.

The principle of vortex flowmeter-it brings the principle of vortex flowmeter.

Electromagnetic Flowmeter

The electromagnetic flowmeter operates by Faraday's law of electromagnetic induction, which states that it will cause the voltage conductor to pass through the magnetic field when it moves.

The liquid acts as a conductor and the magnetic field coil is energized to create a flow outside the tube.

The voltage generated is proportional to the flow rate.

Two electrodes are installed on the inner wall of the pipeline to detect voltage, which is a secondary factor to measure.

. Electromagnetic flowmeters can measure difficult and corrosive liquids and muds, and they can measure flow in both directions with equal accuracy.

Electromagnetic flowmeters have a relatively high power consumption and can only be used for conductive liquid water.

The principle of electromagnetic flowmeter-it brings the principle of electromagnetic flowmeter

Ultrasonic Doppler Flowmeter

The effect of the movement of the sound source, its frequency of sound, was observed and described by Christian John Doppler.

The frequency of the reflected signal is modified by the speed and direction of the fluid flowing

If the liquid is moving towards a sensor, the election of frequency signals will increase.

As the hydraulic moves away from the transducer, the return signal frequency drops.

The frequency difference is equal to the reflection frequency minus the original frequency, which can be used to calculate the speed of fluid flow.

Ultrasonic Doppler flowmeter and time of flight
.Ultrasonic Flowmeter Tutorial-Basic tutorial on ultrasonic flowmeter.

Volumetric flowmeter

The volumetric flowmeter measures the fluid flow rate in the process of precise flow measurement device rotor element.

The known and fixed numbers are displaced between the rotors.

The fluid proportional to the amount of rotation of the rotor is replaced.

The number of rotations calculated by the rotor is made up of a complete electronic pulse transmitter and converted into volume and flow.

The construction of the positive displacement rotor can be in the following aspects:

  • Reciprocating piston flow meters are single and multiple piston types.
    The ellipse has two rotating gear meters, and the ellipse gear is synchronized with the teeth, close to the teeth.
  • A fixed amount of liquid flows through each revolution of the meter.
    The shaft rotation can be monitored to obtain a specific flow rate.
    There is a removable disk m Nutating disk installed in a concentric ball located in the side wall chamber of the ball.
    Pressured liquid passing through the measurement chamber will cause the disk rock circulation path to have no axis of rotation of its own.
    This is the only moving part in the measurement room.
    The meter is equal to the rotating vane, the rotating impeller, two or more compartments, and the outer casing of the instrument.
    The continuous impeller is in contact with the casing.
    A fixed volume of liquid is swept to the exit of the meter from the impeller rotating in each compartment.
    The impeller in the revolution is counted and registered in volume units.

The positive displacement flowmeter can be used for all relatively non-abrasive fluids such as heating oil, lubricating oil, polymer additives, animal and vegetable grease, ink, freon, etc.

The accuracy can be as high as 0.1% full scale rate and more than 70:1.

Mass flowmeter

Measure the mass flow directly.

Thermal flow meter

Thermal mass flow meters operate independently of density, pressure and viscosity.

Use warm water thermal sensor element to isolate the fluid flow path to carry out the sensor element in the hot air flow.

The heat carried out is proportional to the mass flow and temperature difference, and he calculates the mass flow.

The accuracy of the reliability of the thermal flow calibration device depends on the actual process and changes in temperature, pressure, flow, heat capacity and viscosity of the fluid.

Coriolis flowmeter

Direct mass measurement Coriolis flowmeter sets apart other technologies

Insensitive to changes in mass measurement, pressure, temperature, viscosity and density.

.Since it can measure liquid, mud and gas,
Coriolis flow meters are universal meters.

Coriolis mass flow meters use the Coriolis effect to measure the amount of mass moving through elements.

The fluid to be measured flows through a U-shaped tube, which is an angular harmonic oscillation that causes vibration.

Due to the Coriolis force, the deformable tube and an additional vibration component will be added to the oscillation.

This additional component will cause a phase shift in some places where the tube can measure the sensor.

Coriolis flowmeters are generally very accurate, better than +/-0,1% with a bed rate exceeding 100:1.

Coriolis meters can also be used to measure the density of liquids.

Open channel flowmeter

A common method of measuring the height of liquid flowing through an open channel is to measure the height of the liquid because it passes through a multi-obstructed trough or weir channel.

Commonly used are Sharp crested weir, Cipolletti weir with V-notch weir, rectangular tip weir, Parshall flume or Venturi flume.

  • Weir flow measurement standards-important and commonly used standards in weir flow measurement
  • Flow measurement and weirs-Weirs are usually used to measure flow velocity in open channels and connect river water supply and sewage treatment plants
  • Weir flow measurement standards-important and commonly used standards in weir flow measurement