In order to get the best value and most effective technology for your specific application and process, it’s important to consider all the attributes of the many flow meter choices.
In this two parts series, we’ll discuss how the different types of meter technologies work and then what are the advantages and typical applications.
Coriolis Mass Flow Meters
Technology: Based on Newton’s second law of motion.
How it Works: An electromagnetic coil mounted between two curved tubes and stimulated to vibrate at the natural frequency. At a zero flow rate, the tubes move in phase. When flow is introduced, a slight twisting of the tubes in opposition to one another occurs resulting in a phase shift between the sensing coils on the tubes. The time difference is directly proportional to the mass flow rate.
What is Measured: Direct mass flow rate and density
View the Theory of Coriolis video here.
Magnetic or “Mag” Meters
Technology: Based on Faraday’s Law of Induction, the concept of electromagnetic induction.
How it Works: Sensing electrodes transmit induced voltage which vary according to the velocity of material flowing through the meter.
What is Measured: Fluid velocity
Introduction to Magnetic Flow Meter Technology
Why Choose a Rosemount Magnetic Flow Meter?
Positive Displacement (PD)
Technology: Mechanical displacement of components of fixed volume
How it Works: Rotating parts pass fluid repeatedly in a fixed volume with the rate of revolution determining the flow rate.
What is Measured: Volume flow rate
Turbine Meters
Technology: Mechanical rotor
How it Works: A multi-bladed rotor spins from the inside of the sensor body at right angles to the flow, suspended by two end supports which straighten the flow before the turbine. Velocity of the flow is measured as it sets the rotor in motion and is captured by sensors above, and when the rotor is moving at a steady rotation speed, it is proportional to fluid velocity.
What is Measured: Fluid velocity
Ultrasonic Meters
Technology: Based on the Doppler Effect and transit time
How it Works: These meters measure the shift in frequency to an ultrasonic beam caused by flow, calculate the velocity of sound as it passes through fluid flowing in a pipe. Transit time meters measure the effect of flow on the speed of a signal between two transducers.
What is Measured: Fluid velocity
View the Ultrasonic video here.
Vortex Meters
Technology: Based on the von Karman effect.
How it Works: An obstruction in the flow path, called a shedder bar, causes process fluid to separate and form areas of alternating differential pressure known as vortices around the back side of this blunt body. These vortices then cause a small sensing element either behind or within the shedder bar to oscillate back and forth at a specific frequency. The velocity of the working fluid is directly proportional to this frequency generated by the shedder bar’s unique geometry.
What is Measured: Fluid velocity
Differential Pressure (DP)
Technology: Applied using Bernoulli’s principle
How it Works: A primary element restricts the flow in a pipe to cause pressure to drop from one side to the other (with the primary element in between). Built as one integrated unit, this flow meter eliminates the issues associated with the multiple connections of traditional flow meters.
What is Measured: Differential Pressure
View the Differential Pressure video here.
Each flow meter uses a unique design and theory of operation to assess fluid flow rate. Some meters measure flow rate directly, others calculate the rate from parameters measured by the meter and other external instruments. Your choice will depend largely on the specific needs of your company, the criticality of the measurement, and the work practices for your processes.
Learn more about these technologies, and what will work best for you by connecting with technical experts.
