This article contains all the information you need to know about Coriolis Flow Meters.
You will learn more about topics such as:
- What is a Coriolis Flow Meter?
- How a coriolis Flow Meter works
- Types of Coriolois Flow Meters
- Coriolis Flow Meter installation
- And much more…
Chapter One – What is Coriolis Flow Meter?
A Coriolis flow meter measures mass by the inertia of a liquid or gas flowing through a vibrating tube that is equipped with a set of sensors at the inlets and outlets of the meter. The increased movement of the flow produces measurable oscillation that is proportional to the mass. The design and function of Coriolis flow meters has made them the most reliable form of fluid and gas measuring instruments.
Chapter Two – How a Coriolis Flow Meter Works
To understand how a Coriolis flow meter works, it is necessary to understand the Coriolis principle that was postulated by Gaspard-Gustave de Coriolis with his publication of a paper in 1835 titled On the Equations of Relative Motion of a System of Bodies. The principles of the paper were used to develop what has come to be known as “The Coriolis Effect”.
The simplification of the Coriolis effect says, “Any moving body on or above the earth’s surface, such as an ocean or air current, will tend to drift sideways from its course because of the earth’s rotation.” In the case of a Coriolis flow meter, the tubes in the meter begin to twist when fluid flows through them, which provides the flow meter reading that is like the sideways drift caused by the rotation of the earth.
How a Coriolis Flow Meter Works
Fluids, gases, and various other substances are regularly transported by pipelines. Each type of substance has different properties resulting in a different set of principles for their measurement. Flow measurement by a Coriolis flow meter is one of the methods used to collect data and measurements. It is a direct measurement of the flow of mass and density.
Coriolis flow meters are considered to be true mass meters since they directly measure the mass flow rate and not the volumetric flow, which measures gallows per minute and not mass. Since mass does not vary, there is no need to adjust the flow meter for the characteristics of different materials..
The U shaped tube on a Coriolis flow meter is the most important part since its movements produce the meter’s readings. When a material enters the tube, it oscillates in an angular harmonic motion, which deforms the tube. The movement of the tube is shown by the fluid force red arrows on the diagram below.
The excitor ensures that the oscillation and movement of the tube continues constantly. When there is no flow, the oscillation is uniform. As can be seen in the image below, the excitor is located at the lowest point of the tube between the measurement sensors.
Sensors are located at the inlet and outlet to record the oscillation. Though the oscillation is uniform when there isn’t any flow, it changes with the introduction of a fluid or gas. The liquid’s inertia forces the oscillation of the inlet and outlet sections of the tube to move in different directions. The sensors pickup the change in oscillation in terms of time and space, which is known as the phase shift.
The phase shift is the direct measurement of how much fluid or gas is flowing through the pipe, which is the result of the oscillation of the tube. Its measurement produces a linear output proportional to the flow. This type of mass flow measurement is independent of what is in the tube allowing it to be applied to any form of material.
Additionally, the sensors also measure the natural frequency of the fluid or gas. The change in frequency, how often the tube moves back and forth in a second, is in direct proportion to the density of the material. Measuring the mass flow rate and density produces a volume flow rate. As part of the various measurements, temperature is recorded to compensate for dynamic changes caused by expansion and contraction of the tube or tubes.
Meter - Controller
The data acquired from the tube fluctuations and phase shift is fed into a flow meter that provides information on the mass, volume, and density of the fluid or gas. The mass flow readings are provided on the display in pounds or kilograms, which can be set on the face of the meter depending on the type of meter.
Coriolis flow meters are very flexible and adaptable. They can be very small such as 0.04 of an inch or 1 mm or very large to meet the needs of oil and petroleum operations. There are a variety of factors that influence the selection of a flow meter and need to be determined before purchasing and installing the meter.
Aside from the size of the meter, the type of data provided depends on the complexity of the meter though most meters supply the same data but have different methods for setting the meter. Some of the settings of a Coriolis flow meter include:
- Flow Direction
- Maximum mass flow - set up at pounds per hour
- Volume flow - measured in gallons per minute
- Density - measured by the meter in kilograms or pounds per hour
- Temperature - maximum load temperature
- Fraction Totalizer - totalizer values can be in volume flow, mass flow.
Chapter Three – Types for Coriolis Flow Meters
The types of measurement instruments used to measure the flow of fluids and gases are an important part of the larger picture for producers. Their accuracy determines profitability and efficiency. The tiniest flaw or error can be costly and necessitates constant monitoring of all parts of the measurement system.
The differentiation between the various types of Coriolis flow meters is determined by the tube design, which can be one and two tubes as well as differing and unique configurations. The initial type of Coriolis flow meter was the single tube design, which has been perfected over the years.
Types of Coriolis Flow Meters
Single Tube Flow Meter:The single tube design measures high fluid velocity that is created by reducing the cross sectional area in relation to the pipe. Tube distortion is measured in relation to a fixed point or plane. The tube is excited at a high amplitude bending force that is created at an anchored point.
Dual Tube Flow Meter:In the dual tube design of a Coriolis flow meter, a manifold splits the flow into each of the tubes. The vibrating tubes rotate around two fixed end points to create the Coriolis effect. When fluid is flowing through the U shaped tubes, the twist in the tubes accelerates on the inlet side and decelerates on the outlet side. The force between the inlet and outlet sides slightly twists the tubes in proportional to the mass flow rate. To enhance the Coriolis effect, a magnet and pickoff coil are attached at the inlet and outlets of the tubes. The coil moves into the magnetic field producing a sine wave proportional to the motion.
Continuous Loop Flow Meter:The continuous loop design is a form of single tube configuration where the flow is not divided but goes through a series of tubes. The Coriolis principle is the same in this type and supplies the same kind of data. In addition to the normal features, this design may have drivers and magnets connected. The continuous loop Coriolis flow meter is preferred for materials that can coat or clog the meter. To avoid clogging, they are sized with larger tubes.
Straight Tube Flow Meter:The straight tube design of a Coriolis flow meter can be either dual or single tubed. During fluid flow, the Coriolis forces act on the tubes and create distorted flexure that is detected by its sensors. A unique requirement of straight tube designs is strain gauges due to the rigidity of the tubes, which are used to detect dimensional changes in the tubes.
U Shaped Flow Meter:U shaped flow meters are the dual tube variety with two tubes shaped like a U with a magnetic and coil assembly. Sensors are placed at the inlet and outlets of the tubes. The Coriolis forces caused by the flow of the material determine the mass flow rate and density.
Micro-Bend Flow Meter:The micro-bend type of Coriolis flow meter has a U shape configuration, which has an extremely small radius. The smaller radii allow for a more compact design and a reduced pressure differential.
Triangle Shaped Flow Meter:The triangle shaped flow meter is very compact and designed for low pressure applications. The singular tube flow is smaller than U shaped models, which makes it more compact to save on installation space. Most triangle shaped flow meters produce multivariable measurements.
Chapter Four – Coriolis Flow Meter Installation
Coriolis flow meters can be installed in any type of pipe regardless of pipe vibrations or whether the pipe is horizontal or vertical. For the best results, piping supports should be located on both sides of the meter. When installation instructions require special supports, it is very likely that the meter is sensitive to vibrations. Manufacturers provide pulsation dampeners, flexible connectors, or clamping brackets to compensate for vibrations.
There are several types of supports available for Coriolis flow meters, which include U rest, Y rest, U bolt clamp, pipe hangers, and block clamps. These support mechanisms are not normally necessary, especially for newer versions.
Coriolis Flow Meter Installation
There are a variety of factors to consider prior to beginning the installation process. Each element of the process must be carefully examined to ensure the proper performance of the meter. Though vibrations may be a concern, modern Coriolis flow meters are not affected by vibrations but should be supported by standard piping supports on either side of the meter.
Prior to purchasing the meter, the space where it will be installed must be examined for temperature and hazardous conditions to ensure that there aren’t any environmental considerations that need to be addressed. Special meters are available that are designed to fit high temperature and hazardous conditions.
Each Coriolis flow meter is rated and classified as Class I, Class II, Class II, and so on. The classifications are divided into divisions, which have groups, A, B, C, D, and on, that describe how the meter can be used. The classification, division, and groups describe the type of meter as well as the fluids or gases that it can monitor. It is crucial that the meter selected for any function has the correct classification for the job since getting the wrong meter can provide inaccurate data or be harmful.
The installation orientation is an indication of the type of material that is to be monitored since meters must be positioned to fit the types of fluids, gases, liquids, water, or slurries that are to be monitored and measured. A brief overview of the different orientations can be seen in the chart below. Please note the preferred orientation compared to the alternates and the inclusion of three of the different types of Coriolis flow meters.
Hydrogenated Nitrile Butadiene (HNBR)
HNBR is produced by the hydrogenation of NBR, which removes the olefinic that are vulnerable to degradation. It is known for its strength and resistance to heat. HNBR rubber compounds are resistant to petroleum based oils and fuels, aliphatic hydrocarbons, vegetable oils, silicone oils and greases, ethylene glycol, water and steam, dilute acids, bases, and salt solutions. It is extensively used in the auto industry.
Ethylene Propylene Diene Monomer (EPDM)
EPDM is made from combining ethylene, propylene, and a diene comonomer that allows for crosslinking. The structure of EPDM makes it resistant to heat, light, and ozone as well as capable of withstanding temperatures up to 150o C. EPDM is highly durable and lasts in an application for a long time. It is used for steam systems, panels on cars and trucks, and braking systems.
The sensor should be placed away from any form of interference such as a pump since the vibrations of a pump can interfere with readings. When sensors are installed in a series, they should be at least two meters apart. Regardless of the temperature range of the flow meter, the expansion and contraction of pipes should be accounted for.
Depending on the substance being measured, aside from the rules for orientation, the meter should be mounted along a straight line of piping and not at a high or low point or drop line. When the Coriolis flow meter is being installed, the measuring tube or tubes should be filled with the medium that will be measured.
The zeroing for every model, type, design, and size of Coriolis flow meter is unique to the meter. The zeroing of a Coriolis flow meter is an automated process performed by the meter, which is found on its zero setting menu. All that is necessary is to select yes for the meter to do the zero calibration.
Prior to zeroing a Coriolis flow meter, it is best to let the meter warm up according to the manufacturer’s specifications, which can be anywhere between five to ten minutes up to fifteen and twenty minutes depending on the type of meter.
To ensure that the zeroing is accurate, it is important that the tube or tubes of the meter are filled with fluid or gas such that air cannot be trapped in the tubes. The removal of air can be accomplished by circulating fluid through the meter for several minutes at two to six feet per second.
For the calibration process to be successful, the meter must be full of the material being monitored under zero flow conditions. The error factor is a fixed value of 0.05 kilograms per minute, which affects the measurement of flow by that much during operation.
Once the zero stability is set, the flow meter will offer optimum performance that is several times superior to any other method of measurement. It is suggested to repeat the zeroing function three or four times to determine if there is any interference.
Chapter Five – Readings Provided by a Coriolis Flow Meter
Of the different types of flow meters, Coriolis flow meters are the most versatile, accurate, and adaptable. They measure mass flow, density, and temperature using the Coriolis effect. When a fluid is flowing through a pipe, it experiences deflecting force from the Coriolis inertial effect, which is the function of the mass flow rate. The force exerted by the flow of a substance on the rotating tube provides a mass flow rate
The unique design of Coriolis flow meters allows them to be used for measurement of viscous and non-conductive fluids, which cannot be measured by other meters. A single Coriolis flow meter can measure mass flow, volume flow, density, and temperature. The oscillation movement of the meters tubes creates the Coriolis force that is dependent on mass.
Readings Provided by a Coriolis Flow Meter
The measurement of mass flow is preferred over volumetric flow, which measures in terms of gallons per minute. Mass flow meters measure fluid flow in terms of weight such as pounds or kilometers per second, which is considered to be a more accurate measure especially in custody transfer.
In the flow tube of the meter is a drive coil that vibrates the tube at its natural frequency. When there isn’t any flow, the tube still vibrates, and the pickoffs produce a signal from the tube’s vibrations. The movement is relative to one tube to the other.
When a fluid is introduced into the tube or tubes of the meter, they begin to twist or oscillate, rapidly. The acceleration produces a measurable force on the tube or tubes that is proportional to the mass of the material. The force in the tube is reacted to by the material passing through, which is the Coriolis force. The difference between no flow and flow can be seen in the diagram below.
The time delay between the inlet and outlet sensors provides the data for mass flow. Another aspect of this signal can be used to measure the density of the material. The drive coil of a Coriolis flow meter makes its measurements by the movement of the tube or tubes at its frequency. When the density of the material changes, the frequency changes. The higher the density, the frequency will reduce. The lower the density, the frequency increases. When measuring the density of a gas, a different form of measurement, other than a Coriolis flow meter, needs to be used. In the diagram below, the frequency can be seen at the top of the image as a blue and red parabolic wave.
The viscosity of a fluid is measured by torsional action at the middle of the tube where a counter oscillating mass is located. The motion of the tube produces a shear force on the flowing fluid. The viscosity of the fluid changes the oscillating motion, which the meter is able to read and convert to a numerical reading.
The viscosity lessens the torsional oscillation of the tube. When viscosity is high, there is more power required from the current to maintain the torsional oscillation. The dynamic viscosity is measured by the power that is required to continue the oscillation. The oscillation of a dual tube Coriolis flow meter can be seen in the diagram below by the blue arrows pointing up and down to indicate A and B movement.
Process Temperature Effect
The process temperature effect is the change in sensor accuracy due to a change in the process temperature, which is different from the calibrated temperature. This is controlled during the zeroing of the process conditions.
The effect of the process temperature can also be found in the accuracy of the density measurement where the temperature varies from the calibrated temperature.
Chapter Six – Benefits of a Coriolis Flow Meter
Coriolis flow meters are the most popular method for measuring the mass, density, temperature, and viscosity of a wide variety of substances due to their ability to be adapted and adjusted to meet flow conditions without being influenced by material disturbances. They can be located anywhere on a pipe length.
The natural capability of measuring mass flow as well as their characteristic linearity and accuracy has made Coriolis flow meters ideal for custody transfer operations during the purchase of a fluid or gas.
Benefits of Coriolis Flow Meters
Accuracy: The main reason for the choice of a Coriolis flow meter over other types of meters for mass and density measurement is their accuracy, which is 0.1 of a percent. This one factor has been the reason for their rapid growth over the last decade.
Adaptability: There are few limits to the types of substances a Coriolis flow meter can measure. Since they are not influenced by ambient conditions, they can be used to measure a wide assortment of gases, liquids, and fluids including high viscosity fluids, liquid-solid two-phase fluids, liquid-gas two-phase fluids containing trace gases, and dense high pressure gases.
Flow Effect: When the flow of the material has a non-uniform or varying velocity from upstream and downstream pipelines, such disturbances and changes do not have an effect on the ability of the meter to take flow readings. This can be further improved by installing the meter on a straight line pipe as seen in the diagram below.
Viscosity: One of the more difficult characteristics to measure in a fluid is viscosity, the thickness or texture of a material or the rate at which it deforms. This particular characteristic of fluids can be a challenge for standard meters but does not affect the readings of a Coriolis flow meter. Viscosity readings provide data on the thickness of a fluid as well as how easily it flows. The flow characteristic of different fluids can be seen in the image below where the fluid on the left flows easier than the fluid on the right.
Data: A Coriolis flow meter is a multifunctional device that provides a set of readings regarding the movement and motion of a material through a pipeline. Though its primary function is to provide mass flow readings, it produces data regarding volume, density, temperature, and various other types of signals. The types of readings may vary across the different types of Coriolis flow meter producers but have basic similarities regarding measurements of mass, density, temperature, and viscosity.
Bidirectional Flow Measurement: Bidirectional flow is not a very common factor in production operations but requires the same measurement as normal one directional flow. In bidirectional flow, the piping is used for flow in opposite directions. For most meters, a great deal of adjustment is necessary to measure flow in an opposite direction. This is not the case for a Coriolis flow meter due to its adaptability and ease of adjustment.
Unique Fluid Measurement: Certain types of fluids are a mixture of fluids and gas. Measurement of such substances with these unique characteristics can be difficult due to their unusual nature. The ability of Coriolis flow meters to adapt to this type of unusual condition is another example of the meter’s ability to perform regardless of the material being measured. Coriolis mass flow meters can be used to monitor the movement of asphalt, molasses, syrup, glucose, and slurry, which is another reason for the rapid growth of their use.
Food Production: A basic requirement for food production is that all equipment must meet the exacting standards of the government Food and Drug Administration (FDA) that requires that devices used in food production be cleaned and sanitized regularly. Coriolis flow meters are used to measure the transfer of oils, cooking solutions, and water. They are the choice of the food industry because they can be easily cleaned multiple times to meet FDA standards.
- A Coriolis Flow Meter measures mass by the inertia of a liquid or gas flowing through a vibrating tube that is equipped with a set of sensors at the inlets and outlets of the meter.
- The sophisticated nature of Coriolis Flow Meters produces accurate and reliable data for the determination of mass flow rate, a necessary measurement for accurate flow movement.
- To understand how a Coriolis Flow Meter works, it is necessary to understand the Coriolis principle that was postulated by Gaspard-Gustave de Coriolis with his publication of a paper in 1835 titled On the Equations of Relative Motion of a System of Bodies.
- Coriolis Flow Meters are considered to be true mass meters since they directly measure the mass flow rate and not the volumetric flow.
- Coriolis Flow Meters are the most popular method for measuring the mass, density, temperature, and viscosity of a wide variety of substances due to their ability to be adapted and adjusted to meet flow conditions without being influenced by material disturbances.