What is a Coriolis flow meter

 

Coriolis Mass Flow Meter

Coriolis mass flow meter is a device to measure mass flow directly by using the principle of Coriolis force which is proportional to the mass flow rate when the fluid flows in the vibrating pipeline. It consists of flow detecting element and converter. Coriolis mass flow meter achieves the direct measurement of mass flow. With high accuracy, it can measure multiple media and multiple process parameters. It’s widely used in petrochemical, pharmaceutical, food and other industries.

Basic Introduction

Fluid, in order to resist this forced vibration, will exert a perpendicular reaction force on the tube in the direction of its flow. This reaction force is called the Coriolis effect force. The tube’s vibration is not synchronized, resulting in a phase time difference between the inlet and outlet sections of the pipe (this difference occurs because the fluid flow at the inlet and outlet sections is opposite). This phase time difference is proportional to the magnitude of the fluid mass flow through the tube. If this time difference can be detected by a circuit, the mass flow rate can be measured.

This type of flow meter is called a Coriolis direct mass flow meter. The main difference between this and dozens of conventional volumetric flow meters currently in use around the world is that it measures the mass of the fluid, using units of kg/h. Flow meters that use mass (such as kilograms) as the unit are more accurate and constant compared to volumetric flow meters that use volume (such as liters or cubic meters). This is because mass follows the law of conservation.

The invention of the Coriolis mass flow meter is the result of decades of painstaking research in the scientific and technological community. It not only offers accuracy, repeatability, and stability but also features no flow-blocking elements or movable parts in the fluid channel, making it highly reliable and long-lasting. Additionally, it can measure the flow of high-viscosity fluids and high-pressure gases. Its applications are becoming increasingly widespread in industrial sectors such as petroleum, chemicals, building materials, metallurgy, paper making, medicine, bio-engineering, food, energy, and aerospace. Its introduction has brought about a profound change in fluid measurement technology and is regarded by experts as the mainstream flow meter of the 21st century.

Coriolis Mass Flow Meters

Advantages and Disadvantages

Advantages

Coriolis mass flow meter directly measuring mass flow, has a high degree of measurement accuracy.

Can measure a wide range of fluids, including high-viscosity liquids of various liquids, slurries containing solids, liquids containing traces of gases, high pressure gases with sufficient density.

The vibration amplitude of the measuring tube is small, so it can be regarded as inactive, and there is no obstruction or movable parts in the measuring pipeline.

Corresponding to the on-stream flow velocity distribution is not sensitive, so there is no upstream and downstream straight pipe section requirements.

Measured value is not sensitive to the viscosity of the fluid, and the change of fluid density has little effect on the measured value.

Can do multi-parameter measurement, such as simultaneous measurement of density, and thus derived from the measurement of the concentration of the solute contained in the solution.

Disadvantages

Coriolis mass flow meter zero point instability to form zero drift, affecting its accuracy to further improve, so that many models of instruments have to be used only the total error is divided into two parts of the basic error and zero instability metric.

Coriolis mass flow meter can not be used to measure low-density media and low-pressure gases; liquid gas content above a certain limit (according to the model) will significantly affect the measured value.

Coriolis mass flow meter is more sensitive to external vibration interference, in order to prevent the influence of pipeline vibration, most models of Coriolis mass flow meter flow sensor installation fixation requirements.

Can not be used for larger pipe diameter, currently limited to 150 (200) mm below.

Measuring tube wall wear and corrosion or scaling will affect the accuracy of measurement, especially for thin-walled pipe measuring tube Coriolis mass flow meter more significant.

Pressure loss is large, comparable to volumetric instruments, and some models of Coriolis mass flow meters are even 100% larger than volumetric instruments.

Most models of Coriolis mass flow meter weight and volume.

Expensive. Foreign prices 5000 ~ 10000 U.S. dollars a set, about the same diameter as the electromagnetic flow meter 2 ~ 5 times; domestic prices for electromagnetic flow meter about 2 ~ 8 times.

How to Select Model

Coriolis meters are available in a variety of models, it is important to choose a meter that is optimised for your application. Key considerations include:

  • Fluid conditions

Fluid type – consider density, viscosity, corrosivity

Flow rate – as the requirement you need, High regulation ratios allow for greater variability.

Process temperature and pressure – Make sure you do not exceed the instrument’s rating.

  • Installation Factors

Pipe Size- Instrument diameter (pipe size) does not necessarily need to match the pipe size as long as the process connections are the same.

Available Space – Larger instruments may require more clearance. Compact design helps.

Remote Capability – Remote transmitters allow for flexible installation.

  • Performance Requirements

Accuracy Requirements- More critical applications require higher accuracy.

Density Measurement- Determine if a density output is also needed.

Output Requirements- Choose analogue, digital, wireless or bus communication outputs.

Discussing these factors with a Coriolis Flow Meter expert will ensure you find the best equipment for your application.

Installation and Use

In order for a Coriolis Mass Flow Meter to function properly, safely and with high performance, it is important that it is installed and used correctly. This includes mechanical installation, electrical installation and use and maintenance.

Installation

Mechanical installation should pay attention to such issues:

  1. The flow sensor should be installed on a solid foundation. Small-diameter mass flow meters with an inner diameter of less than 10mm are installed on a balanced hard and vibration-free substrate, such as a wall, floor or specialised foundation. If used in a high vibration environment, attention should be paid to the vibration absorption of the foundation, and the sensor inlet and outlet and the pipeline should be connected with flexible piping. Larger calibre flow meter is installed directly in the process piping, the application of pipe clamps and supports to the flow meter firmly fixed.
  2. In order to prevent the mutual influence of CMF, in more than one flow meter in series or parallel use, the distance between the flow sensor should be far enough, pipe clamps and supports should be set up in their respective independent foundation.
  3. In order to ensure that the use of the flow sensor will not be deposited in the gas or liquid residual value, for the elbow type flow meter, measurement of liquid, the elbow should be facing down, measurement of gas, the elbow should be facing up. When measuring slurry or discharging liquid, the sensor should be installed in a vertical pipe with the flow direction from bottom to top. For straight pipe type flow meter, horizontal installation should be avoided on the highest point, so as to avoid the accumulation of air mass. When connecting the sensor and process piping, be sure to do a stress-free installation, especially for some straight pipe-type measuring tube flow sensor should pay more attention.

Coriolis Mass Flow Meters

Use and Maintenance

  • Flow meter zero point adjustment.

To be full of measured fluid flow sensor sensor downstream valve closed, in close to the operating temperature conditions to adjust the zero point of the flow meter. When adjusting the zero point to ensure that the downstream valve is completely closed to confirm that there is no leakage of fluid is very important. If there is leakage from the valve when adjusting the zero point, it will bring great error to the whole measurement.

  • Set the flow rate and density calibration coefficients.

Correctly set the flow and density calibration coefficients flow meter work is very important. (Units are often grams per second). Flow temperature coefficient represents the degree to which the sensor’s modulus of elasticity is affected by temperature. These are directly related to the measurement accuracy of the flow meter, density calibration coefficient on behalf of the sensor in the tube at 0 ℃ for the air and the tube for the water when the self-oscillation period (unit is often microseconds) and the density of temperature coefficient, it is clear that the accuracy of these and the measurement of density are directly related.

  • Use in the maintenance of flow meter normal work.

Timely detection of faults and troubleshooting is very important to the normal work of the flow meter, the actual work of the following common faults:

  1. Without output. It means the flow through the sensor and the sensor has no signal output;
  2. Output does not change. Although the flow rate changes, but the output remains unchanged;
  3. Output is not normal, the output changes randomly, unrelated to changes in flow, that is, the output perverse;
  4. Intermittent output. intermittent output, the beginning and end of the irregular, but when there is an output, the output signal can correctly reflect the size of the flow rate.

 

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