Coriolis Mass Flow Measuring Principle

• Coriolis mass flow meters rely on using Coriolis forces to measure the actual mass of the flow, whereas thermal mass flow meters measure the volume of the flow
• Mass flow measurement is not affected by changing temperature, pressure, etc., and eliminates the inaccuracies of volumetric flow meters caused by the physical properties of the fluid being measured
• Coriolis flow meters and controllers can be used for both gas or liquid flows and its fluid-independent flow measurement means there’s no need for recalibration

The operating principle of a Coriolis mass flow meter is basic but very effective. This phenomenon is all around us in the physical world; for example the earth’s rotation and its effect on the weather.

Bronkhorst Coriolis Flow Meters and Controllers

A Coriolis flow meter contains a tube which is energized by a fixed vibration. When a fluid (gas or liquid) passes through this tube the mass flow momentum will cause a change in the tube vibration, the tube will twist resulting in a phase shift. This phase shift can be measured and a linear output derived proportional to flow. The two most commonly selected flow meters from Bronkhorst are the CORI-FLOW Series mass flow meters and controllers and its compact counterpart, the mini CORI-FLOW Series mass flow meters and controllers.

Coriolis Flow Measurement Principle

As this principle measures mass flow independent of what is within the tube, it can be directly applied to any fluid flowing through it, liquid or gas, whereas thermal mass flow meters are dependent of the physical properties of the fluid.  Furthermore, in parallel with the phase shift in frequency between inlet and outlet, it is also possible to measure the actual change in natural frequency. This change in frequency is in direct proportion to the density of the fluid – and a further signal output can be derived. Having measured both the mass flow rate and the density it is possible to derive the volume flow rate.

Difference Between Volumetric Flow and Mass Flow

Coriolis flow meters measure real mass flow, whereas thermal mass flow meters are dependent of the physical properties of the fluid. True mass flow measurement is an important development across the industry as it eliminates inaccuracies caused by the physical properties of the fluid, not least being the difference between mass and volumetric flow. Mass is not affected by changing temperature and pressure. This alone makes it an important method of fluid flow measurement.

Volumetric flow remains valid, in terms of accuracy, provided that the process conditions and calibration reference conditions are adhered to. Volumetric measuring devices, such as variable area meters and turbine flow meters, are unable to distinguish temperature or pressure changes. 

Coriolis Flow Versus Thermal Mass Flow for Gases and Liquids

• Fluid independent flow measurement and control – no need for recalibration
• Gas and liquid can be measured with the same sensor
• Ability to measure undefined or variable mixtures
• Suitable for supercritical fluids, e.g. carbon dioxide (CO₂) or ethylene (C₂H₄)
• Same compact footprint
• High accuracy ± 0.2% of rate ± zero stability for liquids ± 0.5% of rate ± zero stability for gases
• Large turndown range of up to 1:2000
• Fast sensor response time: down to 50…100 msec

Coriolis Mass Flow Meters and Controllers for Gas and Liquids

We offer a series of compact, cost-effective Coriolis mass flow meters and controllers for accurate measurement and control of (very) low flow rates. Bronkhorst manufactures multiple model options for their CORI-FLOW Series of Coriolis mass flow meters and controllers. The CORI-FLOW mass flow meter and controller is a compact, standard model that is commonly used in pilot plants, laboratory research, for pharmaceutical production. The CORI-FLOW Series is suitable for both gas or liquid flows and does not require recalibration when changing the fluids being measured. Additionally, all instrumentation in the CORI-FLOW Series offers integrated PID control for direct control of valves or pumps, thus constituting compact Coriolis mass flow control loops.

The CORI-FLOW Series includes a miniature line of its already incredibly compact design instrumentation. The mini CORI-FLOW mass flow meter and controller was designed to be easily retrofitted in place of existing thermal mass flow meters. The mini CORI-FLOW Ex d mass flow meter and controller was designed for hazardous areas and can be installed in Zone 1, outside the Ex d box and offers IP65 housing.