Coriolis mass Flow Meter

The Coriolis effect was discovered by physicist Gustave Gaspard Coriolis during the 1830’s, and is described as “the inertial force exerted on an object as a result of movement relative to a rotating frame of reference.” This science has been applied to many technologies: hydraulics, machine performance, missiles, ergonomics, ocean and atmospheric circulation and, of course, mass flow metering. 

 

Coriolis mass Flow Meter

 The use of the Coriolis effect as a technique for liquid and gas mass flow measurement was firmly established over 20 years ago. Since then, a number of different designs have been produced. With the tremendous electronic signal processing technology advances that have been made, Coriolis mass flowmeters have become highly accurate and reliable instruments. Rheonik remain at the forefront of this technology and now produce the world’s largest and most comprehensive range of meters. Only the Rheonik range has all of the following features:

• Liquid, sludge and gas measurement capability 
• Models to measure flow rates from as low as 0.03 kg/h up to 1,500,000 kg/h (0.07 lb/h to 3,300,000 lb/h)
• Sizes up to 12” / DN300
• Pressure ratings up to 900bar / 13,050 psig
• Temperature ratings from -255°C to +400°C / -425°F to +750°F
• Fiscal/custody transfer approvals (OIML R117 / NTEP)
• ATEX and CSA hazardous area approvals covering most of the world
• Extreme resistance to gas bubbles entrained in the process stream when compared to conventional Coriolis meters 
• Unaffected by viscosity, density or pressure changes 
• Multifunction measurement capability includes density and temperature 
• Available with stainless steel, hastelloy, monel and tantalum wetted materials as standard.Other materials on request

Operating Principle 

The flexibility of the Rheonik range in terms of applicability and accuracy is due to the patented mechanical arrangement of each meter. Each flowmeter has two measuring tubes parallel to one another and formed into the unique Omega shape, oscillating in opposing directions. 

The oscillating system is driven with two high mass cross bars mounted on vertical torsion rods:

1. The high mass cross bars stabilize the torsional movement, either eliminating or greatly reducing interference from external vibration and providing continued, reliable operation with the presence of oscillation dampening factors such as entrained gas bubbles or non-homogeneity in the process stream. 
2. The torsion rods minimize stress on the tubing, guide tube movement and help “energize” the torsional motion. 

This rugged mechanical arrangement is energy conserving and requires very little power input (typically less than 300mW) to maintain oscillation amplitude. The design provides for an exceptionally well balanced mechanism that approaches perpetual motion once energized, with a natural frequency that is tuned by the mass of the cross bars and the elasticity of the torsion rods.

Amplitude is controlled by a pair of electromagnetic coils mounted at each side of the Omega tubes. The whole mechanism is symmetrical, ensuring that internal acceleration forces from the measured process are counterbalanced. Whenever mass (either liquid or gas) flows through the oscillating Omega shaped tubes, a Coriolis force is generated, causing a “bending” or “deflection” in the top of the tubes. This deflection is sensed as a phase shift between two electronic pick ups mounted on the tubes. The degree of phase shift is directly proportional to the mass flowing within the tubes. 

This can perhaps be better understood by imagining that the oscillation of the meter measuring tubes (the upper semi-circle of the Omega tubes) is taking place on an imaginary disc with points “a” and “b” on the circumference of the disc. Process material, starting at point “a” and moving across the imaginary disc to point “b” (the path of “effective massflow”) will pass through a range of differing velocities along the way. The Coriolis force (“FC”) generated from the oscillations of the disc and the effective mass flow vector is perpendicular to the movement of the mass across the disc and is proportional to the mass flow. In the meter, this force causes the deflection that is sensed by the two pick-up coils.