A Coriolis meter measures the mass flow rate of fluids, including liquids, gases, and slurries. Unlike traditional flow meters that determine volume, Coriolis meters provide a direct measurement of mass, which remains constant regardless of changes in temperature or pressure. This capability makes them valuable for their accuracy and reliability across diverse industrial applications.
The Fundamental Principle
The operation of a Coriolis meter relies on the physical phenomenon known as the Coriolis effect. This effect describes an apparent force that acts on objects moving within a rotating system. This deflection is not a true force, but rather an observed consequence of an object’s inertia interacting with the rotating frame of reference.
In the context of flow measurement, this principle is applied to the fluid itself. When fluid flows through a tube that is oscillating, the inertia of the moving fluid interacts with the tube’s motion. This interaction creates an inertial force, often referred to as the Coriolis force, that acts perpendicular to the direction of the fluid’s motion and the axis of oscillation. This force manifests as a subtle twisting action on the vibrating tube, which is directly related to the fluid’s mass and its velocity through the system.
Inside a Coriolis Meter
A Coriolis meter is composed of several key components. At its core are one or more measuring tubes, often U-shaped or straight, through which the process fluid flows. These tubes are typically made from durable materials like stainless steel or other corrosion-resistant alloys. Electromagnetic exciters, also known as drivers, make these tubes vibrate continuously at a specific, controlled frequency. Sensors, or pick-offs, are strategically placed at the inlet and outlet sections of the tubes to detect their motion and vibration patterns as fluid passes through them.
How Flow is Measured
The measurement process begins with the continuous vibration of its measuring tubes. As fluid flows through these vibrating tubes, it experiences the Coriolis effect. As the fluid moves towards the peak of the tube’s vibration cycle, it resists this upward motion, exerting a downward force on the tube. Conversely, as the fluid moves away from the peak, it resists the downward motion, exerting an upward force. This interaction creates a subtle twisting motion of the tubes.
This twisting results in a measurable phase shift, or time delay, between the vibrations detected at the inlet and outlet sensors. For instance, the inlet sensor might detect a vibration slightly before the outlet sensor, due to the fluid’s inertial resistance causing the tube to twist. The magnitude of this phase shift is directly proportional to the mass flow rate of the fluid passing through the meter. The meter’s integrated electronics precisely measure this time difference and convert it into an accurate mass flow rate reading. This direct relationship allows the meter to provide reliable data without needing to account for external factors like fluid density or viscosity.
Where Coriolis Meters Excel
Coriolis meters offer distinct advantages in industrial settings. Their primary strength lies in their ability to directly measure mass flow, which is unaffected by changes in fluid density, temperature, or viscosity. This contrasts with volumetric meters, which often require additional calculations and compensations to determine mass flow, leading to less precise results.
These meters are known for their high accuracy, achieving precision within 0.1% to 0.5% of the measured flow rate, making them suitable for critical applications like custody transfer. They are also versatile, capable of measuring various fluid types, including liquids, gases, and slurries, across a wide range of flow rates. Industries like chemical processing, oil and gas, food and beverage, and pharmaceuticals widely adopt Coriolis meters due to their reliability and precision.