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Mass Flow Meter Working Principle: Coriolis Force and Inertial Twist Mechanics

Quick Answer: A Coriolis mass flow meter measures true mass flow directly in kg/h. The meter vibrates the flow tube and detects an inertial twist caused by Coriolis force. The phase shift between two sensor points is proportional to mass flow, so the meter does not need pressure and temperature compensation for mass units.

This article is for engineers and buyers in Southeast Asia, Oceania, Latin America, Africa, and the Middle East. Silver Automation Instruments supplies Coriolis mass flow meters for oil and gas, chemical, food and beverage, water and wastewater, and marine service. The working principle below explains the mechanism in practical field terms.

What the Coriolis Force Does in a Vibrating Tube

Inside a Coriolis meter one or two flow tubes vibrate at a known frequency from a drive coil. When process fluid enters the tube it moves forward and also moves with the tube vibration. The combined motion creates a Coriolis force inside the tube.

On the inlet side the fluid resists the tube motion. On the outlet side the fluid pushes in the opposite direction. The result is a small inertial twist of the tube. Two electromagnetic sensors measure tube position at the inlet and outlet sections.

With zero flow both sensors see the same phase. With flow the tube twists and the two signals shift apart. That phase shift or time delay is the direct mass flow signal. This is the essence of the Coriolis mass flow meter working principle.

How the Transmitter Converts Twist to a Mass Flow Output

The transmitter receives the sensor signals and calculates mass flow from the time difference. Because the tube also vibrates at its natural frequency the transmitter can calculate fluid density from the frequency change. A built in PT100 sensor tracks tube temperature.

In a chemical batch process in Thailand the output may be 0 to 500 kg/h through a DN15 meter. The transmitter sends a 4-20 mA HART signal and a pulse output for total flow. Operators can read mass flow in kg/h, density in kg/m3, and temperature in °C from one device.

In practice most engineers skip the full math. The meter computes in real time. You receive mass flow, density, temperature, and derived volume flow from a single instrument.

Where Direct Mass Flow Pays Off

Volumetric flow meters need compensation when pressure and temperature change fluid density. A Coriolis meter does not. For liquid ammonia loading or fuel oil batching the mass reading is the value you control or invoice.

We have seen this on customer sites many times. A food additives plant in Vietnam measured syrup with an oval gear meter and had trouble when density shifted between batches. After changing to a Coriolis meter the batch weight became stable at 1200 kg per run.

Installation Notes That Reduce Field Problems

A Coriolis mass flow meter does not need long straight pipe runs like a vortex or electromagnetic flow meter. That saves space in skids and offshore platforms. Mount the meter so the tubes remain full of liquid. For gas service follow the supplier drain and purge instructions.

Entrained gas in liquid batching creates measurement noise. A degassing step upstream solves most cases. In high vibration areas use the standard mounting supports from the supplier.

Key Specification Points for a Quote

When you send an inquiry include pipe size such as DN15 or DN50, fluid type, flow range, operating pressure in bar, temperature in °C, viscosity in cP, and required accuracy. Also specify wetted materials such as 316L stainless steel or Hastelloy C22. For hazardous areas ask for ATEX Zone 1 or IECEx certification.

A typical specification from a desalination plant in Saudi Arabia is DN25, seawater at 35 °C, flow range 0 to 300