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Coriolis Flow Meter Working Principle: Phase Shift and Oscillating Tube Twist Physics

Quick Answer

A Coriolis mass flow meter measures mass flow directly by detecting the phase shift between two ends of an oscillating tube. When fluid flows through the tube, Coriolis force twists the tube and creates a time difference in the inlet and outlet vibration signals. That time difference is linear with true mass flow in kg/h. If you are evaluating a meter for a process line, send your fluid name, flow range, pressure, temperature, and pipe size to Silver Instruments for a specific model and price.

What the Phase Shift Actually Looks Like

Think of a twin tube design from DN15 up to DN150. A drive coil shakes the tubes at their natural frequency, usually between 80 Hz and 1200 Hz depending on tube size. When flow is zero, the inlet and outlet sides cross the zero position at the same moment. Two electromagnetic sensors or optical sensors detect the sine wave at both sides. With no flow, the signals overlap. With flow, the fluid has inertia. The tube on the inlet side lags and the outlet side leads. That lag is a phase shift measured in microseconds. In a DN25 meter with water at 1000 kg/h, you may see a phase shift in the range of 10 to 15 microseconds. That small time offset is enough for the transmitter to calculate mass flow to better than 0.1 percent of rate on many liquid applications.

Here is the thing. The twist angle is tiny, often less than 0.01 degree. You will not see it with your eyes. The electronics do not need a visible movement. They measure the timing between two sine waves with a precision clock. This is why a Coriolis meter can measure very low flow and very high flow on the same pipe size without wearing parts.

Why Phase Shift Tracks Mass Flow and Not Volume Flow

The Coriolis force depends on the mass of fluid moving through the vibrating tube. A high density liquid at low velocity can generate the same Coriolis twist as a low density gas at high velocity. The meter does not care if the volume is small. It cares about mass inertia. This is why a Coriolis meter reads kg/h directly. You do not need a separate pressure transmitter and temperature transmitter to correct for density. The meter also measures density from the oscillation frequency. The tube frequency drops when heavier fluid fills the tube. A built in PT100 sensor measures process temperature and compensates the tube stiffness.

Most engineers skip this part. If your product density changes, a volume flow meter will make you compensate again and again. A Coriolis meter avoids that correction loop. We have seen this with a food processor in Thailand. They mix fruit pulp with different sugar content every batch. A magnetic flow meter measured volume, and the control room had to convert volume to mass with a density table. The table was never accurate. A Silver Instruments SIC-M Coriolis meter on the same DN40 line reported kg/h directly and removed that calculation.

Design Details That Matter on a Real Skid

The wetted parts are usually 316L stainless steel. For acids, caustic, or seawater, select Hastelloy C22 or super duplex. Process temperature ratings go from minus 200 degrees C up to 200 degrees C, and some high temperature versions go to 350 degrees C. Pressure ratings often reach 100 bar on DN15 to DN50. Outputs include 4-20 mA HART, pulse for batch control, and Modbus RTU. For oil and gas installations in the Middle East, specify ATEX Zone 1 or IECEx. Silver Instruments can also supply a remote transmitter if the pipe is hot or if vibration is high.

Do not install a Coriolis meter on a thin unsupported pipe that can shake. The meter is a mass measurement device, but external vibration can still introduce noise. Use rigid pipe supports on both sides. For liquid service, keep the tubes full. For gas service, avoid liquid slugs because they cause a sh