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『How Coriolis Flow Meter Works: Physics of Oscillating Tubes and Phase Shift Deflection』Related information(clamp on meter|electromagnetic meter|venturi meterrotameter|orifice meter|ultrasonic flow meter|mass flow meter|coriolis mass flow meter|coriolis flow meter|magnetic flow meter|magmeter flow meter|magflow flow meter|mag meter flow meter|electromagnetic flow meter|vortex flow meter|turbine flow meter|thermal mass flow meter|thermal flow meter|rotameter flow meter)
How a Coriolis Flow Meter Works: Oscillating Tubes and Phase Shift
Quick Answer
A Coriolis mass flow meter measures flow by driving one or two tubes into a small oscillation. When fluid passes through, the tube twists slightly due to inertia. Two sensors pick up a phase shift in the oscillation at the inlet and outlet sides. The time difference is directly proportional to the mass flow rate. Silver Automation Instruments supplies Coriolis meters from DN3 to DN150 for gases, liquids, and slurries across oil and gas, chemical, food, and water treatment plants.
Why Engineers Care About the Tube Oscillation
Most engineers skip the textbook physics and jump straight to what matters. The meter body has one or two parallel tubes. An electromagnetic drive coil excites them at their natural frequency, typically 80 to 120 Hz. The amplitude is tiny, often less than 1 mm. You do not feel it by touching the pipe.
When there is zero flow, the tubes oscillate symmetrically. Inlet and outlet sensor signals stay in phase. Once fluid moves, the Coriolis effect introduces a twist. The inlet side lags slightly behind the outlet side. That lag is the phase shift. A digital transmitter measures the time difference in microseconds and converts it to mass flow, density, and temperature. You get three variables from one device.
Phase Shift, Not Angular Momentum
Here is the thing. Many articles talk about Coriolis force as if the meter spins. It does not. The tubes oscillate in a straight plane. The twist comes from the fluid resisting the change in direction as it travels along the vibrating tube. In practice, a DN25 meter handling 2000 kg/h of crude oil will show a phase shift of a few microseconds. The transmitter digitizes this at high speed. That is why a Coriolis meter works well for custody transfer and batch dosing. It gives you direct mass, not a calculated value from velocity and density.
What Happens Inside a Bent Tube vs Straight Tube
Silver Instruments offers two tube geometries: U-shaped and straight single-tube. U-shaped meters concentrate the twist at the bend. That geometry gives high sensitivity even at low flow. A straight tube meter has a longer tube length to capture the same phase shift. This design drains better and handles viscous fluids like heavy fuel oil at 5000 cP.
We have seen this on customer sites many times. A food plant in Thailand needed to meter chocolate syrup at 45°C. The straight tube meter did not plug. The bent tube model would have held solids at the curve. Choose based on your cleaning needs, not just price.
Where the Real Measurement Happens: Transmitter Electronics
The mechanical twist is useless without a fast DSP board. Silver Instruments uses a 32-bit digital transmitter. It samples sensor signals at 20 kHz. The board separates the frequency shift for density and the phase shift for mass flow. Temperature compensation uses a built-in PT100 RTD. Output options include 4-20 mA HART, pulse, Modbus RTU, and Profibus DP. For hazardous areas, we supply ATEX Zone 1 and IECEx certified transmitters.
A Typical Installation That Works
Last year a customer in Vietnam asked us to replace an oval gear meter on a varnish filling line. The old meter drifted because viscosity changed with solvent evaporation. We installed a DN15 Coriolis meter with a remote transmitter. The pipe was 1/2 inch Schedule 10 stainless steel. Flow range was 0 to 50 kg/h. The meter sat between two isolation valves with no straight run requirement. That is a real advantage. Coriolis meters do not need upstream and downstream straight pipe. You can mount them vertically or horizontally. Just avoid
Density and Temperature Are Bonus Variables
The resonant frequency of the tube drops when fluid density rises. The transmitter calculates density from that frequency shift. In a desalination plant in Oman, engineers used the density output to monitor brine concentration in real time. They set a 4-20 mA output to density and a pulse output to totalized mass. One meter did two jobs. Most users ignore density and only use mass flow. That is fine. But if you pay for a Coriolis, you might as well tap the extra data for process diagnostics.
Common Flow Ranges and Accuracy Claims
Silver Instruments Coriolis meters achieve ±0.1% of rate for liquids and ±0.5% for gases. Repeatability is better than ±0.05%. Below is a practical sizing reference for liquids at 1 cP.
DN3 handles 0 to 120 kg/h with a pressure drop of 0.2 bar at full scale. DN15 covers 0 to 2500 kg/h and fits 1/2 inch lines. DN50 reaches 0 to 60000 kg/h for bulk chemical transfer. Always size for 50 to 80% of the maximum flow to keep tube amplitude stable. Do not oversize. A meter running at 5% of its range may lose accuracy.
Fluid Compatibility and Wetted Parts
Standard tube material is 316L stainless steel with Hastelloy C22 available for seawater and aggressive acids. The process connections can be Tri-Clamp, DIN flanges, or NPT threaded. For seawater flow meter applications in a desalination plant, we recommend the Hastelloy version. For food-grade CIP lines, specify Ra ≤ 0.8 µm electropolish finish and EHEDG compliant seals.
Power and Signal Wiring in the Field
The transmitter accepts 24 VDC or 85-265 VAC. Most sites use 24 VDC from a DCS cabinet. Wire the 4-20 mA loop with shielded twisted pair cable. Keep the cable run under 300 meters. The sensor cable between the detector and remote transmitter is pre-wired with a 10-meter standard length. Extension up to 30 meters is possible without signal degradation. Silver Instruments ships the meter with a calibration certificate traceable to NIST and ILAC.
FAQ
What is the minimum conductivity required for a Coriolis meter?
None. Unlike a magnetic flow meter, a Coriolis flow meter does not need conductive liquid. You can measure deionized water, oil, and hydrocarbons.
Can a Coriolis meter handle gas entrainment?
Very small amounts of bubbles are tolerated, but high gas void fraction will stop tube oscillation and trigger an alarm. For two-phase flow, we recommend a dual bent tube meter with advanced bubble correction firmware.
How often should I calibrate a Coriolis meter?
Most plants check zero every 6 months under process temperature and pressure. A full factory calibration is done every 2 years. Silver Instruments offers recalibration service at our Nanjing facility.
What is the typical turndown ratio?
Turndown ratio is up to 20:1 for calibrated accuracy. You can run the meter at 2000 kg/h and still get good readings down to 100 kg/h.
Do I need a straight run upstream?
No. A Coriolis mass flow meter is immune to velocity profile distortion. You can install it directly after a pump or elbow.
Send us your fluid name, pressure (bar), temperature (°C), pipe size (DN), and flow range for a quote with lead time and freight cost to your destination. Email [email protected], Tel +86-135-1213-1526, WhatsApp 86-135-12131526, or WeChat +86 13512131526. Ask for our product line: Coriolis mass flow meter, electromagnetic flow meter, ultrasonic flow meter, vortex flow meter, oval gear flow meter, thermal mass flow meter, pressure transmitters, and paperless recorders.