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Coriolis Mass Flow Meter Principle & Design
Quick Answer: A Coriolis meter directly measures mass flow, not volume. It gives you density and temperature from one sensor with no straight pipe needed. If you send us your fluid type, pipe size (DN), flow range in kg/h, and process pressure, Silver Instruments will return a price within one working day.
Most engineers who handle syrups, fuel oil, or aggressive chemicals learn fast that a Coriolis meter solves problems other flow technologies cannot touch. The sensor has no obstacles in the flow path, no bearings, and no mechanical parts that wear out. We build ours from 316L stainless steel, Hastelloy C22, or titanium for seawater and acid lines. The design is simple in concept, but the execution needs tight digital signal processing on the primary transmitter board.
How the Measuring Principle Works
Inside the meter, an exciter coil makes one or two tubes vibrate at their natural frequency. Inlet and outlet pickoff coils sit on each side of the tubes. When fluid is at rest, the inlet and outlet signals are in phase. As fluid starts to move, the Coriolis force twists the tubes and the pickoff coils register a phase shift. That phase shift is directly proportional to mass flow. No pressure or temperature compensation is needed to get a mass reading. A built in PT100 platinum sensor measures tube temperature, and the transmitter uses this to trim for stiffness changes in the metal.
Let me give you a real number. On a DN25 U-shaped tube meter from our production line, the tubes vibrate around 80 Hz to 100 Hz with air. When a customer in Thailand tested it with coconut oil at 40 degrees Celsius and 800 kg/h, the phase shift was a few microseconds, but our DSP captured it and gave ±0.15% accuracy right out of the box. That is the power of a direct mass measurement.
Sensor Design and Material Decisions
The tube shape is not just marketing. U-shaped and delta-shaped tubes give a longer path for the Coriolis force to act, which makes the signal stronger on low viscosity fluids. Straight tube designs exist too, and they are easier to drain, but they need a more sensitive drive system. We keep both designs in stock for DN15 up to DN200.
Material is the first question we ask. For standard water, diesel, or palm oil, 316L is enough. For hydrochloric acid or seawater with high chloride content, a Hastelloy C22 wetted part is mandatory. We delivered a Hastelloy DN50 Coriolis meter to a desalination plant in Oman last year. The brine line runs at 65 bar and they measure antiscalant dosing. Titanium is an option for urea and nitric acid, though few suppliers keep it ready. Silver Instruments holds titanium wetted parts for DN25 and DN40 as standard.
Electronics and Output at the Field Level
The transmitter mounted on the sensor does the heavy work. It generates the drive signal, measures the phase shift, calculates density from the resonant frequency, and then pushes data out. Standard output is 4-20 mA HART with a passive or active configuration. Most of our shipments go with Modbus RTU on RS485 and a pulse output for batch control. The housing is rated IP67, and for oil and gas sites we supply ATEX Zone 1 or IECEx Ex d versions with 316L conduit entries.
Here is a detail that technicians in Mexico and Vietnam pointed out to us. The zero calibration routine stored in the transmitter memory should run on an empty, vented, and pressurized line to match operating stiffness. If you skip that step, your low flow reading drifts. Ou
Silver Instruments Coriolis Range in Practice
We group meters by pipe size and application, not by a confusing product family name. A typical setup for a paint manufacturer in Malaysia uses a DN15 meter with 1/2 inch tri-clamp connections. Flow range is 0 to 2000 kg/h for solvent and resin. The meter outputs data to a PLC over 4-20 mA HART, and the density value is used to check batch consistency. The whole unit weighs less than 9 kg and fits into a mixing skid without extra supports.
For marine fuel oil measurement on a barge in Singapore, we supplied a DN80 meter in 316L with a maximum flow of 80,000 kg/h. The process pressure was 25 bar at 120 degrees Celsius. Because the customer needed custody transfer accuracy, we provided a factory calibration traceable to ISO 17025 with an uncertainty of ±0.10%.
Another application: a wastewater treatment plant in Chile uses our DN50 Coriolis to dose flocculant polymer. The fluid viscosity reaches 8000 cP, and a magnetic flow meter cannot work because the polymer is not conductive. The Coriolis meter has no electrode to foul, and the density reading gives the operator a second check on concentration. They sent us the fluid sample to test viscosity and density at our calibration rig before finalizing the sensor material. We do this free of charge for serious inquiries.
Common Questions from Engineers and Buyers
What is the minimum flow you can measure with a Coriolis meter?
With a DN15 sensor and thin wall tubes, the threshold is around 0.5 to 1 kg/h for liquids with density above 0.8 g/cm3. At that low rate, the accuracy may widen to ±0.5% of reading, but the repeatability stays below 0.1%.
Does the meter need straight pipe runs upstream or downstream?
No. That is one reason plants choose Coriolis. You can mount it right after a 90-degree elbow, a pump, or a control valve. The meter does not care about the velocity profile because it senses mass directly.
Can the same meter handle liquid and gas?
Yes, but gas measurement needs higher density or higher velocity to generate a usable signal. For compressed air or nitrogen at 6 bar and above, we often specify a DN25 or DN40 meter with a flow computer that switches between gas and liquid modes. Typical gas accuracy is ±0.5% of rate.
How do I know if a Coriolis meter will withstand my cleaning process?
Send us the CIP or SIP temperature and chemical concentration. We expose the wetted material coupon to your cleaning agent for 48 hours in our lab, then check for weight loss and pitting. We did this for a dairy in Australia with 2% nitric acid at 85 degrees Celsius and confirmed 316L was acceptable.
What is the quickest way to get a price from Silver Instruments?
Send an email to [email protected] with your fluid, pipe size (DN), flow range in kg/h, pressure in bar, and temperature in degrees Celsius. Give us your required signal output and hazardous area classification. We respond with a datasheet and quote within one business day, often the same morning for standard requests.
If you are replacing an existing flow meter, include a photo of the nameplate or the old wiring diagram. That helps us match the electrical connections exactly. We ship from our warehouse in China, and most orders to Southeast Asia, the Middle East, and Latin America reach the site within five to seven days via air freight.