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Mass Flow Meter Working Principle: Comparing Coriolis and Thermal Physics
Quick Answer: A Coriolis mass flow meter measures mass directly by detecting the phase shift of vibrating tubes. A thermal mass flow meter measures mass flow by sensing how much heat a flowing gas carries away from a heated sensor. Coriolis meters work with liquids and gases, handle high viscosity, and deliver ±0.1% accuracy. Thermal meters are best for dry, clean gases, offer wide turn-down ratios, and need no pressure or temperature correction. Choose Coriolis for high-precision liquid batching. Choose thermal for gas flow measurement in aeration lines or biogas pipes.
What Is a Mass Flow Meter?
Volumetric flow meters measure the volume passing through a pipe. That volume changes with temperature and pressure. A mass flow meter measures kilograms per hour (kg/h) or standard cubic meters per hour (Nm³/h). It ignores temperature and pressure swings. Two mainstream technologies dominate industrial mass flow measurement. These are the Coriolis principle and the thermal dispersion principle. Silver Instruments supplies both types. We help process engineers in Southeast Asia, the Middle East, and South America pick the right one for their fluid, pipe size, and budget.
Coriolis Mass Flow Meter Working Principle
A Coriolis meter contains two parallel flow tubes. A drive coil vibrates these tubes at their natural frequency. Fluid enters the tubes, splits, and flows through both branches. When mass flows through a vibrating tube, Coriolis forces deflect the tube upward on the inlet side and downward on the outlet side. Two pickoff sensors measure the resulting twist as a time delay. The time difference is directly proportional to mass flow rate. A Coriolis meter also measures density from the resonant frequency of the tubes. Temperature from a built-in PT100 sensor corrects for tube stiffness changes. One instrument gives mass flow, density, and temperature in real time. No straight pipe runs needed. No Reynolds number corrections. Just clamp it in and measure.
Silver Instruments manufactures the SICOR series Coriolis flow meter. Line sizes go from DN 3 to DN 150. It covers flow ranges from a few kg/h up to 1,000,000 kg/h. Wetted materials are 316L stainless steel or Hastelloy C22. The transmitter outputs 4-20 mA HART, pulse, or Modbus RS485. Accuracy is ±0.1% of rate for liquids and ±0.35% for gases. The meter handles fluid temperatures from -50 °C to +200 °C. A paint plant in Vietnam uses the SICOR DN25 meter to dose solvent at 100 kg/h into a mixing tank. They needed ±1 gram repeatability. The Coriolis meter delivered ±0.5 grams. Another food factory in Thailand measures chocolate syrup at 3,000 kg/h and 500 cP viscosity. A volumetric meter would have drifted with temperature. The SICOR meter ignores the viscosity and gives stable mass totals.
Thermal Mass Flow Meter Working Principle
Thermal mass flow meters use two resistance temperature detectors (RTDs). Both sit in the gas stream. One RTD acts as the temperature reference. The other RTD is heated by a constant power or kept at a constant temperature difference above the reference. Flowing gas cools the heated RTD. The cooling rate depends on the mass velocity, the gas thermal properties, and the temperature difference. In a constant-temperature-difference design, the circuit supplies more power to maintain the set ΔT as flow increases. That power demand gives the mass flow signal. The meter outputs a 4-20 mA HART signal proportional to mass flow. It needs no pressure transmitter or temperature sensor for gas density compensation. Thermal meters work only with dry, clean gases. Wet gas or liquid droplets destroy the RTD sensing film.
Silver Instruments SITF thermal mass flow meter suits air, nitrogen, biogas, natural gas, and stack gas. Probe sizes fit pipes from DN 25 to DN 3,000. It handles flow velocities from 0.1 Nm/s to 100 Nm/s. Process temperatures can range from -40 °C to +200 °C. A wastewater plant in Chile installed a SITF meter on a DN 80 biogas line. Gas temperature varies between 25 °C and 35 °C. Pressure is 0.3 bar. The meter sends a 4-20 mA HART signal to the PLC that controls the gas engine. The plant operator says the meter handles the dirty, saturated biogas without fouling. They just wipe the probe during quarterly inspections.
Coriolis vs. Thermal: Key Differences
Coriolis meters measure liquids and gases with high accuracy. They handle slurries, viscous oils, and high-pressure fluids. No mechanical parts contact the flow, but the tubes vibrate, so abrasive wear is possible without proper material selection. Thermal meters measure gas only. They have no moving parts, not even vibrating elements, so they tolerate some suspended particles if the gas is dry.
Accuracy tells the first big difference. A Coriolis meter gives ±0.1% of rate for liquids. A thermal meter gives ±1% of full scale for gas, sometimes better after in-situ calibration. Turndown ratio is 20:1 for Coriolis and up to 100:1 for thermal. Thermal meters win on low-flow gas detection. A Coriolis meter can measure
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Installation is another factor. Coriolis meters can mount in any orientation as long as the tubes stay full. No straight pipe upstream or downstream needed. Thermal meters need a minimum straight run of 15 diameters upstream, sometimes more if a single elbow disturbs the velocity profile. Coriolis meters come in compact or remote transmitter versions. Thermal meters usually insert through a weld-o-let or flange connection.
Cost tips the scale in many projects. A DN 15 Coriolis meter with 4-20 mA HART output costs more than a thermal mass flow meter for a DN 100 air line. But in a batching system where every gram counts, the Coriolis meter recovers its cost through reduced waste and off-spec batches. We help you run the numbers. Send us your process data and we will compare quotes.
Which One Should You Choose?
Ask these three questions. One: Is the fluid a liquid or a gas? For liquid, Coriolis is almost always the answer. For gas only, thermal may be simpler. Two: Do you need density measurement? Coriolis gives density free. Thermal cannot. Three: What is your turndown need? If you must measure from 0.5 Nm³/h to 500 Nm³/h of nitrogen in a blanketing line, thermal handles the range better.
Coriolis meters appear in batching, hydrocarbons, chemical injection, and edible oil loading. A refinery in Nigeria recently bought two SICOR DN80 meters for crude oil export. They needed ±0.1% accuracy for customs transfer. Silver Instruments delivered the meters with ATEX Zone 1 certification and 316L tubes. The thermal meters appear more in aeration basins, boiler air feed, and flare gas monitoring. A landfill in Brazil uses a SITF thermal meter to measure landfill gas with 45% methane. The probe has a special coating to resist H₂S.
If you still have doubts, give our engineers a scenario. We get calls from marine engineers who need a mass flow meter for fuel oil on a ship. The answer is a compact Coriolis meter with DN 15 size and marine type approvals. We get calls from ceramic tile factories measuring hot air at 180 °C. Our thermal meter with a high-temperature probe works well. Just tell us the fluid, pipe size, temperature, and flow range. We will suggest a model number and list price in one working day.
Silver Instruments Mass Flow Meters: What to Expect
Silver Instruments designs and builds both Coriolis and thermal mass flow meters in a dedicated factory. We test each meter with water, air, or nitrogen before shipping. Standard documentation includes a calibration certificate, wiring diagram, and material traceability. We ship to 60 countries. Our typical lead time is 2 to 3 weeks for standard models. Custom ranges and exotic materials take 5 to 6 weeks.
All meters come with a 12-month warranty. We provide local support through distributors in Australia, Qatar, Indonesia, and Mexico. Our engineers speak English, Spanish, and Mandarin. Remote start-up help over video call is included. You can also send a technician and we will train them in our Nanjing facility.
Send us your process data now: Fluid name, flow range (kg/h or Nm³/h), pipe size (DN), pressure (bar), and temperature (°C). We will reply with a recommended model and a firm quotation within 24 hours. Email: [email protected], Tel: +86-25-68650347, WhatsApp: +86-25-52155837, WeChat: +86 15365082610.
Frequently Asked Questions
Can a Coriolis mass flow meter measure gas accurately?
Yes. Silver Instruments SICOR gas meters achieve ±0.35% of rate for gas at densities above 2 kg/m³. Light gases like hydrogen need a dedicated high-frequency sensor. Our engineers will confirm the minimum gas density for your application.
What is the turndown ratio of a thermal mass flow meter?
Most thermal meters give 100:1. Silver Instruments SITF can reach 200:1 when calibrated for a specific gas at constant pressure. This is useful for burner air control where the flow varies from 0.5 Nm/s to 80 Nm/s.
Do I need viscosity compensation for a Coriolis meter measuring heavy fuel oil?
No. A Coriolis meter measures mass directly. The phase shift has no dependence on Reynolds number or viscosity. This is a key advantage over turbine and DP meters that drift when viscosity changes with temperature.
How many diameters of straight pipe does a Coriolis meter need?
Zero. You can install a Coriolis meter right after an elbow, a tee, or a pump discharge. The tube vibration signal is immune to flow profile distortion. Thermal meters need 15D upstream straight run as standard. Less if a flow conditioner is built in.
Which meter do you recommend for ammonia gas in a fertilizer plant?
SITF thermal mass flow meter with Hastelloy C276 probe and PTFE insulation. Ammonia gas at 2 bar and 30 °C is dry enough for thermal measurement. The C276 material resists ammonia corrosion. For liquid ammonia transfer, use a SICOR Coriolis meter with secondary containment.