Coriolis Mass Flow and Density Meters

What Is a Coriolis Mass Flow Meter and What Does It Measure?

Most industrial flow technologies measure volume. To arrive at mass they need additional density, temperature and pressure data plus a calculation chain. A Coriolis mass flow meter works differently: it senses the mass of the fluid directly through the inertial force the fluid exerts on the vibrating measuring tubes. Measurement accuracy is a function of mass flow, so the mass value reported by the meter does not drift when operating temperature, pressure or fluid composition change.

By tracking the natural frequency of the tubes, the same sensor also measures fluid density, and an integrated temperature element provides the process temperature. Volumetric flow is then calculated from the measured mass and density. This multivariable design also forms the basis for derived values — such as concentration, net oil or gas void fraction — calculated by application software in the transmitter.

The instruments described on this page are not a single product but a sensor platform with a range of tube geometries, sizes, wetted materials and transmitter options. Accuracy, pressure rating, temperature range and process connection therefore depend on the sensor size, material and configuration chosen. The right meter is identified through a sizing study based on process data; for a broader comparison between technologies, see the flow measurement category page.

How Coriolis Mass and Density Measurement Works

The Coriolis effect is the inertial force acting on a mass that moves within a rotating frame of reference. In a Coriolis flow meter, this rotation is replaced by a controlled vibration of the measuring tubes. The measuring chain consists of the following steps:

Driving the Measuring Tubes

A drive assembly inside the sensor keeps the tubes carrying the fluid in continuous, sinusoidal oscillation. Although this motion is not a full circular rotation, it provides the rotating reference frame that the Coriolis force requires.

Flow-Induced Twist and Time Difference

With no flow, the two tubes oscillate in phase and the pickoff sensors on the inlet and outlet sides produce identical signals. Once fluid starts to move, its mass creates Coriolis forces of opposite direction in the inlet and outlet sections, the tubes twist, and a measurable time difference appears between the two pickoff signals.

Calculating Mass and Volume Flow

The time difference between the inlet and outlet signals is directly proportional to mass flow. The transmitter converts it into mass flow using the calibration factors; volumetric flow is obtained by dividing mass flow by the measured density.

Density from the Natural Frequency

The tubes are driven at their natural frequency. When the mass of fluid inside them changes, the natural frequency shifts accordingly — a denser fluid lowers it. This frequency change is converted into a density value and reported at the same time as mass flow.

Temperature Measurement and Material Compensation

The temperature element in the sensor is used to correct for the effect of temperature on the modulus of elasticity (Young's modulus) of the tube material. The measured process temperature can also be sent to the control system as an independent output.

Mach Number and Pressure Drop in Gas Service

In gas applications, sensor selection is governed mainly by the Mach number: the ratio of gas velocity in the tubes to the velocity of sound in that gas. Typical nominal gas flow is calculated at Mach 0.2 and the recommended maximum at Mach 0.3. Above Mach 0.3, the gas behaves as a clearly compressible flow and pressure drop climbs steeply — a fluid-mechanics limit that applies whatever the measuring technology.

The maximum gas flow calculated for a sensor can never exceed the maximum liquid flow of the same sensor; the lower of the two values applies. Because pressure drop and usable turndown in gas depend on operating temperature, pressure and composition, every gas application should be sized individually, taking the actual velocity and the velocity of sound into account together.

The Role of Drive Frequency in Two-Phase Flow

Gas bubbles carried in a liquid, or liquid droplets in a gas stream, affect a Coriolis measurement in two ways. A drop in the fluid's velocity of sound can cause over-reading through interaction between the acoustic mode and the drive mode, while relative movement of bubbles or particles against the fluid (decoupling) can cause under-reading. Following the NAMUR NE 132 view, sensors with a higher drive frequency respond more sensitively to gas bubbles in liquid.

For this reason the platform's sensors are grouped by drive frequency: ultra-low (below 100 Hz) and low (100–150 Hz) are the preferred choice for two-phase flow; mid-range (150–300 Hz) is acceptable in some cases; and high frequency (above 300 Hz) is not recommended for two-phase service. Large sensors of DN150 and above fall into the ultra-low class. Correct sizing, the right mounting orientation, multiphase severity alerts and high-speed digital signal processing are the main tools for keeping measurement uncertainty in check under these conditions.

Zero Stability and Low-Flow Accuracy

Nominal flow is defined as the rate at which water under reference conditions produces a pressure drop of about 1 barg across the sensor. When flow falls well below nominal, zero stability starts to govern accuracy, which is then calculated as zero stability divided by the actual flow rate. In one example sensor, accuracy holds at 0.05% up to a 30:1 turndown and may rise to 0.25% at 60:1, while pressure drop over the same range falls quickly, in proportion to the square of the flow rate.

Although the measured mass value is unaffected by operating temperature, pressure and composition, the pressure drop across the sensor does depend on them. If the process temperature differs from the calibration temperature, the resulting flow offset can be removed by performing the zero at the usual operating temperature; the process pressure effect is compensated either with a live pressure input from a pressure transmitter or with a fixed meter factor.

Key Platform Features

The features below describe the platform as a whole; some options may not be offered for a given size or material.

·         Multivariable measurement in one sensor: Mass flow, density and process temperature are measured simultaneously and volumetric flow is derived from them. This reduces the need for a separate chain of density meter, temperature element and flow computer.

·         Wide range of sizes and capacities: Sensors run from DN1 up to the DN250–DN300 class; maximum liquid flow capacity ranges from about 40.9 kg/h to 3,266,000 kg/h depending on sensor size.

·         Separately specified liquid and gas performance: Liquids and slurries have standard and premium accuracy options, while gases have their own accuracy and linearity specification. On request, calibration in an independent gas laboratory with multi-point linearization can be applied.

·         Low-frequency tubes for two-phase flow: Sensors with ultra-low and low drive frequencies are designed to limit the influence of entrained gas, or of liquid in gas. A multiphase detection function reports these conditions and their severity proactively.

·         In-situ meter verification: The integrity of the tubes, electronics and calibration is tested without interrupting the process. The test can be scheduled or started from the field or the control room, and a result is available in under 90 seconds.

·         Zero check function: Quickly assesses whether re-zeroing is needed and whether process conditions are stable enough to zero the meter. The sensor design is intended to keep on-site zeroing to a minimum.

·         Application-specific software: Licensed measurement software in the transmitter covers batching, concentration measurement, petroleum measurement, net oil and gas void fraction reporting, and mitigation of two-phase flow effects.

·         Extensive communication and I/O options: Up to five configurable I/O channels; two-wire, Ethernet and wireless connectivity; and open protocols such as 4–20 mA, HART, Modbus, PROFIBUS, PROFINET, EtherNet/IP and FOUNDATION Fieldbus, depending on the transmitter type.

·         Flexible mounting architecture: Electronics can be mounted on the sensor itself, remotely, on a wall or on a DIN rail. With extended-mount electronics, insulation can be applied to the sensor body while the transmitter or junction box stays clear of it.

·         Safety-oriented case options: The stainless steel sensor case can be ordered with a rupture disk or a purge connection. On high-pressure models a rupture disk is standard, with a standard activation pressure of 4.4 barg.

·         Audit trail and event logging: Time-stamped digital audit trails, a real-time clock and an internal data logger make it easier to trace measurement history during legal metrology and quality audits (depending on the transmitter selected).

Technical Specifications and Performance Data

The table shows ranges that span the whole platform. The values that apply to a specific measuring point should be confirmed at project stage for the chosen sensor size, wetted material, process connection, calibration option and transmitter type.

Performance reference conditions: for liquids, water at 20–25 °C and 1–2 barg with tubes-down installation; for gases, air or natural gas at 20–25 °C and 34–100 barg with tubes-up installation. The stated flow accuracies cover repeatability, linearity, hysteresis and the influence of mounting orientation together; at low flow rates zero stability becomes the deciding factor.

Key Advantages

·         Mass measurement independent of fluid properties: For fluids whose composition, temperature or pressure varies, mass is measured without conversions or assumed density values — removing sources of uncertainty from recipe, mass balance and inventory calculations.

·         More process data from fewer instruments: Taking density and temperature from the same sensor reduces the number of separate instruments, mounting points and maintenance tasks; derived values such as concentration can be calculated from the same data.

·         Data-driven calibration planning: In-situ verification results allow the meter to be assessed without removal and help base calibration intervals on the actual condition of the instrument.

·         Resilience in difficult flow conditions: Low-drive-frequency tube designs, multiphase detection and high-speed signal processing support measurement continuity with bubbly liquids, aerated fluids and fast-changing processes such as batching.

·         Broad temperature and pressure coverage: Cryogenic, standard, high-temperature and high-pressure sensor options let different process conditions be covered within one measurement platform, which simplifies standardization of spare parts and site know-how.

·         Traceable calibration infrastructure: Performance figures are based on ISO/IEC 17025 accredited calibration standards; an optional accredited calibration certificate and extra verification points ease documentation for legal metrology and quality audits.

·         Straightforward system integration: Analog, pulse, fieldbus, industrial Ethernet and wireless options allow measurement data to be passed to PLC, DCS, SCADA or safety instrumented systems in line with the plant standard.

·         Environmental effects that can be compensated: The influence of process temperature and pressure on the reading is specified with defined coefficients; zeroing at operating temperature and live pressure compensation correct these effects systematically.

Industries and Applications

Coriolis mass flow meters are used wherever direct knowledge of mass, density or concentration is critical for process control, product quality or commercial settlement. The material, temperature and approval options of the platform support the following areas.

Oil and Gas

Used with petroleum measurement software on crude oil and refined products, for net oil calculation in streams with water cut, and for mass flow measurement in natural gas lines. At custody transfer points, transmitter and calibration options with legal metrology approval are evaluated.

Chemicals and Petrochemicals

Preferred for mass-based ratio control, concentration monitoring and batching. Nickel alloy C22 wetted parts can be selected for corrosive fluids, and dedicated sensor versions are available for high-pressure and high-temperature duties.

Hygienic Processes

In plants that require hygienic design such as 3A and EHEDG, sensors can be supplied with a 0.8 µm flow-path finish and hygienic clamp or standard hygienic connections; the drainable design simplifies cleaning.

Cryogenic Fluids and Liquefied Gases

Special-order cryogenic sensors can be used at process temperatures down to −240 °C. Below −100 °C, liquid mass flow accuracy is specified as ±0.35% of rate; special fluids such as liquid helium or liquid hydrogen require a separate assessment.

Marine, Offshore and Bunkering

Sensors holding approvals from international classification societies can be installed on ships and offshore facilities. For certain large sensor sizes, an MID calibration option for marine bunkering is available.

Filling, Batching and Recipe Control

Fast digital signal processing and batching software help apply mass-based cut-off points repeatably in short filling and dosing operations.

Oxygen Service and High-Pressure Gas Lines

A declaration-of-cleanliness option for oxygen service and high-pressure sensors rated up to 413.69 barg enable mass measurement in industrial gas and high-pressure process lines.

Critical Parameters for Coriolis Flow Meter Selection and Sizing

A Coriolis sensor is not chosen by line size alone; fluid behavior, allowable pressure drop and target accuracy must be assessed together. For a technical assessment we recommend clarifying the following:

Fluid and Process Data

·         Fluid type: liquid, slurry, gas or two-phase flow; likelihood of entrained gas or liquid in gas

·         Minimum, normal and maximum flow; density and viscosity (viscosities above 500 cSt should be reviewed separately for DN100 and larger flanges)

·         Minimum / normal / maximum process temperature and pressure

·         Chemical compatibility with wetted materials; chloride, H₂S or abrasive solids content

·         For gas applications: gas density and velocity of sound at operating conditions

Sizing and Performance Targets

·         Ratio of normal operating flow to nominal flow; on lines where two-phase flow is expected, flow should not fall below a 5:1 turndown from nominal

·         Maximum allowable pressure drop and pump/compressor capacity

·         Sensor size for gases based on the Mach 0.2 (nominal) and Mach 0.3 (maximum) limits

·         Effect of zero stability on accuracy at minimum flow

·         Required mass flow and density accuracy (standard or premium calibration option)

Mechanical Design and Materials

·         Wetted material: 316L, 304L, nickel alloy C22 or super duplex

·         Process connection standard and pressure class; maximum working pressure allowed by sensor and connection together

·         Case pressure limit; need for a rupture disk or purge connection

·         Hygienic finish and connection requirements; need for a heating jacket or steam tracing

Installation and Ambient Conditions

·         Mounting orientation suited to the fluid type (different preferred tube orientations for liquids and gases)

·         Remote-mounted electronics where ambient temperature goes outside −40 °C … +60 °C

·         Extended-mount electronics on insulated high-temperature lines

·         Hazardous-area classification, gas group and temperature class

·         Pipeline vibration level and access to the sensor for maintenance

Electronics, Communication and Documentation

·         Transmitter power supply (AC, DC or two-wire loop-powered) and mounting style

·         Analog, pulse, fieldbus or Ethernet protocol and number of I/O points required by the control system

·         Use in a safety instrumented system (SIS) and the target safety integrity level (SIL2 or SIL3)

·         Need for custody transfer approval, an in-situ verification package and application software

·         Documentation requests such as accredited calibration, EN 10204 3.1 material certificates, pressure and leak tests, and radiographic examination

If only volumetric flow of a conductive liquid is needed, magnetic flow meters may be the more economical choice; for steam and general-purpose volumetric measurement, vortex flow meters; and for very large natural gas lines, ultrasonic gas flow meters. The technology decision should be made by comparing the options against the process data.

Approvals, Certifications and Applicable Standards

The approvals and conformities below are defined at platform level; not every one applies to every combination of sensor size, material and electronics.

Hazardous-area approvals are defined for sensor electronics with a remote four-wire connection; configurations with integral electronics may have a narrower approval scope. The final approval combination should be confirmed for each project together with the TLY Enerji engineering team.

Coriolis Metering Point Engineering with TLY Enerji

Whether a Coriolis metering point succeeds is usually decided before the order form is filled in: does the fluid carry gas, what Mach number will a gas line run at, can the pump or compressor handle the pressure drop, and how will the sensor be oriented? The TLY Enerji engineering team works through these questions using your process data and prepares a technical proposal that considers sensor size, wetted material, process connection and calibration option together.

On projects that call for custody transfer, safety instrumented systems or hygienic design, we help clarify the approval combination and support transmitter integration into the PLC/DCS/SCADA architecture, project documentation and commissioning. After start-up, we help interpret zero check and in-situ verification results and provide field support that feeds into maintenance and calibration planning, so that the long-term reliability of the metering point is looked after jointly.

·         Process data collection and application analysis

·         Sensor sizing, pressure drop and Mach calculations

·         Review of material, connection and approval combinations

·         Control system integration and project documentation

·         Commissioning and field support

Frequently Asked Questions

What is a Coriolis flow meter and which variables does it measure?

A Coriolis flow meter is an instrument that obtains mass flow directly by sensing the Coriolis force that flowing fluid generates in vibrating measuring tubes. The same sensor determines density from the natural frequency of the tubes and process temperature from a built-in temperature element. Volumetric flow is calculated from the measured mass and density, so a single instrument provides mass, volume, density and temperature data.

Can a Coriolis flow meter be used for gas measurement?

Yes. For gases, mass flow accuracy is specified as ±0.25% of rate with 0.20% repeatability; with calibration in an independent gas laboratory and multi-point linearization, ±0.1% against reference can be reached. Gas velocity in the tubes drives sizing: Mach 0.2 is used for nominal flow and Mach 0.3 for the recommended maximum. At higher velocities pressure drop rises sharply.

How accurate is density measurement with a Coriolis meter?

For liquids, density accuracy is ±0.5 kg/m³ with standard calibration and ±0.2 kg/m³ with premium calibration; for the smallest sensors the figure is ±2 kg/m³. Density can be measured up to 5,000 kg/m³. With the optional density temperature calibration, the specification applies between −17.8 °C and 60 °C. No density accuracy specification applies in cryogenic applications.

Does a Coriolis meter measure correctly with entrained gas or two-phase flow?

Two-phase flow adds uncertainty for every Coriolis sensor, but its effect can be limited considerably through sensor selection and installation. Sensors with a low drive frequency (below 100 Hz or 100–150 Hz) are preferred for these conditions, and sensors above 300 Hz are not recommended. Keeping flow above a 5:1 turndown from nominal, the right mounting orientation, multiphase severity alerts and two-phase measurement software should be used together.

Can a Coriolis flow meter be used for custody transfer?

Yes. The platform includes configurations with approvals under MID and OIML R 117 / R 137 as well as legal metrology approvals such as NTEP, Measurement Canada and INMETRO. Custody transfer suitability depends on the combination of sensor, transmitter and calibration. Local legal metrology requirements, including those in Türkiye, and the requirements for the metering system as a whole should be evaluated separately for each project.

What is in-situ meter verification, and can it replace calibration?

In-situ meter verification is a diagnostic function that tests the integrity of the tubes, electronics and calibration without removing the sensor or stopping the process. The test can be scheduled or started from the field or the control room and returns a result in under 90 seconds. Its results are a valuable input for setting calibration intervals; whether they satisfy periodic verification requirements under legal metrology must be judged against the applicable regulations.

How do you size a Coriolis flow meter?

Size is chosen according to flow range, allowable pressure drop and target accuracy, not line size. Nominal flow is the rate at which water under reference conditions creates a pressure drop of about 1 barg. A smaller sensor gives better low-flow performance but increases pressure drop; in a larger sensor, zero stability dominates at low flow. For gas applications the Mach limits, and for two-phase flow the minimum flow ratio, must also be checked.

When is a zero adjustment needed?

The sensor is designed so that zeroing on site is seldom required. However, if the process temperature differs markedly from the calibration temperature, a zero performed at the usual operating temperature compensates for the temperature effect on flow. The zero check function shows whether re-zeroing is necessary and whether process conditions are stable enough for it. Zeroing should be done with the line full and flow completely stopped.

What process temperatures can Coriolis flow meters handle?

Standard sensors can be used between −100 °C and +204 °C, high-temperature versions between −50 °C and +350 °C, and special-order cryogenic versions down to −240 °C. Electronics ambient temperature must stay between −40 °C and +60 °C; outside these limits, or at high process temperatures, remote-mounted electronics are selected. For super duplex models, applications above 177.2 °C should be reviewed in advance