All About Coriolis Flow Meters

A Coriolis flow meter is used for monitoring and measuring the flow of liquid, steam, and high-pressure gas within a piping system. Typically, Coriolis flow meters are only used in heavy-duty industrial applications, whereas other flow meter technology types can be used in applications that aren’t necessarily considered “industrial” in nature.

Coriolis flow meters are also used in applications requiring exceptionally high accuracy and can also be found in lab settings as well. By using the measurement principle of the Coriolis effect, a Coriolis flow meter can compute the flow rate of the media passing through it. Understanding the flow rate of a process ensures that the process is functioning properly.

Sometimes Coriolis flow meters are referred to as just “Coriolis Flow Meters” and sometimes they also are referred to by the manner of measurement principle that the flow meter technology is using. This can lead to them also being referred to as “Coriolis mass flow meters”. There are two types of measurements that a flow meter can deliver. One is a measurement of mass, and the other is a measurement of volume.

Understanding the difference between mass and volumetric measurement can be complicated in nuance. To oversimply it, a general way to think about it is that mass measurements express the quantity of matter (relative weight) and volumetric measurements express the amount of space the media takes up. Volumetric measurements are more affected by certain process variables like temperature.

For some reason, it is common practice to refer to both Coriolis flow meters and thermal flow meters with the term “mass” included in the title, while other flow meter technology types are rarely referred to with “volumetric” in how people refer to them.

There are two key points to understanding how Coriolis flow meters work. The first point, and the element they are named after, is the Coriolis effect principle. It can simplistically be summed up as the idea that movement causes inertia. For example, kids on a merry-go-round not only experience the force moving them in circles, but they also experience a force pushing them off the merry-go-round as well. This is an example of a Coriolis force. The second key point to understand is that the Coriolis force is the cause of the inertia within the pipe that causes deformation/movement of the pipe. It is not what is technically being measured in and of itself.

With those two points clarified, the operation becomes a bit easier to understand. For common dual-bent-tube architecture, the flow is immediately split into two separate tubes directly after the connection point to the process piping system. There is an excitor coil on these tubes that cause artificial oscillation and causes the tubes to vibrate in opposition to each other. On either side of the excitor coil are two magnetic sensors. The media moving through the bend of the tubes causes inertia and the tube twists. This tube movement is picked up by the sensors as a phase shift in the sine waves formed between the two sensors. When there is no flow, the two sensors are in phase with each other. When flow is present, they are not. The motion of the pipes in relation to the magnetic sensors is directly proportional to the mass flow rate.

Because the Coriolis effect measurement principle delivers a mass measurement, the density of the media can easily be extrapolated through the flow meter electronics by dividing the mass measurement by the known unchanging volume of the measuring tubes themselves. Many Coriolis flow meters include this as an integral part of the flow meter capabilities, like our TM and TMU Coriolis flow meters with integral density measurement.

For certain application areas, Coriolis flow meters are the clear choice. If your application would be well served by some of these Coriolis flow meter advantages, then they are worth considering.

• Extremely accurate and repeatable
• Not affected by changes in media density
• Good for applications where the media’s properties aren’t already well known
• Do not require straight piping runs
• Some models can also measure density, temperature, volumetric flow, or viscosity

All these things sound great, don’t they? However, there are also clear disadvantages to Coriolis flow meters. The top one being the relatively higher cost. In general, they are arguably the most expensive type of flow meter technology.

Other disadvantages that standard sized Coriolis flow meters have are that they are generally large and heavy, they are not available as insertion technology and require an inline installation, and they are not good for dual-phase media. They also are limited by certain parameters that must be considered. Sometimes there are characteristics inherent in your exact application that preclude the use of Coriolis flow meters.

Coriolis flow meters are suitable for a wide variety of applications, but most fall within general industrial or process industry applications. Some sample application areas are as follows.

• Pulp and Paper
• Chemical Processing
• Water and Wastewater
• Custody Transfer
• Oil and Gas
• Mining and Mineral Processing
• Power Generation
• Petrochemicals

Due to the complex nature of the technology and the higher cost of the instrumentation, we strongly suggest that you partner with an industry expert like KOBOLD who can confidently choose the correct Coriolis flow meter for you. Our sales engineers know exactly what questions to ask to correctly narrow down the suitable options. Here are some application variables that are good to know to assist in the selection process.

• The exact media and any specific media characteristics
• The nature of the flow pattern and any elements that may create turbulent flow
• The orientation of the flow, like bottom to top
• The maximum and minimum temperature for the media
• The desired units of measurement
• The maximum and minimum anticipated flow rate
• The process piping size
• The type of connections desired
• The maximum pressure
• Pressure-drop limitations
• Accuracy requirements
• Any required communication protocols like HART®
• Any certifications or approvals like those for hazardous areas

Here are some side-by-side comparison points about Coriolis and Magnetic flow meters.

• Neither have moving parts to wear and tear and offer a long service life
• Both are popular and well-known flow technology choices
• Both can be made in materials that accommodate aggressive media
• Both require the process pipe to be completely full
• Magnetic flow meters cannot measure non-conductive liquids while Coriolis meters can
• Magnetic flow meters are more sensitive to turbulence in the flow profile and may require longer upstream and downstream piping requirements
• Magnetic meters can be made in insertion models while Coriolis meters cannot
• Magnetic meters are affected by any magnetic force around them
• Magnetic flow meters must be grounded
• Coriolis meters can measure gases and magnetic meters cannot
• Coriolis meters will generally cost more than magnetic meters
• Coriolis flow meters are not as affected by fluctuations in media characteristics
• Coriolis meters measure by mass and magnetic flow meters measure by volume
• Coriolis flow meters generally have less or no straight piping requirements in comparison to magnetic flow meters
• Coriolis flow meters can provide density measurement, magnetic meters cannot
• Coriolis flow meters usually offer higher accuracy than magnetic flow meters
• Coriolis flow meters typically offer a higher turndown ratio where larger fluctuations in the flow rate can be accommodated
• Certain Coriolis meters can handle much higher temperatures, pressures, and flow rates than magnetic flow meters
• Coriolis meters are more affected by vibration than magnetic meters
• Although there are exceptions, like our compact HPC Low Flow Coriolis Flow Meter, Coriolis meters are generally larger and heavier than magnetic meters
• Coriolis flow meters have the reputation of having a higher pressure drop than magnetic meters
• Certain Coriolis flow tube-shapes can be prone to accumulation, which is less prevalent in magnetic meters

While Coriolis flow meters can handle a wide variety of liquids, higher viscosity means less accuracy from Coriolis flow meters. High viscosity liquids are better served by positive displacement flow meters. To see examples, view our positive displacement flow meter line that offers some of the highest viscosity solutions in the industry.

Here are some examples of media measured by Coriolis flow meters. Each meter offers different capabilities, so please verify that your media would be compatible with any Coriolis flow meter you are considering.

• Water
• Caustics
• Chemicals
• Acids
• Cleaning Agents and Solvents
• Fuels
• Silicon Oils
• Suspensions
• Molasses
• Paint
• Varnish and Lacquer

While most Coriolis meters are used for liquid applications, Coriolis flow meters can also be used to accurately measure gases. Coriolis gas flow meters offer almost all the same benefits as Coriolis liquid flow meters do. One notable exception that you may notice is that gas measurement produces a slightly reduced accuracy if the measuring tubes are of thicker construction for durability and longevity.

Although thicker measuring tubes offer a significant cost benefit through enabling a longer service life, they also do not receive as much pressure from gas flow as they do from liquid flow. Liquid has the capability to produce much more force because it has so much more mass. That mass moving around in the measuring tubes of a Coriolis flow meter help the technology to function more accurately. To take this element into account, Coriolis gas flow meters with thicker tubes require higher process pressures to create more force within the measuring tubes to create enough movement to deliver accurate results.

Coriolis meter sizing is not as straightforward as other flow meter technologies and can depend greatly on specific process variables. Because of the highly technical nature and the combination of elements that can affect proper functioning, it is highly recommended that you work with a company well versed in the intricacies of Coriolis technology, like KOBOLD.

There are many statements online that indicate that the size of the pipe should determine the size of the meter. Meaning that if the inlet process piping is 6”, the right meter to choose is a 6” meter. This is not true and following that advice can lead to headaches down the road. One of the prominent considerations in Coriolis meter sizing is the element of pressure drop, which must be accounted for.

Pressure drop in flow meters is the decrease in pressure that happens as the media passes through the flow meter. It is the difference in pressure that the line has before the meter inlet and after the meter outlet. Coriolis flow meters, especially those with dual tube measuring technology, have an inherent restriction in the design. The flow coming from the pipe into the meter inlet is split into two small tubes that have a significantly smaller pipe diameter than the process piping.

Because of this decrease in tube size, the pressure of the flow decreases while it is moving through the meter. Other flow meter technologies, like magnetic and ultrasonic flow meters do not have this sort of reduction/obstruction in their principles of operation and there is minimal flow restriction as the flow body of the meter is very close in diameter to the process piping. This explains why other technologies do not create as much of a drop in pressure.

This general principle is referred to as the CV value, which quantifies the fact that a smaller line requires more pressure to produce the same flow rate as a larger line.

Coriolis meters are known for having the potential for significant pressure drop in comparison with other flow meter technology types. This difference in flow tube size between the external piping and the internal meter tubes is why you will sometimes hear the suggestion being made that you need to “size up” for a Coriolis flow meter to decrease the pressure drop. A bigger size meter will have bigger flow tubes. Bigger tubes create less constriction. Less constriction creates less pressure drop. Less drop in pressure means higher flow rates downstream.

It is also worth noting that the higher the flow rate, the more pressure drop will occur across the meter. In essence, pressure drop is exponentially worse at higher flows than lower flows which is why you will see some data tables in flow meter datasheets that show the pressure drop in a graph and it appears as a curve and not a straight line in the graph.

Coriolis flow meters are also more susceptible to an increase in pressure drop when the liquid is more viscous in nature. High viscosity media decreases the ability for the liquid to move through the decreased pipe size. An analogy would be trying to blow honey through a straw as opposed to water. Which one can move through the straw with less force (pressure) applied to it? Obviously the less viscous one, the water. So, not only do you have to accommodate for pressure drop by the nature of the measurement principle, but you also must compensate for it in reference to the media as well.

Pressure drop matters because it affects the potential flow rate on the downstream side of the meter. With a significant enough pressure drop from the flow meter, there may not be enough pressure left to create adequate flow rates for the process.

As listed above, one advantage to Coriolis flow meters is that they generally do not require any length of pipe before or after the flow meter to operate correctly and deliver accuracy. Many flow meter technology types cannot provide as much precision in measurement when there is turbulence present in the flow from bends in the pipe, valves, pumps, etc. They require a straight flow profile. Fortunately, Coriolis flow meters do not and can handle turbulent flow without a significant degradation in accuracy.

In tight installation spaces or in applications where straight piping requirements are simply impossible due to the orientation of the process lines, Coriolis flow meters offer a distinct advantage. There are other types of flow meter technologies that do not require straight piping runs. To learn more about flow meter options that do not require straight runs, visit our article on flow meter straight piping run requirements.

Coriolis flow meters deliver the highest level of accuracy in the industry. They can be used to verify the accuracy of other flow meters and are typically used in test benches for flow meter manufacturing. Coriolis flow meter accuracy is better for liquids than gas. Typical liquid accuracy is 0.1% and typical gas accuracy is 0.5%. Other technologies deliver much less accuracy. For example, paddle wheel flow meters typically offer an accuracy of 2.5% to 5%. To learn more, visit our article on flow meter accuracy.

Coriolis flow meter technology can deliver some of the lowest and highest flow rate measurements in comparison to other flow meter technologies. For example, our TM Coriolis Flow Meter comes in ranges from 0.003...0.3 lbs/min to 220...2,400 lbs/min, delivering a turndown ration of 100:1. Our HPC Coriolis Flow Meter offers one of the lowest flow rates in the industry in a compact size.

Before choosing a flow meter for your application it is essential to consider all the ways that the installation can affect the operation of the flow meter. While it is possible to state some generalities about Coriolis flow meter installation, there is no “one size fits all” set of directions. Product manuals for each Coriolis flow meter should always be consulted for exact installation requirements. However, here are a few sample considerations for installing a Coriolis flow meter to minimize damage and inaccuracy.

• Coriolis flow meters should be installed with the guidance of a qualified engineer
• Ensure that the media is compatible with the meter's wetted parts
• The meter is recommended to operate mostly in the mid to upper range of stated flow rate
• Accuracy will be affected if you select a meter larger than the line size to try and manage pressure drop
• For high flow rates, make sure the piping diameter is not too small, so it does not cause significant pressure drops
• Ensure that the pipe will always be full when the meter is in operation
• Coriolis flow meters cannot tolerate bubbles so ensure they will not be created in the line
• Back pressure should be kept at a sufficient level to prevent cavitation
• Reduce any vibration/noise as much as possible by properly supporting the meter
• The meter should be installed in an area that will not experience direct sunlight to avoid changes in the flow tube’s ability to modulate and should not be placed near heat sources
• Allow the meter to fully “warm up” before use
• Perform the necessary zero-point calibration to enable density measurement and empty pipe recognition
• Ensure there is no pressure surge upon start-up
• Ensure a stable flow profile by decreasing turbulence in the flow as much as possible. Pay attention to valves, manifolds, and sharp pipe ends, particularly upstream of the meter
• Do not use an impact tool to fasten the installation screws as the sensor can be damaged by corresponding vibrations
• Do not use the meter to support a pipe and do not install the meter without any support
• Do not adjust the surrounding piping by pulling on the meter
• Do not use the meter to try and align pipes by installing it
• To avoid pressure surges and subsequent damage, quick-closing valves should be mounted downstream of the sensor. If this is not possible, then they should be mounted a distance of 10x the pipe diameter upstream and/or the valve speed can be adjusted.
• Ensure a leak-tight installation, ideally verifying with a liquid test or pressure monitoring, before pressurizing and starting up the system
• The installation orientation of the Coriolis flow meter is dependent on the meter and media. Consult your product manual for the exact orientation recommendations as it is as not always best to install it horizontally. Below is an example of the criteria that can be used to determine the best installation position for our TM Coriolis Flow Meter to show the variables that determine Coriolis flow meter installation orientation.

This is only a reference example for our model TM flow meter. For installation requirements and considerations specific to your Coriolis flow meter, please consult the manual that should have been provided with your meter by the manufacturer.

If you have purchased a KOBOLD or Heinrichs Coriolis flow meter and have lost your manual, please contact us directly for a replacement manual and we would be glad to help. Please also contact us for any installation specific questions you may have when commissioning your KOBOLD or Heinrichs Coriolis flow meter.

To avoid headaches down the road, choose a flow meter that has integral self-test functionality, like our line of Coriolis flow meters. This can quickly and painlessly pinpoint the variable that may be causing problems by displaying an error code indicating which type of issue it may be. The manuals supplied with our meters not only explain the problem but offer tips to resolve issues. Here is a very small sample from our TM Coriolis Flow Meter manual that shows a sample of Coriolis flow meter troubleshooting included with our meters.

If you have purchased a KOBOLD Coriolis flow meter and need assistance in troubleshooting your meter, please call us and our expert engineering staff can help walk you through any issues that you may be experiencing.

To ensure that your Coriolis flow meter operates correctly after installation, it is necessary to perform a zero-point calibration before commissioning the meter. Here are the steps to the procedure.

• Install the meter according to the manufacturer’s instructions
• Check to ensure that the meter is completely full and there are no gas bubbles in the flow tubes
• Define the process conditions such as pressure, temperature, and density
• Close any potential shut-off valves behind the meter
• Operate the flow meter in accordance with the meter’s instructions
• Make sure the electronics are fully warmed up
• Allowing flow to occur during the procedure will skew the zero point and cause false readings

Occasionally your Coriolis flow meter may need to be removed and sent back to the factory for calibration or for repairs. If that is necessary, it is important to contact the manufacturer for their exact procedural requirements for receiving and servicing the meter. Most manufacturers will require that you sign-off that you have thoroughly cleaned the meter of any material or residue, including the crevices, recesses, gaskets, and cavities.

One of the remarkable things about Coriolis flow meters is their large turndown ratio. This means that one flow meter can accurately measure a wide range of flow rates. They typically offer a turndown ratio of 100 to 1. For a more in-depth explanation of what turndown is and the turndown capabilities of all the flow meter technology types, visit our article on flow meter turndown.

Coriolis flow meters come in many shapes in sizes. Some are remarkably small, like our HPC Coriolis Flow Meter and some are exceptionally large. We have built some of the largest custom Coriolis flow meters and some of the smallest.

To view all the Coriolis meter dimensions for our line, please visit our Coriolis flow meter products and refer to the corresponding product datasheet.

The initial cost of Coriolis flow meters is higher than most other flow technology types. However, they do not have moving parts to wear so they can deliver a longer service life than other flow meters that employ a more mechanical means of measurement. To determine the true cost of flow meter, you must also consider its overall value and that can include lost revenue from frequent downtimes for cleaning, longevity, and the assurance of process accuracy for optimum products.

The total cost of a Coriolis flow meter will depend on a multitude of things. While many manufacturers state a base price to begin with, every element needed that requires more production time or different/more materials will increase the cost. Some elements that increase the price of a Coriolis flow meter are line size and media compatibility that requires expensive exotic materials, high pressures, and high temperatures.

To estimate the cost of a Coriolis flow meter that meets all your exact application needs, please contact us for full pricing instead of comparing base prices online which may not represent the actual total cost of the flow meter.

Skip the potential for error and disaster by working directly one-on-one with the manufacturer. Because we make, sell, and support our products we are in a position to offer you a unique partnership experience in selecting or customizing a flow meter for your exact application needs. KOBOLD, and its Coriolis flow meter subsidiary, Heinrichs, have decades of experience in Coriolis flow meter design, production, and sales and can deliver exceptional customer service as a result. We are recognized worldwide as a leader in Coriolis flow meter innovation.

We also can manufacture solutions that other companies cannot and can accommodate more extreme application specifications like high flow, high pressure, and exotic metals. We were also the first to produce a OIML certified flow meter for the transfer of hydrogen gas to fuel cars. We have made some of the smallest and some of the largest Coriolis flow meters in the industry and look forward to partnering with you.

Learn more about why you should partner with KOBOLD for your application.