The Coriolis principle
Coriolis mass flow meters offer many benefits above other measuring devices. First of all, Coriolis flow instruments measure direct mass flow. This is an important feature for the industry as it eliminates inaccuracies caused by the physical properties of the fluid. Besides this benefit, Coriolis instruments are very accurate, have a high repeatability, have no moving mechanical parts, and have a high dynamic range.
Do vibrations influence the measuring accuracy of a Coriolis mass flow meter?
In industrial applications, all kinds of vibrations with different amplitudes are very common. A Coriolis meter measures a mass flow using a vibrating sensor tube, which fluctuation gets intentionally out of phase when the fluid flows through. As explained in the video.
This measurement technique is somewhat sensitive to unwanted vibrations with a frequency close to the resonance frequency of the sensor tube (this depends on the sensor tube design, e.g. 360 Hz) or a higher harmonic of this frequency (see picture).
Coriolis flow meters are only sensitive for the resonance frequency or a higher harmonic of this frequency
The likelihood of the occurrence of these unwanted vibrations is higher in an industrial environment. Coriolis flow meter manufacturers do their utmost to reduce the influence of vibrations on the measured value by use of common technical solutions, such as using:
- higher driving frequencies
- dual sensor tubes
- different sensor shapes
- mass inertia (e.g. mass blocks)
- passive and active vibration compensation
- pigtails
So yes, vibrations can influence the measuring accuracy of your Coriolis flow meter, but only if the vibrations have a frequency close to the resonance frequency. What can you do about this? This depends on the kind of vibration.
What kinds of vibrations do exist?
In an industry zone, frequencies can be generated by:
- environmentally related vibration sources (such as, trucks, rail transportation, industry activities)
- building-based vibration sources (mechanical and electrical installations, like air conditioning)
- usage-based vibration sources (installed equipment and machines, e.g. pumps, conveyor belts).
These vibrations travel through a medium like the floor, in the air, through pipes, or the fluid itself. If these vibrations disturb the Coriolis frequency, the measured flow could be incorrect in some extent.
To minimize the effects of vibration, it is useful to identify these sources. Sometimes, it is possible to move the flow meter just a little bit, turn it (Coriolis flow meters are, in most cases, less sensitive to vibrations if the meter is rotated 90 degrees), make use of a big(ger) mass block, use flexible tubes or U-bend metal tubes or use suspension alternatives.
How could you check the performance of a Coriolis flow meter?
A well-performing flow meter and controller will give the best process result. Therefore, it is advisable to test a Coriolis flow meter in your application if you expect heavy industrial vibrations before you trust it to the full extent. Be careful when filtering the measuring signal. In some cases, it makes sense (e.g. when a quick response isn’t required), but if you want to test the performance of a flow meter, filtering could blur your judgement.
If, in specific circumstances the Coriolis flow meter isn’t performing the way it should, the operator will see a shift in the process output – for example in an application dosing color to a detergent it can result in differences in product color by incorrect dosing and/or unexpected measuring signal behavior. In these cases, it makes sense to check the raw measuring signal (without filters!), because it will give you a good insight in the performance of the flow meter. Ask your flow meter manufacturer how to switch off all signal filtering.
Standards regarding vibrations
Remarkably, the influence of external vibrations is not clearly defined in a standard for Coriolis flow meters. Several standards are written about vibrations, but none in respect to measuring accuracy in relation to vibrations. However, two useful standards in relation to vibration are:
- IEC60068-2, Environmental testing for electronic equipment regarding safety
- MIL STD 810, Environmental engineering considerations regarding shock, transport and use
As a user of Coriolis flow meters, it is important to understand your application, especially about potential external vibration sources. As a low flow Coriolis specialist, we work together with knowledge partners like the University of Twente and TNO (a Dutch organization for applied scientific research) to get a continuously improved understanding of this topic.
With in-house test facilities, we are able to do special vibration tests. Together with the experience we gained from customer applications and custom-made solutions, we are always aiming to improve our Coriolis flow meters to give our customers the best performance they need.
Need more information?
Are you interested or do you want to learn more about this subject?
Related blog articles
Development of micro-Coriolis flow sensors
Coriolis flow meter working principle
10 Tips for installing flow instruments