Jul. 15, 2022
A Coriolis mass flow meter is known as a very accurate instrument and it has many benefits compared to other measuring devices. However, every measuring principle has its challenges, as also the Coriolis principle. It can be a real challenge using Coriolis instruments in low flow applications in the heavy industry where you may have to deal with all kinds of vibrations.
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, etc.
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 at the end of this article.
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.
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:
ㆍhigher driving frequencies
ㆍdual sensor tubes
ㆍdifferent sensor shapes
ㆍmass inertia (e.g. mass blocks)
ㆍpassive and active vibration compensation
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.
In an industry zone frequencies can be generated by:
ㆍenvironmentally related vibration sources (such as: truck, rail transportation, industry activities)
ㆍbuilding-based vibration sources (mechanical and electrical installations, like air conditioning) or
ㆍusage-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 minimise 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.
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 colour to a detergent it can result in differences in product colour by incorrect dosing and/or unexpected measuring signal behaviour. 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.
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:
ㆍIEC60068-2, Environmental testing for electronic equipment regarding safety
ㆍMIL STD 810, Environmental engineering considerations regarding shock, transport and use
There are a variety of Flowmeters available to measure different types of fluids like liquid, gas, slurry, vapour, etc. The vital criterion for the selection of the right Flowmeter is to know its intended use - which application it is required for or what it is going to measure.