Measurement issues of mass flow meters
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The mass flow meter installed on the product transfer pipeline provides inaccurate readings; upon checking the design parameters, the actual specific gravity of the material is 0.92, while the value specified in the design is 0.89. I’m not in the instrumentation field; specialists in that area state that the measurement of mass flow meters has nothing to do with specific gravity. May I ask, is mass flow measurement related to the specific gravity of the fluid? What are the factors that affect measurement accuracy?
Working principle: The fluid flows from A to B at a velocity V within a branch pipe, which is placed in a system rotating at an angular velocity ω. Let the axis of rotation be X, and the point of intersection with the tube be O. Since the fluid particles inside the tube move axially at a velocity V and radially at an angular velocity ω, they are subjected to a tangential Coriolis force Fc. This force acts on the measuring tube, in directions opposite to each other on either side of point O, with equal magnitudes; namely, δFc = 2ωVδm. Therefore, by directly or indirectly measuring the Coriolis force generated by the fluid flowing within the rotating tube, it is possible to determine the mass flow rate. This is the basic principle of the Coriolis mass flow meter. In principle, the magnitude of the Coriolis force acting on the measuring tube depends only on the mass flow rate of the fluid, and is independent of the fluid’s density and viscosity. But changes in density result in additional inertial forces ； Changes in viscosity result from different adhesive layers on the inner wall of the measuring tube, thereby producing varying boundary layer effects. As a result, the mass distribution within the measuring tube becomes unstable, affecting the accuracy of the measurement results.
The presence of liquid in the gas, or gas in the liquid, can affect the accuracy of the measurement. Improper installation can also affect measurement accuracy; for example, the verticality of the container is important – the container used for measuring gases should be oriented upward, while those used for measuring liquids should be oriented downward. Additionally, the pipes should not vibrate.
If used continuously, the error is small, within 0.2%； But when used intermittently, it’s hard to say about the accuracy
When using a Coriolis flow meter, the density, temperature, and pressure of the medium have little impact on the pressure experienced by the flow meter.
The main issue with mass flowmeters is related to setting values; it seems you’re referring to the conversion from volume to mass. Otherwise, density does not affect the accuracy of the measurement. Check the parameter settings.
The measurement value of a Coriolis flowmeter is calculated after compensating for pressure, temperature, and density. Therefore, changes in these three parameters will not affect the measurement accuracy of the mass flow meter. If it seems inaccurate, you can perform an online full-scale calibration to adjust the zero point, and then check how it performs. Generally speaking, mass flow meters have relatively high accuracy; when compared to other types of meters, it is advisable to trust mass flow meters more.