Emerson Exchange 365

Hi Alan,

technically speaking the meters operate perfectly fine, but the application is not within the recommended scope.

The density measurement with a coriolis meter is based on the natural frequency of a system which is made up by the mass of the coriolis tubes and the mass of the fluid they are filled with.
As the mass and the volume of the tubes is constant the shift in frequency is based on the change in density of the fluid that fills the tube volume.

In the technical data sheet there is an accuracy stated for the density measurement of liquids and slurries, but not for the density measurement of gases.
Reasons for that are the compressibility of the gas and the very small mass of gas in the tubes compared to the mass of the tubes.

Applying the density accuracy of liquids to the gas would lead to the following:
The stated accuracy of +-0.5 kg/m³ equals +- 0.031 lb/ft³.
At a given density of 0.59 lb/ft³ you would have to expect an error of at least +- 5.3 %.

Does the application require an exact measurement of the density, which is out of scope or would it be good enough to see a trend, which should work?

To wrap this up, the meter is working fine within technical and physical limits.

Best regards

Thomas

In reply to Thomas Otten:

Hi Alan.

Coriolis meters are extremely good at measuring gas flow in mass or in standard volume units. However, for the reason Thomas has already explained, they are not as accurate for measuring actual density. If you need to measure actual density, we have some other excellent products at Micro Motion called the GDM (Gas Density Meter) and the SGM (Specific Gas Meter) that are designed specifically to measure the actual density and specific gravity of live gas flow streams.