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            Density/Mass Proving for Coriolis meters using inferred mass method


Density proving for Coriolis and Densitometers, using our Pycnometer, we can prove the density registration on relatively clean products. We use MPMS API Chapter 14.6 for our procedures and requirements for proving. It requires a density meter proof to have a minimum of 2 runs that repeat within .05%. 

 

Pycnometer Slip stream, Temperature has to be within .02 F between inlet and outlet

Mass Proving

When a Coriolis meter is configured for mass measurement and is being proved against a volumetric prover, the prover volume must be converted to mass units to allow comparison to the mass measured by the meter. In order to convert the prover volume to mass, an accurate density determination at the prover must be made. Any error in the determination of the density will result in an equivalent error in the meter factor. The fluid density can be determined from any of the following methods:

 

1. Calculated from measured temperature

and pressure. This method is limited to

well characterized products of known

composition.

2. Determined from an in-line density meter

located at the prover. A density sampling

system is used to determine a density

factor for the density meter.

3. Determined from the Coriolis meter

density measurement. The Coriolis meter

should be located close to the prover. A

density sampling system is used to

determine a density factor for the Coriolis

meter.

 

For many process fluids the actual flowing density (not the density at standard conditions) does not remain constant, due to fluctuations in product composition or process conditions. This is particularly true of light hydrocarbons. If the fluid density varies while the meter is being proved, it will be difficult to obtain acceptable repeatability, and the meter factor may be in error. In this situation, it is recommended that the average fluid density during the proving run be determined, and this average density be used in the meter factor calculation. If a density measurement device is used, it will be necessary to prove the density measurement to obtain a density factor (DF ). It would be reasonable to prove the density measurement every time the Coriolis meter’s flow measurement is proved. The frequency of  determining the density factor may be reduced if the density factor continually remains consistent from one proving to the next.

 

Imagine from "Proving Coriolis Meters"1998, Micro Motion, Inc.

 

 

A significant difference between mass and volume proving is the method that is used to determine proving repeatability. For volume to volume proving, the repeatability can be based on the number of pulses accumulated. However, for mass-to-volume proving, the pulse repeatability would not account for variations in product density. If the product density were to vary during the proving, the pulse repeatability may be unacceptable. Therefore, when performing a mass-tovolume proving, the repeatability should be based on the meter factor for the individual provings, not the accumulated pulses.

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