ASME MFC-11 pdf download Measurement of Fluid Flow by Means of Coriolis Mass Flowmeters
Repeatability, expressed as a percentage of the reading, may also be a separate parameter.Accuracy and repeatability statements are usuallymade at reference conditions that are specified by themanufacturer.These reference conditions shouldinclude temperature, humidity, pressure, fluid densityand flow range.
3.3 Factors Affecting Mass Flow Measurement
3.3.1 Density and Viscosity. A broad range of densi-ties and wiscosities have a negligible effect on the Coriolisflowmeter performance capability, consequently, com-pensation is usually not necessary. (See para. 4.4.8 forother viscosity effects.)
Density and viscosity variations can induce an offsetin the Coriolis flowmeter output at zero flow. Thus, itmay be necessary to check the flowmeter zero at theprocess conditions.(See para.3.4)
3.3.2 Multiphase Flow.Multiphase applicationsinvolving nonhomogeneous mixtures can cause measurement errors and in some cases stop the Coriolisflowwmeter operation.(See para.4.4.3.) Increased nonhomogeneity of the liquid mixture can lead to deteriorationin performance and may result in loss of signal attributedto the absorption of the oscillation energy required tovibrate the flow sensor.(See Section 8.) n liquid servicecare should be taken to ensure that gas bubbles and /orsolids are not allowed to accumulate in the sensor. Ingas service, means should be provided to prevent liquidcondensate or oil carryover from a compressor fromsettling in the sensor. Flow velocity should be sufficientto carry gas bubbles, pooled liquids, or settled solidsout of the sensor.
results will beThe overallmeasurement oertormanceleast affected when the multiphase period occurs at thebeginning and/or end of the measurement process andthe duration of this period is veryshort compared tothe entire measurement period
While the Coriolis flowmeterwill not be damagedwhen beginning and ending the measurement with anempty flow sensor, the results of the measurement maybe outside the expected performance accuracy. ACoriolis flowmeter systemsolution may be designedcapable of starting and finishing the measurement pro.cess from an empty or partially full pipe and/or sensorcondition. The system may include, but is not limitedto, an air/vapor eliminator for liquid service or a liquidtrap for gas service, a reverse flow check valve, and aflow computer, or transmitter software algorithms usedto manage expected measurement errors. Contact theCoriolis flowmeter manufacturer for additional infor-mation regarding this type of application.
3.3.3 Temperature. Temperature changes affect themechanical structure of the flow sensor and compensation is necessary. This compensation, based on an integral temperature sensor, is performed by the transmitter.