ASME MFC-11:2006 pdf free download

ASME MFC-11:2006 pdf free download Measurement of Fluid Flow by Means of Coriolis Mass Flowmeters
Repeatability, expressed as a percentage of the read-ing. 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 density,and flow range.
3.3 Factors Affecting Mass Flow Measurement
3.3.1 Density and viscosity. A broad range of densi-ties and viscosities have a negligible effect on theCoriolisflowmeter 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 mea-surement errors and in some cases stop the Coriolisflowmeter operation.(See para.4.4.3.) Increased nonho-mogeneity 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.) In liquid service,care 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.
The overall measurement performance results will beleast affected when the multiphase period occurs at thebeginning and/ or end of the measurement process andthe duration of this period is very short compared tothe entire measurement period.
While the Coriolis flowmeter will 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 system solution may be designed,capable 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 compensa-tion is necessary.This compensation, based on an inte-gral temperature sensor, is performed by the transmitter.
However, large differences in temperature between theoscillating tube(s) and the ambient temperature cancause errors in the temperature compensation.The useof insulation materials can reduce these effects.
NOTE: The temperature measured in the Coriolis flowmeter isthat of the oscillating tube walls and may not be the same as theprocess fluid temperature.
3.3.4 Pressure.Coriolis flow sensor designs varysignificantly between manufacturers and even withinthe designs of a single manufacturer. Some designs orflow sensor sizes may be more susceptible to pressureeffects than other designs.Thus,it is not possible toherein describe specific installation recommendations.Check with the manufacturer for recommendations andprocedures to adjust the calibration factors or enableactive compensation for pressure effects.
Pressure changes can also induce an offset in theCoriolis flowmeter output at zero flow. This effect maybe eliminated by performing a zero adjustment (see para.3.4) at the process pressure.
3.3.5 Installation. Stresses exerted on the flow sen-sor from the surrounding pipe work can introduce anoffset in the Coriolis flowmeter output at zero flow.Thisoffset should be checked after the initial installation orafter any subsequent change in the installation. A zeroadjustment (see para.3.4) should be performed if theoffset is unacceptable.
3.4 Zero Adjustment
After the Coriolis flowmeter installation is complete,a zero adjustment may be needed. It is recommendedthat zero be checked and adjusted if the offset is unac-ceptable. Zero adjustments should be made accordingto the manufacturer’s instruction. In general, to checkor adjust the zero flow, the flowmeter should be full ofthe process fluid and all flow stopped.Zero adjustmentshould be made,if possible, under process conditionsof temperature, pressure, and density. It is essential thatthe fluid remain stable and there are no bubbles or heavysediment and no fluid movement. Therefore, it is recom-mended that both upstream and downstream valves areclosed during the zero adjustment process.
3.5 Calibration of Mass Flow
3.5.1 Definition
calibration:
(a) the process of comparing the indicated flow to atraceable reference standard
b)the process of adjusting the output of a device tobring it to a desired value, within a specified tolerancefor a particular value of the input
3.5.2 Calibration Guidelines.The uncertainty of thecalibration can be no less than the uncertainty of thereference standard and any errors that are introducedduring the calibration.