How to determine the density value of mass flow meter?

The density displayed by the mass flowmeter is the density under the working conditions. Before calculating the density coefficient, the density displayed by the mass flowmeter must be corrected to the same condition as that of the reference device, or the density measured by the reference device must be corrected to the working condition of the mass flowmeter. Under certain conditions, this procedure cannot be ignored. The average density under the working conditions of the mass flowmeterρm, can take a certain time interval to take the average value, or take the ratio of the mass to volume of the corresponding interval. Corrected to the density under the measurement conditions of the reference device, the density is calculated according to the following formula:ρm(s)=ρm/(Ctlm X Cplm) (3) where,ρm(s)— The average density of the mass flow meterρm corrected to reference densityρs Density under the same conditions; Ctlm— Liquid temperature correction coefficient at the mass flow meter, Ctlm=1+γ(t-to), where,γis the temperature coefficient of liquid density (°C-1), obtained from relevant standards according to the density range, t is the average temperature of the liquid (°C), and to is the temperature at which the reference device measures the density; Cplm— Liquid pressure correction coefficient, calculated according to the following formula: Cplm=[1-F(Pm-Pe)] (4) where, F— Compressibility factor (kPa-1), according to liquid densityρm, temperature t look-up table or calculation; P.— Reference device to measure density pressure (gauge pressure) kPa); Pm— The average pressure (gauge pressure) (kPa) of the mass flowmeter under working conditions. In the same principle, when using a closed pycnometer to measure the density under reference conditions, if there is a certain pressure in the bottle during measurement and the temperature deviates from the reference temperature, the measured value of the pycnometer can be corrected to the reference condition according to the following formula :ρ(s) =ρs/(Ctlm X Cplm) (5) where,ρ(s)— Will be a certain temperature. Density under pressure corrected to density at reference conditions; Ctlm— Correction factor for pycnometer liquid temperature, Ctlm=1+γ(to), where,γis the temperature coefficient of liquid density (°C-1), t is the liquid temperature of the pycnometer (°C), to is the reference temperature (°C); Cplm— Liquid pressure correction coefficient, calculated according to the following formula: Cplm=[1-F(Ps-Pe) (6) where, F— Compressibility coefficient (kPa－1), according to liquid densityρs, temperature t look-up table or calculation; P.— Saturated vapor pressure (gauge pressure) of the liquid in the pycnometer of the reference device (kPa): Ps— The internal pressure (gauge pressure) of the reference device pycnometer (kPa). 4. Density coefficient calculation and use The density coefficient is the ratio of the density measured by the reference device to the density measured by the instrument under the same conditions. The formula is: DF=ρs/ρm (7) where, DF— Density coefficient for mass flow meter density determination, dimensionless quantity. The density coefficient first confirms the reliability of the density measurement results of the density meter, and can calculate the density measurement error; secondly, in order to use the density meter scientifically and reasonably, Micro Motion clearly requires in the 'Mass Flowmeter Calibration Manual', The actual value of mass flowmeter density measurement should be calculated according to the following formula:ρactual=DF XρMeasured (8) where,ρactual— Actual value of mass flow meter density measurement;ρMeasured— Mass flow meter density measurement display value. The author believes that the calibration and use of the mass flowmeter density coefficient will have a positive impact on the use of the mass flowmeter; at the same time, the author also reminds users that the method introduced in this article is not a standard. It is recommended that users calibrate the density coefficient of mass flowmeters or online density meters When doing so, try to explore the possibility of adopting relevant national standards or standards, so as to realize the control of the measuring equipment and the measuring process.

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