Electromagnetic flowmeter

Yes, electromagnetic flowmeters deliver volumetric flow rate; if you know the density of the fluid, you can convert this volumetric flow rate into mass flow rate by multiplying it by the density factor. .

You’re welcome! Feel free to ask more questions if you have any .

Those that are not sensitive to temperature changes are fine. Sensitive to temperature compensation

In certain processes, for specific known fluids, the density varies little within a certain range; by presetting a relatively accurate average density value for conversion, it may be possible to meet the basic requirements for mass flow measurement. However, in complex operating conditions where high precision in mass flow rate is required, or where the fluid density varies significantly, it may not be suitable; in such cases, a dedicated mass flow meter is needed to directly measure the mass flow rate.

If the medium density remains constant, it is possible to add secondary meters in the DCS configuration or on-site for conversion; however, this is not feasible in the pharmaceutical industry where GMP compliance is required, as it presents difficulties from a documentation standpoint

To convert volumetric flow rate to mass flow rate, it is necessary for the density of the medium to remain constant; otherwise, changes in density can lead to significant errors. Additionally, the effect of temperature on density must also be taken into account. If it is an analog signal output, simply use a data conversion unit to redefine an appropriate quality unit. If it is a pulse signal, then it is sufficient to redefine the mass flow rate represented by one pulse. If the medium density changes significantly, it is advisable to add a density detector, and then perform integrated measurement of the mass flow rate based on the changes in volume flow rate and density.

Just go with a mass flow meter; it’s just a bit expensive. For feeding or discharging, you can use weighing or level measurement (differential pressure level gauge) to indirectly obtain the flow rate. If it is a pure liquid substance, the density depends only on temperature; a thermometer is used, and a program is written in the DCS to determine the density based on the temperature value. The density is then multiplied by the volume to obtain the flow rate.

Using a mass flow meter, will the measurements be accurate if the density changes frequently? Thank you!

No problem; it is detected using two U-shaped tubes. There are two coils at the inlets and outlets of these U-shaped tubes, which generate oscillations. The vibrations at both ends of the U-shaped tubes are then measured. The oscillations produced by these coils cause resonance in the U-shaped tubes at a certain frequency, and it is through this resonance frequency that the density of the liquid flowing inside the U-shaped tubes can be determined, as the resonance frequency is proportional to the density. If the liquid in the two U-tubes is fully filled and stationary, the phases of the detected inlet and outlet frequencies are the same. For a sine wave, phase and amplitude are important parameters for describing it. If the liquid is flowing, the phases of the oscillation frequencies at the inlet and outlet of the two U-tubes will differ, and the phase difference is proportional to the mass flow rate. It is unaffected by pressure, density, and temperature. If the substance inside is water, the resonance frequency is around 80 Hz; for simplicity’s sake, let’s assume it’s 100 Hz. In that case, the period of the sine wave is 10 milliseconds. Typical mass flow meters can achieve an accuracy of plus or minus 0.1%. Assuming that the phase difference between two sine waves at full scale is 180 degrees, then 1000 subdivisions are necessary within 5 milliseconds, meaning each subdivision corresponds to 5 nanoseconds. An increase of 5 nanoseconds in delay represents an increase of 0.1%.