Advances in instrumentation now make it possible to measure accurately flow of such diificult-to-measure liquids as mining slurries. A mass flowmeter, which introduces no restrictions in the line, will measure the mass flow of slurry equal to the volume flow times the mass/unit volume.
In the mass flowmeter system a volume flow measurement is electrically multiplied by a density measurement in order to give mass flow.
The magnetic flowmeter, which is used for the volume measurement, operates on the principle of a
generator. This principle states that when a moving conductor cuts lines of force in a magnetic field, a voltage is induced in it. Moreover, if the dimensions of the conductor remain constant, then the induced voltage is directly proportional to the velocity of the conductor.
The metering tube is constructed of nonmagnetic stainless steel. To prevent short circuiting of the generated voltage, the tubes are lined with a suitable liner, depending upon the corrosive, erosive or other properties of the liquid or slurry to be measured.
Because the meter electrically averages all of the incremental velocities in an irregular flow profile, it is ideally suited for turbulent flow and suspended solids. Straight runs of pipe are therefore not required. The transmitter can be installed close to pipe elbows, valves, or even adjacent to a pump discharge without suffering the slightest loss of accuracy.
The gamma gauge density cell operates on the basis that gamma rays are absorbed as they pass through various materials, this absorption being a function of the density of the materials. When rays from a radiation source are directed through the flowing liquid, the amount of radiation reaching the detector (opposite the source) depends on the mass of the intercepting materials. The detector allows a current to flow which is proportional to the amount of radiation it receives.