Density measurement

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Density is mass per unit volume. It is a characteristic property of a substance.

Generally, fluids are measured by relative density or specific gravity. Relative density is the density of the fluid to the density of reference fluid.

The measurement of density is crucial in many industries to maintain conditions. It gives complete chemical properties of a substance (composition or concentration).

The following are the ways to measure density:

  1. Hydrostatic pressure: This type of measurement relies on the difference in pressure at a constant height of the liquid. Consider a tank in which a liquid is filled, the height of the liquid is constant. Now the pressure change is measured, as change is a due change in density in the column.
  2. Radiation: Density measured by increased absorption of gamma radiation for an increase in the specific gravity of substance being measure. We need a constant gamma-ray generator and a detector. This type of measurement is often used in dredging where the density of the mud indicates the effectiveness of the dredging vessel.
  3. Vibration: By vibrating, an object in a fluid will increase the density. It is measured in two ways: one by measuring resonance when the object is energized constantly and changes in the amplitude of vibration can be measured when the object is struck periodically.
  4. Differential Pressure: Differential pressure is measured from two points from a fixed known distance apart.
  5. Temperature Effects: Density increase with the increase in temperature. For accurate measurement, the measurement of specific gravity must be corrected considering temperature effects.

There are other methods for measuring density; there is a wide range of applications like in thermal plants, food processing industries, etc.

Back to: Instrumentation and Control

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