Density and Viscosity Sensors

When product flow is measured, it's affected by density, viscosity, and temperature of the product. Density is also measured when products such as maple syrup, pudding, paint, petrochemicals, and others are produced. Density is a measurement of mass per unit volume and it's also called specific gravity. Specific gravity is a measurement of the density of a product at a set temperature compared to the density of water. The specific gravity of water is 1. A simple way to discuss density is to define how "runny" something is at a set temperature when compared to water. The product will be more or less runny than water when the two are compared at the same temperature.

The formula for density is:

D = M/V

where M is the mass of the liquid and V is the volume.

The common units for density are grams per cubic centimeter and pounds per cubic foot. The formula for specific gravity is the density of a liquid at a set temperature divided by the density of water at the same temperature. it's important that the temperature of the liquid and the temperature of water during the comparison are identical.

SpGr=(D_L at T₁)/(D_W at T₁)

where D_L is the density of the liquid being measured.
T₁ is the control temperature for both liquids.
D_W is the density of water (approximately 62.4 lb/ft³)

Exercise

Determine the density of a latex paint that has mass of 64 lb. and a volume of 1 ft³. Use the density to calculate the specific gravity of the paint at 81°F. The specific gravity of water at 81°F is 1, and the density of water is 62.4 lb/ft³.

Solution

Use the formula D = M/V to determine the density: D = 64 lb/ft³

Use the formula SpGr=(D_L at T₁)/(D_W at T₁) to calculate the specific gravity.

Sp Gr = ((64lb/cu. ft.)/( 62.4lb/cu. ft.))

Sp Gr = 1.02

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