A density scale, density meter or digital hydrometer, measures the specific gravity, density, American Petroleum Institute (API) gravity and density-related values of liquids and solids quickly. The most common scales of specific gravity are API gravity, Baume, Brix, Oechsle, Plato, and Twaddell. Density units are typically displayed in kilograms per cubic meter (kg/m3), per the International System of Units (SI). Hydrometer readings also can be displayed as kilograms per liter (kg/L), grams per milliliter (g/mL) or metric tons per cubic meter (t/m3).
The density meter measurement of liquids is most commonly done on battery acids, various alcohols, food solutions, petroleum and other custom liquids. Oscillating tube technology is the most common and accurate type of liquid density measuring technology for handheld density meter devices. The eigenfrequency of the tube is influenced by the sample’s mass, then the mechanical oscillation of the tube is converted into an electronic voltage of the same frequency and can be converted into a sample density based on a simple formula. This type of density measurement is highly accurate and automatically temperature compensated.