densimetre

A densimetre is an instrument used to measure the density or specific gravity of a substance. It is applied to liquids, gases and solid materials by determining mass per unit volume or by comparing the sample to a reference substance, typically water. The term is used interchangeably with density meter or densitometer in some contexts.

Various operating principles are used. Simple hydrometers rely on buoyancy: a calibrated float sinks to a level that corresponds to density. Pycnometers determine density by measuring the mass of a known volume. Modern laboratory densimetres commonly use an oscillating U‑tube: the sample’s density changes the tube’s natural frequency and is converted to a density reading with high precision. Industrial and geotechnical instruments include nuclear (gamma‑ray) densitometers for in situ soil and asphalt density, and ultrasonic or optical methods for noninvasive measurements.

Densimetres report results in units such as kilograms per cubic metre (kg/m3), grams per cubic centimetre (g/cm3) or as dimensionless specific gravity. Accuracy depends on method, instrument quality and temperature control; many instruments include temperature compensation or require calibration with reference fluids. Limitations include sensitivity to air bubbles, contaminants and sample heterogeneity.

Applications span chemistry and pharmaceuticals, food and beverage quality control, petroleum and petrochemical industry, environmental monitoring and construction materials testing, as well as continuous process control in manufacturing.