manomètre

A manomètre (manometer) is an instrument for measuring pressure by balancing a fluid column against a reference pressure. In a simple U-tube design, the pressure difference ΔP between two points equals ρ g h, where ρ is the liquid density, g the acceleration due to gravity, and h the height difference of the liquid. Manometers indicate gauge pressure (relative to atmosphere), absolute pressure, or differential pressure depending on configuration and reference.

Common types include U-tube, inclined, and differential manometers. A single-column open-tube manometer measures pressure against the atmosphere; a closed-tube manometer can measure absolute pressure when one side is sealed or evacuated. A differential manometer compares two pressures. Digital manometers convert hydrostatic pressure into electrical signals for readout and data logging.

Materials and fluids vary: mercury is dense but hazardous; water, oil, or other liquids are common. Temperature and liquid density affect readings, so calibration and temperature compensation are important. Proper anchoring, isolation from vibration, and correct zeroing are essential for accuracy.

Applications span laboratories, meteorology (barometers are a type of manometer), HVAC, process control, and instrumentation calibration.

Origin: The concept emerged in the 17th century with Torricelli’s experiments leading to the mercury barometer. The term derives from Greek roots meaning "pressure" and "measure".