djupmätare

Djupmätare, or depth gauge, is an instrument used to determine the depth of a liquid from the surface to the bottom, most commonly water. It operates by measuring the hydrostatic pressure at a given depth and converting that pressure to depth using the relation depth ≈ (P − P0) / (ρ g), where P is the absolute pressure at depth, P0 is the atmospheric pressure at the surface, ρ is the fluid density, and g is gravitational acceleration. Because density varies with salinity and temperature, and atmospheric pressure changes, depth readings may require calibration for accuracy.

The term is used in several domains. In diving, a depth gauge is essential safety equipment and can be a standalone instrument or part of a dive computer that also tracks bottom time, ascent rate, and decompression limits. In marine navigation and oceanography, depth measurement may also be performed with electronic depth gauges and related devices, though these often rely on different principles. In older or simpler applications, depth was measured with a weighted line or sounding line.

Depth gauges come in mechanical and electronic forms. Mechanical depth gauges typically use a sealed capsule, bourdon tube, or similar mechanism connected to a display; they are rugged and do not require power but may need periodic calibration. Electronic depth gauges use pressure transducers and onboard electronics, offering higher accuracy, automatic calibration, and data logging. Some systems pair a pressure-based depth gauge with sonar-based depth finders or echo sounders to map seabed profiles, especially in shallow waters and surveying.

Typical limitations include sensitivity to temperature and salinity changes, sensor lag during rapid movement, and zeroing errors at the surface. Proper calibration and maintenance are important for reliable measurements.