Sub-sea level measurement is achieved using pressure sensors. Typically an ROV (Remotely Operated Vehicle) is lowered into the ocean with a pressure port either installed inside an enclosure or completely exposed to the seawater. As the ROV is submerged, water pressure is exerted on the diaphragm of a pressure sensor.
The deeper the system is submerged, the higher the pressure.
By calculating salt water density at 1.025 (or 2.5% more dense than fresh water at 4°C) a correlation between pressure and output signal can be made to measure equipment depth.
Pressure sensors submerged in seawater need certain mechanical considerations to survive the corrosive environment.
American Sensor Techno- logies packages its AST 4000 Series of Pressure Sensors with all 316L stainless steel wetted parts including the pressure sensing element, housing and electrical connection to survive sub-sea environments.
Even deep in the ocean where oxygen levels are low and water movement continuous, pitting and crevices of the pressure sensors is minimal due to the construction.
Because the pressure sensors have a one-piece 316L construction and a thick diaphragm membrane without any welds or O-rings the sensors are ideal for sea level measurement.