Pressure sensors for installing underwater which are constructed to prevent water entering sensitive components and causing damage to the sensor. Underwater pressure sensors are IP68 rated for permanent use underwater to a specified maximum water depth.
- LMK 487 Submersible Ballast Tank and Draught Level Pressure Transmitter
- DMK457 Marine Approved Pressure Transmitter
- LMK387 Cleanable Sewage and Sludge Pressure/Level Sensor
- DMP457 Marine Approved Pressure Transmitter
Applications that use underwater pressure sensors.
Level of water inside hollow structure below water line
There many types of structures permanently fixed to the seabed or river bend, and some of these structures have a hollow interior. Since there maybe equipment below the water surface line or concerns over long term corrosion of the internal structure, it is necessary to monitor and control the level of any water that has seeped into the structure. A pressure sensor is fitted to the outer case of the underwater structure at the lowest necessary point to measure the head of water above that point that has accumulated in the hollow space.
Ballast tank level measurement
Ballast tanks are fitted to underwater equipment and structures to control buoyancy. Pressure sensors are fitted to the external bottom surface of the ballast tank underwater to measure the head pressure of water inside the ballast tank, which is used to calculate the quantity of water and ultimately the amount of buoyancy.
Ballast tank blow pressure
Compressed air or other gas is used to control the level of water in a ballast tank. To reduce the water level the air pressure is raised, and likewise air pressure is lowered to increase the water level. Pressure sensors are fitted to the external top surface of ballast tanks to measure the air pocket inside the ballast tank.
Pressurised pipework, vessel and systems
Where there is a pressurised equipment underwater, it is often required to monitor the pressure directly, and this may require the fitting a pressure sensor externally underwater to measure the working pressure.
Help with selecting, installing and using underwater pressure sensors.
Make sure it will remain watertight at the required depth.
An underwater pressure sensor should have an IP68 rating for permanent immersion, and be rated to the required depth or external pressure.
Surface cable length
Don’t forget to consider the cable length required above out of the water.
If the sensor cable is run to the water surface, ensure that you leave enough cable to reach the surface plus the necessary length of cable to reach the termination point. When specifying a pressure sensor it’s very easy to mistakenly select a cable length that corresponds to the required depth and not account for the extra cable required to make the link to the surface instrumentation which could be several metres away from the location where the cable runs below the surface.
Removable cable connection
Always follow the manufacturer’s procedure for breaking and re-making an underwater cable connector.
Follow installation instructions precisely when using a removable cable assembly, since underwater proofing maybe compromised if incorrectly fitted. During the service life of a re-mountable submersible cable connection, it is sometimes necessary to disconnect the watertight connection for various reasons, such as replacing the pressure sensor or cable assembly. When the connection is re-made it is important that you follow the advice in the operation manual to ensure the best chance retaining the integrity of the underwater seal. This submersible IP rated seal is only guaranteed if you follow the re-fitting procedure precisely.
Water often includes other chemicals and minerals and than make it highly corrosive to exposed pressure sensor components.
Select materials that are going to provide long term corrosion free protection to the type of water the pressure sensor will be immersed. Groundwater can contain high level of minerals creating a acidic or alkaline solution, and seawater is highly corrosive to many metals including stainless steel.
Underwater cable termination
If the electrical connection to the pressure sensor is to be terminated underwater then it becomes difficult to provide a true atmospheric pressure reference. This is required for vented gauge reference pressure sensors which rely on a connection between surface ambient air pressure and the rear or negative side of the measurement diaphragm. However, many underwater applications do not require a surface atmospheric pressure reference, and instead the sensor is referenced to the ambient air pressure inside a watertight enclosure where the cable is terminated. Alternatively an absolute, sealed gauge or differential pressure range can be used, since either of these do not need a physical reference pressure or a vented reference tube running through the cable.