Underwater sensors require either pressure and water resisting housings or pressure exposed but water isolated packaging. This paper describes types of housings and their characteristics.
Pressure exposed packages are lightweight and inexpensive, relying upon the inherent pressure tolerance of many electronic circuits and discrete components. But most sensors and complete instruments are more conservatively constructed, tested, and calibrated in dry accessible packages that are housed in pressure resisting cases.
Criteria of corrosion resistance, size, weight, cost, and compatibility with associated other housings and cables must be considered. Choices of material include glass, ceramic, aluminum, stainless steel, and titanium. Closures often influence choice of material. Design of closure from vacuum sealed dry lapped glass to O-ring seals offer economy versus user accessibility. Penetrators for electrical connections are easily installed in metal end caps but optical or inductive connections can be made through glass. Corrosion protection and/or isolation from dissimilar metals are essential with metal housings. Plastics, including fiber reinforced plastics, offer some of the advantages of metals with reduced corrosion but bring new concerns including cold flow and water wicking. Metal backed plastic housings obviate some of these concerns at a cost in complexity.
All of these play a role in design and selection of sensor or instrument housings. Experiences with most of these housings are presented with lessons learned and cost to benefit analysis is offered for each. This should serve as a guide for design of instrument housings for various applications
