Problem
Many oceanographic instruments incorporate heavy and expensive machined pressure cases to protect the electronics from salt water and the pressures of the ocean depths. Often the majority of the cost of the instrument is this pressure case. Alpha Omega began experimenting with urethane castings to produce lightweight inexpensive enclosures for instruments that would withstand most ocean environments.
Solution
Two problems had to be solved to produce a reliable enclosure casting. First we had to determine which electronic components could withstand the large distributed pressures within the somewhat flexible castings. We used a pressure chamber to test circuits at pressures up to 8000 psi. Some components crushed at these pressures and others exhibited variations in their electrical properties. Careful circuit design overcame the variations and the fragile parts were avoided. When necessary, small parts like crystals were provided with miniature presure cases made of common materials like aluminum.
The second problem was providing a leak proof seal around wires and sensors that extended into the surrounding water. Again, a series of experiments revealed the combinations of casting materials and electrical insulation that bonded securely to give a water tight seal.
Results
AO has produced a variety of inexpensive and reliable instruments that use urethane encapsulation. This technique produces devices that can withstand all but the greatest ocean depths, at prices that allow several units to be purchased for the price of a single instrument with a machined pressure case.
