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Prior experience with existing Vector Averaging Current Meters (VACM) led us to design a much smaller and cheaper replacement. Existing units were large and expensive primarily because of the machined metal pressure case.


We experimented with urethane castings to produce lightweight inexpensive enclosures for instruments that would withstand most ocean environments. We found that simple, light weight and inexpensive castings could replace the machined metal housings for use in all but the greatest ocean depths. We developed the electronics to sense the rotation of a rotor driven by water movement, and a vane to sense the relative direction of water flow. AO developed its own flux gate compass to determine the VACM's orientation in the Earth's magnetic field. Pressure and temperature sensors rounded out the detection suite.

A processor accumulated data from the sensors and processed the information to calculate the direction and speed of water flow relative to the Earth's magnetic field. The data were stored in internal nonvolatile memory. Because the assembly was completely enclosed in the casting we had to develop a means to recover the data without opening the assembly. The Alpha Omega Inductive Communications Interface used coils inside the casting as half of a transformer, and coils on an external adapter as the other half.


The new AO VACM was a low cost, light weight replacement for the older instruments. It served as the precursor of an inexpensive Expendable VACM.

VACM Retrofit Expendable VACM Inductive Interface