A new linear variable-differential transformer (LVDT), the submersible SSIR 937, from Macro Sensors, Pennsauken, N. J. can withstand deep-sea environments with external pressures up to 5,000 psi (7,500 psi of proof pressure). Like all LVDTs, the SSIR has excellent resolution and comes in 2, 3, and 4-in. measuring lengths. Other ranges can be custom ordered. A high-pressure Seacon-Branter subsea connector is standard. A welded connector is optional.

To get measurement signals to the surface, the output signal travels through a minimal number of pressure-sealed connections and I/Os, thanks to a 4 to 20-mA, two-wire, loop-powered I/O, which also limits noise on transmission lines. Users on the surface can also make offsets in the data-acquisition systems on the surface.

In operation, the LVDT’s primary winding is energized by ac current, known as the primary excitation. The LVDT’s electrical output signal is the differential ac voltage between the two secondary windings, which varies with the axial position of the core within the LVDT coil. Usually this ac output voltage is converted to high-level dc voltage or current that is more convenient to use.