An oil-filled and double bellows-sealed LVDT assembly from Macro Sensors supposedly enhances the reliability of multiple redundant LVDT-based extensometers. The LVDT assembly is designed from 316 SS and Inconel 625. According to Macro Sensors, these materials enable the instrument to operate for at least 10 years. The extensometer housing can be outfitted with mechanical terminations to facilitate connection to the structural members. A 4-20 ma loop-powered I/O is utilized.