Ford Motor Company had a requirement to measure fan belt vibration on their 4.6 liter Cobra-Mustang engine. While this sensor was to be used in the laboratory, it would also be used for field testing of this engine. The general operation temperature was -40 to 120 degrees C, but there was an engine 'soak-back' requirement of up to 200 degrees C. The vibration requirement was 3g continuous at 10 Hz with 20g shock. Humidity was 0-95 percent. Without active cooling, the temperature environment eliminated engine mounted electronics and with it some more common approaches such as laser triangulation based sensing. A laser radar concept was developed which features remotely located electronics, fiber optic delivery and return of the signal and an engine mounted optic head. The three lens design of the receive optics is a compromise choice designed to maximize power at the receiver over the full travel of the belt. The electronic scheme consists of a time-to-amplitude converter based on a precise time interval derived from the phase difference of logic level pulse trains which in turn are formed by the 'exclusive O Ring' of the transmit and receive pulses. In practice, a 10 MHz pulse train is transmitted to the vibrating belt which coupled with some fast electronics results in about 1 0.1 mm resolution, sufficient for this application.