A fiber optic sensing apparatus is provided to measure the relative reflections of two temporarily displaced signals. One of the signals is a reference signal and the other signal represents the magnitude of a sensed variable. A reference mirror is disposed at a preselected position along an optical fiber between a transmitter/receiver and a sensor mirror. The transmitter provides an energy pulse into a first end of the optical fiber. When the energy pulse encounters the reference mirror, a first portion of the energy pulse is reflected back toward the receiver which is located at the first end of the optical fiber. The remaining portion of the energy pulse continues toward the sensor mirror. A second portion of the energy pulse is reflected by the sensor mirror. The second portion is of a magnitude that is analogous to the sensed parameter. Fiber optic delay lines are provided between the reference mirror and the transmitter/receiver and also between the reference mirror and the sensor mirror. The delayed lines separate the reference pulse and signal pulse from other pulses which are caused by reflections at other components within the optical fiber, such as bulkhead connectors.