A fiber optics level sensor (FOLS) or flow sensor (FOFS) system for use in hazardous environments, process control, and industrial and environmental control applications. The system includes a pair of fiber optic bundles arranged between a remote sensor and a control module. The remote sensor detects the position of a movable vane--which is mechanically coupled to a float in the sensed environment--by means of a transmission gap between confronting ends of the pair of fiber optic bundles. The control module includes a light output device driven by an oscillator which thereby generates pulses of light which are optically coupled to the end of one of the bundles. The end of the other bundle is coupled to a photodetector which generates electrical pulses in response to the returning light pulses. The electrical pulses are amplified and then gated through a sampling circuit which is internally synchronized by means of and in resonse to the oscillator. The gated electrical pulses are then coupled to a staircase generator the output of which is coupled to a comparator. When the output of the staircase generator falls below a predetermined level the output of the comparator changes state to provide an indication that the vane has interrupted the light path in the gap. The output of the comparator controls a relay which is coupled to an external utilization device such as an alarm or a valve control.