Abstract: Apparatus and method for determining the level of a material in a vessel. In one embodiment, and optical emitter emits light onto a rotating mirror. The light reflects off of the rotating mirror and propagates into a vessel. At a first time, the light reflects back and is detected by a first detector. At a second time, the light is reflected back and is detected by a second detector. The distance to the surface of the material in the vessel can be determined using the difference between the first and second times. The volume of the material may also be determined based on this distance. Additional embodiments include rotating the light source itself, maintaining an inert gas near a surface of a window located between the steering mirror and an interior area of the vessel, tilting the steering mirror and first and second detectors to obtain a reflection at maximum intensity, and accounting for the tilt in calculating the volume.

Abstract: Apparatus for determining the level of fluid in a vessel comprises a fixed optical emitter for emitting light into the vessel, a light steering means for steering light emitted by the fixed optical emitter, the light steering means for steering the light to reflect from a surface of one of the vessel and a substance within the vessel, a window for receiving the steered light prior to transmission to the vessel, a detector for receiving light from the vessel, and a processing system for determining distance from the vessel or substance in accordance with a predetermined geometric relationship. The apparatus may additionally comprise a level for determining a number of degrees out of plumb of the vessel. Also, the apparatus may comprise an acoustic transmitter and receiver for determining the depths of first and second liquids in the vessel which are immiscible in one another.