Differential Spectral Liquid Level Sensor

A method for measuring a height of liquid in a reservoir, comprising:

• placing a side-emitting optical fiber and a side-receiving optical fiber in the reservoir having respective locations whereat the side-emitting optical fiber and side-receiving optical fiber are mutually parallel and separated by a distance;
• guiding a series of time-division-multiplexed optical pulses into one end of the side-emitting optical fiber, wherein the time-division-multiplexed optical pulses comprise alternating optical pulses having the first and second wavelengths respectively;
• side-emitting at least some of the optical pulses received by the side-emitting optical fiber toward the side-receiving optical fiber;
• guiding at least some of the time-division-multiplexed optical pulses received and output by the side-receiving optical fiber onto an optical detector;
• converting time-division-multiplexed optical pulses that impinge on the optical detector into time-division-multiplexed electrical signals;
• demultiplexing the time-division-multiplexed electrical signals output by the optical detector to generate first and second electrical signals;
• and
• calculating an estimated level of liquid in the reservoir based on a difference of the first and second electrical signals.

A system for measuring a level of liquid in a reservoir, comprising:

• one optical source which alone or two optical sources which collectively outputs light comprising a first wavelength and light comprising a second wavelength different than the first wavelength;
• a side-emitting optical fiber optically coupled to the one or two optical source(s);
• a side-receiving optical fiber that is positioned parallel to and at a distance from the side-emitting optical fiber;
• and
• a differential receiver optically coupled to the side-receiving optical fiber and configured to convert light having the first wavelength into first electrical signals and convert light having the second wavelength into second electrical signals, wherein the differential receiver comprises:
• a dichroic mirror that passes light having the first wavelength and reflects light having the second wavelength;
• a first optical detector positioned to receive light passed by the dichroic mirror;
• and
• a second optical detector positioned to receive light reflected by the dichroic mirror.

A method for measuring a height of liquid in a reservoir, comprising:

• placing a side-emitting optical fiber and a side-receiving optical fiber in the reservoir having respective locations whereat the side-emitting optical fiber and side-receiving optical fiber are mutually parallel and separated by a distance;
• outputting light having a first wavelength and light having a second wavelength different than the first wavelength from a single broadband optical source or from respective optical sources, wherein the light having a first wavelength and the light having a second wavelength have different attenuations when propagating through the liquid;
• guiding the outputted light having the first and second wavelengths into the side-emitting optical fiber;
• side-emitting at least some of the light received by the side-emitting optical fiber toward the side-receiving optical fiber;
• guiding at least some of the light received by the side-receiving optical fiber onto a dichroic mirror that reflects light having the first wavelength and passes light having the second wavelength;
• converting light having the first wavelength that is reflected by the dichroic mirror into first electrical signals representing an amount of detected light having the first wavelength;
• converting light having the second wavelength that passes through the dichroic mirror into second electrical signals representing an amount of detected light having the second wavelength;
• and
• calculating an estimated level of liquid in the reservoir based on a ratio of the first and second electrical signals.