The Boeing Company
Non-contact time-of-flight fuel level sensor using plastic optical fiber

Abstract:

A fuel sensing system utilizes non-contact plastic optical fiber (POF) to optically sense the level of liquid fuel in a fuel tank. In one implementation, the fuel level sensing system includes the following elements: (i) a high-speed and high-power red laser diode; (ii) an ultra-high-sensitivity photon-counting avalanche photodiode; and (iii) a large-diameter and large-numerical-aperture graded-index POF. The fuel level is sensed when the avalanche photodiode first detects impinging light reflected by the POF end face and then detects impinging light reflected by the fuel surface in response to emission of a laser pulse by the red laser diode. A time delay detection circuit calculates the time interval separating the respective times of arrival. A fuel level calculator calculates the fuel level based on the time interval provided by the time delay detection circuit.