Optical tank-level gauge

Abstract

An optical tank-level gauge includes an elongated gauge rod magnetically coupled at its lower end to a float for rising and falling with the liquid level. The outer surface of the rod is provided along most of its length with alternating reflecting and non-reflecting circumferential stripes of equal height, the rod having non-reflecting zones at its opposite ends. An optical read head is fixed on the tank and includes LEDs for illuminating the rod and four optical sensors spaced apart longitudinally along the rod and arranged into quadrature pairs relative to the stripes, so that each pair reads a longitudinal extent of the rod substantially equal to the height of one stripe. Each of the non-reflecting end zones has a height such that, in either the full or empty condition, the fields of view of all four optical sensors will be completely within one or the other of the end zones. The LEDs are modulated on and off at a high frequency and the output of each optical sensor is rectified and compared to a predetermined threshold to produce a logic level output corresponding to the nature of the stripe being read and which is substantially insensitive to ambient light. A microcontroller controls the modulation of the LEDs and processes the logic levels produced by the detection circuitry to integrate a serial output pulse train indicative of the liquid level. The processor can be switched between a continuous readout mode and a mode to generate discrete alarm level signals.