Importance

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Abstract

A laser diode distance measurement device includes a laser diode assembly 10, comprising a laser diode and photodiode, which emits light 17 to a lens 19 which provides collimated light 20 incident on a float 22 which is covered with reflective tape on its top surface 24. The light 20 is reflected from the float 22 back to the laser diode assembly 10 which causes the assembly 10 to provide a signal having magnitude pulses (due to coherent interference) on a line 15 to a liquid level measurement circuit 14 related to the distance L to the float 22. Use of the collimated beam 20 and reflective tape on the float 22 minimizes speckle while providing adequate optical intensity feedback. The laser assembly 10 is driven by a sawtooth waveform signal that reduces electronic processing. The distance measurement circuit 14 blanks-out the feedback signal during discontinuities of the laser diode drive signal to minimize associated noise from distorting the distance measurement. Alternatively, the float may be omitted and the tube 11 made small enough to provide a meniscus effect curvature at a liquid surface 250 which provides a curved reflective surface to reflect the incident light 20, in a consistent fashion, back to the laser assembly 10.

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First Claim