US 5,257,090 A · Laser diode liquid-level/distance measurement

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.

Claims14

Dependent claims

A laser-based distance measuring device for measuring the distance to a cooperative target having predetermined highly reflective properties, comprising:

a laser assembly, having a laser with a variable optical operating frequency, emitting an output light toward the target;
collimating means, disposed in the path of the output light, for providing a collimated light, the collimated light being incident on the target and being reflected by the target back into said laser assembly;
said laser assembly also providing a feedback signal having a magnitude related to the distance from said laser assembly to the target based on coherent interference within said laser between light reflected from the target and light within said laser;
the collimated light from said collimating means together with the highly reflective properties of the target providing reduced speckle noise and substantially constant speckle noise floor over the travel range of the target;
laser drive means, for providing a variable laser drive signal to said laser assembly for varying the optical operating frequency of said laser;
and
distance measurement means, responsive to said feedback signal from said laser assembly, for providing a distance signal indicative of the distance to the target.

4 more elements

Dependencies are inferred from the claim text.

Laser diode liquid-level/distance measurement

Life of this patent

Laser diode liquid-level/distance measurement

Life of this patent

Abstract

Claims14