Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2008-07-09
2009-12-22
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S577000, C073S293000, C356S436000
Reexamination Certificate
active
07635854
ABSTRACT:
A method and apparatus provide for non-contact optical measurement of the level of a fluid stored in a tank or container, the surface of the fluid being possibly agitated. The method processes numerically the digitized signal waveforms generated by a lidar apparatus based on a pulsed time-of-flight modulation scheme. A key step of the numerical processing is the computation of a waveform in which each data point is obtained from a statistical estimator of the variability of the amplitude signal echo measured at the distance from the lidar apparatus that corresponds to the rank of the data point in the waveform. The statistical estimator is preferably the standard deviation. By using a statistical estimator of the variability of the captured signal amplitude, the specific signal echo returned from an agitated fluid surface can be greatly amplified as compared to the signal echoes returned from any obstacle or medium that could be present along the path of the optical beam radiated by the lidar apparatus. The method then allows for an efficient retrieval of the useful signal echo from which the level of the fluid surface can be reliably measured with greater accuracy, particularly in situations where the useful signal echo would be buried in a strong signal echo returned from any optically scattering or absorbing medium that would fill in the volume of the tank above the fluid surface.
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Maatta, Kari et al. “High Accuracy Liquid level meter based on pulsed time of flight principle” SPIE vol. 3100 pp. 268-277, Sep. 1997.
Institut National D'Optique
Merchant & Gould P.C.
Pyo Kevin
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