Optical level measurement device and method
A method and system for determining a level of a substance in a container, the method comprises emitting one pulse from a light source in a field of illumination toward a surface of said substance in said container. A backscatter signal of said pulse is detected by an optical detector. A lidar trace is created from said backscatter signal, said lidar trace including at least one reflection peak; A surface reflection is identified among said at least one reflection peak in said lidar trace, said surface reflection being a reflection of said pulse from said surface. The surface reflection is signal-fitted to provide a fitted surface trace. A level of said substance is determined in said container using said fitted surface trace.
1. A method for determining a level of a substance in a container, the method comprising:
emitting one pulse from a light source in a field of illumination toward a surface of said substance in said container;
detecting a backscatter signal of said pulse by an optical detector;
creating a lidar trace from said backscatter signal, said lidar trace including at least one reflection peak;
identifying a surface reflection among said at least one reflection peak in said lidar trace, said surface reflection being a reflection of said pulse from said surface;
signal-fitting said surface reflection to provide a fitted surface trace; and
determining a level of said substance in said container using said fitted surface trace.
2. The method as claimed in claim 1 , wherein said identifying said surface reflection comprises signal-fitting each of said at least one reflection peak and determining a best matched reflection peak to be said surface reflection.
3. The method as claimed in claim 1 , wherein said identifying said surface reflection comprises identifying a last one of said at least one reflection peak to be said surface reflection.
4. The method as claimed in claim 1 , wherein said substance is a transparent liquid and wherein said identifying said surface reflection comprises eliminating a container bottom reflection from said at least one reflection peak using a known shape for a reflection from a bottom of said container.
5. The method as claimed in claim 1 , further comprising:
detecting a reference backscatter signal of said pulse by a reference optical detector at said emission of said pulse thereby acquiring a reference zero value and a reference trace for said pulse;
comparing said reference trace for said pulse to said combined trace; and
determining a distance traveled by said pulse based on said comparison.
6. The method as claimed in claim 1 , wherein said signal-fitting comprises curve-fitting a non-symmetrical quasi-Gaussian function on said trace.
7. The method as claimed in claim 6 , wherein said curve-fitting uses the point corresponding to the peak of the curve as the reference position, wherein the curve is quasi-Gaussian in that the exponent is not 2, the equation being:
f
(
x
)
=
y
=
A
*
ⅇ
-
x
-
μ
n
v
,
where y is the sampled trace as a function of x which corresponds to the sampling time and n is a predetermined value that is different depending on whether (x−μ) is positive or negative.
8. The method as claimed in claim 7 , wherein finding the values of the parameters A, μ and v, comprises plugging the combined trace in the equation f(x) and a minimization algorithm is used with the following equations:
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f
ⅆ
A
=
ⅇ
-
x
-
μ
n
v
=
0
ⅆ
f
ⅆ
μ
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s
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A
*
ⅇ
-
x
-
μ
n
v
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n
*
x
-
μ
n
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1
v
=
0
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v
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x
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μ
n
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A
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-
μ
n
v
v
2
=
0.
9. The method as claimed in claim 8 , wherein finding the value comprises using the following starting point: A=the highest value of y, μ=the x position of the highest value and v=5.8.
10. The method as claimed in claim 1 , wherein said detecting further comprises
using at least one other optical detector for detecting at least one other backscatter signal of said pulse; and
multiplexing said backscatter signal with said at least one other backscatter signal.
11. The method as claimed in claim 1 , wherein said determining the level comprises determining the level of one of a liquid, a paste and a solid.
12. The method as claimed in claim 1 , further comprising controlling said light source by a pulse driver to modify an output power of said light source.
13. The method as claimed in claim 12 , further comprising providing a detection parameter and wherein said controlling uses said detection parameter.
14. The method as claimed in claim 13 , wherein said providing said detection parameter comprises providing a reflectivity parameter, said reflectivity parameter being indicative of a reflectivity of at least one of said substance and walls of said container.
15. The method as claimed in claim 13 , wherein said providing said detection parameter comprises providing a range parameter, said range parameter being indicative of a level of said substance in said container.
16. The method as claimed in claim 13 , wherein said providing said detection parameter comprises providing a clarity parameter, said clarity parameter being indicative of a dust density inside the container.
17. A fill-level sensing device for determining a level of a substance in a container comprising:
a light source for emitting light in a field of illumination toward a surface of said substance in said container;
a pulse driver for driving the light source into emitting one pulse;
an optical detector adapted to detect a backscatter signal of said pulse; and
a data/signal processor for creating a lidar trace from said backscatter signal, said lidar trace including at least one reflection peak, for identifying a surface reflection among said at least one reflection peak in said lidar trace, said surface reflection being a reflection of said pulse from said surface; for signal-fitting said surface reflection to provide a fitted surface trace; and for determining a level of said substance in said container using said fitted surface trace.
18. The fill-level sensing device according to claim 17 , wherein the light source is one of a light-emitting diode (LED) and a laser.
19. The fill-level sensing device according to claim 17 , further comprising a timer, the timer being triggered by the data/signal processor to calculate a time elapsed between said emission of said pulse and said detection of said backscatter signal, the data/signal processor determining a distance traveled by said pulse based on said time elapsed.
20. The fill-level sensing device according to claim 17 , further comprising an analog-to-digital converter for sampling the backscatter signal of said pulse, and a pre-processing and synchronisation unit for controlling parameters of said pulse from the analog-to-digital converter.
21. The fill-level sensing device according to claim 20 , wherein the parameters are at least one of the optical power of the light pulse, the number of pulses used for pre-process operation, a gain of amplifier, a synchronization between the pulse driver and the analog-to-digital converter, and a sample rate of analog-to-digital converter.