Optical sensor for opaque and non-opaque materials

Details Optical sensor for opaque and non-opaque materials Optical sensor for opaque and non-opaque materials

1999-10-22

2004-02-03

Font, Frank G. (Department: 2877)

Optics: measuring and testing

For light transmission or absorption

Of fluent material

C440S102000, C440S102000

Reexamination Certificate

active

06687004

ABSTRACT:

FIELD OF THE INVENTION
The present invention is related to a; sensor. More particularly, the present invention is related to a sensor capable of detecting the presence of non-opaque (e.g., translucent, clear or transparent) and opaque (non-transparent) materials.
BACKGROUND OF THE INVENTION
Detecting the presence of materials, such as, liquids can be done by either non-invasive or invasive methods. For example, a liquid may be transported under pressure through conduits or tubing within a system, such as an automobile cooling system, an industrial cleaning system, or a blood purification system. If a portion of a conduit within such a system is transparent, the presence of liquid within the conduit may be optically detected non-invasively (i.e. by apparatus located external to the conduit).
In other cases, use of a conduit may not be feasible, in which case liquids may be detected invasively (e.g., by bringing the sensor into direct contact with the liquid). For example, if ground water is believed to be contaminated with gasoline or oil, sensors may be lowered through bore holes into direct contact with the ground water. Direct contact often exposes the sensor to harmful environments and makes repair and retrofitting of sensors in existing systems more difficult. Further, to protect the sensor from corrosion (e.g. if the liquid to be detected is corrosive) and prevent contamination of the liquid by the sensor, an invasive system often requires an expensive housing made of materials such as stainless steel.
Non-invasive sensor systems often employ a photo detector and a light source aligned such that light from the light source passes through the liquid medium and is detected by the photo detector. Typically, such sensor systems require critical and time-consuming alignment of the source and detector. Because a liquid has a different refractive index than air, light transmitted through the medium is refracted to a different position depending on the presence or absence of liquid. Thus, the detector must be aligned to compensate for refraction related to the detected medium. Also, as light passing through a translucent medium is passed at an angle related to the refractive properties of the medium, critical and time-consuming alignment must be repeated each time a new medium is to be detected. To avoid repetition of the alignment process, additional detectors must be located at each location of possible refraction. Additional sensors increase both initial and recurring system costs. Further, each additional sensor must be carefully aligned with respect to the light source. Notably, a physical jarring may misalign the components requiring the alignment process to be repeated. In addition to alignment considerations, the sensitivity of the sensors is related to the transparency of the medium; the less transparent the medium, the less sensitive the detector. Thus, sensor sensitivity often must be adjusted for each medium to be detected.
Other types of sensors—typically non-invasive—direct a light source directly through the medium to a detector (e.g., not at an angle). These sensors, however, depend on the refractive properties of a present liquid to concentrate light onto the detector which measures the intensity of light impinging thereon. However, the less transparent the liquid, the less light will reach the detector; thus light intensity detected is also a function of the transmissive characteristics of the medium to be detected. These sensors are inherently less sensitive in detecting non-transparent (e.g., opaque) liquids, and need to be re-calibrated to detect materials with different transmissive characteristics. Therefore, detectors must be calibrated to detect either the presence of a clear (e.g., non-opaque) liquid or the presence of a substantially opaque liquid. Liquid detectors which are configured to detect a clear liquid must be reconfigured to detect an opaque liquid.
Thus, there is a need for an inexpensive, sensitive, easily-calibrated sensor or method which lends itself to non-invasively detecting the presence of a material. Further still, there is a need for a sensor or method of detecting a material which is resistant to mis-alignment of its components. Even further still, there is a need for a clear and opaque material detectors which are configured to optically detect a clear and opaque materials without recalibration.
SUMMARY OF THE INVENTION
An exemplary embodiment relates to an apparatus for detecting a material in a translucent conduit. The apparatus includes a light source and a light detector. The light source generates a narrow-beam of light and is disposed adjacent an outside surface of the conduit. The light detector has an active surface disposed adjacent the conduit along an axis defined by the light source. The light detector is operable to detect the surface area of light which impinges on the active surface and provides an output signal proportional thereto. The light from the light source is refracted by the material in the conduit so the detector provides an output signal proportional to the surface area of the impinging light.
Another embodiment in the invention relates to a method of detecting a material in a translucent conduit. The method includes steps of providing a narrow beam of light through the conduit, detecting light from the conduit, and determining a presence of the material in the conduit. The light from the conduit is detected with an active surface. The active surface provides an output signal proportional to the surface area of the light on the active surface. The presence of material in the conduit is determined in response to the output signal being above a threshold window or below the threshold window.
Yet another embodiment relates to a system for detecting presence of a material. The system includes a first translucent surface, a second translucent surface substantially in opposition to the first translucent surface, a narrow beam light source, and a light detector. The material is located between the first translucent surface and the second translucent surface. The light source is disposed adjacent the first surface. The light detector has an active surface disposed adjacent the second surface and along an axis defined by the light in substantial apposition to the light source. The light detector is operable to detect the surface area of light which impinges on the active surface and to provide an output signal proportional thereto. The light from the light source which patches through the material interposed between the first and second surfaces is refracted and impinges on the active surface. The output signal indicates a presence of the material when the output signal is above or below a threshold window.


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Cole Parmer, Liqui-Sense®

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