Abstract:
The present invention includes a level detector having a collimator being operable to block first electromagnetic radiation having a first range of orientations with respect to the level detector from passing through. The collimator is further operable to allow second electromagnetic radiation having a second range of orientations with respect to the level detector to pass through. The level detector includes a sensor that is positioned, with respect to the collimator, such that the sensor is operable to detect magnitudes of the second electromagnetic radiation. The sensor may be further operable to convert incident photon flux associated with the second electromagnetic radiation to electrical signals. In accordance with a particular embodiment of the present invention, the level detector includes an electronic unit that is operable to detect a radiation step in the second electromagnetic radiation, based upon changes in the magnitudes of the second electromagnetic radiation.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates to measurement devices, and more particularly to a level detector for measuring the level of a fluid in a container.  
         BACKGROUND OF THE INVENTION  
         [0002]    Level detection is used in a vast number of applications to monitor the level of liquid, gas or other material in a container. Typically, a probe or transducer is installed within the container. Many traditional level sensors require the installation of a probe inside the container. Such sensors cannot be used in tanks that are not specifically designed for the particular sensor.  
           [0003]    In the gas industry, for example, a widely used level measuring device is a float level meter. This type of meter requires the installation of a float inside the tank. The float is connected to the body of the meter by a metal arm. The arm allows the position of the interface between the liquified gas and gas which is in a gaseous state to be monitored. The movement of the float is translated to a rotational displacement by the arm. The displacement of the arm requires quite a bit of space, making it difficult to use this type of level meter in small tanks (e.g., gas grill, and portable tanks).  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides a level detector and method of level detection for materials contained in tanks that substantially eliminates or reduces at least some of the disadvantages and problems associated with the previous level detectors and methods.  
           [0005]    In accordance with a particular embodiment of the present invention, a level detector is provided. The level detector includes a collimator being operable to block first electromagnetic radiation having a first range of orientations with respect to the level detector from passing through. The collimator is further operable to allow second electromagnetic radiation having a second range of orientations with respect to the level detector to pass through. The level detector also includes a sensor positioned, with respect to the collimator, such that the sensor is operable to detect magnitudes of the second electromagnetic radiation. The sensor may be further operable to convert incident photon flux associated with the second electromagnetic radiation to electrical signals.  
           [0006]    In accordance with another embodiment of the present invention, the sensor is electrically coupled with an electronic unit. The electronic unit is operable to detect a radiation step in the second electromagnetic radiation, based upon changes in the magnitudes of the second electromagnetic radiation.  
           [0007]    In accordance with yet another embodiment of the present invention, a method for detecting a level of fluid in a container includes scanning a surface of the container with a remote sensor, the container having a gas and a liquid within the container. The method also includes measuring radiation intensities along the surface of the container. Variations in radiation intensities may be identified adjacent at interface between the gas and the liquid.  
           [0008]    Technical advantages of particular embodiments of the present invention include a level detector that may be used to detect a level of fluid in a container of practically any material, without touching the container. Operation of such a level detector may be conducted remotely, from a distance of a few inches to several miles from the container.  
           [0009]    Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some or none of the enumerated advantages.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    For a more complete understanding of particular embodiments of the invention and their advantages, reference is now made to the following descriptions, taken in conjunction with the accompanying drawings, in which:  
         [0011]    [0011]FIG. 1 is a diagram illustrating a level detector and a tank in accordance with an embodiment of the present invention;  
         [0012]    [0012]FIG. 2 is a diagram illustrating a relationship between IR radiation/temperature, and the location along the surface of the container of FIG. 1;  
         [0013]    [0013]FIG. 3 is a schematic diagram illustrating circuits suitable for use within the teachings of the present invention;  
         [0014]    [0014]FIG. 4 is a schematic diagram illustrating various components which may be utilized in accordance with the teachings of the present invention;  
         [0015]    [0015]FIG. 5 is a schematic diagram illustrating the operation of a collimator of the level detector of FIG. 1, in accordance with a particular embodiment of the present invention; and  
         [0016]    [0016]FIG. 6 illustrates top and side views of a level detector incorporating aspects of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    [0017]FIG. 1 illustrates a level detector  10  in accordance with a particular embodiment of the present invention. Level detector  10  may be used to determine the level of a fluid  12  in a container  14 . In various embodiments of the present invention, container  14  may be a variety of shapes and sizes. Furthermore, container  14  may be sealed, and include the capability to maintain pressure exerted from various fluids contained therein.  
         [0018]    For the purposes of this description, container  14  will be described as a sealed container able to withstand pressure differentials between its contents, and ambient environment. The level of liquid  12  in container  14  is defined by interface  16  between fluid  12  and fluid  18 . Since fluid  18  is collected near the top of container  14 , it is evident that fluid  18  is less dense than fluid  12 . For example, fluid  12  may represent a liquid, such as liquid propane. Also in this embodiment, liquid  18  may comprise a gas, such as propane gas, air, or some combination thereof. As will be described later in more detail, level detector  10  may be used to detect the interface  16  between fluid  12  (liquid) and fluid  18  (gas).  
         [0019]    Level detector  10  may be used to scan the surface  20  of container  14  vertically, as indicated by directional arrow  22 . Furthermore, level detector  10  may scan surface  20  using a vertical sweeping motion, along surface  20  of container  14 , back and forth between the top  24  and bottom  26  of container  14 . In a particular embodiment of the present invention, the scanning movement of level detector  10  is made beginning from the top  24  or the bottom  26  of container  14  until interface  16  between gas  18  and liquid  12  inside container  14  is detected.  
         [0020]    Level detector  10  reads electromagnetic radiation that is radiated from the surface  20  of container  14 . The radiation detected at any point along surface  20  is approximately proportional to the temperature of the material that makes up container  14  at a specific point along surface  20 . This type of radiation may be referred to as long wavelength infrared radiation. Long wavelength infrared radiation may be measured using sensors that convert an incident photon flux associated with the electromagnetic radiation, into an electrical signal. Different types of sensors may be used for this purpose, for example, thermal sensors and quantum sensors.  
         [0021]    A thermal sensor is one which absorbs incident radiation flux. The energy provided by the flux increases the temperature of the sensor. The increase in temperature thereby changes a measurable physical property of a component of the sensor, for example, voltage and/or resistance.  
         [0022]    A quantum sensor, on the other hand, senses radiation in a different way. A quantum sensor employs a semiconductor crystal. The incident photon flux interacts with a crystal lattice of the semiconductor crystal. This generates free electrons or carriers, which changes the electrical balance, and produces a signal voltage in the sensing element.  
         [0023]    These types of sensors may be used to detect interface  16 , because the temperature over surface  20  of container  14  is not equal at every spot. Instead, the temperature over surface  20  generally has a geometric distribution which increases or decreases along vertical axis  22 . In a particular embodiment, where the container is partially filled with a liquid such as fluid  12 , a step in the temperature distribution may be detected at interface  16  where liquid  12  and gas  18  make contact. The temperature distribution along surface  20  of container  14  will be described in more detail with regard to FIG. 2.  
         [0024]    [0024]FIG. 2 illustrates a particular thermal distribution that may occur along surface  20  of container  14 , and the infrared radiation corresponding to the temperature. Vertical axis L of FIG. 2 corresponds to the distance vertically upward along surface  20  of container  14 . A radiation step  28  is evident at the location of interface  16  between liquid  12  and gas  18 . The vertical thermal distribution illustrated in FIG. 2 is generated by the physical convection in liquid  12  and gas  18  contained in container  14 . Convection is stronger in liquids, which makes temperature distribution in the “wet” zone different.  
         [0025]    Referring again to FIG. 1, level detector  10  includes an elongate housing  29  having a thermal sensor disposed at least partially therein. Thermal sensor  30  receives electromagnetic radiation that is radiated from surface  20  of container  14 . In the illustrated embodiment, a collimator  32  is used to allow only radiation that is generally perpendicular to the sweeping axis (e.g., vertical axis  22 ) to penetrate inside of level detector  10  and be exposed to thermal sensor  30 . A particular collimator suitable for use within the teachings of the present invention is described in more detail in FIG. 5.  
         [0026]    Thermal sensor  30  converts such incoming infrared radiation to a voltage signal that is processed by an electronic unit  34 . In accordance with a particular embodiment of the present invention, when detector  10  is perpendicular to liquid interface  16 , a signal  36  is generated. Signal  36  may be an audible signal (e.g., audible alarm), or a light (visual) signal.  
         [0027]    Thermal and quantum radiation sensors, such as thermal sensor  30 , are also sometimes known as thermopile and pyroelectric sensors. These type of sensors often need a “warm-up,” after they are first activated. For example, some such sensors require up to sixty seconds of warm-up in order to function properly. This can be problematic if the operator intends, or needs to use the sensor immediately after it is powered on. In this case, signals that are generated internal to the sensor during the warm-up period must be compensated with an electronic circuit. This electronic circuit is used to separate signals coming from outside the detector from warm-up signals generated inside the detector during the warm-up period.  
         [0028]    The signal generated by thermal sensor  30  may be very small. In this case, the signal must be amplified. The amplifier used to accomplish this may have a very high gain, combining DC and low frequency response. The exact combination of gain and frequency response compensates for variations in scanning speed. For example, if the sweeping speed of level detector  10  is not fairly uniform, variations of that speed can give false “step” (e.g., radiation step) readings.  
         [0029]    [0029]FIG. 3 is an electronic circuit diagram that illustrates aspects of the circuitry of thermal sensor  30 , a compensating circuit  38 , and a sweep stabilization network  40 . As illustrated in FIG. 3, sensor  30  is coupled to “warm-up” compensating circuit  38 . Compensating circuit  38  is amplified with two inputs  42 ,  44 . Input  42  is connected to the output of sensor  30 . Input  44  receives a short duration signal opposed to that of thermal sensor  30 . In this embodiment, the compensating period is less than forty seconds. Output  46  is connected to sweep stabilization network  40 . In this configuration, sweeping speeds from 0.2 m/sec to lm/sec will not affect the detection of interface  16  of container  14 .  
         [0030]    An amplifier  48  and a voltage comparator  50  activate signal  36 , to indicate that interface  16  is approximately perpendicular to level detector  10 . This indicates that the level of liquid inside the container is approximately in front of the thermal sensor  30 . In a particular embodiment of the present invention, visual signal  36  can be a narrow, focused light-emitting diode. Such a diode may be used to automatically project a light spot on the surface  20  of container  14 , to indicate the exact level of the liquid, or the precise location of interface  16 .  
         [0031]    A switch  52  and a resistor  54  may be used to alter the detector&#39;s sensitivity. This allows level detector  10  to detect liquid levels in containers either stored or in use. This is helpful because the radiation step, for example radiation step  28 , at interface  16  is stronger when a gas tank is in use, because of a decrease of pressure inside the tank. The decrease in pressure lowers the temperature of the gaseous material inside.  
         [0032]    [0032]FIG. 4 illustrates a system and method for improving sweep variation during operation of level detector  10 . This solution also improves the immunity of level detector  10  to ambient temperature. In accordance with FIG. 4, radiation  11  passes through collimator  32  and contacts thermal sensor  30 , as described above. Compensating circuit  38  corrects for any warm-up “noise” generated by components of level detector  10 . The signal received by amplifier  48  is amplified and subsequently received at an analog to digital converter  56 . Analog to digital converter  56  allows the signal to be digitally processed.  
         [0033]    The signal is then received at a micro-controller  58 . Micro-controller  58  takes readings, or “samples” incoming infrared radiation several times per second. Micro-controller  58  uses these readings to calculate the rate of change of the incoming infrared radiation. This allows micro-controller  58  to identify a “step,” in that rate, for example, radiation step  28  of FIG. 2.  
         [0034]    Micro-controller  58  allows the magnitude of the radiation step to be predetermined, such that microcontroller  58  will automatically look for a particular magnitude of radiation step. Once a radiation step equal to or greater than a predetermine magnitude is identified, micro-controller  58  initiates signal  36 . Signal  36  alerts the operator that the detector is directly in front of, or perpendicular to the interface  16  between liquid  12  and gas  18 .  
         [0035]    [0035]FIG. 5 illustrates a system and method for compensating for variations in the input radiation that correspond to unintentional movements that the operator makes during the scanning process, in accordance with a particular embodiment of the present invention. To obtain the most accurate readings using level detector  10 , it is helpful that the scanning direction of level detector  10  is vertical. It is also helpful to maintain an equal distance between level detector  10  and container  14  during scanning. This is due to the fact that radiation intensity is distance-dependent.  
         [0036]    Collimator  32  of FIG. 5 allows for horizontal movement of level detector  10  by an operator, without affecting accurate level detection. Collimator  32  controls the amount of radiation that reaches thermal sensor  30 . Reference number  32   a  illustrates a horizontal cross-section of collimator  32 . Similarly, reference number  32   b  illustrates a vertical cross-section through collimator  32 .  
         [0037]    Targets T 1  and T 2  represent targets (e.g., containers  14   a ,  14   b ) set at different distances from collimator  32 . Distance dl illustrates the distance between collimator  32  and target T 1 . Distance d 2  illustrates the distance between collimator  32  and target T 2 . As illustrated in FIG. 5, the area of the target detected by sensor  30  does not vary with distance dl and d 2  if only the vertical cross-section  32   b  of collimator  32  is considered. However, the area of the target sensed does vary according to the angle α and the distance dl and d 2  in the horizontal plane illustrated by cross-section  32   a  of collimator  32 .  
         [0038]    In accordance with the present invention, it is possible to design collimator  32  with an angle a that automatically compensates for variation of intensity caused by moving the sensor closer or farther with a smaller or wider input window, respectively. This type of collimator compensates by incorporating a wider area of the target as the sensor moves away from it, but only in the horizontal plane. No vertical compensation should be made, because the sensor is attempting to detect a step in radiation along the vertical plane. In accordance with a particular embodiment of the present invention, collimator  32  is made of materials that are opaque for wavelengths used in level detector  10 . In accordance with various embodiments, the wavelength used in level detector  10  may comprise 4-14 microns.  
         [0039]    [0039]FIG. 6 illustrates a level detector  60 , that incorporates aspects of the present invention. Level detector  60  includes a collimator/wave guide  62  that controls the amount of radiation that reaches thermal sensor  64 . In essence, collimator wave guide  62  is a free window with thermal sensor  64  placed at one end.  
         [0040]    Due to the design of level detector  60 , there is no protection provided in front of thermal sensor  64 , in the illustrated embodiment. This is due to the fact that materials that are transparent to wavelengths are very expensive. Such materials cannot be glued, and are difficult to handle. Therefore, the enclosure of level detector  60  illustrated in FIG. 6, is designed to allow level detector  60  to be placed over any horizontal surface with the collimator/wave guide  62  entrance  66  facing down. This avoids contamination from dust and other particles that may reach thermal sensor  64  when level detector is not in use.  
         [0041]    Level detector  60  includes a switch  68  that is used to toggle level detector  60  between the “on” and “off” positions. Switch  68  includes a shaft  70  that projects from the bottom plane  72  of level detector  60 , when the power is on. In the illustrated embodiment, shaft  70  projects approximately 5-7 millimeters from bottom plane  72 . This prevents level detector  60  from being placed horizontally with entrance  66  facing down when switch  68  is in the “on” position. This eliminates the possibility that battery  74  can discharge when level detector  60  is not in use. When switch  68  is off, shaft  70  will remain recessed with respect to horizontal surface  72 , within a spherical void area  76 . Spherical void area  76  allows a fingertip of the operator to activate the switch to the “on” position.  
         [0042]    Level detector  60  includes a printed circuit board  78 . Printed circuit board  78  and all electronics are placed near horizontal plane  72 , in order to lower the center of gravity of level detector  60 , which provides stability to the body of level detector  60  when it is placed over a flat surface.  
         [0043]    Two light indicators, or sensors  80  are mounted in a 45-degree angle with respect to the line of scanning, in order to direct the signal light to the eyes of the operator. Light indicators  80  can be installed facing in the direction of the target (e.g., container) in order to project a light spot on the surface of the container, to indicate the level of liquid inside.  
         [0044]    Although the present invention has been described in detail, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as falling within the scope of the appended claims.