No assignee for this patent application has been made.
News editors obtained the following quote from the background information supplied by the inventors: "(1) Field of the Invention
"The invention is related to an optical liquid level sensor.
"(2) Description of Related Art
"Precise sensing of the level of liquids in tanks or containers is important for different reasons: prevention of overfilling of tanks, computation of the actual liquid consumption, identification of low liquid level, etc. From a safety point of view, it is even more important to know the exact level for tanks with inflammable liquids such as fuel. It is therefore necessary to control the filling and consuming processes as well as determining the current level if filling or consuming is to be started. Especially with inflammable liquids it is furthermore important for safety reasons to reduce or to eliminate all kind of electricity from inside the tank or container. It is important to avoid any kind of spark or ignition source inside the area/space of the liquid. Furthermore, in cases of liquid level sensors in a tank/container for aircrafts or vehicles it is important to design the liquid level sensor in such a way, that the components satisfy the crash requirements and that the liquid level sensor in case of a crash does not cause any damage to the tank/container, even if the tank/container is made of soft material.
"The document U.S. Pat. No. 7,710,567 describes determining the density and/or temperature of a fluid in a tank, based on the optical energy affected as it propagates across a gap between opposing end faces of optical waveguides. A housing includes a cylindrical body, a top portion and a bottom portion. The top and bottom portions are secured to the body by fasteners. A conduit is positioned in a volume within the housing. The top and bottom portions each have a through hole formed therein. The through holes are aligned with a passage defined by the conduit. The through holes permit the fluid in the tank to enter. Legs are attached to the bottom portion to a bottom surface of the tank. A plurality of sources of optical energy are in optical communication with an associated one fiber optic cables, e.g. light-emitting diodes having emission in the visible green wavelength. Also, each light detector is e.g. a photo detector sensitive in the visible green wavelength.
"The document US 2004/0021100 describes fiber optic measuring of levels of fluid. An ordered array of multiple optical fibers contains each a single sensitive element located on a specific level within the range of fluid level change. Each single sensitive element transmits different light signal, depending on either the sensitive element is immersed or located above the level of liquid. The making of optical contact of the fiber is with cladding disposed from the tank bottom with the fiber without cladding disposed from the top at a certain level of the range of liquid levels By removing a section of cladding near the end of the fiber the latter is equipped with a fluorescent element at its end. The fibers are connected to a common reflective mirror or a fluorescent element at the bottom of a housing. A bundle of optical fibers is disposed along a holder with the sensitive sections distributed along the holder. In side cross-sectional view, the U-shaped sensitive sections are of different types formed by e.g. a fiber without cladding or isolation, however with metallic cover or cladding at the lower part of U-shape or loop. Receiving parts of the fibers form a feedback bundle of fibers guiding the light signals to the light detector. The light signals modulated in frequency domain are detected by a single light detector which transforms them in current/voltage signals.
"The document U.S. Pat. No. 3,844,171 describes a liquid level indicator having a probe which is inserted within a container holding the liquid, and an external readout device. A unit includes a connector end which holds coupling lines by means of a clamp, into a middle section which holds a sensing device axially extended therefrom. The sensing device is a hollow tube from glass or plastic with the middle section having one end thereof knurled for manipulating and the other end with a screw thread to connect the unit to a holder, permanently attached to the top of the container. The probe contains a vertical prism and pairs of light guides spaced at preselected levels along the prism. The light guides are spaced from the prism. In an elevation sectioned view of the unit, the sensing device is mounted on a retaining member located adjacent a notch longitudinally cutting a section of the wall of the tube. Part of the middle section is having an external thread thereon to permit attaching the unit on the container for permanent connection. The tube needs not be transparent. The fiber optics continues from the upper section in a semicircular arrangement around the tube.
"The document WO2010051806 discloses an optical sensor arrangement for detecting a first liquid medium in a second liquid medium by means of reflection of an emitted light beam at a wavelength, with a light source and an associated receiver, wherein two round glass rod lenses which are encapsulated in a housing are arranged parallel to one another. The glass rod lenses have an optical refractive index which is different from that of the liquid media. A reflection surface which is connected to the housing is arranged opposite the glass rod lenses. There is also a control device having a beam splitter, a second receiver and a third receiver which are arranged opposite one another. This sensor is suited only for measuring whether the liquid has reached a certain predefined level or not, but it is not suited for continuous measurements of varying levels. This sensor is therefore especially useful as a low level or maximum level sensor, but it cannot provide information e.g. for computing the consumption.
"The document U.S. Pat. No. 4,134,022 discloses a level sensing apparatus having a source for supplying a signal having a predetermined frequency, a level sensor connected to the source and having an output for supplying an output signal having the predetermined frequency as long as the material, the level of which is being sensed, is not at a predetermined level. The level sensing apparatus further has a frequency sensitive circuit for receiving the output signal from the level sensor and for providing an output whenever the frequency of the signal is above or below the predetermined frequency, and a load which is connected to be responsive to the output from the frequency sensitive circuit. The level sensing apparatus is only capable to determine whether the liquid has reached a predefined level or not. Even the extension of the basic concept to several sensors is limited in its use, because it can only determine whether the liquid in one of the tanks has reached the respectively defined level or not. It is not possible to determine the exact level of the liquid.
"The document U.S. Pat. No. 3,535,933 discloses a liquid level indicator in which a plurality of depending parallel light transmitting rods having different lengths are adjacently positioned, but maintained physically separated substantially throughout the entire longitudinal extent thereof. The upper portions of each of the light rods are interconnected and spaced apart by a flange section which in turn is clamped to the liquid container. The lower portions of the rods are integrally connected by a separator element between the rods and the upper portions provided an exposed liquid level indicating surface. The lower extremities of the light rods are positioned in the liquid and define a conical tip having an included angle of 90.degree. for receiving light rays from and reflecting light rays to the upper indicating surface. The liquid level indicator needs a plurality of elongated members or rods and each of them needs a respective sensing unit. In order to provide the required stability, these members or rods need to be massive and have therefore significant weight. In addition, the light source and the light measuring device need to be positioned on the same end of the members or rods.
"The document EP1533598 discloses a fiber optic level measurement device for use with transparent liquids in containers. Said fiber optic level measurement device has at least one optical fiber that is at least partially immersed in the liquid with the liquid level determined from the difference between injected light intensity and exiting light intensity. An input leg of the optical fiber has a spiral shape which extends to the lowest level of the container, while the output leg of the fiber is straight. Only one fiber measures the level of liquid based on the amount of refraction in the liquid. Therefore the measurement and the comparison of the light intensities of the input light and the output light needs to be very precise in order to determine the liquid level. Respective devices for measuring the light intensity need to be calibrated very precisely and are fairly expensive. Furthermore, the resolution of the sensor is limited due to the measuring principle.
"The document DE3235591 discloses a fiber-optic liquid-level display device with a first optical fiber, assigned to a light source, and a second optical fiber, assigned to a light detector. The two optical fibers are coupled via a fiber coupler to a third optical fiber and a fourth optical fiber. The third optical fiber and the fourth optical fiber reach with their ends to different depths into the vessel containing the liquid to be measured. Depending on the level, the light at the ends of the optical fibers is coupled out or reflected and fed to the photodiode, with the result that the level range of the liquid can be detected by means of the current of said photodiode. The teaching of DE3235591 allows a reduction of the number of components needed, but it increases the requirements for the photo diode significantly, since it needs to discriminate the exact light intensity. The more different levels are to be detected, the more difficult is the realization of this sensor. This is therefore limited with respect to the achievable resolution.
"Capacitive sensors as proposed in documents DE102008064019, DE102008042254 or DE102009029099 suffer from the disadvantage that electricity has to be transmitted into the container/tank which is not desirable, especially for sensing the level of inflammable or explosive liquids. In addition, most capacitive probes contain metal probes and therefore tend to be in conflict with the crash requirements.
"For preparing the application, the following prior art documents were considered: DE102008064019 KOSSIRA 2008; DE102008042254 ROESSLER 2008; DE102009029099 STAMMLER 2009; DE3235591 SPENNER 1982; DE4204212 WITTKOWSKI 1992; EP0152644 MULDER 1983; EP1533598 SCHNELL 2003; U.S. Pat. No. 3,535,933 PLIML 1969; U.S. Pat. No. 3,844,171 RODGER 1971; U.S. Pat. No. 4,134,022 JACOBSEN 1976; U.S. Pat. No. 4,373,389 DECKER 1979; U.S. Pat. No. 5,802,728 KARNICK 1995; U.S. Pat. No. 7,710,567 MENTZER 2006; US 2004/021100 GOUZMAN 2002 and WO2010051806 WILDSHUTZ 2008."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "The object of the invention is to provide an optical liquid level sensor for determination of the exact level of a liquid in a container or tank, especially an optical liquid level sensor for a container or tank in a vehicle, such as an aircraft. For instance, this aircraft is a rotary wing aircraft.
"The solution is provided with an optical liquid level sensor according to the features of claim 1.
"According to the invention an optical level sensor for detection of liquid levels is mounted to a container or tank. The optical level sensor comprises a light source, a light detector with a processing unit and at least one optical fiber with one input side of it assigned to the light source and reaching from the light source into said container or tank, and at least one output side assigned to the light detector and reaching from inside said container or tank to the light detector. A tube is provided with support and guidance elements which collect and guide all of the at least one optical fibers into or out of the tank/container. Preferably 50, 100, 200, 1000 or any number of optical fibers in between are provided in order to allow for detection of 50, 100, 200 or 1000 liquid levels. Each optical fiber is very small in dimension with typical diameters between 0.1 mm and 1.0 mm and embedded into a separate support and guidance elements made of plastic or metal. Each optical fiber is linked to detection of a specific liquid level.
"The sensing of the light detector is such that if the light intensity of the light input communicated by the output optical fiber to the light detector is below a certain threshold I.sub.c, the processing unit identifies the light to be off, i.e. the environment of the support and guidance element with the respective fiber is surrounded by liquid. If the light intensity is above the critical level I.sub.c, the processing unit interprets it as surrounded by air, i.e. outside the liquid. Depending on the exact optical characteristics, especially the refractive index of the liquid, the diameter and the material of the fiber as well as the number of small turns of the fiber, such as 1-20 turns with radii
"An optical liquid level sensor according to the present invention allows for a continuous sensing of the liquid level in a container/tank with a very high resolution without introducing electricity into the container/tank with the liquid;
"Despite the high resolution, the light source and the sensing electronics are very compact and simple;
"The inventive sensor is based on modular components and easy to assemble;
"Due to the possibility to use plastics or plastics skeletons for the sensor tube, it can easily be made crash worthy/crash tolerant; and
"Because of the multitude of sensor elements it is possible to provide for self-monitoring of the inventive sensor, e.g. by applying plausibility checks for the results of consecutive sensor elements.
"According to a preferred embodiment of the invention the input sides and the output sides of the optical fibers are collected in groups respectively.
"According to a further preferred embodiment of the invention the collection of input sides/ends of the fibers is fed collectively by a homogeneous planar light source.
"According to a further preferred embodiment of the invention the collection of output sides of the fibers are sensed collectively by a Charged Coupled Device (CCD) as light detector.
"According to a further preferred embodiment of the invention the optical fibers are made of glass or plastic.
"According to a further preferred embodiment of the invention the optical fibers have a diameter between 0.1 mm and 1.0 mm.
"According to a further preferred embodiment of the invention the support and guidance elements are made of plastic or metal.
"According to a further preferred embodiment of the invention 50, 100, 200, 1000 or more sensor head elements are assembled.
"According to a further preferred embodiment of the invention each optical fiber is guided in its half-length through its support and guidance element which is bending the fiber with a small radius
"According to a further preferred embodiment of the invention a reference optical fiber is used to provide a reference for the light intensity from an optical fiber which is exclusively in air.
"According to a further preferred embodiment of the invention spacing elements and a spiral spring are provided, the support and guidance elements and spacing elements being compressed with the spiral spring in order to guarantee the density of the elements.
"According to a further preferred embodiment of the invention the optical fibers can be arranged outside the fiber collecting tube with the optical fibers being more or less unprotected.
"According to a further preferred embodiment of the invention the support and guidance elements including the optical fibers can be completely inside a caging basket.
"According to a further preferred embodiment of the invention the transparent input window is an optical filter in order to reduce the light intensity or to increase the light discrimination level.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS:
"Preferred embodiments of the invention are presented in the following description with reference to the attached drawings.
"FIG. 1 shows a cross sectional view of an optical liquid level sensor according to the invention;
"FIG. 2 shows a spherical view of an extract of FIG. 1;
"FIG. 3 shows a preferred interpretation function of the optical liquid level sensor according to the invention;
"FIG. 4 shows a schematic view of an operation of an extract of FIG. 2;
"FIG. 5a, 5b show schematic views of operational modes of different optical fibers of the optical liquid level sensor according to the invention;
"FIGS. 6 to 10 show schematic views for the support and guidance element of the optical liquid level sensor according to the invention, FIG. 10 showing an example of 'star-shaped' guideways."
For additional information on this patent application, see: Kreitmair-Steck, Wolfgang; Singer, Frank. Optical Liquid Level Sensor. Filed
Keywords for this news article include: Patents.
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