WO2020180673A1

WO2020180673A1 - Universal liquid level sensing

Info

Publication number: WO2020180673A1
Application number: PCT/US2020/020368
Authority: WO
Inventors: Razmik B. Boodaghians; Volker Antonczyk; Nguyen TRAM; Lutz Neumann
Original assignee: Zodiac Cabin Controls Gmbh
Priority date: 2019-03-01
Filing date: 2020-02-28
Publication date: 2020-09-10

Abstract

Liquid level sensing using radar technology. The disclosure provides a system that can measure liquid levels enclosed in a tank or other container, in which the tank does not maintain a static position. The system thus collects information about the liquid level at many points, rather than at a single point reading, such that it can determine liquid level independent of liquid level angle. The system is also designed to function regardless of the pressure, vacuum, or other environmental conditions of the tank, such as foam vapor, temperature, liquid type, or other conditions.

Description

UNIVERSAL LIQUID LEVEL SENSING

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to and claims priority benefits from U.S. Provisional Application Serial No. 62/812,611, filed on March 1 , 2019, entitled“Universal Liquid Level

Sensing,” the entire contents of each of which are hereby incorporated by this reference.

FIELD OF THE INVENTION

[0002] The field of this disclosure relates to liquid level sensing using radar technology. The disclosure provides a system that can measure liquid levels enclosed in a tank or other container, in which the tank does not maintain a static position. The system thus collects infonnation about the liquid level at many points, rather than at a single point reading, such that it can determine liquid level independent of liquid level angle. The system is also designed to function regardless of the pressure, vacuum, or other environmental conditions of the tank, such as foam vapor, temperature, liquid type, or other conditions.

BACKGROUND

[0003] There are various methods and systems for measuring liquid levels contained in a tank or other container. Some systems use liquid level sensors that contact the liquid and relay a signal back to a unit that can determine the level of liquid based on the position of the liquid with respect to the sensor(s). Such systems may use optical level switches that have a sensor tip that can detect whether the tip is in air or in liquid and relay an appropriate signal. Other systems may rely on conductivity or resistance based on voltages transmitted by probes positioned within the fluid. Some challenges with these systems are that build up on the probes or sensors can occur. Other systems may use float sensors, with a float that moves with the change in liquid and can cause a switch to either open or close depending upon whether the switch is in air or liquid. Further systems may rely on capacitance level sensors, which function by measuring the change in capacitance between two plates. A non-limiting example of various types of sensing is disclosed by U.S. Patent No. 9,718,549. Some of these technologies can be contact based, and the reliability of the sensors can be heavily influenced by the type of fluid being measured. Ultrasonic liquid level sensors calculate the duration and strength of high- frequency sound waves that are reflected off the surface of the liquid and back to the sensor. These sensors are sensitive to elements in the atmosphere such as turbulence, foam, temperature, air pressure, and build up inside the tank. Ultrasonic technology is limited to atmospheric pressure measurements in air or other gases. [0004] Although various forms of these sensors have been used for liquid level sensing in various contexts, sensing liquid levels in aircraft can present specific challenges. For example, in the context of aircraft technology, the vehicle (and thus the liquid-holding tank(s) on board the vehicle) does not remain static or stationary. During takeoff, cruise, and landing, liquids contained in tanks are shifted greatly, such that there is a large angle created with respect to the surface of the fluid and sides of the tank. This presents liquid level sensing challenges. This may also be the case with other passenger transportation vehicles that are subject to increased speeds, which can cause fluctuation of liquid levels in tanks.

[0005] However, is still important to be able to obtain accurate level s for vari ous liquids carried on board. In one example, it is necessary to be able to determine how much material or liquid is contained within an aircraft waste tank. Such tanks are typically maintained under vacuum and can present specific liquid level sensing challenges. In a different context, it may be necessary to determine how much liquid is contained within an aircraft potable water tank. In a further context, it may be necessary to determine how much liquid is contained within an aircraft fuel tank. All of these liquid level measurements can be useful to determine on-ground pumping or re-filling needs, to limit onboard water usage, to predict future usage or servicing, or for any other reason. Accordingly, liquid level sensing improvements are desirable.

SUMMARY

[0006] Accordingly, the present inventors have designed the disclosed liquid level sensing system. The system is designed to use radar sensing technology in order to measure and determine the level of liquid present in a tank or other container. The described embodiments are envisioned useful for any appropriate fluid-containing enclosure, including but not limited to a waste tank intended to be under vacuum in use, a potable water tank, a fuel tank, or any other appropriate tank or container.

[0007] The terms “invention,” “the invention,” “this invention” “the present invention,”“disclosure,”“the disclosure,” and“the present disclosure,” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this patent, any or all drawings and each claim.

[0008] According to certain embodiments of this disclosure, there may be provided a level sensing system for measuring liquid levels in a vehicle tank via radar level sensing, wherein the liquid levels are expected to change angularly over time, the system comprising a radar level sensing system comprising a radar signal lens configured to emit a plurality of microwave signals in a cone shape. The level sensing system may generally use more than a single measurement point in order to identify a liquid level angle alpha within the tank. The cone shape may be defined by more than one microwave signal that is transmitted along a dimension that is angled outwardly from a vertical axis aligned with the radar signal lens. In some examples, the radar level sensing system is mounted directly to the tank. The tank may have a window to shield the radar signal lens from a tank interior. In other examples, the radar level sensing system is mounted remotely from the tank.

[0009] In use, the radar level sensing system transmits a plurality' of microwave signals toward a surface of liquid enclosed in the tank, receives the plurality of microwave signals as reflected against the surface of the liquid, calibrates an angle (alpha) of the surface of the liquid with respect to an upper surface of the tank, and calculates the level of the liquid in the tank from the propagation time of the transmitted and reflected microwaves. There may be a signal processing device configured to receive information about the propagation time and calculate the level of the liquid contained in the tank. There may be calibration software configured to receive and send infonnation to the signal processing device. In a specific example, the vehicle is an aircraft.

[0010] There is also provided a method of sensing liquid level in an aircraft tank in which liquid levels are expected to change angularly over time, the method comprising: transmitting a plurality of microwave signals toward a surface of liquid enclosed in the tank, receiving the plurality of microwave signals as reflected against the surface of the liquid; calibrating an angle (alpha) of the surface of the liquid with respect to an upper surface of the tank; and calculating the level of the liquid in the tank from the propagation time of the transmitted and reflected microwaves. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a side plan view of one embodiment of a radar level sensing system mounted on a fluid tank.

[0012] Figure 2A is a side plan schematic view of an aircraft fluid tank with fluid maintained at a stable level.

[0013] Figure 2B is a side plan schematic view of the fluid tank of FIG. 2A when the aircraft is on descent, such that fluid contained within the tank is at an angle.

[0014] Figure 3A is a side plan view of a radar level sensing system mounted within the tank of Figure 2A.

[0015] Figure 3B is a side plan view of a radar level sensing system mounted within the tank of Figure 2B.

[0016] Figure 4 is a side plan view of one embodiment of a radar level sensing system mounted externally to a fluid tank.

[0017] Figure 5A is a side perspective view of a radar level sensing system mounted externally to a horizontal tank with the fluid maintained at a stable level.

[0018] Figure 5B is a side perspective view of the tank of Figure 5 A, showing fluid within the horizontal tank at an angle.

[0019] Figure 6A is a side perspective view of a radar level sensing system mounted externally to a vertical tank with the fluid maintained at a stable level.

[0020] Figure 6B is a side perspecti ve view of the tank of Figure 6A, showing fluid within the vertical tank at an angle.

[0021] Figure 7 is a flowchart illustrating flow of information during liquid level sensing.

DETAILED DESCRIPTION

[0022] The described embodiments provide liquid level sensing using radar technology. The disclosure provides a system that can measure liquid levels enclosed in a tank or other container that does not maintain a static position. For example, aircraft and other vehicles experience various types of movement that can cause liquid level to change independently from the amount of liquid actually present in the tank. This may be due to a taxiing (or an ascent) angle, a landing (or a descent) angle, turbulence, or other aircraft movement. The system is thus designed to sense liquid level at many points, rather than at a single point reading. The system is also designed to function independent of the pressure level, vacuum, temperature, geometry, shape, or environment of the tank. For example, a liquid level may be sensed in a tank that has air or a vacuum in the space above the liquid contained therein.

[0023] The system is also designed to function without contacting the fluid. This prevents errors due to accumulation of dirt or foreign bodies on sensors or sensor components. This also prevents the need to clean sensors or sensor components in order to obtain accurate sensing. The system is also designed to function accurately in sensing fluids that are soapy, foamy, viscous, or sticky. The system may sense liquid level of fluids such as water, fuel, or liquid waste. The system may sense liquid level of fluids that are considered mixed-media (e.g., liquids that may be mixed with solids or that form a slurry or other type of viscous media), one example of which may be an aircraft waste tank.

[0024] hi a specific embodiment, this disclosure relates to use of radar for liquid level measurement in a tank. Using radar for liquid level sensing generally involves transmitting microwaves toward the surface of the liquid, receiving the microwaves as reflected against the surface of the liquid, and calculating the level of the liquid in the tank from the propagation time of the transmitted and reflected microwaves. For example, as illustrated by Figure 1, a radar level sensor system 10 may be mounted on (or otherwise associated with, as described further below) a tank 12 filled with liquid 14. When a level sensing process is initiated, the system 10 transmits a microwave signal 16 toward the surface of the liquid 14 in the tank 12 and receives the microwave signal 16 as reflected against the surface of the liquid 14, as illustrated by arrow 18. The system 10 is generally connected to (or associated with) a signal processing device for calculating, from the propagation time of the transmitted and reflected microwave signal, the level of liquid in the tank. There is no need for an intrusive sensor that is in contact with the fluid for level sensing using this method.

[0025] It has been found that one of the benefits of using radar level sensing on aircraft is that radar level sensing does not require a particular atmosphere and is not affected by pressure. More specifically, radar level sensing can function in a vacuum. Specifically, the air pressure on the head of the liquid is irrelevant. The tank may be under vacuum or at very high pressure. Aircraft waste tanks, potable water tanks, or other tanks may often be under vacuum. (For example, an order for an aircraft toilet to flush, a pressure differential between the toilet bowl and the main waste tank is required, which may be provided either by a vacuum generator or via aircraft pressure differential provided in flight.) By contrast, use of ultrasonic level sensing requires that the signal be sent through air, and does not work in a vacuum. [0026] Radar level sensing can also be adapted to be used with different types of fluids. All that is required is the ability to reflect a microwave signal off of a surface of liquid. The radar measures that distance based on the travel time of the microwave signals.

[0027] It is generally envisioned that the radar signal lens that delivers the microwave signal can be calibrated based on the size of th e tank 12 so that tank volum e can be taken into account during these distance calculations. The tank volume can be dependent upon tank geometry or shape; this relationship can be stored in one or more calibrations or lookup tables that can be stored in the software of the system, which calibration can be pre-programmed to be specific to a specific tank. The system 10 measures distances, and for each distance, a related volume is provided. For example, the software of the system 10 can be calibrated to “know” what a tank“full” level would be and what a tank“empty” level would be. This calibration only need take place when the system 10 is installed.

[0028] However, as described above, there may be instances when the liquid 14 in the tank 12 is not level. For example, referring now to Figures 2A and 2B, Figure 2A illustrates an example of a tank 12 that is generally stable or otherwise stationary, allowing the liquid 14 contained therein to be generally level. Yet there are instances when the tank 12 will not be stable or stationary. Figure 2B illustrates an example in which the tank 12 is angled, which results in the liquid 14 contained therein to form angles other than generally 90° with respect to tank sides 20. In this example, the tank 12 is mounted within an aircraft that is descending, causing the liquid 14 to slosh forward in the tank 12. Some prior liquid level sensing systems have attempted to address this liquid angle by retying on aircraft data about acceleration, deceleration, altitude, and other parameters in order to compensate for liquid movement. The present disclosure provides a solution that does not rely on aircraft data in order to obtain accurate liquid level sensing.

[0029] Referring now to Figures 3A and 3B, rather than sending a microwave signal along a single line to obtain a single data point, the disclosed radar level sensor system 10 transmits its microwave signals 16 in a cone shape 22. This means that the sensor uses more than a single point in order to determine a liquid level calculation. In one example, the cone shape may be defined by more than one microwave signal 16 that is transmitted along a dimension that is angled outwardly from a vertical axis 24 aligned with a radar signal lens 26 (which fimctions as the“eye” or transmitter/receiver of the microwave signals). Figure 3A illustrates how this transmission may take place with a level fluid 14A. Figure 3B illustrates how this transmission may take place with an angled fluid 14B. In Figure 3B, the radar signal lens 26 sends more than one microwave signal 16. A signal processing device can calculate, from the propagation time of the transmitted and reflected microwave signals, the level of liquid in the tank. This may be done by also determining the angle alpha 28 that the angled liquid 14B makes with the upper surface 30 of the tank 12. In one example, the disclosed radar signal -based angle measurement may be done by use of one transmitter and two receivers. In another example, the measurement may be done by use of two transmitter/receiver combinations. The receiver (antennas) may be located a certain distance in the sensor. The two distances to the liquid surface are measured, one from each receiver. When the liquid is not angled within the tank, both distances will be about equal. When the liquid within the tank is angled, the measured distances are different due to receiver locations. With the receiver location difference being a known variable, the angle can be calculated with the two measured distances to the liquid surface using trigonometric functions. This allows the system to compensate the value based on the measure distances and the calculated angle in order to determine the liquid level in the tank as if the aircraft were flying steadily. This compensation and use of more than a single point allows the radar level sensor system 10 to map out the surface of the liquid 14 and calculate the angle alpha 28 without using additional data or parameters from the aircraft system.

[0030] Alternative means of angle measurement can be performed e.g. by use of a G- sensor located in the level sensor. This provides the X- Y- Z- components of a 3 dimensional acceleration vector. On ground, the X- (longitudinal) component and the Y- (lateral) component are zero. The Z-(normal) component is equal to gravity G. When tank with the level /G sensor is inclined (e.g. due to various flight events already described), the gravity force dissipates on X- Z- components. Given that X- and Z- components are orthogonal to each other, the angle can be calculated by trigonometric functions as G-force is the resultant in a XZ vector diagram (in a 2-dimensional view).

[0031] The measurement procedure may be as follows:

[0032] The level sensor measures distance to liquid surface and a determines surface inclination angle. The liquid level is calculated with regard to tank constant data. Depending on tank shape and geometry, a lookup table may be used for tank content conversion. In some cases, a mathematical approach based on tank location data can be used as well. Calculated level represents value for a non-inclined tank. It is then possible to calculate either a percentage value 0% to 100% or to a certain volume in gallons or liter. Depending on tank geometry volume, conversion table(s) may be used. This calculation may all be done via various processors, software, and hardware configured with the calculation parameters. An example of this flow of information is provided at Figure 7.

[0033] Figure 1 shows the system 10/radar signal lens 26 as being mounted to the tank 12 itself. In this example, certain components of the system 10 may be positioned external to the tank, with a window 32 positioned within one of the tank walls to protect the radar signal lens 26. This embodiment may be particularly useful for use with tanks that are stainless steel, carbon fiber, or other type of material that is not penetrable by microwave signals. The window 32 may function as a shield for the radar signal lens 26 so that the surface of the lens is not affected by accumulation of dirt, debris, foam, or any other material contained within the tank 12 that could otherwise compromise the radar signal lens 26. This isolates the radar signal lens

26 from any liquid contained in the tank 12. There is no contact between the internal portion of the tank on the radar signal lens 26. The mount may be done via a flange mount on the tank surface. The window 32 is generally made of a material that is transmissive or otherwise penetrable by microwave signals. The window 32 may be transparent, but that is not required. Exemplary materials for the window include but are not limited to plastic, fiberglass, glass, composite materials, or any combination thereof.

[0034] Figure 4 shows the entire system 10, including the radar signal lens 26, mounted externally to the tank 12. In this example, the tank 12 itself is of a material that can be penetrated via the microwave signal delivered by the system 10 for example, the tank itself may be a plastic tank, fiberglass, glass, composite materials or any other material that transmits microwave signals. In this embodiment, there is no opening on the tank 12 required for mounting the system 10.

[0035] Figures 5A-5B and 6A-6B show the system 10/radar signal lens 26 as being mounted a distance X from the tank 12. Figures 5A and 5B illustrate a horizontal tank, and Figures 6A and 6B illustrate a vertical tank. In other words, the system 10 is not fixed directly onto the tank, but may be mounted to a surface 34 raised away from the tank 12. In these examples, the tank 12 is of a material that can be penetrated via the microwave signal delivered by the system 10 as described immediately above. One advantage of this embodiment as that the system 10 can be replaced without affecting the tank. The tank structure integrity is not disturbed. This version may also offer modularity as to if and when the tank itself needs to be replaced. Replacement of the tank may be done independently of the status of the system 10. Just as the tank calibration is described above, this embodiment of the system 10 would be calibrated so that the distance X between the mount location of the system 10 and the tank 12 is a known variable and accounted for with the calibration.

[0036] In an alternate version of this remote installation, it is possible to provide a telescopic mechanism 36 that allows the system 10 to travel up or down with respect to the tank 12. For example, the system 10 may be mounted along a ceiling area, with the tank 12 mounted along a floor area. The telescopic mechanism 36 can be activated to move the radar signal lens 26 closer to the tank 12 if necessary. In a specific example, the telescopic mechanism 36 may be concentric tubular sections that are designed to slide into one another, which can prevent intrusion into headspace in the environment where the tank 12 is installed. Calibration and information about the position of the telescopic system (whether retracted or extended) is incorporated into the calibration tables.

[0037] In one embodiment, a previous liquid level can be stored in memory, for example, the last value stored. If the next measured value is out of an expected range (which range may be set by predetermined values), an alarm or other monitor may be activated.

[0038] In a further embodiment, liquid level data collected over a period of time can be stored for future reference and servicing of the tanks based on historical data.

[0039] In a further embodiment, the readings obtained from the system can be transmitted wirelessly to handheld devices for ease of monitoring and servicing of the system and/or the tank. Accordingly, the technology may be applied to fuel level detection and monitoring or servicing.

[0040] In summary, advantages of the disclosed system may be beneficial for application to water and waste level sensing and an aircraft fitted with the water and waste system for use with galley and lavatory needs and flight. Advantages of the disclosed system may also be beneficial for other fluid systems on board an aircraft, such as potable water tanks and/or fuel tanks. The data collected provides a nonintrusive way to accurately detect liquid levels. This data may be used for ease of use and servicing, calculating and reporting volume/weight of fluid in a given tank, assisting with reloading of water or emptying waste as needed. In general, accurate liquid level sensing can assist airline operators with more efficient turnaround time and cost savings.

[0041] Although this disclosure is described with respect to a waste tank, a water tank, or a fuel tank of an aircraft or other passenger transportation vehicle, it should be understood that the technology described herein as potential for use in any instance when liquid levels may change in a tank. [0042] The subject matter of certain embodiments of this disclosure is described with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described.

[0043] It should be understood that different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and sub-combinations are useful and may be employed without reference to other features and sub-combinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications may be made without departing from the scope of the claims below.

Claims

CLAIMS That which is claimed is:

1. A level sensing system for measuring liquid levels in a vehicle tank via radar level sensing, wherein the liquid levels are expected to change angularly over time, the system comprising: a radar level sensing system (10) comprising a radar signal lens (26) configured to emit a plurality of microwave signals (16) in a cone shape (22).

2. The level sensing system of claim 1, wherein the system uses more than a single measurement point in order to identity a liquid level angle alpha (28) within the tank (12).

The level sensing system of claim 1 , wherein the cone shape (22) is defined by more than one microwave signal (16) that is transmitted along a dimension that is angled outwardly from a vertical axis (24) aligned with the radar signal lens (26).

4. The level sensing system of claim 1, wherein the radar level sensing system (10) is mounted directly to the tank.

5. The level sensing system of claim 4, wherein the tank comprises a window (32) to shield the radar signal lens (26) from a tank interior.

6. The level sensing system of claim 1, wherein the radar level sensing system (10) is momited remotely from the tank.

7. The level sensing system of claim 1, wherein the radar level sensing system (10) transmits a plurality of microwave signals (16) toward a surface of liquid enclosed in the tank (12), receives the plurality of microwave signal s as reflected against the surface of the liquid, calibrates an angle alpha (28) of the surface of the liquid with respect to an upper surface (30) of the tank (12), and calculates the level of the liquid in the tank from the propagation time of the transmitted and reflected microwaves.

8. The level sensing system of claim 7, further comprising a signal processing device configured to receive information about the propagation time and calculate the level of the liquid contained in the tank.

9. The level sensing of claim 7, further comprising calibration software configured to receive and send information to the signal processing device.

10. The level sensing of claim 1, wherein the vehicle is an aircraft.

11. A method of sensing liquid level in an aircraft tank in which liquid levels are expected to change angularly over time, the method comprising: transmitting a plurality of microwave signals (16) toward a surface of liquid enclosed in the tank (12), receiving the plurality of microwave signals as reflected against the surface of the liquid; calibrating an angle alpha (28) of the surface of the liquid with respect to an upper surface (30) of the tank (12); and calculating the level of the liquid in the tank from the propagation time of the transmitted and reflected microwaves.