WO2019140055A1

WO2019140055A1 - Radio frequency based liquid level sensor

Info

Publication number: WO2019140055A1
Application number: PCT/US2019/012996
Authority: WO
Inventors: Martin N. Andersson; Cyrus M. Healy; Gerald J. LAMARR Jr.; Robby L. LINTON
Original assignee: Walbro LLC
Current assignee: Walbro LLC
Priority date: 2018-01-11
Filing date: 2019-01-10
Publication date: 2019-07-18
Anticipated expiration: 2020-07-11

Abstract

In at least some implementations, a liquid tank and liquid level measuring assembly includes a liquid tank having an interior and an exterior, the interior configured to hold liquid, a carrier received within the interior of the liquid tank and moveable in response to changes in the level of liquid in the interior, a first RF device received outboard of the interior, and a second RF device coupled to the carrier for movement with the carrier. The first RF device and second RF device are wirelessly communicated with each other via a radio frequency transmission to permit determining one or both of: a distance between the first RF device and second RF device and a time for RF transmissions between the first RF device and the second RF device, wherein the distance or time is a function of the liquid level in the liquid tank.

Description

RADIO FREQUENCY BASED LIQUID LEVEL SENSOR

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Serial No. 62/616,120 filed on January 11, 2018 the entire contents of which are incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to measuring the level or volume of a liquid in a liquid tank.

BACKGROUND

A fuel level sensor may include a float linked to a wiper of a variable resistor assembly to vary the resistance value of the resistor in accordance with the position of the float which tracks the level of fuel in a fuel tank. As the level of fuel within the fuel tank changes, the float moves and thereby moves the wiper which varies the effective resistance of the variable resistor. In accordance with the change in resistance, an output signal changes and, thus, effects a change- -such as from“full" toward "empty"— in a remote fuel level indicator. The accuracy of the fuel level indication may be affected by the placement of the fuel level sensor (e.g. the float) within the fuel tank and changes in the position of the fuel level sensor. Further, the fuel or other liquid used with the level sensor may fowl the resistor and or the wiper and thus inhibit or prevent suitable electrical contact between the wiper and the resistor. This can negatively affect or destroy the operation of the level sensor. SUMMARY

In at least some implementations, a liquid tank and liquid level measuring assembly includes a liquid tank having an interior and an exterior, the interior configured to hold liquid, a carrier received within the interior of the liquid tank and moveable in response to changes in the level of liquid in the interior, a first RF device received outboard of the interior, and a second RF device coupled to the carrier for movement with the carrier. The first RF device and second RF device are wirelessly communicated with each other via a radio frequency transmission to permit determining one or both of: a distance between the first RF device and second RF device and a time for RF transmissions between the first RF device and the second RF device, wherein the distance or time is a function of the liquid level in the liquid tank. One or both of the first RF device and second RF device may be integrated with or in communication with a controller capable of determining a time for a radio frequency transmission from one of the first RF device and second RF device to the other.

In at least some implementations, a restriction device is carried by the liquid tank and arranged to constrain the path of movement of the carrier. At least a majority of the path of movement of the carrier may be parallel to the direction of the force of gravity or within 20 degrees of being parallel to the direction of the force of gravity. The restriction device may include a tube having an inner volume in which the carrier is received and having one or more openings that communicate with the interior. Thus, liquid in the tank may enter the inner volume of the tube and act on the carrier within the tube.

In at least some implementations, a third RF device and a fourth RF device are provided and both the third RF device and the fourth RF device are outboard of the interior of the liquid tank and in communication with the second RF device via radio frequency transmission, and the distance from the second RF device to the other RF devices is a function of the liquid level within the liquid tank. The first RF device, third RF device and fourth RF device may all be spaced apart from each other at predetermined distances. And a first line between the first RF device and the third RF device, a second line between the third RF device and the fourth RF device, and a third line between the fourth RF device and the first RF device may form a triangle. The carrier may be buoyant in the liquid in the interior and movement of the carrier in at least some implementations is restrained only by the liquid and walls of the liquid tank.

In at least some implementations, the carrier is buoyant in the liquid within the interior. In at least some implementations, the radio frequency transmission between the first RF device and second RF device passes through a wall of the liquid tank.

In at least some implementations, a method of determining the level of a liquid within a liquid tank includes:

a) sending a first radio frequency transmission from a first RF device;

b) receiving the first transmission at a second RF device;

c) sending a second radio frequency transmission from the second RF device;

d) receiving the second transmission at the first RF device;

e) determining a lapsed time between steps (a) and (d); and

f) determining a level of liquid within the liquid tank as a function of the time determined in step (e).

The method may also includes the steps of:

g) receiving the second transmission at a third RF device that is spaced apart from the first RF device;

h) determining a lapsed time between steps (c) and (g), and wherein the determination of the level of liquid in step (f) is accomplished as a function of the determined times in steps (e) and (h).

And the method may further include the steps of:

i) receiving the second transmission at a fourth RF device that is spaced apart from the first RF device and third RF device;

j) determining a lapsed time between steps (c) and (i), and wherein the determination of the level of liquid in step (f) is accomplished as a function of the determined times in steps (e), (h) and (j)·

In at least some implementations, a liquid level measuring assembly includes a pressure sensor that provides an output as a function of the mass of a liquid acting on the pressure sensor, a first RF device configured to receive radio frequency transmissions, and a second RF device associated with the pressure sensor to provide a radio frequency transmission that varies as a function of a pressure sensed by the pressure sensor and which is receivable by the first RF device. A liquid tank may be provided that has an exterior that is defined at least in part by a lower wall and an interior in which a supply of liquid is maintained, and the interior includes a lower portion in which liquid is maintained and an upper portion above the liquid, and the pressure sensor may be carried by the lower wall.

In at least some implementations, a barrier is disposed between the liquid in the lower portion and the pressure sensor so that the pressure sensor is not directly contacted by the liquid.

The barrier may be moveable in response to the mass of liquid above the barrier to transmit a force to the pressure sensor that corresponds to the mass of liquid above the pressure sensor. In at least some implementations, the first RF device is carried by the lower wall or the upper wall.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of certain embodiments and best mode will be set forth with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side view of a liquid tank including a Radio Frequency (RF) level sensor assembly; FIG. 2 is a flow chart of a method of operating a RF level sensor assembly;

FIG. 3 is a diagrammatic perspective view of a liquid tank;

FIG. 4 is a schematic view showing representative RF transmissions between multiple RF devices;

FIG. 5 is a flow chart of a method of operating a RF level sensor assembly;

FIG. 6. is a diagrammatic side view of a liquid tank including a RF and pressure sensor level sensor assembly; and

FIG. 7 is a diagrammatic side view of a liquid tank including a RF and pressure sensor level sensor assembly.

DETAILED DESCRIPTION

Referring in more detail to the drawings, FIG. 1 illustrates a liquid tank 10 with a liquid level sensor 12 arranged to provide an indication of the level of liquid (i.e., volume of liquid) within the liquid tank 10. The liquid level sensor 12 may include multiple radio frequency (RF) devices arranged to permit a determination of the relative amount of liquid with the tank. Various implementations of the liquid level sensor that include different arrangements of RF devices, are set forth below.

The liquid tank 10 may be utilized to hold fuel that is delivered to an engine for a vehicle (e.g., automobile, snowmobile, marine vehicle, ATV, etc.) or tool (e.g., chainsaw, lawn mower, blower, etc.), to hold any other type of liquid for a vehicle (e.g., transmission fluid, power steering fluid, washer fluid, etc.), or any other liquid, as desired. The liquid tank 10 may be made of any suitable material (e.g., plastic such as nylon or high-density polyethylene (HDPE), steel, aluminum, etc.), may be formed in a single layer or multiple layers, and may be manufactured by any suitable metalwork process (e.g., hemming, soldering, brazing, etc.) or any suitable molding process (e.g., blow molding, injection molding, etc.). The liquid tank 10 may, among other features, have at least one closable opening for filling the liquid tank 10 with liquid and may have at least one outlet from which liquid exits the tank. The liquid tank 10 has an interior 14 defined at least in part by a wall 16. The tank wall 16 may have any suitable thickness, may have a uniform or a variable thickness, and may be of any desired shape.

The liquid level sensor 12 may include a first RF device 18, a second RF device 20 that is wirelessly communicated with the first RF device, and a carrier 22 that is responsive to changes in the level of liquid in the liquid tank 10. In at least some implementations, the carrier 22 is at least somewhat buoyant in and configured to float on the liquid held in the tank interior 14 so that the carrier 22 moves in response to changes in the level of liquid in the tank interior 14. In at least some implementations, the carrier 22 is formed from a polymeric or other material suitable for use in the liquid in the tank 10 and buoyant in the liquid.

The first RF device 18 may be located outside of the interior 14 of the liquid tank 10 and may be integrated with, coupled to, adjacent to, or completely separate from an exterior surface 28 of the tank wall 16. In at least some implementations, the first RF device 18 may be held against movement relative to the fuel tank 10. The first RF device 18 may be any device capable of sending and/or receiving RF transmissions and may include a resonator for tuning or transmitting a specific frequency or frequency range. The RF device may be an active or passive device. An active RF device (e.g., an RF reader or a radio frequency identifier (RFID) reader) is an RF device that may either continuously or intermittently broadcast its own signal, and a passive device may be a device that only responds after receiving a transmission from another RF device. At least some passive devices do not use a local power source and, instead, convert energy from a transmission that is sent from an active RF device into useable energy that powers the passive RF device. The active RF device may be powered by a local power source (e.g., a battery), ignition circuit, or other available power supply. The second RF device 20 may be coupled to or integrated with the carrier 22 so that the second RF device moves with the carrier as the liquid level in the tank 10 changes. And the second RF device 20 is in RF communication with the first RF device 18. The second RF device 20 may also be either active or passive, may be a reader, a tag, or both, and may include a resonator for tuning into a specific frequency or frequency range.

One or both of the RF devices 18, 20 may be in communication with a controller 30, and in FIG. 1 the first RF device 18 is shown as being coupled with or communicated with the controller 30. The controller 30 may include a microprocessor or microcontroller, have or be communicated with suitable memory and may be capable of storing and/or processing programs, instructions, look-up tables, data maps, and/or other information. The controller 30 may be integrated with, coupled to, adjacent to, or completely separate from the liquid tank 10 and may be integrated with or separate from the first RF device 18. The controller 30 may be capable of determining a time for an RF transmission from one of the RF devices 18 or 20 to the other of the RF devices 18 or 20. The communication between the first RF device 20 and the controller 30 could be one or more of an RF communication, other wireless communication, or a hard-wired connection, as desired.

The first RF device 18 and the second RF device 20 are in RF communication with each other without any hard-wire connection, thus eliminating the need for additional holes in the liquid tank 10 for wiring between the RF devices 18, 20. Among other things, fewer holes in the tank 10 results in less hydrocarbon permeation from the tank 10 when the liquid is gasoline, fewer holes to seal against leakage, and less wiring which reduces the cost and complexity of the system. The first RF device 18 and the second RF device 20 described in the above and below embodiments may be interchangeable such that the second RF device 20 may be located external to the tank 10 and the first RF device 18 may be coupled to or integrated with the carrier 22, if desired. In at least some implementations, the carrier 22 is constrained to move along a path that is defined at least in part by a restriction device 31 such that the majority of the movement path of the carrier 22 is parallel or generally parallel to the direction of gravity. Here,“generally parallel” shall mean plus or minus twenty degrees relative to the direction of gravity. In the embodiment shown in FIG. 1, the restriction device is an arm 31 that is coupled to a pivot 32 arranged such that the carrier 22 moves within a known path parallel or generally parallel to the direction of gravity as the liquid level changes in the tank 10. Alternatively or in addition, the restriction device 31 may be any device that keeps the carrier 22 within the path or field of transmissions between the first RF device 18 and the second RF device 20. Some non-limiting examples of restriction devices include: a vertically oriented tube (diagrammatically shown at 34 in FIG. 1) having one or more openings to permit liquid to enter an inner volume of the tube with the carrier 22 disposed within the inner volume of the tube, one or more posts that constrain movement of the carrier to parallel or generally parallel to the direction of gravity, one or more guide rods extending through one or more holes in the body of the carrier 22, a slider integrated with or connected to the tank wall 16, a force generator (e.g., a magnet), or any combination thereof. In FIG. 1, the tube 34 is shown with the arm 31 and pivot 32, so the tube 34 may include a slot or other void in which a bent portion of the arm 31 (or a pin coupled to the arm 31) is received to pass through the slot and be coupled with the carrier 22 and/or second RF device 20.

Referring to FIG. 2, a method 100 for determining the amount or level of liquid in the tank 10 begins with step 102 in which a first RF transmission is sent from the first RF device 18. The first RF transmission may be a transmission of any electromagnetic wave frequency or frequency sub-range within 120 kHz to 10 GHz that radiates away from the first RF device 18 in a consistent or predictable pattern. In at least one embodiment, frequency or sub-range is between 865 MHz and 930 MHz. Some implementations may use frequencies between 865 MHz and 868 MHz, which may provide sufficient range (e.g. 1 to 12 meters), a moderate to high bandwidth, be achieved with relatively low-cost devices and meet various standards (e.g. as presently exist in the European Union). Other implementations may use frequencies between 902 MHz and 928 MHz, which may provide sufficient range (e.g. 1 to 12 meters), a moderate to high bandwidth, be achieved with relatively low-cost devices. Of course, other frequencies and frequency ranges may be used as desired, including but not limited to currently used frequencies/ranges such as between l20-l50kHz, l3.56MHz, 433MHz, 2450-5800MHz, 3.l-l0GHz. The first RF transmission may be sent at predetermined intervals or may be sent when prompted by a user input.

In step 104, the first RF transmission is received at or by the second RF device 20. In at least some implementations, the second RF device 20 may be a passive device that is powered by the electromagnetic energy of the first RF transmission sent from the first RF device 18. The electromagnetic energy from the first RF transmission may“wake up” (i.e., power on) the second RF device 20 when the first transmission is received at the second RF device 20, or the second RF device 20 may already be fully powered and“awake.”

After receipt of the first RF transmission, a second RF transmission is sent from the second RF device 20 in step 106. In some embodiments, the second RF transmission may be sent as soon as possible after receiving the first RF transmission or may occur after a predetermined time lapse. The second RF transmission may be the same frequency or frequency sub-range as the first RF transmission or may be a different frequency or frequency sub-range within a 120 kHz to 10 GHz range. The second RF transmission may then be received by the first RF device 18 or the controller 30, in step 108.

After the second RF transmission is received by the first RF device 18, or by the controller 30, a total transmission time for the first and second transmissions is determined in step 110. The total lapsed time between steps 102 and 108 may be determined by any possible means. In at least some implementations, the controller 30 may record the time the first RF transmission is sent to the second RF device 20 and record the time the second RF transmission is received at the first RF device 18 or controller 30. Once the first and the second times are recorded, the controller 30 may determine the difference between the first and the second times. Alternatively, the first RF device 18 may start a timer when the first RF transmission is sent and then stop the timer when the second RF transmission is received to determine a total lapsed time. In at least some embodiments, the time lapse between receiving the first RF transmission and sending the second RF transmission is subtracted from the total lapsed time between steps 102 and 108 to determine the total transmission time for the first and second transmissions without such time including the time needed for the second RF device 20 to wake-up and transmit. With any delay caused by the second RF device 20 removed, the resulting time is a function of the distance between the first and second RF devices 18, 20. More specifically, the resulting time is the time required for RF transmission to travel twice the distance between the first RF device 18 and second RF device 20. In this way, the relative position of the second RF device 20 and carrier 22 can be determined and this corresponds to a fluid level or volume within the tank.

In some embodiments, the time lapse between steps 104 and 106 may be determined, at least in part, by determining the“wake up” time of the second RF device 20. The“wake up” time may be determined through testing, or an average expected“wake up” time may be used. Some embodiments may include determining the lapsed time between steps 104 and 106 by determining the time it takes for the second RF device to generate the second transmission and adding that time to transmit to the“wake up” time. Other embodiments may include any other means for determining the lapsed time between steps 104 and 106 before subtracting that time from the time lapse between steps 102 and 108. The method may then transition to step 112 or to step 114. In step 112, the distance between the first RF device 18 and the second RF device 20 is determined. The distance calculation of step 112 may be conducted using the controller 30 that is either integrated with or in communication with the first RF device 18, the second RF device 20, or both the first and second RF devices 18, 20. In one embodiment, the distance is determined by multiplying the velocity of electromagnetic waves (i.e., the speed of light) by half of the time lapse determined in step 110 (with the time to wake-up and generate a transmission from the second RF device 20 removed) to find the total distance between the first RF device 18 and the second RF device 20. This distance may be correlated to the instantaneous liquid level or volume within the tank, and the controller may provide a signal indicative of the fuel level to another controller or to a fuel level indicator viewable by an end user.

In step 114, a level of liquid within the liquid tank 10 is determined. In some embodiments, the level of liquid within the tank may be determined as a function of the time determined in step 110, as a function of the distance determined in step 112, or as a function of both the time determined in step 110 and the distance determined in step 112. In at least some embodiments, a lookup table or predetermined algorithm may be used to determine the level of liquid within the tank as a function of the time calculated in step 110 or the distance determined in step 112, or both. In one non-limiting example, a lookup table may be compiled from an initial calibration used to determine the relationship between the time calculated in step 110 and the distance calculated in step 112 for various levels of liquid within the specific liquid tank 10 being used. In other embodiments, the lookup table or predetermined algorithm may be the result of mathematical calculations, computer aided simulations, or exp erimentations .

FIG. 3 illustrates another embodiment of a liquid tank 10 with a liquid level sensor 40 arranged to provide an indication of the level of liquid within the liquid tank 10. The embodiment shown in FIG. 3 shares many of the same components as the embodiment shown in FIG. 1. The components and features that are the same as or substantially similar to those already described will not be described again, and the following description of the level sensor 40 will focus on the differences between this sensor 40 and the sensor 12 described above.

Some implementations may include more than two RF devices, and FIG. 3 shows four

RF devices: a first RF device 18, second RF device 20, third RF device 42 and a fourth RF device 44. The third RF device 42 and the fourth RF device 44 may be constructed and arranged like the first RF device 18 described above. In at least some embodiments, the first, third, and fourth RF devices 18, 42, 44 may be positioned outside of the tank interior 14, and the second RF device 20 may be coupled to or integrated with a carrier 22 such that the first, third, and fourth devices 18, 42, 44 remain static relative to one another, and the second RF device 20 moves relative to the other devices 18, 42 and 44. In other embodiments, the first, third, and fourth RF devices 18, 42, 44 may be coupled to or integrated with the carrier 22 inside of the liquid tank 10 and the second RF device 20 may be positioned external to the interior 14 of the liquid tank 10 such that the first, third, and fourth RF devices 18, 42, 44 remain static relative to one another. The first, third, and fourth RF devices 18, 42, 44 may each be in communication with the second RF device 20, and the first, third, and fourth RF devices 18, 42, 44 are spaced apart at predetermined distances such that lines drawn between each pair of RF devices (i.e., a line drawn between the first and third RF devices, between the third and fourth RF devices, and between the fourth and first RF devices 18) would result in a triangle.

In the embodiment shown in FIG. 3, the carrier 22 is restricted only by an interior surface 24 of the tank wall 16 and so the carrier 22 is able to move freely within the 3-dimensional space in the tank interior 14.

FIG. 4 illustrates one possible set of communication transmissions between the first, third, and fourth RF devices 18, 42, 44 and the second RF device 20. In this embodiment, the first RF device 18 sends a transmission 46 to the second RF device 20 and the second RF device

20 sends a transmission 48 that is received by each of the first, third, and fourth RF devices 18, 42, 44. In another embodiment, the second RF device 20 may receive transmissions from each of the first, third, and fourth RF devices 18, 42, 44. Other embodiments may include any combination of transmissions between the first, second, third, and fourth RF devices 18, 20, 42, 44.

FIG. 5 illustrates one method 120 for determining the level, amount or volume of liquid within the tank 10 based upon the transmissions between the RF devices 18, 20, 42 and 44. In step 122 a first RF transmission is sent from the first RF device 18, in step 124 the first RF transmission is received at the second RF device 20, and in step 126 a second RF transmission is sent from the second RF device 20. In this regard, steps 122, 124, and 126 may be the same as or similar to steps 102, 104, and 106, respectively, from method 100 described above.

In step 128 of method 120, the second RF transmission is received at each of the first, third, and fourth RF devices 18, 42, 44 and in step 130, one or more times are determined for the first and second RF transmissions. For example, one or all of the RF devices may be communicated with the controller 30, such as by a wireless or wired connection. In at least some implementations, each of the first, third and fourth RF devices 18, 42, 44 are coupled to the controller 30 so that the time at which transmissions are sent or received by these devices 18, 42, 44 may be determined by or via the controller. In the example where the first RF device 18 sends the transmission 46 to wake up the second RF device 20 and cause the second RF device 20 to send the second RF transmission 48, the first RF device is an active RF device and the second RF device 20 may be active or passive. Further, the third and fourth RF devices 42, 44 can also be active or passive, as desired.

In at least some implementations, the time from sending the first RF transmission (e.g. step 122) to the time that the first RF device receives the second RF transmission (e.g. step 128) is determined. As discussed above with regard to step 100, the time for the second RF device 20 to wake up and then send the second transmission may be subtracted to aid in determining the distance between the first RF device 18 and second RF device 20 as a function of the net time for the first and second RF transmissions to travel between the devices 18, 20. The distance between the second RF device and the third RF device may be determined, in at least some implementations, as a function of the time from when the second RF transmission is sent by the second RF device 20 and when that transmission is received by the third RF device. This may be done by comparison with one-half of the net time determined above with regard to the first RF device 18. That is, if the time from sending the second RF transmission to receipt by the third RF device 42 is greater than one-half of the net time determined above, then the second RF device 20 is farther away from the third RF device 42 than it is from the first RF device 18. Conversely, if the time from sending the second RF transmission to receipt by the third RF device 42 is less than one-half of the net time, then the second RF device 20 is closer to the third RF device 42 than it is to the first RF device 18. Similar determinations can be made with respect to the fourth RF device 44. And so, in step 132, the relative distance of the second RF device 20 to each of the first, third and fourth RF devices 18, 42, 44 can be determined as set forth above. Such distance determinations are optional and the method may instead use the relative elapsed times for the transmissions to determine the liquid level in the tank 10. That is, no discrete or separate distance determination may need to be performed and the calculations or determinations can be made as a function of the transmission and receipt times of the devices. That is, the transmission travel times and distances may be directly related and interchangeable in the method. The third and fourth RF devices 42, 44 could also or instead receive the first RF transmission and the distance between the second and third RF devices 20, 42 and the second and fourth RF devices 20, 44 can be determined as a function of the elapsed time between when the first RF transmission is received by the third and fourth RF devices 42, 44 and when the second RF transmission is received by the third and fourth RF devices 42, 44.

Wake-up and response times for each RF device may be subtracted or otherwise managed in the method, as desired.

In step 134, a level or volume of liquid within the liquid tank 10 is determined. In some embodiments, the level of liquid within the liquid tank 10 may be determined by triangulation or other trigonometric method using one or more of the various times determined in step 130 and/or the various distances calculated in step 132 to determine the position of the second RF device within the tank 10. If desired, an accelerometer or other inclination or attitude sensor can be provided in the system to determine the plane of the liquid in the tank 10 (a function of the orientation of the tank) in relation to gravity which can account for inclination or high G- force maneuvers that cause the plane of the fuel to change relative to the tank 10.

FIGS. 6 and 7 show two different embodiments of liquid level sensors 150, 152 arranged relative to a liquid tank 10 to provide an indication of the level of liquid within the tank 10. The liquid tank in each embodiment may be the same as the liquid tank 10 described in each of the above embodiments.

Both embodiments 150, 152 include a pressure sensor 154 in a lower portion of the liquid tank 10 so the pressure sensor is beneath, covered or overlied by liquid in the tank. In at least some implementations, the tank includes a lower wall 155 that defines a bottom of the tank (relative to the direction of gravity) and the pressure sensor may be fixed to or otherwise carried by the lower wall 155, such as within a carrier or housing 157 that is coupled to an inside surface of the lower wall 155. The pressure sensor 154 is responsive to the mass of the liquid maintained inside the liquid tank 10. In at least some implementations, the pressure sensor 154 may be protected from the mass of liquid in the liquid tank 10 by a barrier 156 (FIG. 7) disposed between the liquid and the sensor 154. The barrier 156 may be moveable in response to changes in the mass of the liquid above the barrier 156 to transmit a force to the pressure sensor 154 so that the pressure sensor 154 is responsive to changes in the mass of the liquid. In another embodiment, the barrier 156 is a flexible diaphragm made of corrosion resistant material with an air pocket 158 between the diaphragm 156 and the pressure sensor 154 such that, when the mass of fluid in the liquid tank 10 presses against the diaphragm, the air pressure inside of the air pocket asserts pressure on the pressure sensor 154, and a change in liquid mass results in a change in air pressure on the pressure sensor 154.

Both sensors 150, 152 include a first RF device 18 outside of the tank 10 and a second RF device 20 that is associated with the pressure sensor 154. As shown in FIG. 6, the first RF device 18 may be coupled to an upper wall 159 of the tank 10 and, as shown in FIG. 7, the first RF device may be coupled to the lower wall 155. Of course, other arrangements may be used, including connecting the first RF device to a sidewall of the tank or to a structure adjacent to the tank 10, as desired. The second RF device 20 may be coupled to or integrated with the pressure sensor 154 such that the second RF device 20 receives pressure information from the pressure sensor 154. In some embodiments, the second RF device may be a near field communications (NFC) device as shown in FIG. 7. An NFC device is an RF device that communicates with devices in near proximity.

The second RF device 20 sends a RF transmission that varies as a function of the signal from the pressure sensor 154. The RF transmission is received by the first RF device 20 which, as noted above, may be located outboard of the interior 14 of the liquid tank 10 and configured to receive the RF transmission from the second RF device 18. The first and second RF devices 18, 20 may also have the same characteristics as the devices described above or may be NFC devices. The first RF device 18 may be mounted to the liquid tank 10 or may be separate from the liquid tank 10.

The first RF device 18 (and optionally also the second RF device 20) may be in communication with a controller 30. The controller 30 may be integrated with, coupled to, adjacent to, or completely separate from the exterior surface 28 of the wall 16 of the liquid tank 10 and may be integrated with or separate from the first RF device 18. The communication between the first RF device 18 and the controller 30 could be an RF communication, other wireless communication, or a hard-wired communication. The second RF device 20 may transmit pressure information from the pressure sensor 154 to the first RF device which may in turn transmit the information (e.g. a signal that corresponds to the pressure information) to the controller 30. The pressure information may then be used to determine the level of liquid in the liquid tank. In one non-limiting example, the controller 30 would determine the level of liquid in the liquid tank as a function of the pressure information received from the second RF device 20

In some embodiments, the controller 30 may be in communication with other components external to the tank interior 14, such as communication with a user interface in a motored transport. Communications between the controller 30 and other components external to the tank interior 14 may be transmitted via RF communication, other wireless communication, or a hard- wired communication. In at least some implementations, a higher data bandwidth frequency or range of frequencies, such as (but not limited to) 3.1 to lOGHz, may be used in the implementation shown, for example, in FIG. 6, as the high data bandwidth may be useful in transmitting pressure data.

It is to be understood that the foregoing description is not a definition of the invention, but is a description of one or more preferred embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. For example, a method having greater, fewer, or different steps than those shown could be used instead. All such embodiments, changes, and modifications are intended to come within the scope of the appended claims.

As used in this specification and claims, the terms“for example,”“for instance,”

“e.g.,”“such as,” and“like,” and the verbs“comprising,”“having,”“including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.

Claims

CLAIMS What is claimed is:

1. A liquid tank and liquid level measuring assembly, comprising:

a liquid tank having an interior and an exterior, the interior configured to hold liquid; a carrier received within the interior of the liquid tank and moveable in response to changes in the level of liquid in the interior;

a first RF device received outboard of the interior; and

a second RF device coupled to the carrier for movement with the carrier, the first RF device and second RF device being wirelessly communicated with each other via a radio frequency transmission to permit determining one or both of: a distance between the first RF device and second RF device and a time for RF transmissions between the first RF device and the second RF device, wherein the distance or time is a function of the liquid level in the liquid tank.

2. The assembly of claim 1 which also includes a restriction device carried by the liquid tank and arranged to constrain the path of movement of the carrier.

3. The assembly of claim 2 wherein the at least a majority of the path of movement is parallel to the direction of the force of gravity or within 20 degrees of being parallel to the direction of the force of gravity.

4. The assembly of claim 1 wherein one or both of the first RF device and second RF device is integrated with or in communication with a controller capable of determining a time for a radio frequency transmission from one of the first RF device and second RF device to the other.

5. The assembly of claim 1 which also includes a third RF device and a fourth RF device, both the third RF device and the fourth RF device are outboard of the interior of the liquid tank and in communication with the second RF device via radio frequency transmission, wherein the distance from the second RF device to the other RF devices is a function of the liquid level within the liquid tank.

6. The assembly of claim 1 wherein the carrier is buoyant in the liquid within the interior.

7. The assembly of claim 1 wherein the radio frequency transmission between the first RF device and second RF device passes through a wall of the liquid tank.

8. The assembly of claim 2 wherein the restriction device includes a tube having an inner volume in which the carrier is received and having one or more openings that communicate with the interior.

9. The assembly of claim 5 wherein the first RF device, third RF device and fourth RF device are all spaced apart from each other at predetermined distances.

10. The assembly of claim 9 wherein a first line between the first RF device and the third RF device, a second line between the third RF device and the fourth RF device, and a third line between the fourth RF device and the first RF device forms a triangle.

11. The assembly of claim 5 wherein the carrier is buoyant in the liquid in the interior and movement of the carrier is restrained only by the liquid and walls of the liquid tank.

12. A method of determining the level of a liquid within a liquid tank, comprising:

a) sending a first radio frequency transmission from a first RF device;

b) receiving the first transmission at a second RF device;

c) sending a second radio frequency transmission from the second RF device;

d) receiving the second transmission at the first RF device;

e) determining a lapsed time between steps (a) and (d); and

13. The method of claim 12 which also includes the steps of:

14. The method of claim 13 which also includes the steps of:

j) determining a lapsed time between steps (c) and (i), and wherein the determination of the level of liquid in step (f) is accomplished as a function of the determined times in steps

(e), (h) and (j)·

15. A liquid level measuring assembly, comprising:

a pressure sensor that provides an output as a function of the mass of a liquid acting on the pressure sensor;

a first RF device configured to receive radio frequency transmissions; and

a second RF device associated with the pressure sensor to provide a radio frequency transmission that varies as a function of a pressure sensed by the pressure sensor and which is receivable by the first RF device.

16. The assembly of claim 15 which also includes a liquid tank having an exterior that is defined at least in part by a lower wall and an interior in which a supply of liquid is maintained, and the interior includes a lower portion in which liquid is maintained and an upper portion above the liquid, and wherein the pressure sensor is carried by the lower wall.

17. The assembly of claim 15 which also includes a barrier disposed between the liquid in the lower portion and the pressure sensor so that the pressure sensor is not directly contacted by the liquid, wherein the barrier is moveable in response to the mass of liquid above the barrier to transmit a force to the pressure sensor that corresponds to the mass of liquid above the pressure sensor.

18. The assembly of claim 16 wherein the first RF device is carried by the lower wall.

19. The assembly of claim 16 wherein the first RF device is carried by the upper wall.