Magnetostrictive liquid density detector

A fluid level probe for use in a tank containing a first fluid, including a probe shaft, a first float with a first magnet that is slidably disposed for movement along the probe shaft and adapted to float at the top surface of the first fluid, a second float with a first magnet that is slidably disposed for movement along the probe shaft beneath the first float and adapted to float within the first fluid, and electronics adapted to determine a first distance between the first magnet of the first float and the first magnet of the second float which is used to determine a first density of the first fluid.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method used in a fuel storage tank that can be used to determine the density of the fuel stored within the fuel storage tank.

BACKGROUND OF THE INVENTION

This application incorporates herein by reference in its entirety the disclosures of U.S. Pat. No. 7,403,860, issued Jul. 22, 2008, and U.S. Published Application No. 2006/0169039, published Aug. 3, 2006.

Fueling environments typically store fuel in large storage tanks located beneath the ground, sometimes referred to as “underground storage tanks” (UST). To comply with environmental laws, rules, and regulations, these storage tanks may be double-walled and equipped with various leak detection sensors and inventory reconciliation systems. One popular leak detection sensor is sold by Veeder-Root Company of 125 Powder Forest Drive, Simsbury, Conn. 06070, the assignee of the present application, under the name “The MAG Plus Inventory Measurement Probe” (Mag Probe). This probe is typically matched with a tank monitor, such as the TLS-350R, also sold by Veeder-Root Company. Such probes measure a height of fuel within the storage tank and may optionally measure a height of water (if present). The measurements are reported to the tank monitor for usage by the operator of the fueling environment to evaluate and reconcile fuel inventory and/or detect leaks, as is well understood.

While the United States has many rules and regulations relating to leak monitoring within fueling environments, other locales have additional requirements for fueling environments. For example, countries such as India and Russia have seen a rise in fraud at fueling environments, and have consequently taken steps to combat such fraud. Specifically, these countries have become aware that dilution of the fuel within storage tanks may be used as a technique to defraud a customer. One way in which the diluted fuel is created is through the addition of alcohol to the fuel storage tank. The alcohol allows the water at the bottom of the fueling tank to mix with the fuel, and the diluted mixture is then dispensed as normal through the fuel dispensers.

To combat this fraud, some governments have mandated that fuel density be measured. If the density is outside of a predetermined allowable range, it may be inferred that the fuel has been adulterated. Even if some countries or governments do not have such legislation requiring measurement of fuel density, some fuel distribution companies that operate service stations may nonetheless find it desirable to monitor the density of their fuels for quality control purposes.

Density measurements also assist in calculation of the mass of fluid within a storage container. Differences in mass may be used to perform leak detection for fluids in situations where normal volume detection techniques are inadequate (e.g., waste oil storage containers). These situations create additional demand for density measuring devices.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a fluid level probe for use in a tank containing a first fluid, including a probe shaft with a top end and a bottom end. A first float carrying a first magnet is slidably disposed for movement along the probe shaft and adapted to float at the top surface of the first fluid and a second float carrying a first magnet is slidably disposed for movement along the probe shaft beneath the first float and adapted to float within the first fluid such that there is magnetic repulsion between the first magnet of the first float and the first magnet of the second float. Electronics are operative to determine a first distance between the first magnet of the first float and the first magnet of the second float.

Another embodiment provides a fluid level probe for use in a tank containing a first fluid and a second fluid forming an interface therebetween. The fluid level probe includes a probe shaft with a top end and a bottom end. A first float carrying a first magnet is slidably disposed for movement along the probe shaft and adapted to float at the interface between the first fluid and the second fluid and a second float carrying a first magnet is slidably disposed for movement along the probe shaft above the first float and adapted to float within the first fluid such that there is magnetic repulsion between the first magnet of the first float and the first magnet of the second float. Electronics are operative to determine a first distance between the first magnet of the first float and the first magnet of the second float.

Yet another embodiment provides a fluid level probe for use in a tank containing a first fluid including a probe shaft with a top end and a bottom end. A first float carrying a first magnet and a second magnet is slidably disposed for movement along the probe shaft and a second float carrying a first magnet is slidably disposed for movement along the probe shaft between the first magnet and the second magnet of the first float and adapted to float within the first fluid such that there is magnetic repulsion between the first magnet of the first float and the first magnet of the second float and also between the second magnet of the first float and the first magnet of the second float. Electronics are operative to determine a first density of the first fluid adjacent the second float based on spacing between the first magnet and the first float and the first magnet of the second float and between the second magnet of the first float and the first magnet of the second float.

Another embodiment provides a fluid level probe for use in a tank containing a first fluid, including a probe shaft with a top end and a bottom end, a first repulsion magnet and a second repulsion magnet being disposed at fixed positions along the probe shaft, and a first float carrying a first magnet that is slidably disposed for movement along the probe shaft between the first repulsion magnet and the second repulsion magnet and adapted to float within the first fluid such that there is magnetic repulsion between the first magnet of the first float and the first repulsion magnet and also between the first magnet of the first float and the second repulsion magnet. Electronics are operative to determine at least a first distance between one of the first repulsion magnet and the second repulsion magnet and the first magnet of the first float.

Yet another embodiment provides an apparatus for determining density of a fluid including a first magnet, a float carrying a second magnet oriented such that there is magnetic repulsion between the first magnet and the second magnet, and structure constraining movement of the float toward and away from the first magnet as the density of the fluid changes. Electronics are operative to determine the density of the fluid utilizing spacing between the first and second magnets.

Another embodiment provides a method of determining the density of a fluid, including providing a probe shaft including a top end and a bottom end; providing a first float, the first float being slidably disposed for movement along the probe shaft and float at a top surface of the fluid; providing a second float, the second float being slidably disposed for movement along the probe shaft beneath the first float and adapted to float within the fluid; determining a first position of the first float relative to the probe shaft; determining a second position of the second float relative to the probe shaft; determining a first distance that exists between the first position and the second position; and determining a first density of the fluid adjacent the top surface by utilizing the first distance.

Yet another embodiment provides a method of determining the density of a fluid dispersed in a tank with a fluid level probe including a probe shaft, a first float and a second float, including determining a first position of the first float relative to the probe shaft; determining a second position of the second float relative to the probe shaft; determining a first distance between the first position and the second position; and utilizing the first distance to determine a first density of the fluid adjacent the first float and the second float.

Other objects, features and aspects for the present invention are discussed in greater detail below. The accompanying drawings are incorporated in and constitute a part of this specification, and illustrate one or more embodiments of the invention. These drawings, together with the description, serve to explain the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention provide a fuel level probe that measures fuel density as well as fuel height in a fuel storage tank. An exemplary fuel level probe is a magnetostrictive probe which has a probe shaft inserted into and fixed with respect to the storage tank. The probe has a reference magnet positioned proximate to a terminal end of the probe shaft. A water level float, typically an annular float, is positioned on the probe shaft and floats at the level of the water-fuel interface. A water level magnet is associated with the water level float so that the level of the water in the fuel storage tank can be ascertained.

A fuel level float, also generally an annular float, is positioned on the probe shaft and floats at the air-fuel interface. A fuel level magnet is associated with the fuel level float so that the level of the fuel in the fuel storage tank can be ascertained. The water level and fuel level floats move freely up and down the probe shaft as the respective levels of fluids (water and fuel) change.

To determine the fuel level and the water level within the fuel storage tank, the probe sends an electric current down a magnetostrictive wire within the probe shaft. The current in the magnetostrictive wire interacts with the magnets and introduces torsional wave reflections in the wire which are detected by a sensor in the probe. The time elapsed between the signal generation and the arrival of the reflections may be used to measure the distance from the sensor to the respective magnet. In accordance with the present invention, the probe is also adapted to determine fuel density. The probe may either perform the calculations to arrive at the density of the fuel or may report its measurements to a tank monitor or other controller so that the controller may perform the calculations to determine the density of the fuel. The density of other fluids may also be measured with the probe of the present invention and the invention is not strictly limited to use in a fueling environment.

A discussion of a conventional magnetostrictive fuel level probe10(hereinafter “probe”) is first presented herein with reference toFIG. 1. The discussion of preferred embodiments of the present invention follows beginning with reference toFIG. 2below.

Thus, referring now toFIG. 1, the probe10is a magnetostrictive probe, such as the MAG PROBE™ magnetostrictive probe sold by the assignee of the present invention, namely Veeder-Root Company of 125 Powder Forest Drive, Simsbury, Conn. 06070. The probe10is positioned partially in a fuel storage tank12. Specifically, the probe includes a probe shaft14that extends into the fuel storage tank12while a canister16is positioned outside of the fuel storage tank12. As shown, the canister16is attached to the probe shaft14via fittings18. However, fittings may or may not be used depending on the application. The canister16includes electronics19, which enable operation of the probe10as further explained below.

In use, most fuel storage tanks, such as fuel storage tank12, have a small amount of water therein. This water collects at the bottom of the fuel storage tank12, forming a water-fuel interface34. The fuel sits on top of the water and has an air-fuel interface36at the ullage35of the fuel storage tank12. The probe shaft14extends through both interfaces34and36. The probe shaft14has a reference magnet38positioned proximate a terminal end28of the probe shaft14at a fixed, known distance from the terminal end28. The reference magnet38may be positioned internal to the probe shaft14as is conventional, or externally in a boot (not shown) that slips over the end of the probe shaft14. A water level float40, typically an annular float, is positioned on the probe shaft14and floats at the level of the water-fuel interface34. A water level magnet42is associated with the water level float40so that the level of the water in the fuel storage tank12can be ascertained.

A fuel level float44, also generally an annular float, is positioned on the probe shaft14and floats at the air-fuel interface36. A fuel level magnet46is associated with the fuel level float44so that the level of the fuel in the fuel storage tank12can be ascertained. It should be appreciated that the floats40and44move freely up and down the probe shaft14as the respective levels of fluids (water and fuel) change. Likewise, the buoyancy of the floats40and44is determined by the fluid on which they will be floating. Such parameters are conventional and well understood by someone of ordinary skill in the art. However, the interested reader is directed to the MAG 1 & 2 PLUS! PROBES ASSEMBLY GUIDE, published by Veeder-Root, which is available online at http://www.veeder.com/page/search.html?keywords=mag+probe. The ASSEMBLY GUIDE is hereby incorporated by reference in its entirety.

To determine the fuel level and the water level within the fuel storage tank12, the probe10generates an electric current with a current source within the electronics19positioned in the canister16and sends the electric current down a magnetostrictive wire48in the probe shaft14. Then, the probe10detects torsional wave reflections induced by the magnets42and46of the floats40and44, respectively, and the reference magnet38. The torsional wave reflections are detected with a detector such as a sensing coil (not shown explicitly) of the electronics19.

The first reflection to arrive at the detector is a reflection from the fuel level magnet46associated with the fuel level float44. The second reflection to arrive at the detector is a reflection from the water level magnet42associated with the water level float40. A third reflection arrives from the reference magnet38. Since the speed of the torsional wave in the magnetostrictive wire48is known (typically about 3000 m/s), it is possible to calculate the distance between the detector and the magnet that induced the torsional wave. The detector thus measures the time elapsed between the origination of the pulse and the arrival of each torsional wave reflection. If the distance from the detector to a particular magnet is known, it is a well known exercise to determine the level of that particular magnet within the fuel storage tank12.

Alternatively, the difference in arrival times of torsional waves is used to measure the distance between the level magnets and the reference magnet38. That is, the distance from the bottom30to the reference magnet38(the height of the reference magnet) is known. By measuring the time difference between arrival of torsional waves from, for example, the water level magnet42and the reference magnet38, the distance between the two magnets38and42may be determined. Specifically, the velocity of the torsional wave is multiplied by the time, and a distance is generated. This distance is added to the height of the reference magnet and from this calculation, the height of the water level magnet42is determined. Similar calculations may be made for the fuel level magnet46. Put another way, the heights of the magnets relative to the bottom of the fuel storage tank12are determinable.

The probe10reports the measured reflections to a tank monitor88, such as the TLS-350R manufactured and sold by Veeder-Root Company. The tank monitor88uses the data from the probe10, and specifically, the measured reflections to determine the level and thus, the volume of fuel, within the fuel storage tank12. For example, the tank monitor88may determine a volume of fuel within the fuel storage tank from the height of the fuel level, as determined by the height of the fuel level float44(and as measured by the first reflection or it's relationship to the reflection of reference magnet38). From this height, a conventional tank strapping algorithm or other conventional technique may be applied, as is well understood in the art, to convert the fuel level to arrive at the volume of fuel within the fuel storage tank12. For more information on the operation of a magnetostrictive fuel level probe, the interested reader is referred to U.S. Pat. No. 5,076,100, which is hereby incorporated by reference in its entirety.

Referring now toFIGS. 2 through 4, a magnetostrictive density detector31for determining fuel density at the surface layer of the fuel is shown. Magnetostrictive density detector31includes a fuel level float44and density float51, and may be used in combination with a magnetostrictive probe10such as shown inFIG. 1. Fuel level float44includes ballast45, a fuel level magnet46, balancing lips47, a repulsion magnet49and a body61. In the embodiment shown, repulsion magnet49is added to a fuel level float44of an existing magnetostrictive probe10, such as previously discussed. Repulsion magnet49is provided in the shown embodiment because fuel level magnet46is positioned on an upper portion of fuel level float44, thereby limiting its ability to interact with density float51, as discussed in greater detail below. Balancing lips47ensure that fuel level float44is free to move vertically along probe shaft14as the fuel level36within the tank changes.

Density float51includes a density magnet53, balancing lips57, ballast55and a body59. Density magnet53is positioned on density float51such that adequate magnetic repulsion forces are present between repulsion magnet49of fuel level float44and density magnet53of density float51. Similarly to balancing lips47of fuel level float44, balancing lips57ensure that density float51is free to move along probe shaft14as the fuel level36and density of the fuel change. Also similar to fuel level float44, ballast55is provided and may be changed as necessary such that the buoyancy of density float51may be adjusted as necessary, as determined by the fluid in which it will be floating.

Referring additionally toFIG. 5, the determination of fuel density by magnetostrictive density detector31is based on the effects of magnetic repulsion forces between repulsion magnet49positioned on fuel level float44and density magnet53positioned on density float51. In short, magnetic repulsion forces generated between repulsion magnet49and density magnet53will affect the position of density float51relative to fuel level float44, or more specifically, the position of density magnet53relative to repulsion magnet49along magnetostrictive wire48of probe shaft14.

For the surface layer magnetostrictive density detector31, density float51is calibrated such that it is less buoyant than fuel level float44in the fluids for which the detection of density changes is desired. As well, density float51is preferably less massive than fuel level float44such that the position of density float51along probe shaft14will change as the fuel density changes but the position of fuel level float44will be relatively unaffected. As such, fuel level float44and density float51are designed such that density float51is most affected by the magnetic repulsion forces that exist between repulsion magnet49and density magnet53. Note, however, that density magnet53of density float51exerts an upward force on fuel level float44. As such, it may be necessary to adjust the amount of ballast45on fuel level float44in order to maintain the desired amount of buoyancy and, therefore, accurate fuel level measurement by fuel level magnet46.

As is known, the vertical position of a float disposed within a fluid will be altered as the density of the fluid changes. For example, as the density of the fluid increases, the float will rise, and as the density decreases, the float will move lower in the fluid. As such, when fuel level float44and density float51are placed in fuel, the less-massive density float51will be repelled by fuel level float44due to magnetic repulsion forces between repulsion magnet49and density magnet53, and density float51will be made to sink deeper into the fuel as the fuel density decreases. Density magnet53will move lower in the fuel along probe shaft14until the repulsion forces between the magnets can no longer overcome the buoyant force exerted on density float51by the fuel. When the opposing forces null and density float51reaches equilibrium, it levitates at a constant position relative to probe shaft14and, therefore, magnetostrictive wire48. The distance at which repulsion magnet49and density magnet53are separated when at equilibrium in a fluid of known density is a log function of the magnetic repulsion forces. As such, using the previously discussed magnetostrictive probe10as shown inFIG. 1, the separation distance between repulsion magnet49and density magnet53can be determined and a formula derived to determine the fuel density at the surface of the fuel.

Referring now toFIGS. 6 and 7, an alternate embodiment of a magnetostrictive density detector31for determining surface layer fuel densities is shown. Magnetostrictive density detector31operates similarly to the density detector as shown inFIGS. 2 through 5, with the exception that fuel level magnet46also functions as a repulsion magnet49. More specifically, in contrast to the previously discussed embodiment, fuel level magnet46is positioned on a bottom portion of fuel level float44such that it is disposed within the fuel. As such, it is in close proximity to density float51and therefore generates adequate magnetic repulsion forces with density magnet53such that it provides the functionality of the repulsion magnet49discussed with regard to the embodiment of density detector31shown inFIGS. 2 through 5. Other than this difference, the present embodiment of magnetostrictive density detector31functions almost identically to the previously discussed embodiment. As such, the previous description of magnetostrictive density detector31, as shown inFIGS. 2 through 5, applies to the present embodiment and will not be repeated here.

Referring now toFIGS. 8 and 9, a magnetostrictive density detector33for determining fuel density at a water layer34within the fuel is shown. Magnetostrictive density detector33includes a water level float40and density float51, and is used in combination with a magnetostrictive probe10shown inFIG. 1. Water level float40includes ballast41, a water level magnet42, balancing lips47, and a body61. Balancing lips47ensure that water level float40is free to move along probe shaft14as the water-fuel interface34within the tank changes.

Density float51includes a density magnet53, balancing lips57, ballast55and a body59. Density magnet53is positioned on density float51such that adequate magnetic repulsion forces are present between repulsion magnet42of water level float40and density magnet53of density float51. Similarly to balancing lips47of water level float40, balancing lips57ensure that density float51is free to move along probe shaft14as the water level34and density of the fuel change. Also similar to water level float40, ballast55is provided and may be changed such that the buoyancy of density float51may be adjusted as necessary as determined by the fluid in which it will be floating.

Referring additionally toFIG. 10, the determination of fuel density by magnetostrictive density detector33is based on the effects of magnetic repulsion forces between water level magnet42(also functioning as a repulsion magnet) positioned on water level float40and density magnet53positioned on density float51. In short, magnetic repulsion forces generated between water level magnet42and density magnet53will affect the position of density float51relative to water level float40, or more specifically, the position of density magnet53relative to water level magnet42along magnetostrictive wire48of probe shaft14.

For the water layer magnetostrictive density detector33, density float51is calibrated such that it is more buoyant than water level float40in the fluids for which the detection of density changes is desired. As well, density float51is preferably less massive than water level float40such that the position of density float51along probe shaft14will change as the fuel density changes but the position of water level float40will be relatively unaffected. As such, water level float40and density float51are designed such that density float51is most affected by the magnetic repulsion forces that exist between water level magnet42and density magnet53. Note, however, that density magnet53of density float51will be exerting a downward force on water level float40. As such, it may be necessary to adjust the amount of ballast41on water level float40in order to maintain the desired amount of buoyancy and, therefore, accurate water level measurement by water level magnet42.

As is known, the vertical position of a float disposed within a fluid will be altered as the density of the fluid changes. For example, as the density of the fluid increases, the float will rise, and as the density decreases, the float will move lower in the fluid. As such, when water level float40and density float51are placed in fuel, the less-massive density float51will be repelled by water level float40due to magnetic repulsion forces between water level magnet42and density magnet53, and density float51will be made to rise further in the fuel. Density magnet53will move upwardly in the fuel along probe shaft14until the repulsion forces between the magnets can no longer overcome the ballast force exerted on density float51by its weight. When the opposing forces null and density float51reaches equilibrium, it levitates at a constant position relative to probe shaft14and, therefore, magnetostrictive wire48. The distance at which water level magnet42and density magnet53are separated when at equilibrium in a fluid of known density is a log function of the magnetic repulsion forces. As such, using the previously discussed magnetostrictive probe10as shown inFIG. 1, the separation distance between water level magnet42and density magnet53can be determined and a formula derived to determine the fuel density at the surface of the fuel.

Referring now toFIG. 11, an embodiment of the present invention is shown in which a magnetostrictive density detector31as shown inFIG. 3is used to measure fuel density of the fuel surface layer and a magnetostrictive density detector as shown inFIG. 9is used to measure fuel density at the water layer. The principles of operation of this combined embodiment are similar to the previous discussion of the noted density detectors31and33, and therefore, those discussions are not repeated here.

Referring now toFIGS. 12 through 14, an alternative embodiment of a magnetostrictive density detector31for determining fuel density at the surface layer of the fuel is shown. Magnetostrictive density detector31includes a fuel level float44and an internal density float51, and is preferably used in combination with a magnetostrictive probe10shown inFIG. 1. Fuel level float44includes balancing lips47, a body61, an upper repulsion magnet63and a lower repulsion magnet65. As shown, upper and lower repulsion magnets63and65are positioned on opposing portions of the frame of fuel level float44such that internal density float is disposed between repulsion magnets63and65. Balancing lips47ensure that fuel level float44is free to move along probe shaft14as fuel level36changes within the tank.

As shown, density float51includes a density magnet53, balancing lips57and a body59. Similarly to balancing lips47of fuel level float44, balancing lips57ensure that density float51is free to move along probe shaft14as fuel level36and density of the fuel change.

As best seen inFIG. 15, unlike the previously discussed surface layer magnetostrictive density detectors, density float51of the present embodiment is subject to magnetic repulsion forces in both the upward and downward directions due to the fact that density float51is positioned between upper and lower repulsion magnets63and65, respectively. Referring additionally toFIG. 13, because both the mass and volume of density float51are predetermined fixed values, a force balance can be derived to predict the density of the fuel in which magnetostrictive density detector31is submerged. More specifically, the force balance equation is:
FM1−FM2+FB−FW=0
wherein, FM1is the magnetic repulsion force produced between lower repulsion magnet65and density magnet53; FM2is the magnetic repulsion force produced between upper repulsion magnet63and density magnet53; FB is upward force produced by the buoyancy of the density float; and FW is the downward force produced by the weight of the density float51. When fuel level float44and density float51achieves equilibrium in the fuel, the sum of these forces equals 0.

Referring now toFIG. 18, an exemplary graph representing the distances between density magnet53and upper and lower repulsion magnets63and65, respectively, for varying fuel densities is shown. To determine a fuel density measurement using magnetostrictive density detector31, the distance between upper repulsion magnet63and density magnet53(line81on the graph) and the distance between lower repulsion magnet65and density magnet53(line83on the graph) is measured. These two distances are measured using the methods and algorithms previously discussed with regard to magnetostrictive probe10as shown inFIG. 1. Note, as would be expected, the graph shows that as the fuel density goes up, density float51rises relative to fuel level float44and the distance from upper repulsion magnet63to density magnet53decreases as the distance from lower repulsion magnet65to density magnet53increases. The converse is shown for when fuel density goes down.

The relationship between the displacement of density float51and the density of the fuel depends on four factors: the fixed distance between upper repulsion magnet63and lower repulsion magnet65; the material density of density float51; the volume of density float51; and the strength of the magnets used. More specifically, the greater the distance between upper repulsion magnet63and lower repulsion magnet65, the greater the resolution that the fuel density measurement will have. However, having too great a distance between upper and lower repulsion magnets63and65may adversely affect the ability to measure low fuel levels in the tank because, the greater the separation, the greater the length of fuel level float44. Next, the density of density float51determines the center of the range of fuel densities that density detector31can measure. Preferably, the density of density float51is determined by the average density of the fuel to be measured. Next, the volume of density float51is important because the smaller the float, the larger the density range that can be measured. However, a larger density float gives more stable measurements. Lastly, the stronger the magnets that are used in density detector31, the larger the measurable density range becomes and the more stable the system becomes. By varying these four factors, the magnetostrictive density detector31can be designed to cover the desired range of densities for a given fluid.

Referring now toFIG. 16, an alternative embodiment of a magnetostrictive density detector33for determining fuel density at the water layer of the fuel is shown. Magnetostrictive density detector33includes a water level float40and an internal density float51, and is preferably used in combination with a magnetostrictive probe10shown inFIG. 1. Water level float40includes balancing lips47, a body61, an upper repulsion magnet63and a lower repulsion magnet65. As shown, upper and lower repulsion magnets63and65are positioned on opposing portions of the frame of water level float40such that internal density float51is disposed between repulsion magnets63and65. Balancing lips47ensure that water level float40is free to move along probe shaft14as water level34changes within the tank.

As shown, density float51includes a density magnet53, balancing lips57and a body59. Similarly to balancing lips47of water level float40, balancing lips57ensure that density float51is free to move along probe shaft14as the fuel level and density of the fuel change. The principles of operation of water level density detector33are the same as those previously discussed with regard to surface layer density detector31, as shown inFIG. 12. As such, that discussion is not repeated here.

Referring now toFIG. 17, a magnetostrictive density detector71for determining fuel density at a desired location along a magnetostrictive probe10is shown. Magnetostrictive density detector71includes a frame73and an internal density float51. Frame73is secured to a fixed position on probe shaft14of magnetostrictive probe10and includes an upper repulsion magnet63and a lower repulsion magnet65. As shown, upper and lower repulsion magnets63and65are positioned on opposing portions of frame73such that internal density float51is disposed between repulsion magnets63and65. As such, density magnet53of density float51is also positioned between upper and lower repulsion magnets63and65. The primary difference in construction between density detector71and previously discussed density detectors31and33, as shown inFIG. 14andFIG. 16, respectively, is that upper and lower repulsion magnets63and65are secured to probe shaft14in a fixed position that does not vary as the fuel level and water level within the tank vary. As such, the previous description of the operation of density detectors31and33as shown inFIG. 14andFIG. 16, respectively, is sufficient to describe the operation of fixed density detector71, and is therefore not repeated here. This embodiment is desirable because it can be used to detect density across the depth of fuel, thus indicating fuel stratification and other such fuel characteristics. In the illustrated embodiment, for example, a plurality of detectors71are fixed at spaced-apart locations along probe shaft14.

FIG. 19illustrates a fueling environment90that may incorporate the present invention, and includes the systems and devices that calculate and/or communicate the density of the fuel in the fuel storage tank12for the aforementioned purposes. Specifically, the fueling environment90may comprise a central building92and a plurality of fueling islands94.

The central building92need not be centrally located within the fueling environment90, but rather is the focus of the fueling environment90, and may house a convenience store96and/or a quick serve restaurant (QSR)98therein. Both the convenience store96and the quick serve restaurant98may include a point of sale100,102respectively. The central building92may further house a site controller (SC)104, which in an exemplary embodiment may be the G-SITE® sold by Gilbarco Inc. of 7300 W. Friendly Avenue, Greensboro, N.C. 27410. The site controller104may control the authorization of fueling transactions and other conventional activities as is well understood. The site controller104may be incorporated into a point of sale, such as the point of sale100, if needed or desired. Further, the site controller104may have an off-site communication link106allowing communication with a remote location for credit/debit card authorization, content provision, reporting purposes, or the like, as needed or desired. The off-site communication link106may be routed through the Public Switched Telephone Network (PSTN), the Internet, both, or the like, as needed or desired.

The plurality of fueling islands94may have one or more fuel dispensers108positioned thereon. The fuel dispensers108may be, for example, the ENCORE® dispenser sold by Gilbarco Inc. The fuel dispensers108are in electronic communication with the site controller104through a LAN or the like.

The fueling environment90has one or more fuel storage tanks12adapted to hold fuel therein. In a typical installation, fuel storage tanks12are positioned underground, and may also be referred to as underground storage tanks. Further, each fuel storage tank12has a liquid level probe50such as those described herein. The probes50report to the tank monitor (TM)88associated therewith. Reporting to the tank monitor88may be done through a wire-based system, such as an Ethernet LAN, or a wireless system conforming to IEEE standard 802.11g or the like, as needed or desired. The tank monitor88may communicate with the fuel dispensers108(either through the site controller104or directly, as needed or desired) to determine amounts of fuel dispensed, and compare fuel dispensed to current levels of fuel within the fuel storage tanks12, as needed or desired. In a typical installation, the tank monitor88is also positioned in the central building92, and may be proximate the site controller104.

The tank monitor88may communicate with the site controller104, and further may have an off-site communication link110for leak detection reporting, inventory reporting, or the like. Much like the off-site communication link106, the off-site communication link110may be through the PSTN, the Internet, both, or the like. If the off-site communication link110is present, the off-site communication link106need not be present, although both links may be present if needed or desired. As used herein, the tank monitor88and the site controller104are site communicators to the extent that they allow off-site communication and report site data to a remote location.

The present invention may utilize the off-site communication link110by forwarding data from the probes50to the remote location. This data should preferably be protected from tampering such that the site operator cannot alter the data sent to the remote location through either of the off-site communication links106or110. The data from the probes50may be provided to a corporate entity from whom the site operator has a franchise, a governmental monitoring agency, an independent monitoring agency, or the like, as needed or desired. One way to prevent tampering is through an encryption algorithm.

An alternate technique that helps reduce the likelihood of tampering is the use of a dedicated off-site communication link112, wherein the probes50report directly to a location removed from the fueling environment90. In this manner, the operator of the fueling environment90does have not have ready access to the dedicated off-site communication link112.

For further information on how elements of a fueling environment90may interact, reference is made to U.S. Pat. No. 5,956,259, which is hereby incorporated by reference in its entirety. Information about fuel dispensers108may be found in U.S. Pat. Nos. 5,734,851 and 6,052,629, which are hereby incorporated by reference in their entireties. For more information about tank monitors88and their operation, reference is made to U.S. Pat. Nos. 5,423,457; 5,400,253; 5,319,545; and 4,977,528, which are hereby incorporated by reference in their entireties.