GB2311373A

GB2311373A - Fluid-gauging systems and probes

Info

Publication number: GB2311373A
Application number: GB9704664A
Authority: GB
Inventors: John Edward Pitkin; Frank Charles Bloomfield
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1996-03-23
Filing date: 1997-03-06
Publication date: 1997-09-24
Also published as: FR2746500A1; GB9606151D0; GB9704664D0; JPH109918A; DE19710599A1

Description

2311373 FLUID-GAUGING SYSTEMS AND PROBES This invention relates to

fluid-gauging systems and probes.

The invention is more particularly concerned with ultrasonic fluidgauging systems and probes having multiple reflectors.

In ultrasonic fluid-quantity measurement systems, an ultrasonic transducer is mounted at the bottom of a vertical tube or still well, which fills with fluid to the same height as fluid outside the tube. The transducer transmits bursts of ultrasonic energy upwardly to the fluid/air interface where they are reflected back to the transducer. By measuring the time of travel of the bursts of energy, it is possible to calculate the height of the fluid surface. The speed of sound, however, varies according to changes in fluid density. In order to compensate for this, it is usual practice for the still well to include a number of reflectors spaced apart along its length. The height of these reflectors is known, so the ultrasonic reflections they produce can be used to calibrate the system and improve the calculation of the height and volume of fluid. The amplitude of reflection from one of the lower fixed reflectors can exceed that from the fluid surface in certain circumstances, such as if the fluid surface is high, if the probe is inclined away from the normal to the fluid surface, or if the surface is perturbed by ripples, waves, foam or the like. This can make it difficult to identify which reflection originates from the 2 fluid surface and which originates from the reflectors. This is further complicated by the fact that the fluid surface can produce false reflections at multiples of the fluid height.

False reflections from the fluid surface can, in some circumstances, be identified because there will be no reflections from the fixed reflectors between the actual fluid surface and the position of the false reflection. For example. if the fixed reflectors were spaced at intervals of 5cm, and the fluid surface were at 12cm, there would be reflections from two fixed reflectors, at 5cm and 1 Oem, then from the actual fluid surface at 12cm, and then the false reflection of the fluid surface at 24cm. Because reflections from the third and fourth reflectors at 15cm and 20cm are absent, the system can identify that the fourth signal is a false echo and reject it. A problem, however, arises if the fluid surface is close to the first reflector, say at 5cm, which would produce a false reflection around the position of the second reflector at 1 Ocm. In these circumstances, the system can have difficulty in determining whether the first reflection signal is actually from the fuel surface or from the first reflector and whether the false reflection is really either a false reflection, or the true fuel surface reflection, or the reflection from the second reflector. In high noise environments, the system could misinterpret the fuel surface as being at some location above the second reflector.

It is an object of the present invention to provide an improved fluidgauging system, probe and method.

3 According to one aspect of the present invention there is provided a fluid-gauging system including an acoustic probe having a plurality of reflectors spaced apart along its length and an acoustic transducer located towards the lower end of the probe, the transducer being arranged to transmit acoustic energy upwardly to the fluid surface and to receive energy reflected by the surface and by any reflectors submerged in the fluid, the second reflector above the transducer being located at a height less than twice the height of the first reflector so as to enable identification of a false echo from tile fluid surface when the fluid surface is in the region of said first reflector.

Preferably, all the reflectors are located at heights that are not simple multiples of the heights of any lower reflector.

According to another aspect of the present invention there is provided a fluid-gauging system including an acoustic probe having a plurality of reflectors spaced apart along its length and an acoustic transducer located towards the lower end of the probe, the transducer being arranged to transmit acoustic energy upwardly to the fluid surface and to receive energy reflected by the surface and by any reflectors submerged in the fluid, all of said reflectors being located at heights that are not simple multiples of the heights of any lower reflector.

The probe preferably includes a support member extending vertically above the transducer, the reflectors projecting laterally from the support member. The probe preferably includes a tubular still well, the transducer being located at the lower end of the still well and the reflectors being supported on the still well.

4 According to a further aspect of the invention there is provided a probe for a system according to the above one or other aspect of the invention.

According to a fourth aspect of the present invention there is provided a method of determining the height of fluid in a tank comprising the steps of supplying a pulse of acoustic energy upwardly towards the fluid surface and to reflectors spaced apart upwardly in said tank, the second reflector from the bottom being located at a height that is less than twice the height of the first reflector, receiving acoustic energy reflected from the fluid surface and from any of said reflectors submerged in said fluid, identifying a false echo from the fluid surface when the actual fluid surface is located in the region of said first reflector from the absence of a reflection from said second reflector, rejecting said false echo, and determining the height of fluid from the reflection from the fluid surface.

According to a fifth aspect of the invention there is provided a method of determining the height of fluid in a tank comprising the steps of supplying a pulse of acoustic energy upwardly towards the fluid surface and to reflectors spaced apart upwardly in said tank, all of the reflectors being located at heights that are not simple multiples of the height of any lower reflector, receiving acoustic energy reflected from the fluid surface and from any of said reflectors submerged in said fluid, identifying a false echo from the fluid surface from the absence of reflections from reflectors between the actual fluid surface and the false echo, rejecting any such false echo, and determining the height of fluid from the reflection from the fluid surface.

According to a sixth aspect of the present invention there is provided a method of determining the height of fluid in a tank comprising the steps of supplying a pulse of acoustic energy upwardly towards the fluid surface and to reflectors spaced apart upwardly in said tank, all of the reflectors being located at heights that are not simple multiples of heights of any lower reflector and the second reflector from the bottom being located at a height less than twice the height of the adjacent first reflector, receiving acoustic energy reflected from the fluid surface and from any of said reflectors submerged in said fluid, identifying a false echo from the fluid surface from the absence of reflections from reflectors between the actual fluid surface and the false echo, rejecting any such false echo, and determining the height of fluid from the reflection from the fluid surface.

According to a seventh aspect of the present invention there is provided a system for performing the method according to the above fourth, fifth or sixth aspects of the present invention.

An ultrasonic fuel-gauging system for an aircraft, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawing, in which:

Figure 1 is a schematic view of the system; and Figure 2 is a cross-sectional side elevation view of a probe of the system.

6 With reference first to Figure 1, the fuel-gauging system includes a tank 1, which is typically located in a wing of the aircraft and is of irregular shape, containing several ultrasonic fuel-gauging probes of which three probes 2 to 4 are shown. The probes 2 to 4 are connected to a control unit 10 by wires so that the control unit can supply electrical signals to energize the probes and can receive electrical signals from the probes. The control unit 10 provides an output indicative of fuel mass to a display 11 or other utilization means.

With reference now to Figure 2, there is shown an example of an ultrasonic probe 2, similar to the kind described in GB 2265219, GB 2265005 or GB 2270160. The probe 2 has an outer tube or still well 12, which is open at the top and bottom so that fuel in the still well is at the same height as fuel outside the probe. An ultrasonic transducer 13 is located at the bottom of the probe and transmits bursts of ultrasonic energy upwardly along the still well when energized by the control unit 10. The probe 2 includes nine reflectors 14 to 22 supported on the inside of the still well, spaced apart along its length. The reflectors 14 to 22 take the form of short pegs or studs projecting laterally across about one third of the diameter of the still well. Ultrasonic energy is reflected off the fuel surface and off those reflectors submerged in fuel. Because these reflected signals are produced from reflectors at known heights, they provide calibration signals for the probe in the manner described in GB 2265219. The reflected ultrasonic energy is received by the transducer 13, which converts it into electrical signals and supplies these to the control unit 10 7 In conventional ultrasonic fluid-gauging probes, the reflectors are equally spaced from one another up the height of the probe. By contrast, in the present invention, the reflectors 14 to 22 are not all equally spaced up the probe. In particular, the second reflector 15 is mounted at a height above the transducer 13 that is less than twice the height of the adjacent first reflector 14 above the transducer. The locations of all the reflectors 14 to 22 are such that no reflector is at a height that is a simple multiple of the height of a lower reflector.

One example of a typical spacing of reflectors is given below:

Reflector Spacing from transducer 13 Spacing above adjacent lower reflector 14 10. 1 6cm 17.78cm 7.62cm 16 44.45cm 26.67cm 17 71.12cm 26.67cm 18 86.36cm 15.24cm 19 101.6cm 12.70cm 11 6.84cm 17.78cm 21 137.16cm 20.32cm 22 149.86cm 12.7cm The control unit 10 contains information as to the height of each reflector 14 to 22.

The height of fuel is determined by measuring the height above the uppermost of the 8 submerged reflectors, so as to compensate for the effects of temperature stratification in the fuel, in a known way.

If, for example, the fuel surface were located between the third reflector 16 and the fourth reflector 17, the transducer 13 would receive reflections from the lowest three reflectors 14, 15 and 16, which can be readily identified because the reflected signals occur at known locations. Even if the echo from the fluid surface were of relatively low amplitude, its approximate location could be deduced from the fact that no reflections are received from the reflectors 17 to 22, which are exposed above the fuel surface. From this information, the control unit 10 determines that the fuel surface must lie between the third reflector 16 and the fourth reflector 17. The first false echo from the fuel surface would be at a location equivalent to twice the actual fuel height, or about twice the height of the third reflector 16. However, the control unit 10 readily identifies a return signal equivalent to this heicrht as being a false reflection, because of the absence of reflections from the reflectors between the actual fuel surface and the location of the false reflection. The same would apply for higher multiple false reflections of the fuel surface. The system, therefore, identifies and rejects these false echoes.

At lower fuel levels, however, a problem could arise, if the reflectors were equally spaced. If the fluid surface were at about the same location as the first, lowest reflector, its false reflection would be at twice this height. This false reflection would have a relatively high amplitude, because of its proximity to the transducer, and it would be approximately coincident with the second reflector. The signals returned to the control unit would, therefore, 9 be substantially the same as the signals that would be returned if the fuel surface were located at the second reflector.

In the probe of the present invention, however, the second reflector 15 is spaced above the first reflector 14 by a distance less than the spacing of the first reflector above the transducer 13. When the fuel surface is located at the first reflector 14, the transducer 13 typically receives two signals of significant amplitude, namely, a single return signal equivalent to a height of 10. 16cm, from the fuel surface and from the first reflector, and a lower amplitude, second signal caused by a false reflection from the surface at twice this distance of 20.32cm. Because the transducer 13 does not receive any return signals equivalent to reflector locations higher than the first reflector 14, the control unit 10 can readily determine that the actual fuel surface must lie between the first reflector and some point below the second reflector, so it rejects signals from outside this range.

There will be some fuel height (8.84cm) at which its false reflection will coincide with the second reflector 15. At this height, the control unit 10 will receive two signals of significant amplitude, namely, a signal from the actual fuel surface and a false, harmonic signal from the fuel surface. Because there is no signal from the first reflector 14, the control unit 10 can readily identify that the upper signal is false and reject all signals above the lower signal.

At greater fuel heights, the problem will not be so severe because a false reflection equivalent to twice the actual height will always occur at a location where there is at least one reflector between the true fuel height and its false reflection. For example, if the height of the fuel surface were the same as that of the second reflector 15, the false reflection would be produced at a location between the fourth and fifth reflectors. Because signals from the third and fourth reflectors are absent, the control unit 10 can readily identify the false reflection as being a false reflection. In high noise situations, however, it can be an advantage for all the reflectors to be located such that none is at a height that is a simple multiple of the height of lower reflectors.

The system and probe could be modified in various ways. For example, the probe could have separate transmit and receive transducers. It is not essential for the probe to have a still well, since the reflectors could be supported in some other way. It will be appreciated that the system is not confined to use with fuel but could be used with other fluids. Also, various acoustic frequencies could be used not confined to the ultrasonic range.

11

Claims

A fluid-gauging system including an acoustic probe having a plurality of reflectors spaced apart along its length and an acoustic transducer located towards the lower end of the probe, the transducer being arranged to transmit acoustic energy upwardly to the fluid surface and to receive energy reflected by the surface and by any reflectors submerged in the fluid, wherein the second reflector above the transducer is located at a height less than twice the height of the first reflector so as to enable identification of a false echo from the fluid surface when the fluid surface is in the region of said first reflector.

2. A fluid-gauging system according to Claim 1, wherein all of said reflectors are located at heights that are not simple multiples of the heights of any lower reflector.

3. A fluid-gauging system including an acoustic probe having a plurality of reflectors spaced apart along its length and an acoustic transducer located towards the lower end of the probe, the transducer being arranged to transmit acoustic energy upwardly to the fluid surface and to receive energy reflected by the surface and by any reflectors submerged in the fluid, wherein all of said reflectors are located at heights that are not simple multiples of the heights of any lower reflector.

4.

12 A fluid-gauging system according to any one of the preceding claims, wherein the probe includes a support member extending vertically above the transducer, and wherein the reflectors project laterally from the support member.

A fluid-gauging system according to any one of the preceding claims, wherein the probe includes a tubular still well, wherein the transducer is located at the lower end of the still well, and wherein the reflectors are supported on the still well.

6. A fluid-gauging system substantially as hereinbefore described with reference to the accompanying drawings.

A fluid-gauging probe for a system according to any one of the preceding claims.

8. A method of determining the height of fluid in a tank comprising the steps of supplying a pulse of acoustic energy upwardly towards the fluid surface and to a row of reflectors extending upwardly in said tank, the second reflector from the bottom being located at a height that is less than twice the height of the first reflector, receiving acoustic energy reflected from the fluid surface and from any of said reflectors submerged in said fluid, identifying a false echo from the fluid surface when the actual fluid surface is located in the region of said first reflector from the absence of a reflection from said second reflector, rejecting said false echo, and determining the height of fluid from the reflection from the fluid surface.

13 A method of determining the height of fluid in a tank comprising the steps of supplying a pulse of acoustic energy upwardly towards the fluid surface and to a row of reflectors extending upwardly in said tank, all of the reflectors being located at heights that are not simple multiples of the height of any lower reflector, receiving acoustic energy reflected from the fluid surface and from any of said reflectors submerged in said fluid, identifying a false echo from the fluid surface from the absence of reflections from reflectors between the actual fluid surface and the false echo, rejecting any such false echo, and determining, the height of fluid from the reflection from the fluid surface.

10. A method of determining the height of fluid in a tank comprising the steps of supplying a pulse of acoustic energy upwardly towards the fluid surface and to a row of reflectors extending upwardly in said tank, all of the reflectors being located at heights that are not simple multiples of heights of any lower reflector and the second reflector from the bottom being located at a height less than twice the height of the adjacent first reflector, receiving acoustic energy reflected from the fluid surface and from any of said reflectors submerged in said fluid, identifying a false echo from the fluid surface from the absence of reflections from reflectors between the actual fluid surface and the false echo, rejecting any such false echo, and determining the height of fluid from the reflection from the fluid surface.

11. A method of determining the height of fluid in a tank substantially as hereinbefore described with reference to the accompanying drawing.

14 12. A system for performing a method according to any one of Claims 8 to 11.

13. Any novel feature or combination of features as hereinbefore described with reference to the accompanying drawing.