WO1990010849A1 - Acoustic fluid level detector - Google Patents

Acoustic fluid level detector Download PDF

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Publication number
WO1990010849A1
WO1990010849A1 PCT/EP1989/000248 EP8900248W WO9010849A1 WO 1990010849 A1 WO1990010849 A1 WO 1990010849A1 EP 8900248 W EP8900248 W EP 8900248W WO 9010849 A1 WO9010849 A1 WO 9010849A1
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WO
WIPO (PCT)
Prior art keywords
output
input
circuit
conductor
phase
Prior art date
Application number
PCT/EP1989/000248
Other languages
French (fr)
Inventor
Anton Dukart
Erich Zabler
Original Assignee
Robert Bosch Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Robert Bosch Gmbh filed Critical Robert Bosch Gmbh
Priority to PCT/EP1989/000248 priority Critical patent/WO1990010849A1/en
Publication of WO1990010849A1 publication Critical patent/WO1990010849A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
    • G01F23/296—Acoustic waves
    • G01F23/2966—Acoustic waves making use of acoustical resonance or standing waves

Definitions

  • the present invention relates to a fluid level detector and more particularly to a level detector employing acoustic waves.
  • the present invention seeks to overcome or reduce one or more of the above problems.
  • a fluid level detecting arrangement comprising a sound conductor arranged to extend in the fluid, input and output transducing means coupled to the conductor at spaced regions thereof, and a circuit connected to the transducing means and comprising phase comparison means responsive to the phase difference between the input and output signals, characterised in that the circuit comprises means having an output for controlling the input signal so that said phase difference tends to be maintained at a constant value independent of the fluid level, and in that a further output of the circuit represents the fluid level.
  • An advantage of the above arrangement is that good linearity can be obtained and that accuracy is not impaired by dispersion in the transducers or any coatings or layers of adhesive associated with the conductor.
  • the controlling means is preferably a voltage-controlled oscillator which forms a phase-locked loop with the phase comparison means. This means that the phase difference is maintained at zero and the conductor is always operated at resonance.
  • a Pi-controller is preferably located between the output of the phase comparison means and the input of the voltage-controlled oscillator, the output of the Pi-controller constituting said further output of the circuit. This provides an arrangement capable of high resolution and simple evaluation.
  • a second sound conductor is provided subject to the same temperature conditions as the first sound conductor and having input and output transducing means, and the circuit is responsive to the phase difference signals from both conductors so that its further output is substantially independent of temperature.
  • Fig.l shows a level-detecting arrangement in accordance with a first embodiment of the present invention
  • Fig.2 shows a level detecting arrangement in accordance with a second embodiment of the present invention. . -.
  • Fig.3 is a graph showing the output signal of the arrangement of Fig 1 as a function of liquid level
  • Fig.4 is a graph showing the phase delay of a prior art arrangement as a function of liquid level.
  • a container 10 e.g. the fuel-tank of a vehicle, contains a liquid 11, e.g. petrol, the level "S" of which varies in use. At least partly immersed in the container is a U-shaped metal sound conductor 12 along which flexual waves can propagate. At opposite ends the conductor has input and output piezoelectric transducers 15,16 attached thereto, e.g. by adhesive, and operating at ultrasonic frequency.
  • a liquid 11 e.g. petrol
  • S the level "S” of which varies in use.
  • U-shaped metal sound conductor 12 At opposite ends the conductor has input and output piezoelectric transducers 15,16 attached thereto, e.g. by adhesive, and operating at ultrasonic frequency.
  • Flexural waves with a predeter ined frequency are introduced in a first end of sound conductor 12 by transducer 15. This allows signals to be picked off by transducer 16 at the other end of the conductor, arriving with a phase delay.
  • transducer 16 In dependence on the wavelength of the flexural waves and the length of the sound conductor, several conditions arise in which the effective conductor length divided by the wavelength is a whole number, under which conditions resonance occurs in the sound conductor.
  • Circuit 20 comprises a phase-locked loop 21 and a. Pi-controller 22.
  • the phase- locked loop comprises a phase comparator 23 and a voltage-controlled oscillator (VCO) 24.
  • VCO 24 is so connected that it is operated in a frequency range in which the condition that the phase difference is- -zero occurs only once.
  • the output signal of the VCO is filtered and fed to the transmitter or input transducer 15.
  • the received signal from output transducer 16 arrives, after amplification and broad band filtering, at the phase comparator 23, where it is compared in phase with the transmitted signal.
  • the control deviation " " is fed back from the phase comparator as an analogue voltage via the Pi-controller 22 to the VCO and simultaneously serves as a measured variable "U" for the frequency adjustment.
  • the phase difference is controlled to the constant value of zero as illustrated in Fig. lb_, i.e. the loop locks on to respective frequencys f- j _ or I corresponding to level S ⁇ or S2.
  • the measured characteristic curve of this arrangement is shown in Fig 3 and , in comparison with the conventional phase difference measurement (Fig 4), shows a substantially improved linearity.
  • the above-described embodiment has a number of advantages. It provides a reliable measurement arrangement which is not subject to disturbances and has high resolution, simple evaluation and good linearity. Evaluation can be by analogue or quasidigital voltages.
  • the received signal is generally independent of the level "f" of liquid.- The arrangement is not affected by dispension in the transmitter and receiver transducers. It is also independent of the characteristics of the adhesive layer or coating used to attach the transducers. Moreover the construction of the arrangement is relatively inexpensive.
  • Fig.2 shows a second embodiment of the present invention which comprises both a measurement path (conductor 12) and a reference path.
  • the reference path comprises a similar conductor 32 sound-insulated from the liquid 11, e.g. by means of a suitable coating, the reference path having the same temperature profile as the measurement path.
  • the arrangement conveniently comprises a common input transducer 15 and output transducers 16,36 which supply respective signals and ⁇ 2 '
  • the phase control with regard to the transmitted frequency is undertaken in this embodiment in time multiplex between the reference path and the measurement path.
  • the difference of the control deviation "d" between the measurement and reference paths represents in this case the temperature compensated output value for the level of liquid with regard to the point of origin of the characteristic curve. Control is effected by maintaining ⁇ _ ⁇ - ⁇ 2 at the constant value of zero, and the output U corresponds to the difference between the corresponding output signals for the measurement and reference paths.
  • the conductors may be of any convenient material or shape, e.g. plates, rods and those disclosed in the above-mentioned document.
  • the transducers may be of any suitable electro-mechanical type depending on the sort of waves e.g. flexural waves, to . be propagated.

Abstract

In a fluid level detecting arrangement, e.g. in a vehicle fuel tank, in which acoustic waves are propagated in a sound conductor (12) immersed in the fluid, a phase-locked loop (21) is used to maintain at zero the phase difference between the input and output signals, a control deviation signal (d) from the loop being used to provide an output signal (U) representing the fluid level. In a modification, (Fig. 2 not shown) a reference conductor (32) is also provided, subject to the same temperature conditions as the first conductor (12) but not in contact with the liquid, so that variations in temperature do not affect the output signal (U).

Description

Acoustic Fluid Level Detector
The present invention relates to a fluid level detector and more particularly to a level detector employing acoustic waves.
There has previously been proposed (in DE-A-3738515) a detector for the level of fuel in a vehicle tank, the detector employing acoustic waves. Basically, the difference in the speed of propagation of acoustic waves, e.g. lamb waves, in air and in liquid is exploited to derive a level-indicating signal by measuring the phase delay of waves travelling along a sound conductor partly immersed in the liquid. -
However the appearance of resonances in the sound conductor in operation at constant frequency leads to a strong non-linearity of the characteristic curve. Moreover, any coating of th.e sound conductor and any adhesive used to secure the input and output transducers to the sound conductor can introduce errors.
The present invention seeks to overcome or reduce one or more of the above problems.
According to the present invention there is provided a fluid level detecting arrangement comprising a sound conductor arranged to extend in the fluid, input and output transducing means coupled to the conductor at spaced regions thereof, and a circuit connected to the transducing means and comprising phase comparison means responsive to the phase difference between the input and output signals, characterised in that the circuit comprises means having an output for controlling the input signal so that said phase difference tends to be maintained at a constant value independent of the fluid level, and in that a further output of the circuit represents the fluid level.
An advantage of the above arrangement is that good linearity can be obtained and that accuracy is not impaired by dispersion in the transducers or any coatings or layers of adhesive associated with the conductor.
The controlling means is preferably a voltage-controlled oscillator which forms a phase-locked loop with the phase comparison means. This means that the phase difference is maintained at zero and the conductor is always operated at resonance. A Pi-controller is preferably located between the output of the phase comparison means and the input of the voltage-controlled oscillator, the output of the Pi-controller constituting said further output of the circuit. This provides an arrangement capable of high resolution and simple evaluation.
In one preferred embodiment a second sound conductor is provided subject to the same temperature conditions as the first sound conductor and having input and output transducing means, and the circuit is responsive to the phase difference signals from both conductors so that its further output is substantially independent of temperature.
Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which: Fig.l shows a level-detecting arrangement in accordance with a first embodiment of the present invention;
Fig.2 shows a level detecting arrangement in accordance with a second embodiment of the present invention; . -.
Fig.3 is a graph showing the output signal of the arrangement of Fig 1 as a function of liquid level; and
Fig.4 is a graph showing the phase delay of a prior art arrangement as a function of liquid level.
Referring to Fig.la_, a container 10 e.g. the fuel-tank of a vehicle, contains a liquid 11, e.g. petrol, the level "S" of which varies in use. At least partly immersed in the container is a U-shaped metal sound conductor 12 along which flexual waves can propagate. At opposite ends the conductor has input and output piezoelectric transducers 15,16 attached thereto, e.g. by adhesive, and operating at ultrasonic frequency.
Flexural waves with a predeter ined frequency are introduced in a first end of sound conductor 12 by transducer 15. This allows signals to be picked off by transducer 16 at the other end of the conductor, arriving with a phase delay. In dependence on the wavelength of the flexural waves and the length of the sound conductor, several conditions arise in which the effective conductor length divided by the wavelength is a whole number, under which conditions resonance occurs in the sound conductor.
The tuning of the sound conductor to resonance is achieved by a circuit 20 by phase adjustment between the transmitter and the receiver. Circuit 20 comprises a phase-locked loop 21 and a. Pi-controller 22. The phase- locked loop comprises a phase comparator 23 and a voltage-controlled oscillator (VCO) 24. The VCO 24 is so connected that it is operated in a frequency range in which the condition that the phase difference is- -zero occurs only once. The output signal of the VCO is filtered and fed to the transmitter or input transducer 15. The received signal from output transducer 16 arrives, after amplification and broad band filtering, at the phase comparator 23, where it is compared in phase with the transmitted signal. The control deviation " " is fed back from the phase comparator as an analogue voltage via the Pi-controller 22 to the VCO and simultaneously serves as a measured variable "U" for the frequency adjustment. The phase difference is controlled to the constant value of zero as illustrated in Fig. lb_, i.e. the loop locks on to respective frequencys f-j_ or I corresponding to level S^ or S2. The measured characteristic curve of this arrangement is shown in Fig 3 and , in comparison with the conventional phase difference measurement (Fig 4), shows a substantially improved linearity. By means of the impression of the resonance frequency on the sound conductor, the characteristics of the transmitter and receiver elements 15,16 and the associated adhesive layers between the transducers and the sound conductor are comprehensively suppressed.
The above-described embodiment has a number of advantages. It provides a reliable measurement arrangement which is not subject to disturbances and has high resolution, simple evaluation and good linearity. Evaluation can be by analogue or quasidigital voltages. In operation, the received signal is generally independent of the level "f" of liquid.- The arrangement is not affected by dispension in the transmitter and receiver transducers. It is also independent of the characteristics of the adhesive layer or coating used to attach the transducers. Moreover the construction of the arrangement is relatively inexpensive.
Fig.2 shows a second embodiment of the present invention which comprises both a measurement path (conductor 12) and a reference path. The reference path comprises a similar conductor 32 sound-insulated from the liquid 11, e.g. by means of a suitable coating, the reference path having the same temperature profile as the measurement path. The arrangement conveniently comprises a common input transducer 15 and output transducers 16,36 which supply respective signals and ψ 2' The phase control with regard to the transmitted frequency is undertaken in this embodiment in time multiplex between the reference path and the measurement path. The difference of the control deviation "d" between the measurement and reference paths represents in this case the temperature compensated output value for the level of liquid with regard to the point of origin of the characteristic curve. Control is effected by maintaining φ _ ■ -ψ2 at the constant value of zero, and the output U corresponds to the difference between the corresponding output signals for the measurement and reference paths.
The further advantage of the embodiment of Fig.2 is that compensation is simply provided for the shift in the characteristic curve with temperature.
Various modifications may be made to the above described arrangements. For example the conductors may be of any convenient material or shape, e.g. plates, rods and those disclosed in the above-mentioned document. The transducers may be of any suitable electro-mechanical type depending on the sort of waves e.g. flexural waves, to. be propagated.

Claims

Claims
1. A fluid level detecting arrangement comprising a sound conductor (12) arranged to extend in the fluid, input and output transducing means (15,16) coupled to the conductor at spaced regions thereof, and a circuit (20) connected to the transducing means and comprising phase comparison means (23) responsive to the phase difference between the input and output signals, ° characterised in that the circuit (20) comprises means (24) having an output for controlling the input signal so that said phase difference tends to be maintained at a constant value independent of the fluid level, and in that a further output (U) of the circuit (20) -represents 5 the fluid level.
2. An arrangement according to claim 1, wherein the controlling means (24) is a voltage-controlled oscillator which forms a phase-locked loop (21) with 0 said phase comparison means (23).
3. An arrangement according to claim 2, wherein a Pl- controller (22) is connected between the output of the phase comparison means (23) and the input of the 5 voltage-controlled oscillator (24), the output of the Pi-controller constituting said further output ( ) of the circuit (20) .
4. An arrangement according to any preceding claim, 0 wherein there is provided a second sound conductor (32) subject to the same temperature conditions as the first sound conductor (12) and having input and output transducing means (15,36), and the circuit (20) is responsive to the phase difference signal from both 5 conductors (12,32) so that its further output (U) is substantially independent of temperature.
5. An arrangement according to claim 4, wherein the phase difference signals from the conductors (12,32) are supplied to said circuit (20) in time-multiplex manner.
6.. An arrangement according to claim 4 or 5, wherein the sound conductors (12,32) have a common input transducing means (15).
7. A fuel tank for a vehicle comprising a fuel level detecting arrangement according to any preceding claim.
PCT/EP1989/000248 1989-03-09 1989-03-09 Acoustic fluid level detector WO1990010849A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP1989/000248 WO1990010849A1 (en) 1989-03-09 1989-03-09 Acoustic fluid level detector

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP1989/000248 WO1990010849A1 (en) 1989-03-09 1989-03-09 Acoustic fluid level detector

Publications (1)

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WO1990010849A1 true WO1990010849A1 (en) 1990-09-20

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Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5319973A (en) * 1993-02-02 1994-06-14 Caterpillar Inc. Ultrasonic fuel level sensing device
US5987966A (en) * 1994-06-24 1999-11-23 Gec Alsthom Stein Industrie Device for measuring the quantity of coal in a ball grinder
US9057638B2 (en) 2012-11-09 2015-06-16 Robert H. Cameron System and method for determining the level of a substance in a container based on measurement of resonance from an acoustic circuit that includes unfilled space within the container that changes size as substance is added or removed from the container
US9322697B2 (en) 2012-11-09 2016-04-26 Robert H. Cameron System and method for determining the level of a substance in a container based on measurement of resonance from an acoustic circuit that includes unfilled space within the container that changes size as substance is added or removed from the container
US10184821B2 (en) 2012-11-09 2019-01-22 Robert H. Cameron System and method for determining the level of a substance in a container based on measurement of resonance from an acoustic circuit that includes unfilled space within the container that changes size as substance is added or removed from the container
WO2019167660A1 (en) * 2018-02-28 2019-09-06 日本精機株式会社 Liquid level position detection device
US20220178879A1 (en) * 2020-12-04 2022-06-09 Perceptive Sensor Technologies, Inc. Multi-bounce acoustic signal material detection
US11729537B2 (en) 2020-12-02 2023-08-15 Perceptive Sensor Technologies, Inc. Variable angle transducer interface block
US11788904B2 (en) 2020-12-04 2023-10-17 Perceptive Sensor Technologies, Inc. Acoustic temperature measurement in layered environments
US11846537B2 (en) 2019-05-31 2023-12-19 Perceptive Sensor Technologies, Inc. Non-linear ultrasound method and apparatus for quantitative detection of materials
US11860014B2 (en) 2022-02-11 2024-01-02 Perceptive Sensor Technologies, Inc. Acoustic signal detection of material composition in static and dynamic conditions
US11940420B2 (en) 2022-07-19 2024-03-26 Perceptive Sensor Technologies, Inc. Acoustic signal material identification with nanotube couplant
US11946905B2 (en) 2020-12-30 2024-04-02 Perceptive Sensor Technologies, Inc. Evaluation of fluid quality with signals

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2402861A1 (en) * 1977-09-13 1979-04-06 Marconi Co Ltd LIQUID LEVEL SENSOR
US4326173A (en) * 1977-07-25 1982-04-20 Np Industries, Inc. Digital phase locked loop frequency control system
WO1982001584A1 (en) * 1980-10-29 1982-05-13 Brajnandan Sinha Apparatus for measuring and indicating the fluid level in vessels
EP0316564A1 (en) * 1987-11-13 1989-05-24 Robert Bosch Gmbh Filling level indicator

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4326173A (en) * 1977-07-25 1982-04-20 Np Industries, Inc. Digital phase locked loop frequency control system
FR2402861A1 (en) * 1977-09-13 1979-04-06 Marconi Co Ltd LIQUID LEVEL SENSOR
WO1982001584A1 (en) * 1980-10-29 1982-05-13 Brajnandan Sinha Apparatus for measuring and indicating the fluid level in vessels
EP0316564A1 (en) * 1987-11-13 1989-05-24 Robert Bosch Gmbh Filling level indicator

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5319973A (en) * 1993-02-02 1994-06-14 Caterpillar Inc. Ultrasonic fuel level sensing device
US5987966A (en) * 1994-06-24 1999-11-23 Gec Alsthom Stein Industrie Device for measuring the quantity of coal in a ball grinder
US9057638B2 (en) 2012-11-09 2015-06-16 Robert H. Cameron System and method for determining the level of a substance in a container based on measurement of resonance from an acoustic circuit that includes unfilled space within the container that changes size as substance is added or removed from the container
US9322697B2 (en) 2012-11-09 2016-04-26 Robert H. Cameron System and method for determining the level of a substance in a container based on measurement of resonance from an acoustic circuit that includes unfilled space within the container that changes size as substance is added or removed from the container
US10184821B2 (en) 2012-11-09 2019-01-22 Robert H. Cameron System and method for determining the level of a substance in a container based on measurement of resonance from an acoustic circuit that includes unfilled space within the container that changes size as substance is added or removed from the container
JPWO2019167660A1 (en) * 2018-02-28 2021-02-18 日本精機株式会社 Liquid level position detector
WO2019167660A1 (en) * 2018-02-28 2019-09-06 日本精機株式会社 Liquid level position detection device
JP7076072B2 (en) 2018-02-28 2022-05-27 日本精機株式会社 Liquid level position detector
US11846537B2 (en) 2019-05-31 2023-12-19 Perceptive Sensor Technologies, Inc. Non-linear ultrasound method and apparatus for quantitative detection of materials
US11729537B2 (en) 2020-12-02 2023-08-15 Perceptive Sensor Technologies, Inc. Variable angle transducer interface block
US20220178879A1 (en) * 2020-12-04 2022-06-09 Perceptive Sensor Technologies, Inc. Multi-bounce acoustic signal material detection
US11788904B2 (en) 2020-12-04 2023-10-17 Perceptive Sensor Technologies, Inc. Acoustic temperature measurement in layered environments
US11946905B2 (en) 2020-12-30 2024-04-02 Perceptive Sensor Technologies, Inc. Evaluation of fluid quality with signals
US11860014B2 (en) 2022-02-11 2024-01-02 Perceptive Sensor Technologies, Inc. Acoustic signal detection of material composition in static and dynamic conditions
US11940420B2 (en) 2022-07-19 2024-03-26 Perceptive Sensor Technologies, Inc. Acoustic signal material identification with nanotube couplant

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