WO2008147223A1 - Improvements relating to ultrasonic distance measuring devices - Google Patents

Improvements relating to ultrasonic distance measuring devices Download PDF

Info

Publication number
WO2008147223A1
WO2008147223A1 PCT/NZ2008/000119 NZ2008000119W WO2008147223A1 WO 2008147223 A1 WO2008147223 A1 WO 2008147223A1 NZ 2008000119 W NZ2008000119 W NZ 2008000119W WO 2008147223 A1 WO2008147223 A1 WO 2008147223A1
Authority
WO
Grant status
Application
Patent type
Prior art keywords
ultrasonic
pulse
signal
period
distance measuring
Prior art date
Application number
PCT/NZ2008/000119
Other languages
French (fr)
Inventor
Paul Graham Alexander Beeson
Abraham De Voogd
Original Assignee
Bep Marine Limited
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

Links

Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B17/00Measuring arrangements characterised by the use of subsonic, sonic or ultrasonic vibrations
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00Indicating or measuring liquid level, or level of fluent solid material, e.g. indicating in terms of volume, indicating by means of an alarm
    • G01F23/22Indicating or measuring liquid level, or level of fluent solid material, e.g. indicating in terms of volume, indicating by means of an alarm by measurement of 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
    • G01F23/28Indicating or measuring liquid level, or level of fluent solid material, e.g. indicating in terms of volume, indicating by means of an alarm by measurement of 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 electric or acoustic waves applied directly to the liquid or fluent solid material
    • G01F23/296Acoustic waves
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/523Details of pulse systems
    • G01S7/526Receivers
    • G01S7/527Extracting wanted echo signals
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88Sonar systems specially adapted for specific applications

Abstract

To measure distances with an ultrasonic transducer when the distance is comparable with the width of the transmitted ultrasonic pulse the energy level of the received transmitter 'ringdown' period is used to indicate the distance of a close target, as well as other measures not normally associated with range.

Description

IMPROVEMENTS RELATING TO ULTRASONIC DISTANCE MEASURING DEVICES

FIELD OF THE INVENTION

This invention relates to ultrasonic distance measuring devices, and in particular, but not exclusively, to ultrasonic distance measuring devices for use in measuring fluid levels in a tank'.

BACKGROUND

Ultrasonic distance measuring devices are used in a number of applications, including tank level sensing. One drawback of ultrasonic distance measuring devices is that they are typically not useful at measuring short distances, that is, distances of less than about 0.08 metres. This is because the transmitted acoustic pulse is normally almost as long as or longer than distance to be measured and additionally the mechanical movement of the pulse generator takes time to die away or "ringdown". At very short distances the signal can return before the transmit signal pulse has died away, and in most measuring systems the return signal is gated out for a time longer than the transmit pulse plus the ringdown period to avoid overloading the signal detection circuitry during this time.

It is possible to use separate ultrasonic transmitting and receiving devices to improve the ability to detect close targets but this still does not provide a full resolution of the problem and requires extra expense for separate devices.

This means that when measuring tank levels using ultrasonic distance measuring devices located at the top of the tank,, it can be difficult to measure fluid levels when the tank is near to full.

In some tank level sensing situations this problem can be alleviated by raising the ultrasonic sensor a short distance above the full level, for example by mounting the sensor inside a raised housing which extends above the upper surface of the tank. However, in many circumstances, for example in boat fuel tanks, this may not be possible as the upper surface of the tank may be very close to the deck level of the boat. OBJECT

It is therefore an object of the present invention to provide an ultrasonic distance measuring device which will at least go some way towards overcoming the above mentioned problems, or which will at least provide the public with a useful choice.

STATEMENTS OF THE INVENTION

Accordingly, in a first aspect, the invention may broadly be said to consist in an ultrasonic distance measuring device having a transmitter which transmits a burst of ultrasonic waves and a degrading wave train from mechanical decay of the burst , a receiver receiving waves resulting from that burst and the decay period of the degrading wave train, a detector for the received waves detecting events occurring in the period between the end of the transmitted burst .and all received returns of that burst and providing a received signal output, a received signal output processor interpreting events in addition to the first detected return of the transmit signal in the received signal output as an indication of the detection of a target.

Preferably the output processor detects an increase in the length of the detected decay period of the transmit waveform.

Preferably the output processor detects the average signal level occurring within the decay period and from this provides a target range indication when at least the first return signal falls within the decay period.

Preferably the distance measuring device detects a liquid surface.

Preferably the transmitter and receiver are normally located in air.

Preferably the output signal processor also detects an increased received signal level indicative of a signal transmission medium other than the normal medium in contact with the ultrasonic receiver.

Preferably the ultrasonic transmitter and receiver are combined as an ultrasonic transducer.

In a further aspect the invention relates to a method of providing distance measurements from an ultrasonic distance measuring device having an ultrasonic pulse transmitter and receiver and a receiyed signal processor, the transmitter transmitting a pulse of ultrasonic waves followed by a decay period of a degrading wave train, the receiver receiving ultrasonic waves resulting from the pulse, the received signal processor interpreting the received signal characterised in that where the first returned signal pulse is not separately detectable signal events other than the first returned signal pulse are interpreted to determine the distance of a target.

Preferably the target distance is determined by interpreting the average energy level during the decay period of the received transmit' pulse.

Preferably the target distance is determined by counting the number of detectable return pulses within a specified portion of a pulse return period and equating the number of pulses to a target distance.

Preferably the target distance is determined by detecting changes in the amplitude or width of the decay period of the received transmit pulse.

The invention may also broadly be said to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of the parts, elements or features, and where specific integers are mentioned herein which have known equivalents, such equivalents are incorporated herein as if they were individually set forth.

DESCRIPTION

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

FIG. 1 is a diagram of a fuel tank demonstrating the use of the invention;

FIG. 2 is a graph of the received signal from an ultrasonic sensor in a fuel tank where the fuel level is more than 0.1 metres away;

• FIG. 3 is a graph in the same fuel tank where the fuel level is approximately 0.08 metres from the sensor; FIG. 4 is a graph in the same fuel tank where the fuel level is approximately 0.05 metres from the sensor;

FIG. 5 is a graph in the same fuel tank where the fuel level is approximately 0.02 metres from the sensor;

FIG. 6 is a flow diagram of a method of detecting range when a liquid surface is near the top of a tank.

With reference to FIG. 1, a fuel tank 101 has an outlet pipe 102 and, fitted into the top of the tank, an ultrasonic transducer 103 with a piezo-electric plate 104. The ultrasonic unit is secured at 105 and has leads 106 connecting it to the pulse, creation and echo detection circuitry. A fuel level within the tank is not shown, but clearly can occur anywhere from the bottom of the tank to the top, and in the latter position will be above the face of the transducer. The use of a transducer, rather than a separate transmitter and receiver, is described but the invention is equally applicable to separated devices, albeit the ringdown period is much reduced with separated units since the receiver is excited to the same extent' by the transmit pulse.

With reference to FIG. 2, the graph shows the amplitude of the signal received at the processing circuitry as rectified and filtered, the signal being a waveform with a frequency of 40KHz or more. The graph shows at 201 the signal corresponding to the initial transmit pulse which is typically of four cycles near 100 volts RMS, and the decay of that pulse as the transducer piezo-electric structure ceases ringing to form the decay period, where the detectable echoes are at a level near ImV.

Pulse 202 is the primary return from the surface of the fuel within the tank, and occurs at a time from the commencement of the transmit pulse which corresponds to the distance of the fuel surface from the transducer surface. The width of pulse 202 should correspond approximately to the width of the transmit pulse. Further return pulses 203, 204 are the result of reflections from the fuel surface, back to the tank top and then down again to be reflected from the fuel surface to the transducer. As such these returns have a steadily decreasing amplitude and will normally also suffer some broadening of the pulse due to dispersion effects. ' It should be noted that the times between the pulses are constant for a single transmit pulse since it always corresponds to. the distance between transducer and fuel surface. Not shown are various other pulses due to echoes from the tank sides, the tank bottom and various other combinations of echoes from all the available faces. Typically these are of lower amplitude than those from the fuel surface but they can provide artefacts within the wanted signal.

FIG. 3 shows the situation when the fuel surface is sufficiently close to the transducer that the' primary return pulse falls almost within the transmit pulse, typically about 0.08 meters.

Thus pulse 301 consists of the transmit pulse plus the primary return acting to extend the trailing edge of the decay period. Additional reflections from the fuel surface 302, 303 and 304, etc. have larger amplitudes than in FIG. 2, since the lesser distance from the transducer to the fuel level provides less opportunity for losses.

Such a return signal may be analysed in several different ways. Firstly the number of return peaks occurring after the decay period and before a time corresponding to a distance of about 400mm can be counted. The number of detectable pulses 301, 302, 303 etc. corresponds to the surface distance, with 1 peak within this distance indicating a maximum range of 400mm, 2 peaks 200mm, 3 peaks 133mm, 4 peaks 80mm, 5 peaks 66mm, etc. Realistically it is possible to count up to 6 peaks within this time, and from this to determine the maximum distance to the surface being detected when the distance is greater than 60mm and less than 400mm.

A second alternative is to consider merely the first two pulses detected within a time corresponding to a distance of about 400mm. Having established the time from the transmit pulse of the first return peak a time of half this is taken and a second pulse peak looked for at this time from the first detected peak. If the second return- pulse peak is found at this time it can be assumed that the real first peak was not detected, being buried within the decay period, and that the two pulses concerned are the second and third pulses. The period between them is therefore equivalent to the surface height. This technique is useful up to when the surface is within 100mm of the transducer.

A third alternative lies in the detection of the first appreciable minimum within the decay period of the transmit pulse. Such a minimum corresponds approximately to the midpoint of the upward slope of a pulse return embedded within the decay period, as shown at 301. A ■ measurement of the time of the minimum provides a useful indication of distances below 80mm.

FIG. 4 shows the results with an even higher fuel level, typically about 0.05 metres. Note

. that the primary return pulse and several of the secondary pulses are now fully integrated into the area of the transmit pulse and decay period but that a minimum is. still detectable at

401 as well as other minima at 402. The multiple reflections are now so close together that ' they are merging as a slope part way down the decay pulse trailing edge, however the first minimum is still indicative of the distance of the liquid surface. Pulses 403 still lie clear of the decay period, but may be sufficiently variable that they do not. provide a stable measurement in a moving vessel. The average energy present within the ringdown period may be measured to the quantitative presence of these merged return pulses.

FIG. 5 shows the pulse 501 which results at an even higher fuel level, typically 0.02 meters. In this state the reflections are sufficiently close together that they coalesce into a secondary pulse trailing from the transmit pulse of relatively higher level and somewhat shorter length than that of FIG. 4. The average level of the decay period is much increased and the detection of this level can in itself act as a measurement of distances below about 30mm.

Should the fuel level reach the transducer face the return signal level increases dramatically since there is no longer an air/fuel interface to introduce losses. Instead, the signal level within the fuel itself dramatically increases. The end result is a large and noisy increase in returned signal which extends for some time. The increase in the average amplitude of the ringdown period is of a much increased level over and above anything obtainable with no liquid contact with the transducer.

It is possible to take advantage of all the signal changes, rather than regarding them as nuisance signals to be ignored, to provide a more accurate indication of fuel level when it approaches the transducer. To this end, rather than monitoring the time between the transmit pulse and the primary returned pulse it is proposed to measure the time between any two pulses which are identifiably from the fuel level surface. Secondly it is proposed to monitor the number of return pulses occurring within a certain time of the transmit pulse. Further, where these return pulses coalesce it is proposed to monitor the averaged height of the detected pulse, that is, during the decay period as extended by the coalesced pulses. While this cannot provide a qualitative measurement of fuel level it can provide a quantitative measure. Additionally by monitoring those times when the transmit pulse surges it is proposed to detect those times when the fuel touches the transducer face and to use this as an additional signal of fuel level height.

A flow chart detailing the process of deciding what the liquid level is appears as FIG. 6 and applies to an ultrasonic level measuring circuit in which a transmit pulse is applied to a transducer also serving as the ultrasonic receiver, and the received waveform envelope is demodulated. FIG. 6 shows at 601 the issuing of a transmit, pulse and at 602 the mapping of the received response to that transmit pulse. The received response includes the actual transmit pulse and typically the ultrasonic receiver circuitry is gain controlled so that gain increases with time after the transmit pulse to provide relatively constant height primary received pulses. Secondary pulses, resulting from the double bounce of an ultrasonic pulse, will still be much reduced in comparison with primary pulses from a single bounce.

At 603 the return signal is analysed for a surface hit, that is, for a drastic increase in the average voltage of the waveform during the decay period due to the fuel surface touching the transducer. Typically, as a DC voltage, the average voltage in the decay period may be expressed as 4.1 volts with maximum possible echo returns. When the liquid touches the transducer this increases to typically 4.8 volts. Thus any excursion, above an intermediate voltage, such as 4.5 volts, indicates that the fluid has touched the transducer. Note that where the transducer is in the fuel tank of a vessel under way and the tank is near full there will be occasional episodes of contact, and therefore a reliable system must check for consistent contact over a period of time. If this is found a "full" state is reported at 604.

If no surface hit situation is detected a check is made at 605 for a perceptible trough in the decay period. While very minor troughs may occur under normal conditions a perceptible trough will normally be found when the first returned pulse is within the decay period. Other troughs may be found which are due to bounce pulses also falling within the decay period, but use of the first such trough is preferred. The trough roughly corresponds to the mid point on the leading edge of a returned pulse since the steep trailing edge of the ringdown decay from the transmit pulse compensates for the initial portion of the rising return waveform. From the location of the trough it is therefore relatively easy to calculate what the time period between the transmit pulse and the trough is, and therefore the location of the air/liquid interface. Where such a trough is found the calculated height of the liquid level is returned at 606.

Where no. surface hit situation is found, and a defined trough is not present in the decay period, the number of return peaks present in the detected signal between the end of the decay period and a time equivalent to a distance of approximately 400mm from the transducer is detected at 607. Where the number is two or above the time of the first pulse clear of the decay period is taken and the time of the second pulse compared with that of the first plus half the period from transmit to the first pulse at 608. If the second pulse matches this time it can be assumed that the actual first pulse was not seen (probably buried in the decay period) and that the height of the interface is the same as the period between the first detected pulse and the second detected pulse and this is reported at 609.

If the second pulse does not match the requirements the number of peaks counted at 610 is compared with a lookup table at 611 and a distance equivalent to that number of peaks is reported at 611.

Where none of these criteria is met it is assumed that the distance is greater than 400mm and it is safe to rely on the normal first returned pulse at 612.

In this way the level of a liquid within a tank can be measured accurately over a range from zero to several meters, with much increased accuracy in the region from zero to 0.1 meters compared to prior art level measurement equipment.

VARIATIONS

The invention is described as used in the fuel tank of a vessel, and this also poses problems related to movement of the tank contents in a seaway which may require either averaging the readings over a fairly long period, or ignoring "top of tank" events as being due to vessel movement. It may be desirable to cross-correlate the rate of change of readings with the averaging period in order to reduce the averaging period to a reasonable value while the vessel is alongside a pier with the fuel tanks being filled. While the invention is described in its application to a vessel fuel tank the techniques are applicable to the measurement of level in any gaseous/liquid or liquid/liquid interface.

Aspects of the present invention have been described by way of example only and it should be. appreciated that modifications and additions may be made thereto without departing from the scope thereof.

DEFINITIONS

Throughout this specification the word "comprise" and variations of that word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.

A "pulse" is a burst of ultrasonic waves or the return from that burst.

The signal transmitted by an ultrasonic transmitter is the "transmit pulse".

A "ringdόwn period" is the time during which a piezo-electric transducer acting as transmitter stops mechanically "ringing" from the high power transmit pulse.

A "decay period" is the time period between cessation of a transmit pulse and the time when the detected decay of the transmit pulse plus other entrainments in the received signal return to substantially zero. At distances where the first return is greater than several times the period of the transmit pulse the ringdown period and the decay period are substantially identical.

ADVANTAGES Thus it can be seen that at least the preferred form of the invention provides an ultrasonic distance . measuring device which is capable of providing distance measurements at very short distances when it is not possible to detect the time taken for the primary return signal to return.

Claims

1. An ultrasonic distance measuring device having a transmitter which transmits a burst of ultrasonic waves and a degrading wave train from mechanical decay of the burst, a receiver receiving waves resulting from that burst and the decay period of the degrading wave train, a detector for the received waves detecting events occurring in the period between the end of the transmitted burst and all received returns of that burst and providing a received signal output, a received signal output processor interpreting events in addition to the first detected return of the transmit signal in the received signal output as an indication of the detection of a target. .
2. An ultrasonic distance measuring device as claimed in claim 1, wherein the output . processor detects an increase in the length of the detected decay period of the transmit waveform.
3. An ultrasonic distance measuring device as claimed in claim 2, wherein the output processor detects the average signal level occurring within the decay period and from this provides a target range indication when at least the first return signal falls within the decay period.
4. An ultrasonic distance measuring device as claimed in claim 1, wherein the device detects a liquid surface.
5. An ultrasonic distance measuring device as claimed in claim 1, wherein the transmitter and receiver are normally located in air.
6. An ultrasonic distance measuring device as claimed in claim 1, wherein the output signal processor also detects an increased received signal level indicative of a signal transmission medium other than the normal medium in contact with the ultrasonic receiver.
7. An ultrasonic distance measuring device as claimed in claim 1, wherein the ultrasonic transmitter and receiver are combined as an ultrasonic transducer.
8. A method of providing distance measurements from an ultrasonic distance measuring device having an ultrasonic pulse transmitter and receiver and a received signal processor, the transmitter transmitting a pulse of ultrasonic waves followed by a decay period of a degrading wave train, the receiver receiving ultrasonic waves resulting from the pulse, the received signal processor interpreting the received signal characterised in that where the first returned signal pulse is not separately detectable signal events other than the first returned signal pulse are interpreted to determine the distance of a target.
9. A method as claimed in claim 8 wherein the target distance, is determined by interpreting the average energy level during the decay period of the received transmit pulse. •
10. A method as claimed in claim 8 wherein the target distance is determined by counting the number of detectable return pulses within a specified portion of a pulse return period and equating the number of pulses to a target distance.
11. A method as claimed in claim 8 wherein the target distance is determined by detecting changes in the amplitude or width of the decay period of the received transmit pulse.
PCT/NZ2008/000119 2007-05-28 2008-05-22 Improvements relating to ultrasonic distance measuring devices WO2008147223A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
NZ55542807 2007-05-28
NZ555428 2007-05-28

Publications (1)

Publication Number Publication Date
WO2008147223A1 true true WO2008147223A1 (en) 2008-12-04

Family

ID=40075310

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/NZ2008/000119 WO2008147223A1 (en) 2007-05-28 2008-05-22 Improvements relating to ultrasonic distance measuring devices

Country Status (1)

Country Link
WO (1) WO2008147223A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2964736A1 (en) * 2010-09-15 2012-03-16 Ijinus Method for measuring level of e.g. fuel in fuel reservoir of lorry, involves stopping activation of ultrasonic sensor in emission mode or receiving mode when detected value of variable is in not range of determined values
WO2013072129A1 (en) * 2011-11-16 2013-05-23 Robert Bosch Gmbh Method and device for detecting the environment of a movement aid, in particular for a vehicle

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4785664A (en) * 1986-04-28 1988-11-22 Kay-Ray, Inc. Ultrasonic sensor
US5277065A (en) * 1990-09-04 1994-01-11 Magnetrol International, Inc. Detector with ringdown frequency matching
US5587969A (en) * 1993-03-16 1996-12-24 Siemens Aktiengesellschaft Process for the recognition and separation of useful and interfering echoes in the received signals of distance sensors which operate in accordance with the pulse-echo principle
US6142015A (en) * 1997-04-10 2000-11-07 Endress + Hauser Gmbh + Co. Method and assembly for overfill detection in liquid level sensing in a vessel by the pulse transit time technique
EP1231453A2 (en) * 2001-02-08 2002-08-14 VEGA Grieshaber KG Contactless level measurement device
US20030010116A1 (en) * 2000-02-28 2003-01-16 Paolo Cavazzin Method and device for carrying out contractless measurement of a filling level

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4785664A (en) * 1986-04-28 1988-11-22 Kay-Ray, Inc. Ultrasonic sensor
US5277065A (en) * 1990-09-04 1994-01-11 Magnetrol International, Inc. Detector with ringdown frequency matching
US5335545A (en) * 1990-09-04 1994-08-09 Magnetrol International, Inc. Ultrasonic detector with frequency matching
US5587969A (en) * 1993-03-16 1996-12-24 Siemens Aktiengesellschaft Process for the recognition and separation of useful and interfering echoes in the received signals of distance sensors which operate in accordance with the pulse-echo principle
US6142015A (en) * 1997-04-10 2000-11-07 Endress + Hauser Gmbh + Co. Method and assembly for overfill detection in liquid level sensing in a vessel by the pulse transit time technique
US20030010116A1 (en) * 2000-02-28 2003-01-16 Paolo Cavazzin Method and device for carrying out contractless measurement of a filling level
EP1231453A2 (en) * 2001-02-08 2002-08-14 VEGA Grieshaber KG Contactless level measurement device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2964736A1 (en) * 2010-09-15 2012-03-16 Ijinus Method for measuring level of e.g. fuel in fuel reservoir of lorry, involves stopping activation of ultrasonic sensor in emission mode or receiving mode when detected value of variable is in not range of determined values
WO2013072129A1 (en) * 2011-11-16 2013-05-23 Robert Bosch Gmbh Method and device for detecting the environment of a movement aid, in particular for a vehicle

Similar Documents

Publication Publication Date Title
US4320659A (en) Ultrasonic system for measuring fluid impedance or liquid level
US4815323A (en) Ultrasonic fuel quantity gauging system
US6445192B1 (en) Close proximity material interface detection for a microwave level transmitter
US6078280A (en) Periodic probe mapping
US4628736A (en) Method and apparatus for measurement of ice thickness employing ultra-sonic pulse echo technique
US4805453A (en) Tank sonic gauging system and methods
US5969666A (en) Radar-based method of measuring the level of a material in a container
US6539794B1 (en) Arrangement for measuring the level of contents in a container
US6053041A (en) Noninvasive method for determining the liquid level and density inside of a container
US4748846A (en) Tank gauging system and methods
US5315880A (en) Method for measuring fluid velocity by measuring the Doppler frequency shift or microwave signals
US20050024259A1 (en) Guided wave radar level transmitter with automatic velocity compensation
US5095748A (en) Sonic tank monitoring system
US4248087A (en) System and method for determining fluid level in a container
US5119676A (en) Ultrasonic method and apparatus for determining water level in a closed vessel
US5651286A (en) Microprocessor based apparatus and method for sensing fluid level
US5226320A (en) Measuring device and process for determining the fill level in fluid containers, preferably for tank installations, with a sound waveguide
US5793705A (en) Ultrasonic liquid level gauge for tanks subject to movement and vibration
US4144517A (en) Single transducer liquid level detector
US5015995A (en) Fluid level monitor
US6559657B1 (en) Probe mapping diagnostic methods
US20090158839A1 (en) Method for ascertaining and/or evaluating fill-state of a container containing at least one medium
US5309763A (en) Liquid-level gauging
US5856953A (en) Processing echoes in ultrasonic liquid gauging systems
US5979233A (en) Liquid measuring system and methods

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 08766968

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase in:

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 08766968

Country of ref document: EP

Kind code of ref document: A1