GB2358535A - Time domain reflectometry method and apparatus - Google Patents

Time domain reflectometry method and apparatus Download PDF

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Publication number
GB2358535A
GB2358535A GB0024946A GB0024946A GB2358535A GB 2358535 A GB2358535 A GB 2358535A GB 0024946 A GB0024946 A GB 0024946A GB 0024946 A GB0024946 A GB 0024946A GB 2358535 A GB2358535 A GB 2358535A
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United Kingdom
Prior art keywords
liquid
pulse
generator
probe
time
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GB0024946A
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GB0024946D0 (en
Inventor
Wayne Sherrard
Walter Sacuta
Trent Cherniwchan
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Federal Industries Industrial Group Inc
Milltronics Ltd
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Federal Industries Industrial Group Inc
Milltronics Ltd
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Priority to CA 2286439 priority Critical patent/CA2286439A1/en
Application filed by Federal Industries Industrial Group Inc, Milltronics Ltd filed Critical Federal Industries Industrial Group Inc
Publication of GB0024946D0 publication Critical patent/GB0024946D0/en
Publication of GB2358535A publication Critical patent/GB2358535A/en
Application status is Withdrawn legal-status Critical

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    • 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
    • G01F23/284Electromagnetic 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
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/0209Systems with very large relative bandwidth, i.e. larger than 10 %, e.g. baseband, pulse, carrier-free, ultrawideband
    • 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
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88Radar or analogous systems specially adapted for specific applications

Abstract

A time domain reflectometry method for determining positions of upper and lower interfaces of a first liquid 24 floating on a second liquid 26 within a vessel 20, using a system which includes a probe 2 and an impulse radar system (Figure 3) connected to the upper end of the probe transmission line. The transmission line is constructed so as to have a pulse response substantially free of internal reflections except at its ends, and match the radar system to the probe sufficiently well to avoid the generation of noise or spurious echoes. The positions of the upper and lower interfaces of the liquid are found by determining the time of flight between a fiducial return pulse and a first return pulse and calculating the distance along the probe to the first interface, and determining the time of flight between the first and second return pulses and applying thereto a scaling factor dependent on the dielectric constant of the first liquid to determine a distance between the first and second interfaces. The method is preferably implemented using a microwave impulse radar system, and sampling of reflected energy is preferably under control of a time base generator whose output delay is linearized by negative feedback.

Description

2358535 IMPROVEMENTS IN TIME DOMAIN REFLECTOMETRY

FIELD OF THE INVENTION

This invention relates to time domain reflectometry (TDR) and, more particularly, to techniques for the use of TDR. to determine the depths of superposed layers of immiscible liquids in a tank or other vessel.

BACKGROUND OF THE INVENTION

A typical application for such techniques is in the processing of petroleum products, where it is commonly found that a layer of such a product will float on an accumulated aqueous layer in tanks or other vessels containing such products. It is, of course, desirable that quantities of both the product and the aqueous layer be ascertainable; such quantities can be determined from the depths of the layers provided that the characteristics of the vessel are known.

US Patent No. 5,400,651 (Welch) describes a method for measuring the water level at the bottom of a storage tank using multiple sensors located at different distances from a tank bottom. This requires multiple sensors and. multiple mountings.

US Patent No. 5,811,677 (Cournanc) utilizes a vertical transmission line sensor within a vessel, a swept frequency being applied to the transmission line, and the spectrum of reflections occasioned by reflections along the line being analyzed to determine the spatial distribution of electrical impedance along the sensor. This requires more expensive equipment and sophisticated analysis than can be justified in most process control applications.

US Patent No. 3,812,422 (De Caroll s) measures changes in impedance along the path of a co-axial cable connected to a pulse generator and short-circuited at its distal end with 2 a view to determining interface levels between liquids L d the dielectric constraints of the liquids.

US Patent No. 5,376,888 (Hook) relies on e generation of markers at predetermined points along a pr!) to locate the origin of other reflections occurring all the probe. The probe structure is complex, and the sys appears primarily intended for investigating the moistir content of soils.

US Patent No. 5,610,611 (McEwan) discloses 1.

application of micro impulse radar (MIR) to liquid le detection applications. MIR is a technique developed I McEwan at the Lawrence Livermore National Laboratory of I University of California, which provides a low cost means ( applying radar techniques to a variety of use 1.

applications. There is, of course, a trade-off as compa,e to more complex and expensive radar techniques in that k pulses are of very low power and broadband, which limit both range and the selectivity of the simple samplir detection technique utilized, while accuracy is limited the stability of the time base utilized to control I sampling. Applications such as that of the pres r invention strain the technique to its limit, both beca's the size of tanks used, for example, in the petrochemi a industry can be quite large, and because of the ene, absorption that occurs when seeking to penetrate 't interfaces below the surface of stored liquid. Aqueq layers in particular present problems because contaminat; may render their absorption very high, while the hj. dielectric constant of water greatly increases time flight, thus aggravating absorption problems and increasi the maximum time taken f or a pulse to return f rom the f, end of a probe. The broadband signals also tend t aggravate the generation of spurious signals over the i i of flight due to unwanted reflections to discontinuities the properties of the propagation medium other than those be detected and mismatches to the propagation medium.

US Patent Nos. 5,841,606 and 5,884,231 (Perdue et al) are directed to processing the return signal in an MIR TDR system.

Proposals have also been made for the use of TDR to determine the dielectric constant of liquids. These have usually been based upon measurement of the characteristics of the reflection at the interface at which the signal enters the liquid; the amplitude and width of such pulses are related to the change of dielectric constant which occurs at the interface. in US Patent No. 5,898,308, dielectric constant of a liquid is measured by measuring the time taken for a pulse to propagate to the end of a probe at least the distal portion is submersed in the liquid in an MIR TDR system.

SUMMARY OF THE INVENTION

It is an object of the present invention to enable the positions of upper and lower interfaces of a layer of first liquid floating on a second liquid in a vessel to be determined. If the dimensional characteristics of the vessel are known, this enables the volume and depth of both the first and second liquids to be determined. This is preferably carried out by TDR using a micro-impulse radar system matched to a transmission line extending through anticipated ranges of position of the interfaces. The transmission line is designed to minimize the generation of reflections of microwave energy except at a lower end of the line and at the interfaces, and the matching of the radar system to the line is made such that only a relatively small proportion of the microwave energy generated by the system is reflected at this point, with a view to ensuring that the reflections generated at the interfaces and at the matching to the line are large compared with spurious reflections occurring in the same time domain. Since the dielectric constant of the first liquid, which will usually be a petroleum product, will frequently not be known, it must be determined in order to calculate the position of the lower 4 interface and the propagation velocity of the pulses ig, function of the dielectric constant. This may be determig by a separate measurement, or by measuring the amplitude the reflected pulses at the upper interface, which will.A approximately proportional to the change in dielect:p,:., constant occurring at the interface, or by operating 1:1A system with the second liquid substantially absent, az detecting a pulse reflected at a lower end of the probe, as well as the pulse from the matching interface and from 1.1e upper interface. Since the length of the probe is knon;r the dielectric constant of the first liquid can lie calculated, since the dielectric constant of the air c vapour above the first liquid is close to 1, allowing C a height of the first interface to be calculated, and thx P, also the distance travelled along the probe in the fizclliquid. Since the time of flight within the first liquid! 1 s also known from the delay between the receipt of reflectiri; from the first interface and the end of the probe, dielectric constant can then be calculated. This liE method of determining the dielectric constant, wh c resembles that disclosed in US Patent No. 5,898,308, has disadvantage that it requires the second liquid to 1 removed from the vessel each time it is used, which wi. 1 frequently not be practicable.

It is found that, in TDR systems operating over lOn ranges and under widely differing environmental conditions, it is difficult to maintain stability of time bases usedt-., control sampling of a stream of return signals f#aiL successive pulses, as is carried out in MIR and similat.

pulse radar systems. It is therefore a further object 1 the invention to provide an improved time delay generator control sampling in such a system.

SHORT DESCRIPTION OF THE DRAWINGS

Figure 1 is a diagrammatic representation of th principal components of a system in accordance with -h invention; - Figure 2a is a diagrammatic illustration of the system installed in a tank containing a liquid petroleum product floating over a layer of water; Figure 2b is a graph illustrating the amplitude of the return signal received from the probe of system such as that of Figure 2a; Figure 3 is a block diagram of the probe transceiver and digitizer; Figure 4 is a more detailed circuit of the time delay generator block in Figure 3; Figure 5 is a timing diagram for the circuit of Figure 4; and Figures 6-10 are flow diagrams illustrating aspects of the operation of the system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Figure 1, the system comprises a probe 2 in the form of a transmission line, mounted in a tank 4 to be monitored by top and bottom fittings 6 and 8, a probe transceiver and digitizer unit 10 being mounted at an upper end of the probe both mechanically and electrically. The unit 10 is connected by a cable 12 to a control and display unit 14 which houses a control computer and a power supply for.the unit 10. The unit 14 may be connected to further remote control and display equipment by a cable 16.

We have found that it is desirable to optimize the performance of the probe 2 as a transmission line, both within the line and at its termination at its bottom end and its connection to the unit 10 through interface 18 (See Figure 4). A probe constructed as set forth in US Patent No. 5,781, 019 (Telder), the text and drawings of which are incorporated herein by reference, provides a balanced line 6 which minimizes spurious reflections. High quality coax.

probes constructed to admit f luid between the coax,,.

conductors can also give good results. Single w,'.I transmission lines, while they can be used in less demanding applications, are very prone to developing spuriTus reflection signals which may render difficult the detect: C111 of wanted signals, particularly in deeper tanks.

It must be stressed that successful operation of t1' invention, particularly at longer ranges, is heavil dependent upon the quality of the reflected signal from the probe. Even in systems primarily intended to detect tHe interface between air and a liquid in a tank, a nois. reflected signal can present substantial difficulties in detection, as is well illustrated in US Patent N,-, 5,841,666 and 5,884,231 which are primarily concerned with overcoming these difficulties. Although these patett; discuss the theoretical possibility of detecting furtter liquid/liquid interfaces beneath an air/liquid interf ace,'i will be readily apparent that the detection difficultid, apparent from the examples would be compounded in suc.b a case, particularly systems based on MIR, the use of which is highly desirable for economic reasons, but whose immunitytc) spurious signals is low.

We have further found that it is important that thf transmission line is well-matched to the MIR system so tat reflections occurring at the interface 18 between the systep and the line are limited such that the proportion of pu4s energy lost at this interface is kept to a low level. S,uq reflection is desirable to provide a fiducial or marer signal marking the beginning of the probe, but th reflection of excessive energy at this point results in tke generation of spurious signals and noise distributed in ke time domain, which may mask wanted signals.

Referring to Figure 2a, a tank 20 is shw schematically in which the probe 2 is mounted to extend f3;;c I the top of the tank, through a vapour or air space 22, 7 layer 24 of a first liquid, typically a petroleum product, and a layer 26 of a second liquid, typically water, to the bottom of the tank. Referring to Figure 2b, a pulse from the unit 10 produces a reflection 30 at the interface 18 at the.top of the tank, a first interface reflection 32 as it passes f rom air or vapour above the f irst liquid into the first liquid, and a second interface reflection 34 at the interface between the first and second liquids. Typically, the dielectric constant of a petroleum product will not be very high, so the pulse formed by the reflection at the first interface is of relatively small amplitude. The dielectric constant of water is much higher, and thus the pulse f ormed by the ref lection at the second interface is of substantially greater amplitude. The velocity of propagation within the probe in water will be greatly reduced by the high dielectric constant of water, such that any significant depth of water will result in any reflection from the end of the probe falling beyond the right hand extremity of the graph of Figure 2b. Furthermore, the rate of 'absorption of the pulse will be increased in water, particularly if it is impure, such that there may be no detectable reflection from the far end of the probe.

Referring to Figure 3, the unit 10 includes the interface 18 to the probe 2. The interface is connected to a microwave pulse generator 40 driven by an oscillator 42 which determines the pulse repetition rate through a time delay generator (TDG) 44 described further below. A gate pulse generator 46 is also driven by the generator 44 so as to produce gate pulses with a progressively changing delay relative to the microwave pulses controlled by a ramp signal from a ramp generator 45. The gate pulses control a sampling gate 48 which samples signals reflected from the probe. The samples are digitized by a digitizer 50 which provides an output to the control and display unit 14.

Referring now to Figures 4 and 5,- a nominally 50% duty cycle signal (PRF) is filtered.by the network R-R-CG and introduced to the input of US (signal VCT in Figure 5).

The peak to peak voltage of signal VCT is typically 0.51r, The voltage produced at VX applies an offset to signal Ve,,, When the voltage VX is increased from 0.5V,,,,, the posit--LA duty cycle of the signal at VE becomes greater than 50%.1 larger portion of the filtered waveform VCT becomes grea than the threshold of gate U5. This is the transmit patli. the.TDG circuit.

The PRF signal is also complemented by inverter This inverted signal, denoted VA, is also applied to R-R-CG network similar to that employed in the trans path. The filtered signal at the input of U2, denoted VCC will be the complement to that of VCT. Since this R-R.C filtering network is also tied to VX, the same offset occi2 at VCG and VCT. When the voltage VX is increased fjc O.WDD, the positive duty cycle of the signal at VB becOlLE less than 50%. A larger portion of the filtered waveform a VCG is greater than the threshold of gate U2, as with tl transmit path, but only a single inversion is used to cret wave f orm VB. This branch of the TDG circuit is the g,t path.

The gates used for this part of the circuit may be type 74HCU04. These are unbuffered High Speed Ch inverters. This particular device is used because it has: r limitation on the input rise/fall time and, for slow inplit near the switching threshold, it acts as an amplifier m, than a logic gate. This characteristic is desirable beca' the filtered waveforms VCT and VCG are representative long rise/f all time inputs and the use of a buf f ered C device would tend to exhibit erratic switching behavi with these slow inputs. The capacitance CG of the filter! networks can be provided by the input capacitance of t! 74HCU04 gates which is typically about 1OpF.

The signals at VB and VE are then introduced to gate U3 and U7 (respectively) through a series resistor REI. Th resistors RHI and RHF, along with the associated gates M U4 (gate path), and U7, US (transmit path) effectively fo - 9 hysteresis comparators. Hysteresis is used to help square up the signals VC, W, GATE, and TX to prevent any erroneous switching due to slow inputs at VCT and VCG. The use of hysteresis becomes especially important for TDGs that are 5 required to create long time delays (greater than 10Onsec or > 15m range).

The introduction of the PRF signal to gates U3 and U7 is used to provide a common reference for the transmit and gate paths. The rising edges of VB and VE propagate through the circuit to form the rising edges GATE and TX (respectively) which determine the time delay. The TX rising edge will precede the GATE rising edge when the positive duty cycle of VE is greater than that of VB. This requires the voltage at VX to be greater than 0.5V... The is f alling edges of VB and VE do not propagate because the falling edge of waveform PRF effectively resets the outputs before this can occur. This operation prevents the delay between the falling edges of VB and VE from contributing to the feedback control of the time delay. This reference ensures that the only parameter monitored and controlled by the feedback mechanism is the time delay generated.

The gates used for this feedback part of the circuit are 74ACOO. They are Advanced CMOS buffered NAND gates. These are used because of low input capacitance (4pF), fast output rise times (750psec), and low propagation time delay (10nsec) at low supply voltages. The low input capacitance is useful to minimize the delay introduced by the hysteresis resistor network (RHI and REP) and reduces the power consumption. The fast output rise time is required to generate the large band width pulses required for TDR. The low propagation time delay is useful to assert the hysteresis effect.

A difference amplifier constituted by amplifier U10 and its associated parts monitors the time delay. The DC values at VC and VP are subtracted and the difference voltage &V will be proportional to the time delay generated.

The capacitors CP are used to extract the DC value. e difference amplifier does not monitor the TX and QREE outputs directly. This minimizes the load at the outputs:f U4, U8 which helps to shorten the rise time.

A servo amplifier constituted by amplifier Ull d its associated parts will adjust the control voltage M', force the difference voltage AV to be equal to the 1UL voltage. With the bias network (2R-2R), the circuit wi generate zero time delay when VS equals the digital gro,Iii (VX=0.5VDD) Zero time delay occurs when both VB and VE h 50% duty cycles. The resistor RSC and capacitor CSC t31 used to help compensate the frequency response of tIL feedback loop.

The invariance of the time delay generated component mismatch, temperature, and aging is primartl achieved by the use of the common reference (PRF) introdudE to gates U3, U7 and the use of the differencing amplifier t monitor the time delay. if no reference were used, the tb delay generated would depend on the matching of the R- R?( networks and the propagation time delay balance of le transmit and gate paths. The differencing amplifier hells eliminate any variations introduced by the net propagat,,; time delay for either path that manifests itself in t.

i i corresponding common mode duty cycle at VC or VF. 1 The propagation time delays for the transmit and g4t paths need to be balanced for other reasons. If the tu paths were not balanced, the control voltage VS would holve to offset the additional delay. This is not desirable sii:,ci the propagation time delay of HCMOS has a signific4 1.

temperature dependency and the offset required for ail, in-balance could create instabilities in the feedb4c): mechanism and erroneous control. The extra gate U9 attac e to the output of Ul is included to help balance:h i propagation time delays of both paths. The gate capacita c of U9 mirrors the capacitive load that U6 has on US.1 helps to balance the propagation time delays of U1 and is All the additional gates for each path are equally loaded and the - propagation time delay for each path after Ul, US should be balanced.

It should be understood that circuits operating on the same principles as that of Figure 4 may also be used to control other microwave transceivers depending on sensing of return signals after a progressively changing delay, for example, a transceiver such as that disclosed in W098/36940 may be used in place of the timing control circuit disclosed in that specification.

Aspects of the processing of the signal received from the unit 10 by the control and display unit 14 are illustrated by the flow diagrams of Figures 6-11.

Referring to Figure 6, the successive digitized echo profiles produced by the digitizer unit 10 will typically be summed, the averaging index specifying the number of profiles to be summed (overlaid). The routine tests whether a baseline profile is stored (to provide a reference for amplitude measurements), calculates one if necessary, and applies a temperature dependent scaling value for all subsequent measurements.

Figure 7 shows that the fiducial pulse marking the top of the probe is located - this will typically be of negative polarity relative to the other pulses and thus have the lowest absolute amplitude. The location of the fiducial pulse is tested for validity, and if verified, interface pulses are searched for. If any interface pulse is found, a test is made to determine whether calibration has been performed. If any of these tests f ails, the routine of Figure 9 is entered. otherwise, processing progresses to Figure 8, where successive tests are carried out before processing progresses to Figure 9. If the first interface pulse has a high amplitude (the "water" threshold), it represents a time of flight corresponding to an empty tank (reflection from end of probe), or to a reflection frSm water.

If the first pulse has a lesser amplitude, but abooe the amplitude characteristic of a petroleum prodL,:t Pliquid"), the result is considered invalid. If the pu13e has a still lower amplitude, it is considered characteridlt.c of a liquid interface, and a search is made for a furt,Ar pulse with a greater time of flight. According to wheta!r such a pulse is found, there are considered to be pres: 1 t either upper and lower interfaces (e.g., liquid and wate or only an upper interface (liquid only).

Referring to Figure 9, the routine loads tle equivalent velocity of a pulse in air or vapour, a. id measurement limit values, and then checks the result pastld to it for various characteristics as previously tested,its set forth. In this routine, the velocity ratio is calculated from the amplitude of the liquid interfeme reflection, but it may be varied to substitute a stot velocity ratio (related to dielectric constant), which', is 20 calculated when the result of the processing is Illicp id only", since this will enable the velocity ratio to e calculated based on knowledge of the length of the probe it d the position of the first interface. if such a calculal.. d figure is not available, a preset figure may be employil, based on external measurement of the dielectric constant.. of the liquid.

Figure 10 discloses a preferred pulse search routi.E

Claims (1)

  1. - 13 CLAIMS
    1. A time domain reflectometry method for determining positions of upper and lower interfaces of a first liquid floating on a second liquid within a vessel, using a system comprising a probe in the form of a transmission line extending vertically within the vessel from a point above a highest level to be measured of the upper interface to below a lowest level to be measured of the lower interface, and an impulse radar system connected to the upper end of the transmission line, the micro impulse radar system including a microwave pulse generator; comprising the steps of constructing and installing the transmission line so as to have a pulse response substantially free of internal reflections except at its ends, matching the radar system to the upper end of the probe sufficiently well to avoid the generation of noise or spurious echoes having an amplitude which is comparable to the magnitude of first and second return pulses due to reflections occurring at the upper and lower interfaces, while generating a readily detectable reflection forming a fiducial return pulse marking the end of the probe; and ascertaining the positions of the upper and lower interfaces of the liquid by determining the time of flight between the fiducial return pulse and the first return pulse and calculating therefrom distance along the probe to the first interface, and determining the time of flight between the first and second return pulses and applying thereto a scaling factor dependent on the dielectric constant of the first liquid so as to determine a distance between the first and second interfaces.
    2. A method according to claim 1, wherein the radar system is an 14IR system.
    3. A method according to claim 1, including the step of calculating the scaling -factor based on the amplitude of the first return pulse.
    14 4. A method according to claim 1, including t ie step of determining the dielectric constant of the fir3t liquid to provide the scaling factor.
    5. A method according to claim 4, wherein t:e dielectric constant is derived from an amplitude measureirkett of the first return pulse.
    A method according to claim 4, wherein 6. tl ie dielectric constant is derived by conducting the methodin the absence of the second liquid, detecting a further pul,e formed by reflection from the lower end of the transmiss line in place of the second pulse, and relating the time!6E flight between the second and further pulses to the lenitl of transmission line beneath the first interface so as derive the dielectric constant of the first liquid.
    is 7. A method according to any one of claims 1 to in which a digital signal to be processed is formed 7 applying a series of pulses of microwave energy to 1-.iz transmission line, and sampling reflected energy in a perjAd following each pulse using a progressively changing deliky, 8. A method according to claim 7, wherei j,,,i progression of the delay is obtained by applying a ramp signal to a time delay generator, and applying negati.-% e feedback within the generator to linearize the response c the generator to the ramp.
    9. Apparatus comprising a probe in the form ot a transmission line extending vertically within the ves;E:I.
    from a point above a highest level to be measured of tle upper interface to below a lowest level to be measured,c:..
    the lower interface, and an impulse radar system connectEd to the upper end of the transmission line, the micro impulE radar system including a microwave pulse generator and 1. control computer programmed to implement the method stl; set forth in any one of claims 1 to 8.
    - is - 10. Apparatus according to claim 7, including a time delay generator for use in an impulse radar ranging system containing a transmitter and a receiver, in which a signal to be processed is formed by transmitting from the transmitter a series of pulses of microwave energy, and sampling reflected energy received by the receiver following each transmitted pulse using a progressively changing delay controlled by a delay generator, wherein the delay generator is controlled by a ramp signal, and the generator is configured internally to include a negative feedback loop connected to linearize the response of the generator to the ramp signal.
    11. A time delay generator f or use in an impulse radar ranging system containing a transmitter and a receiver, in which a signal to be processed is formed by transmitting from the transmitter a series of pulses of microwave energy, and sampling reflected energy received by the receiver following each transmitted pulse using a progressively changing delay controlled by a delay generator, wherein the delay generator is controlled by a ramp signal, and the generator is configured internally to include a negative feedback loop connected to linearize the response of the generator to the ramp signal.
    12. A time domain ref lectometry method substantially as hereinbef ore described with reference to the accompanying drawings.
    13. Time domain reflectometry apparatus substantially as hereinbefore described with reference to the accompanying drawings.
    14. A time delay generator for use in an impulse radar ranging system, substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.
GB0024946A 1999-10-15 2000-10-11 Time domain reflectometry method and apparatus Withdrawn GB2358535A (en)

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US8823397B2 (en) 2012-09-27 2014-09-02 Rosemount Tank Radar Ab Interface detection
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DE102004061449A1 (en) * 2004-12-17 2006-06-22 Endress + Hauser Gmbh + Co. Kg After the transit time principle working level measuring device and process for commissioning
DE102007060579B4 (en) 2007-12-13 2019-04-25 Endress+Hauser SE+Co. KG Method for determining and / or assessing the filling state of a container filled with at least one medium
DE102012101725A1 (en) 2012-03-01 2013-09-05 Sick Ag Method for level measurement
EP2759813B1 (en) 2013-01-25 2016-04-13 Sick Ag Method and sensor for measuring the fill level of layered media
DE102015202448A1 (en) * 2015-02-11 2016-08-11 Vega Grieshaber Kg Evaluation procedure for a TDR limit switch

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CN106030259B (en) * 2014-01-23 2019-09-10 霍尼韦尔国际公司 Configuration includes the electronic horizon meter for the position of application
EP3296736A1 (en) 2016-09-20 2018-03-21 SP Technical Research Institute Of Sweden Method and system for measuring the energy content of gas
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