WO2002027349A2 - Procede de detection de l'etat limite d'une matiere et dispositif associe - Google Patents

Procede de detection de l'etat limite d'une matiere et dispositif associe Download PDF

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Publication number
WO2002027349A2
WO2002027349A2 PCT/EP2001/010813 EP0110813W WO0227349A2 WO 2002027349 A2 WO2002027349 A2 WO 2002027349A2 EP 0110813 W EP0110813 W EP 0110813W WO 0227349 A2 WO0227349 A2 WO 0227349A2
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WO
WIPO (PCT)
Prior art keywords
time
rod
sampling window
rods
signal
Prior art date
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PCT/EP2001/010813
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German (de)
English (en)
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WO2002027349A3 (fr
Inventor
Herrmann Best
Markus Hertel
Original Assignee
Endress + Hauser Gmbh + Co. Kg
Kessler, Michael
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.)
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Publication date
Priority claimed from DE20016962U external-priority patent/DE20016962U1/de
Application filed by Endress + Hauser Gmbh + Co. Kg, Kessler, Michael filed Critical Endress + Hauser Gmbh + Co. Kg
Priority to AU2002218183A priority Critical patent/AU2002218183A1/en
Priority to CA002423781A priority patent/CA2423781C/fr
Priority to JP2002530876A priority patent/JP2004519661A/ja
Priority to EP01985756A priority patent/EP1322922A2/fr
Publication of WO2002027349A2 publication Critical patent/WO2002027349A2/fr
Publication of WO2002027349A3 publication Critical patent/WO2002027349A3/fr

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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
    • G01F23/284—Electromagnetic waves
    • G01F23/2845—Electromagnetic waves for discrete levels

Definitions

  • the invention relates to a method for detecting the limit level of a good with a given dielectric constant, using a holder as a process implementation in which at least one electrically conductive rod is arranged with one end, the other end of which immerses in the good to be monitored when the limit level is reached, whereby the end of the rod seated in the holder is connected via an electrical line to an electrical circuit for generating high-frequency transmit pulses, which has an echo amplifier for receiving the echoes, the high-frequency transmit pulses as guided microwaves according to the principle of time-domain reflectometry, TDR Measurement, via the line on the rod are given, the signals reflected at the boundary layer of the material to air are returned to the echo amplifier for evaluation and the reflection signal is stretched in time, and three temporally successive areas, namely transmission pulse (para Section I), transit time (section II) and time sampling window (section III) can be distinguished, the time sampling window starting at a start time, according to the preamble of claim 1.
  • the invention also relates to a time domain reflectometer
  • sensors for fill level or limit level measurement based on time domain reflectometry are known, for which US-A-5,609,059 provides an overview.
  • TDR time domain reflectometry
  • Such sensors work as continuous systems and are based on the transit time measurement of electromagnetic signals that propagate along an open waveguide, namely the evaluation of the transit time and the reflection of a pulse on the waveguide.
  • the waveguide projects into the medium or not and signals a limit value in the former case.
  • the waveguide is, for example, a Sommerfeld line, a Goubau line, a coaxial cable, a microstrip or a coaxial or parallel arrangement of two lines, for example two probe rods.
  • the wave resistance changes due to the different dielectric constants of the medium compared to air.
  • the medium acts at the interface with the external medium or also in the case of layer formation a discontinuity in the transmission properties of the immersing waveguide within the medium due to the sudden change in its dielectric properties, so that pulses propagating along or within the waveguide are at least partially reflected at these locations.
  • the distance or height of a boundary layer can thus be determined from the back-reflected signal by comparing the time of reception of the back-reflected pulse with the time of transmission.
  • a transit time measurement takes place via an evaluation of the echo amplitude. An amplitude evaluation is not possible with small DK values.
  • a transmit pulse is generated and transmitted with each period of a transmit trigger signal.
  • the back-reflected signal is fed to a signal sampling circuit in order to make the short-time process displayable and evaluable. This is triggered with the trigger signal of the sampling frequency, the periodic signal being sampled at the sampling trigger times.
  • the sampling device By means of a time-proportional delay of the sampling trigger signal compared to the transmission trigger signal, the sampling device generates an output signal whose amplitude profile is given by the corresponding instantaneous values of the probe signal.
  • the output signal thus represents a time-stretched image of the probe signal. After amplification and filtering, this output signal or a temporal section of the same forms the reflection profile, from which the transit time of the back-reflected signal and thus the distance of the boundary layer can be determined.
  • the problem with sensors of this type is the high sensitivity to interference from high-frequency interference signals.
  • An interference signal which couples onto the waveguide, is superimposed on the back-reflected signal and is also detected by the broadband scanning circuit.
  • a typical narrow-band interference signal is simulated in tests for electromagnetic compatibility (EMC) by a carrier oscillation with a fundamental frequency of 80 MHz to 1 GHz with a low-frequency amplitude modulation (e.g. 1 kHz). If the carrier frequency is close to an integer multiple of the sampling frequency, i.e. within a so-called "Frequency reception window", this interference cannot be suppressed by low-pass filtering after the sampling device.
  • EMC electromagnetic compatibility
  • the interference signal is sampled at the sampling frequency in the manner of a band-pass sampling, an oscillation is superimposed on the reflection profile compared to the undisturbed case, which complicates its evaluation and may falsify it.
  • a TDR point level sensor which consists of a waveguide immersed in a good, to which a sampling circuit is connected, which has a transmission pulse generator for generating a pulsed high-frequency wave signal, a receiver for receiving the high-frequency wave signal, and a transmission - / Receive separation for separating the transmitted and received radio frequency wave signal, a scanner for sampling the received radio frequency wave signal, a scanning pulse generator for controlling the scanner and a buffer for temporary storage of the received radio frequency wave signal.
  • the sampling circuit has two oscillators, at least one of which can be varied in frequency, one of which controls the transmission generator and the other controls the sampling pulse generator.
  • a frequency mixer forms the difference from the two frequencies, which becomes the setpoint for setting the time expansion factor.
  • the reflected signal from such a device is difficult or difficult to evaluate because the signal and the reflected Almost superimpose the signal and it is very difficult to separate it sufficiently with a great deal of structural effort.
  • the invention has for its object to provide a method for detecting the limit level of a good as well as for determining the dielectric constant of the good and a time domain reflectometer for use as a limit switch for detecting the limit level of a good for performing the method, which on the one hand has increased immunity to interference , universal, namely regardless of temperature, pressure or in particular the nature of the medium, liquid or bulk, should be applicable and should also be suitable for goods with a low dielectric constant DK (DK between 1, 8 to 5).
  • This object is achieved by a method for detecting the limit level of a good with a given dielectric constant, using a holder as a process implementation in which at least one electrically conductive rod is arranged with one end, the other end of which immerses in the good to be monitored when the limit level is reached ,
  • the end of the rod seated in the holder being connected via an electrical line to an electrical circuit for generating high-frequency transmission pulses, which has an echo amplifier for receiving the echoes, the high-frequency transmission pulses as guided microwaves according to the principle of time domain reflectometry, TDR measurement, are applied to the rod via the line, the signals reflected at the boundary layer of the material to the air being fed back into the echo amplifier for evaluation and the reflection signal being stretched in time, and three successive areas, namely Se ndepuls (section I), transit time (section II) and time sampling window (section III) can be distinguished, the time sampling window starting at a start time, characterized by the following features: a) in both operating states of the goods to be recorded,
  • a first covered condition is recognized by the fact that the reflection signal has the following properties within the time sampling window:
  • a third different covered state is recognized by the fact that the reflection signal has the following properties within the time sampling window:
  • a time-domain reflectometer for use as a limit switch for detecting the limit level of a good with a given dielectric constant, with a holder as a process implementation in which at least one electrically conductive rod is arranged with one end, the other end of which is reached when the limit level is reached in immerses the goods to be monitored, the end of the rod seated in the holder being connected via an electrical line to an electrical circuit for generating high-frequency transmission pulses, which has an echo amplifier for receiving the reflection signals, echoes, the high-frequency transmission pulses being guided microwave based on the principle of time domain reflectometry, TDR Measurement, can be applied to the rod via the line, and the signals reflected at the boundary layer of the material to the air are fed back into the echo amplifier for evaluation and time-stretched, the wave resistances of the rod and the process execution being selected such that three are temporally used in the evaluation successive areas, namely transmission pulse (section I), transit time (section II) and time sampling window (section III) can be distinguished,
  • An important advantage of the invention is that, in contrast to the prior art, it enables reliable evaluation even with small DK values.
  • a time-domain reflectometer for use as a limit switch for detecting the limit level of a good with a given dielectric constant consists of a holder for carrying out the process, in which at least one electrically conductive rod is arranged with one end, the other end of which dips into the goods to be monitored when the limit level is reached, wherein the end of the rod sitting in the holder is connected via an electrical line to an electrical circuit for generating high-frequency transmission pulses which can be applied to the rod as a guided microwave according to the principle of time-domain reflectometry, TDR measurement, whereby the signals reflected at the boundary layer of the good to the air are fed back into the electrical circuit for evaluation, the wave resistance of the rod being selected such that it differs from the wave resistance of the good and the curve shape of the reflection signal obtained for the order the level is used, and up to three significant points of the curve shape are evaluated.
  • the material preferably has a dielectric constant greater than 1.8.
  • the invention is based on the fact that the wave reflected at a joint has the same shape as the traveling wave; only the direction of the returning shaft and the amplitude have changed. If two parallel rods are used in the process implementation, the wave resistance is between the bars changed by the good in between.
  • the wave resistance of such an arrangement is calculated as follows:
  • the idle measurement is understood to mean that reflection signal from the transmission pulse which is reflected at the bar ends when idling, that is to say without the bar ends being in contact with the material.
  • the strength of the reflection depends on the DK value, which at high DK values means that the majority is reflected at the transition from air to the medium and the rod ends immersed in the material have hardly any effects on the signal curve.
  • the shape of the reflected pulse is evaluated because, with different wave resistances, there are not only reflections with different amplitudes and different polarities, but also deformations of the reflected signal as a function of the dielectric constant, DK value, of the material and depending on the wetting of the Rods with the good comes. If the DK value of the goods is greater than 10, the momentum is almost completely reversed at the end of the bars, since there is almost a short circuit.
  • Typical media with a high DK value are water with ⁇ r ⁇ 80 or Pril with ⁇ r »40.
  • Mean DK values are in the range of 5-10; typical media here are vinegar, honey and ethanol. Here, only limited reflections form on the rods, which are, however, far higher than in media with DK values less than 5.
  • Low DK values are in the range of> 1-5, where 1 is the DK value of air.
  • Typical media in this area are coffee powder, plaster, rice, salt and sugar. With these DK values, only a small reflection forms on the rods, since the DK values do not differ much from air, so that almost the case of the line with an open end is present.
  • the results obtained with the invention show that the invention is outstandingly predestined to limit the detection of media of all types, in particular bulk goods or liquids or viscous media, such as honey, with adhering behavior, because the method according to the invention and the time domain reflectometer are one can withstand a certain range of attachments without adulteration and is still able to recognize that there is no good or medium on the bars.
  • the time-domain reflectometer according to the invention recognizes considerably more goods than known sensors of the prior art, as it is also insensitive to build-up of the medium on the rods with small DK values of the medium and allows reliable evaluation even with small DK values.
  • the wave resistances and dimensions of the process implementation are preferably selected so that a reflection signal is produced which has up to six significant points for the reliable evaluation of the limit level. Up to six significant points of the curve shape are thus preferably evaluated.
  • the curve shape of the reflection signal is preferably sampled after A / D conversion with the aid of the electronic circuit, significant points falling in the time-sampling window, in particular high point, low point, local high point, local low point, being determined from the curve shape and their position being fed to an evaluation , By evaluating the characteristic curve shape according to the invention, it is advantageously possible to use short rod lengths even with a relatively slow rise time of the transmission pulse of approximately 300-600 ps.
  • the usability of short rod lengths is a further advantage over the amplitude evaluation, in which considerably longer rods have to be used.
  • the process can in particular be a process screw connection.
  • the process implementation is a tubular process implementation with an external metal thread, within which there is at least one insulating body as an insulating holder for the rods and the same.
  • the time sampling window can be variable and the start time of the same can be defined in that the reflection signal deviates from the reference value by a predetermined value or in particular falls below this by a predetermined value.
  • a coaxial line being used as the line, the length of which can be used for the predefinable extension of the propagation time between the incoming transmission pulses and the returning reflection signals and thus for their temporal separability
  • the inner conductor of the coaxial line with one rod and the other rod is connected via the outer conductor to the ground of the electrical circuit or is capacitively coupled to it.
  • the electrical circuit preferably has a delay circuit in which a square-wave voltage is generated for the transmission pulse, which is then applied to two branches and delayed, the delay in the first branch delivering the transmission pulse and being greater than the delay in the second branch which Sampling pulse delivers, the time expansion is carried out by means of a sequential sampling circuit.
  • the time expansion factor does not have to be known.
  • the reflected signal is sampled by a four-diode sampling circuit and fed via the echo amplifier and via an A / D converter to a microprocessor or microcontroller, which evaluates the reflected signal and the result "coverage detected” or “no cover detected” outputs to a display unit or converts it into a switching signal.
  • the starting time of the time sampling window can generally always be recognized on the basis of the reflections which arise on the coupling of the runtime line to the process implementation due to different wave resistances.
  • the determination of the starting time in this way has the advantage that the time expansion factor of the electronic circuit only has to be present with an accuracy of approximately ⁇ 10% to ⁇ 20%, so that the electronic circuit can be implemented with little effort.
  • a plurality of curves can run during section II, e.g. by averaging over a plurality of curves, a baseline is determined which functions as a reference voltage, the starting time of the time sampling window being defined by the fact that the reflection signal deviates from the baseline by a predetermined value, and it is determined whether the time-stretched signal obtained from the reflection signal has a high point, a first low point, a second low point and / or a local low point and a local high point and thus a turning point within the time sampling window.
  • the time-stretched signal obtained from the reflection signal can be converted and evaluated analog-digital several times in one cycle, a plurality of values being determined and a voltage mean value being formed therefrom, which serves as a baseline for evaluating the high point, after which it is determined whether the value of the time-stretched signal is more than a predetermined value below the baseline, with which the start time of the reflection is determined, then the time-stretched signal with the maximum repetition rate of the sampling is determined in further cycles from this determined start time and a query is made as to whether a high point , a second low point or a local low point and a local high point is contained in the time-stretched signal.
  • Either filters e.g. FIR filter
  • two counters namely a counter for "coverage detected” and a counter for "no coverage detected” are used and the detection is then given to one of the counters.
  • the line is preferably a coaxial line, the selectable length of which is used for the predefinable extension of the transit time between the incoming transmission pulses and the returning reflection signals and thus for their differentiation by the electronic circuit, and thus represents a transit time line for the process implementation, the inner conductor of the coaxial line with the one rod and the other rod is connected to the ground of the electrical circuit via the outer conductor.
  • the runtime line is thus coupled to the process execution.
  • the characteristic impedance of the coaxial line can be chosen to match that of the process. In a preferred embodiment of the invention, however, the resistance of the coaxial line is chosen to be unadapted to that of the process implementation.
  • the insulating body in the process implementation consists of layers of different materials with different dielectric constants, for example Peek and Teflon, so that it is a layered dielectric, the materials sealing the process implementation on the one hand and having the minimum thickness that is necessary for the formation of the process Reflection signal for determining the start time of the time sampling window is required.
  • the process is preferably cylindrical and preferably consists of an electrically insulating material, such as Teflon (PTFE) or PEEK, within which the rods are located. This material can also serve to protect the rods when used in chemically aggressive media.
  • the rods have a coating, such as Teflon, ceramic or PEEK, the thickness of the coating preferably being between 0.1 mm and 1 mm when using Teflon or PEEK.
  • the length of the rods projecting from the process is between 2 and 15 cm, preferably between 5 and 7 cm.
  • the length of the delay line from the electrical circuit to the connection to the ends of the rods located in the process implementation is at least 30 cm, preferably 30 cm to 60 cm, in order to simplify the time separation between the transmission pulse and the reflection signal.
  • the distance between the bars is preferably between 10 mm and 30 mm.
  • the wave resistance can be selected via the ratio of this distance to the diameter of the rods.
  • the height of the process is preferably between 2 cm and 5 cm. In one embodiment of the invention the process is carried out pressure-tight, preferably up to pressures of 30 bar.
  • Figure 1 is a block diagram of a measuring device arranged thereon
  • Figures 2 a, b an equivalent circuit diagram of the process implementation (a) with the for
  • FIG. 3 measured echo curves of different goods
  • FIG. 4 a flowchart of an evaluation algorithm for point level detection using two counters for “detection” and “non-detection”,
  • FIG. 5 a schematic cross section through a process implementation
  • FIGS. 6a-d individual echo curves with those used for their evaluation
  • Figure 1 shows the basic structure of a measuring circuit with a cylindrical process implementation 12, which protrudes into a container 10 which contains a good, the medium 11.
  • the coaxial cable 13 is connected to the rear ends of the rods 3, 4 and serves as a delay line.
  • the coaxial cable 13 ends in a TDR circuit 14, which has two branches 18, 19.
  • each period of a transmit trigger signal XTS which is generated by a trigger generator 23 and is delayed by a constant time period by means of a first delay stage 20 and which has a pulse repetition frequency fPRF
  • a transmission pulse XS is generated and transmitted by a transmission stage 17.
  • a typical pulse repetition frequency is between a few 100 kHz to a few MHz.
  • a signal sampling circuit here a four-diode sampling circuit 22
  • the TDR circuit 14 the transmission pulse XS of the transmission stage 17 and the reflection signal XSonde are sampled and time-stretched so that the signal e.g. can be evaluated more easily in a microcontroller or microprocessor 16.
  • the periodically back-reflected signal XSonde is fed to the signal sampling circuit 22 in order to be able to display and evaluate the short process in a time-stretched manner close. This is triggered with the trigger signal XTA of the sampling frequency fA, the trigger signal XTA being delayed with the aid of a second delay stage 21 and a variable period of time and the periodic signal XSonde being sampled at the sampling trigger times.
  • This variable delay can be influenced by the microprocessor 16.
  • sampling trigger signal compared to the transmission trigger signal By a time-proportional delay of the sampling trigger signal compared to the transmission trigger signal, for example by a slightly lower frequency of the sampling trigger signal XTA compared to the transmission trigger signal XTS, or by a phase modulation of the sampling trigger signal XTA compared to the transmission trigger signal XTS
  • Signal sampling device 22 an output signal whose amplitude profile is given by the corresponding instantaneous values of the probe signal.
  • the output signal therefore represents a time-stretched image of the probe signal XSonde.
  • this output signal or a temporal section thereof forms the reflection profile XVideo, from which the transit time of the back-reflected signal and thus the distance of the boundary layer can be determined.
  • the reflection profile XVideo is fed via an A / D converter 24 to the microprocessor 16, which evaluates the reflection profile according to the invention and the result "coverage detected” or "no coverage detected”, e.g. outputs to a display unit 25 or converts it into a switching signal.
  • the measurement curves of the reflection signals are evaluated in software as described above and maxima and / or minima and / or turning points are determined. It follows from these characteristic curve points that the reflected signal changes at different dielectric constants DK, so that the DK value of a good can also be approximately determined with the invention.
  • the course of the curve which is in principle always similar, differs significantly with regard to the DK value of the material to be measured. It can be seen from the curves that the higher the DK value of a good, the higher the curve-like elevation between the transmission pulse and the reflection signal.
  • FIGS. 2a, b show an equivalent circuit diagram of the process implementation (FIG. 2a) with the voltages associated with the equivalent circuit diagram (FIG. 2b).
  • FIG. 2a an equivalent circuit diagram of the process execution is shown to explain the invention, starting on the left with a TDR circuit, followed by a runtime line which is led to the rods in the process execution.
  • TDR circuit and delay line have a characteristic impedance of 75 ohms each.
  • the process implementation is, for example, a tubular, metallic process implementation with several incorporated insulating materials with different dielectric constants, in which metallic rods are arranged as probes with one end each, the rods being wettable or releasable by an increasing or decreasing level of the material.
  • the insulating materials each have a characteristic impedance of 140 ohms or 170 ohms
  • the metallic process implementation itself has one of -245 ohms.
  • the bars have a characteristic impedance of 250 ohms; the wave resistance of the goods or the ends of the bars is not known.
  • This sequence corresponds to the voltages of the reflection signals shown in FIG. 2b when excited with a positive voltage jump. It is important here that when the two rods are idle, the reflection signal on the one hand shows an increase compared to the transmission pulse, which on the other hand has the same sign as the transmission pulse. In the case of a short circuit, the curve of the voltage of the reflection signal shows a decrease, which has the opposite sign as the transmission pulse.
  • FIG. 3 shows measured echo curves of various goods, which were obtained when excited with a pulse 30 with a process implementation according to FIG. 4.
  • To the left of the diagram is the transmit pulse that is applied to the bars.
  • To the right of this are the different reflections of different goods, including an idle curve LLeeriau, namely Pril, honey and coffee.
  • Between the transmission pulse and the reflection signal there is a relatively straight curve part L reflects line and allows sufficient time separation of the transmission pulse from the reflection signal.
  • the curve shape of the time-stretched reflection signal at the echo amplifier is used to determine the limit level, e.g. three significant points of the reflection signal lying within a predetermined time sampling window are evaluated numerically or by means of curve discussion.
  • the idle curve corresponds to a reflection signal with the same sign direction as the transmission pulse. If the voltage value of the reflection signal or of the time-stretched signal exceeds a predetermined value, the free end of the rod or rods is recognized as not wetted, the rods are idle. A switching signal is received if the rods have just gone into idle.
  • the limit level of the goods is considered to be recognized if either only a high point or low point corresponding to the sign direction of the transmit pulse is detected, which is above a predetermined voltage threshold and the high point has the opposite sign direction as the transmit pulse (almost short circuit).
  • the good has a DK value> 10. If two low points or two high points corresponding to the sign direction of the transmission pulse are detected, which are relatively far apart in time and have the same sign direction as the transmission pulse and exceed the one between the two If the voltage difference measured at a low point is a predetermined threshold, then a limit level of a good is also recognized, which has a DK value between 5 and 10.
  • a limit level of the goods is recognized when a low point with the same sign direction as the transmit pulse, or high point corresponding to the sign direction of the transmit pulse, and a subsequent high point with an opposite sign direction as the transmit pulse are recognized, which are close in time and thus a quasi - Form a turning point and the voltage difference measured between the low point and the high point exceeds a predetermined threshold.
  • the quasi-inflection point of the curve for coffee is defined here by two extreme points located close to one another in time, minima and maxima according to FIG. 3. If the material has a high dielectric constant with a DK value above 10, the feature is recognized that only a high point occurs which is above a predetermined voltage threshold and has the opposite sign direction as the transmission pulse (fast short circuit).
  • the material has an average dielectric constant with a DK value between 5 and 10
  • the feature is recognized that two low points occur, which are relatively far apart in time and have the same sign direction as the transmission pulse, the voltage difference measured between the two low points exceeds a predetermined threshold.
  • the good has a low dielectric constant with a DK value ⁇ 5
  • the feature is recognized that a low point with the same sign direction as the transmit pulse and a subsequent high point with the opposite sign direction as the transmit pulse occur, which are close in time and thus one Form a quasi-inflection point, the voltage difference measured between the low point and the high point exceeding a predetermined threshold.
  • the two low points of the reflection signal which are relatively far apart in time, have e.g. a time interval between 3 to 10 msec.
  • the time-stretched signal obtained from the reflection signal is converted and evaluated analog-digital several times in one cycle, a plurality of values being determined and a voltage mean value being formed therefrom, which is the baseline for triggering the starting point of the time sampling window and the evaluation of the high point is used, after which it is determined whether the value of the time-stretched signal is more than a predetermined value below the baseline, with which the starting time of the reflection is determined, and then in further cycles from this determined starting time determines the time-stretched signal with the high repetition rate of the sampling and inquires whether a high point, a second low point or a quasi inflection point is contained in the time-stretched signal.
  • Two counters are preferably used for the level detection, namely a counter for "detection” and a counter for "non-detection", for example using an evaluation algorithm according to the flow chart of FIG. 5.
  • the detection of the state “covered” or “not covered” is preferably filtered, for example, by an FIR filter and only then output.
  • the repetition frequency can be increased, for example, for the purpose of increasing the immunity to interference.
  • FIG. 4 shows a schematic cross section through a process implementation.
  • the process implementation which sits for example on a pressure tank, is a cylindrical process implementation 1 with a metal thread, within which there is a holder 8, 9, which is made of an insulating material, and rods 3, 4, at the ends of which a line 6 is located , 7 of a coaxial line 5, which is a delay line.
  • the characteristic impedance of the coaxial line can be matched to that of the electrical circuit, but it is not matched to the characteristic impedance of the process implementation, so that there are jumps between the characteristic impedances and thus a desired reflection arises at the process implementation, which serves to start the reflection signal to be clearly determined.
  • the characteristic impedance of the coaxial line and the electrical circuit can be, for example, between 65 ohms and 85 ohms, preferably 75 ohms.
  • the electrically insulating material 8 can be a disk 8 made of Teflon, the ends of the rods 3, 4 being additionally guided through a disk 9 made of PEEK (polyether ether ketone), which is placed on the disk made of Teflon.
  • the cylindrical process implementation 1 has a height s of approximately 4 cm.
  • the rods 3, 4 are arranged symmetrically within the cylinder 1, which protrude through the Teflon cylinder 1.
  • the rods 3, 4 have a free rod length between 2 to 15 cm, preferably from 5 to 7 cm.
  • the process can also be carried out in a cylindrical process only from an electrically insulating material, such as Teflon (PTFE) or PEEK (polyether ether ketone), which is a partially crystalline thermoplastic, within which the rods are located.
  • PTFE Teflon
  • PEEK polyether ether ketone
  • the wave resistance is the process implementation not or not exactly adapted to the characteristic impedance of the transit time or the coaxial line.
  • the time-domain reflectometer according to the invention has the advantage that a good reflection of the reflected pulses is achieved, in particular due to two parallel bars, which have sufficient time separation from the transmitting pulses due to the delay line, so that the reflection properties, namely the resulting curve shapes of the reflected signals can be evaluated well.
  • the rods are coated with Teflon or with ceramic, the thickness of the Teflon layer preferably being between 0.1 mm and 1 mm when using Teflon.
  • the distance (d) of the rods is between 10 mm to 30 mm, and the height (s) of the process can be between 2 cm and 5 cm.
  • FIGS. 6a-d show individual echo curves with the extreme values used for their evaluation.
  • 6a shows an idle echo curve.
  • An idle, uncovered, is recognized if the reflection signal within the time sampling window has the following properties: There is only a low point TP, which falls below a predetermined first threshold (threshold 1).
  • the threshold 1 is determined from the baseline and a predetermined offset.
  • the 6b shows an echo curve for Pril.
  • the first covered state is recognized by the fact that the reflection signal within the time sampling window has the following properties: There is a high point HP which exceeds a predetermined second threshold (threshold 2).
  • the threshold 2 is determined from the baseline and the specified offset.
  • 6c shows an echo curve for honey.
  • the second covered state is recognized by the fact that the reflection signal within the time sampling window has the following properties:
  • the second low point TP2 is a predetermined amount ⁇ s below the low point TP1. 6d shows an echo curve for coffee.
  • the third covered state is recognized when the reflection signal within the time sampling window has the following properties:
  • the threshold 1 is determined from the baseline and a predetermined offset.
  • the starting time of the time sampling window is determined as follows:
  • the baseline in area III is undercut by a predetermined amount.
  • the starting time of the time sampling window can generally always be recognized on the basis of the reflections which arise on the coupling of the runtime line to the process implementation due to different wave resistances.
  • the determination of the starting time in this way has the advantage that the time expansion factor of the electronic circuit 14 only has to be present with an accuracy of approximately ⁇ 10% to ⁇ 20%, so that the electronic circuit 14 can be implemented with little effort.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Thermal Sciences (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Resistance Or Impedance (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)

Abstract

Procédé et dispositif de détection de l'état limite d'une matière à constante diélectrique donnée. Ledit dispositif comporte un élément de support dans lequel sont placés deux tiges électriquement conductrices qui sont immergées dans la matière à surveiller lorsque l'état limite est atteint et qui sont connectées à un circuit électrique. Ce dernier produit des impulsions d'émission à haute fréquence qui sont transmises aux tiges par l'intermédiaire d'une ligne, selon le principe de la réflectométrie à dimension temporelle. Les signaux réfléchis par la couche constituant la limite entre la matière et l'air sont évalués à l'aide de leur forme de courbe.
PCT/EP2001/010813 2000-09-27 2001-09-19 Procede de detection de l'etat limite d'une matiere et dispositif associe WO2002027349A2 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
AU2002218183A AU2002218183A1 (en) 2000-09-27 2001-09-19 Method for detecting the limit state of a material, and device therefor
CA002423781A CA2423781C (fr) 2000-09-27 2001-09-19 Procede de detection d'un niveau pre-determine d'une matiere, et dispositif associe
JP2002530876A JP2004519661A (ja) 2000-09-27 2001-09-19 材料のリミットレベルの捕捉検出方法およびこのための装置
EP01985756A EP1322922A2 (fr) 2000-09-27 2001-09-19 Procede de detection de l'etat limite d'une matiere et dispositif associe

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE20016962U DE20016962U1 (de) 2000-09-27 2000-09-27 Zeitbereichsreflektometer für den Einsatz als Grenzwertschalter zur Erfassung des Grenzstandes eines Gutes
DE20016962.9 2000-09-27
DE10115150.0 2001-03-27
DE10115150A DE10115150A1 (de) 2000-09-27 2001-03-27 Verfahren zur Erfassung des Grenzstandes eines Gutes und Vorrichtung hierzu

Publications (2)

Publication Number Publication Date
WO2002027349A2 true WO2002027349A2 (fr) 2002-04-04
WO2002027349A3 WO2002027349A3 (fr) 2002-10-24

Family

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Application Number Title Priority Date Filing Date
PCT/EP2001/010813 WO2002027349A2 (fr) 2000-09-27 2001-09-19 Procede de detection de l'etat limite d'une matiere et dispositif associe

Country Status (6)

Country Link
EP (1) EP1322922A2 (fr)
JP (1) JP2004519661A (fr)
CN (1) CN1250944C (fr)
AU (1) AU2002218183A1 (fr)
CA (1) CA2423781C (fr)
WO (1) WO2002027349A2 (fr)

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WO2005062000A2 (fr) * 2003-12-19 2005-07-07 Endress+Hauser Gmbh+Co. Kg Appareil de mesure d'un niveau de remplissage et procede de mesure et de surveillance du niveau de remplissage
DE102014103212A1 (de) * 2014-03-11 2015-09-17 Sick Ag Sensor und Verfahren zum Erkennen eines auf einer Rollenbahn befindlichen Objekts
EP3045881A1 (fr) * 2015-01-13 2016-07-20 Krohne Messtechnik GmbH Dispositif de mesure du niveau de remplissage d'un fluide dans un récipient
US20220260396A1 (en) * 2021-02-12 2022-08-18 Vega Grieshaber Kg Measuring device with position sensor
EP3258296B1 (fr) * 2016-06-14 2023-07-26 VEGA Grieshaber KG Barriere de micro-ondes de reflexion

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DE102005057053A1 (de) 2005-11-30 2007-05-31 Vega Grieshaber Kg Referenzpulserzeugung
DE102007007024A1 (de) 2007-02-08 2008-08-21 KROHNE Meßtechnik GmbH & Co. KG Verwendung eines nach dem Radar-Prinzip arbeitenden Füllstandsmeßgeräts
GB0822283D0 (en) * 2008-12-06 2009-01-14 Mobrey Ltd Improvements in or relating to level sensors
CN102735313B (zh) * 2012-06-19 2014-07-30 郭云昌 一种确定连续式无源核子料位计中料位曲线的方法
DE102015100415A1 (de) * 2015-01-13 2016-07-14 Krohne Messtechnik Gmbh Vorrichtung zur Bestimmung des Füllstands eines Mediums
HUE036364T2 (hu) * 2015-02-03 2018-07-30 Grieshaber Vega Kg Határszint kapcsoló integrált szintérzékelõvel
DE102015202448A1 (de) * 2015-02-11 2016-08-11 Vega Grieshaber Kg Auswerteverfahren für einen TDR-Grenzstandschalter
WO2018086949A1 (fr) * 2016-11-11 2018-05-17 Leoni Kabel Gmbh Procédé et système de mesure servant à la surveillance d'une ligne
DK3527959T3 (da) * 2018-02-14 2024-01-15 Grieshaber Vega Kg Fyldeniveauradar med vedhæftningsdetektor

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EP0780665A2 (fr) * 1995-12-21 1997-06-25 Endress + Hauser GmbH + Co. Procédé et appareil de traitement de signaux de mesure dans des processus
US5943908A (en) * 1997-09-08 1999-08-31 Teleflex Incorporated Probe for sensing fluid level
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DE4407369A1 (de) * 1994-03-05 1995-09-14 Grieshaber Vega Kg Verfahren und Schaltungsanordnung zur Laufzeitmessung sowie deren Verwendung
EP0780665A2 (fr) * 1995-12-21 1997-06-25 Endress + Hauser GmbH + Co. Procédé et appareil de traitement de signaux de mesure dans des processus
US6085589A (en) * 1996-12-23 2000-07-11 Venture Measurement Company Llc Material level sensing system calibration
US5943908A (en) * 1997-09-08 1999-08-31 Teleflex Incorporated Probe for sensing fluid level

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005062000A2 (fr) * 2003-12-19 2005-07-07 Endress+Hauser Gmbh+Co. Kg Appareil de mesure d'un niveau de remplissage et procede de mesure et de surveillance du niveau de remplissage
WO2005062000A3 (fr) * 2003-12-19 2005-10-06 Endress & Hauser Gmbh & Co Kg Appareil de mesure d'un niveau de remplissage et procede de mesure et de surveillance du niveau de remplissage
US7826309B2 (en) 2003-12-19 2010-11-02 Endress + Hauser Gmbh + Co. Kg Filling level measurement device and filling level measurement and monitoring method
DE102014103212A1 (de) * 2014-03-11 2015-09-17 Sick Ag Sensor und Verfahren zum Erkennen eines auf einer Rollenbahn befindlichen Objekts
EP3045881A1 (fr) * 2015-01-13 2016-07-20 Krohne Messtechnik GmbH Dispositif de mesure du niveau de remplissage d'un fluide dans un récipient
EP3258296B1 (fr) * 2016-06-14 2023-07-26 VEGA Grieshaber KG Barriere de micro-ondes de reflexion
US20220260396A1 (en) * 2021-02-12 2022-08-18 Vega Grieshaber Kg Measuring device with position sensor
US11796354B2 (en) * 2021-02-12 2023-10-24 Vega Grieshaber Kg Measuring device with position sensor

Also Published As

Publication number Publication date
EP1322922A2 (fr) 2003-07-02
JP2004519661A (ja) 2004-07-02
CN1250944C (zh) 2006-04-12
CA2423781C (fr) 2009-02-24
CN1466674A (zh) 2004-01-07
AU2002218183A1 (en) 2002-04-08
WO2002027349A3 (fr) 2002-10-24
CA2423781A1 (fr) 2003-03-26

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