CA2325174A1 - Method and device for determining the limit level of a medium in a vessel - Google Patents
Method and device for determining the limit level of a medium in a vessel Download PDFInfo
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- CA2325174A1 CA2325174A1 CA002325174A CA2325174A CA2325174A1 CA 2325174 A1 CA2325174 A1 CA 2325174A1 CA 002325174 A CA002325174 A CA 002325174A CA 2325174 A CA2325174 A CA 2325174A CA 2325174 A1 CA2325174 A1 CA 2325174A1
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- signal
- conductive element
- medium
- echo signal
- predetermined
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- 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
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
- G01F25/20—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of apparatus for measuring liquid level
Abstract
The invention relates to a device and a method for determining a predetermined level of a medium (9) in a vessel (8). In the method according to the invention a radio-frequency measuring signal is coupled onto a conductive element (6) of a predetermined length and is guided along the conductive element (6), the measuring signal is in each case reflected as a system-dependent echo signal in those regions of the conductive element (6) in which there is a sudden change in the characteristic impedance, the measuring signal is reflected as a useful echo signal when the free end of the conductive element (6) is located in the immediate vicinity of the surface (10) of the medium (9), or in contact with the medium (9), and the fact that the medium (9) has reached the predetermined level in the vessel (8) is determined on the basis of the relative position of the useful echo signal and at least one system-dependent echo signal, or on the basis of the relative position of two system-dependent echo signals.
Description
October 16, 2000 METHOD AND DEVICE FOR DETERMINING THE
LIMIT LEVEL OF A MEDIUM IN A VESSEL
Field of the Invention The invention relates to a device and a method for determining a limit level of a medium in a vessel.
Background of the Invention Capacitive measuring devices or vibration systems are used to detect the limit level of liquids or granular solids in vessels. In addition to such limit level detectors, 1o which signal that a predetermined level has been reached as soon as they come into contact with the medium to be measured, measuring systems exist which operate without making contact and, as the measuring radiation, use ultrasound waves, microwaves - or in particularly critical applications - radioactive radiation.
The known systems have been proven in practice, but cannot be used in all possible applications. Capacitive measuring devices and vibration systems come into direct contact with the medium to be measured. If they are used to detect corrosive media, then they must be very highly resistant to corrosion. Furthermore, deposits on the measuring devices lead to inaccurate measurement results. Their use is problematic if the level of different media, having different electrical characteristics, 2o is intended to be measured.
The application options of the sensors which are known are limited by the temperature and pressure conditions at the measurement point. For example piezo-ceramics which are used in vibration systems irreversibly lose their characteristic properties as soon as the ambient temperature exceeds a specific value, the Curie temperature, which depends on the respective material.
Those measuring devices which operate on the basis of ultrasound waves are also severely dependent on the temperature. Temperature compensation is absolutely essential here in order to obtain reliable measurement results. Ultrasound sensors are also highly dependent on the composition of the gas area located above the medium;
3o in vacuum conditions, or if the pressures in the gas area are high, they cannot be used.
It should furthermore be mentioned that the sensitivity of ultrasound sensors is also influenced by the noise level in the environment.
In many fields of use, for example in the petrochemical, chemical and foodstuffs industries, high-precision measurements are required of the level of liquids or granular solids in vessels (tanks, silos, etc.). For this reason sensors are increasingly being used in which short electromagnetic radio-frequency pulses or continuous microwaves are coupled onto a conductive, elongated element, for example a rod probe or a cable probe, and are introduced by means of the conductive element into the vessel in which the medium is stored.
October 16, 2000 From the physical point of view, this measuring method uses the effect that a proportion of the radio-frequency pulses or microwaves being propagated is reflected on the boundary surface between two different media, for example air and oil or air and water, as a result of the sudden change (discontinuity) in the dielectric constants of the two media, and this reflection is passed via the conductive element back into the receiving device. The reflected portion of the radio-frequency pulses or microwaves in this case becomes greater the greater the difference in the dielectric constants of the two media. The time of flight of the reflected portion of the radio-frequency pulses or microwaves allows the distance to the boundary surface to be 1o determined. If the height of the empty vessel is known it is possible to calculate the level of the medium in the vessel.
Sensors with guided radio-frequency signals (pulses or waves) are distinguished from sensors which emit radio-frequency pulses or waves freely (free-field microwave systems or 'real radar systems') by having considerably less attenuation. The reason for this is that the power flows in an entirely controlled manner along the rod or cable probe, or the conductive element. Furthermore, sensors using guided radio-frequency signals have a higher measurement quality in the near field than freely emitting sensors.
The advantage of sensors using guided radio-frequency signals is, furthermore, 2o the high accuracy and reliability of the level measurement. This is based on the fact that measurement using guided measuring signals is largely independent of the product properties of the medium (moisture, dielectric constant, change of medium), the vessel structure (materials, geometry) or the other operating conditions (dust, deposits, and angle of the granular solids).
Until now, it has not been known for such measuring systems with guided measuring signals to be used as limit level detectors.
The invention is based on the object of proposing a method and a device which allow a predetermined limit level of a medium in a vessel to be detected with high reliability.
3o A first embodiment of the inventive method achieves the object in that a radio-frequency measuring signal is coupled onto a conductive element of a predetermined length and is guided along the conductive element, the measuring signal is reflected as a system-dependent echo signal in those regions of the conductive element in which there is a sudden change in the characteristic impedance, the measuring signal is reflected as a useful echo signal when the free end of the conductive element is located in the immediate vicinity of the surface of the medium, or in contact with the medium, and the fact that the medium has reached the predetermined level in the vessel is determined on the basis of the relative position of the useful echo signal and ' October 16, 2000 at least one system-dependent echo signal, or on the basis of the relative position of two system-dependent echo signals.
According to an advantageous embodiment of the method according to the invention, use is made of the system-dependent echo signal of the signal which occurs upon the transition of the coupling of the measuring signal onto the conductive element (~fiducial launcher). Additionally or alternatively, use is made of the system-dependent echo signal of the signal which is reflected at the free end of the conductive element ('tJend-of-line peak). Furthermore, it is proposed to make use of an additional impedance which is integrated in the coupling unit and produces a 1o system-dependent echo signal. A further alternative is provided by setting a reference zero signal at the same moment when the measurement signal is triggered.
In the case of the method according to the invention, it is thus not absolutely essential for the conductive element to come into contact with the medium to be detected. This variant of the method described above thus also has the abovementioned advantages of measurement methods which make no contact. At the same time, the method according to the invention has the advantage over those measuring methods in which the measuring signals are emitted freely into space that the influence of external interference variables is largely excluded. This preferred variant of the method according to the invention operates particularly well, moreover, 2o when the medium has a high dielectric constant.
According to a further development of the method according to the invention, the fact that the predetermined level has been reached is output as soon as there occurs inside a predetermined time window a useful echo signal which has an opposite sign to the peak of the fiducial launcher signal or of the end-of-line peak signal.
This type of identification of the predetermined level is, of course, highly advantageous since it is based on a simple yes/no question, which can be implemented technically without any problems, for example by means of a threshold value detector. There is no need for complex evaluation methods based on the time of flight of the measuring signals.
Furthermore, one advantageous embodiment of the method according to the invention is the fact that the maximum or minimum level has been reached is output as soon as the end-of-line peak signal occurs inside a predetermined time window.
This embodiment can be used only when the conductive element is immersed in the medium. As soon as this is the case, the position of the end-of-line peak changes (owing to the different times of flight of the measuring signals outside and inside the medium or to an amplitude change due to partial or complete signal absorption in conductive media) with respect to the constant position of the peak which occurs owing to the reflection of the measuring signal upon the transition from the coupling unit to the conductive element.
q EH 370 CA
October 16, 2000 The object is also achieved by the following alternative of the inventive method for determining a limit level of a medium in a vessel. A radio-frequency measuring signal is coupled onto a conductive element of a predetermined length and is guided along the conductive element; the measuring signal is reflected as a system-s dependent echo signal in those regions of the conductive element in which there is a sudden change in the characteristic impedance; the measuring signal is reflected as a useful echo signal when the free end of the conductive element is located in the immediate vicinity of the surface of the medium, or in contact with the medium, and the fact that the medium has reached the predetermined level in the vessel is to determined on the basis of the amplitude change of one system-dependent echo signal, especially on the basis of the amplitude change of the end-of-line peak. Under specific process conditions and depending upon the proximity of the process material to the sensor/probe tip, the end-of-line peak may appear as any value across a spectrum of various positive and negative amplitudes. Critical to the detection then, is to monitor 15 that peak for any change of amplitude.
The object is furthermore achieved by the following alternative embodiment of the method according to the invention. A radio-frequency measuring signal is coupled onto a conductive element of a predetermined length and is guided along the conductive element; the measuring signal is reflected in each case as an echo signal in 2o those regions on the conductive element in which there is a sudden change in the characteristic impedance; a first echo signal and a second echo signal are determined for different levels; a differential signal is then formed from the first echo signal and the second echo signal, and the fact that a predetermined limit level of the medium has been reached in the vessel is determined with the aid of the position of the peak or 25 of the peaks of the differential signal or with the aid of the amplitude change of the peak or the peaks of the differential signal. It has been found that this variant of the method according to the invention is highly advantageous when it is necessary to determine the level of a medium having a relatively low dielectric constant.
According to a development of the embodiment of the method according to 3o the invention described above, the first echo signal is preferably determined when the free end of the conductive element is located in the immediate vicinity of the surface of the medium or is in contact with the medium, while the second echo signal is determined when the free end of the conductive element is not located in the immediate vicinity of the surface of the medium or is not in contact with the medium.
35 One advantageous embodiment of the method according to the invention envisages that the fact that the predetermined level has been reached is output as soon as the differential signal occurs in a time window in which the fiducial launcher peak and/or the end-of-line peak occur/occurs when there is no medium in the immediate vicinity of or in contact with the conductive element.
October 16, 2000 One preferred (since it is simple to implement) embodiment of the method according to the invention provides that the fact that the predetermined level has been reached is output when the amplitude of the useful echo signal or a peak of the differential signal is greater than or equal to a predetermined threshold value.
The device according to the invention comprises a signal-generating unit, a coupling unit, a conductive element, a receiving unit and an evaluation unit, the signal-generating unit generating radio-frequency measuring signals, the coupling unit coupling a measuring signal onto a conductive element of a predetermined length, the conductive element guiding the measuring signal, the measuring signal in each case 1o experiencing reflections as a system-dependent echo signal in those regions of the conductive element in which there is a sudden change in the characteristic impedance, the measuring signal experiencing reflections as a useful echo signal when the conductive element is in the immediate vicinity of the surface of the medium or is in contact with the medium, and the evaluation unit outputting the fact that a predetermined level of the medium has been reached in the vessel when the useful echo signal or a first system-dependent echo signal occurs inside a predetermined time window with reference to the system-dependent echo signal or a second system-dependent echo signal.
Furthermore, the object is achieved by the following variant of the device according to the invention. The device once again comprises a signal-generating unit, a coupling unit, a conductive element, a receiving unit and an evaluation unit, the signal-generating unit generating radio-frequency measuring signals, the coupling unit coupling a measuring signal onto a conductive element of a predetermined length, the conductive element guiding the measuring signal, the measuring signal in each case being reflected as an echo signal in those regions of the conductive element in which there is a sudden change in the characteristic impedance, and the receiving unit/evaluation unit determining a first echo signal and a second echo signal in the case of different levels, forming a differential signal from the first echo signal and the second echo signal, and determining the fact that the predetermined limit level of the 3o medium has been reached in the vessel with the aid of the position of the peak of the differential signal.
According to a preferred embodiment of both device variants according to the invention, the length of the conductive element is selected such that the peak of the fiducial launcher and the end-of-line peak overlap one another at least partially. The conductive element itself may be either a Goubau conductor or a Sommerfeld conductor.
One advantageous development of the inventive device variants envisages that the free end of the conductive element terminates with its front flush with the inner surface of a wall of the vessel or with the outer surface of the coupling unit.
October 16, 2000 It is advantageous and cost-effective if a comparator or discriminator circuit is used to identify the limit level of the medium in the vessel, which comparator or discriminator circuit identifies and outputs the change in sign of the echo signal upon the occurrence of the useful echo signal or the differential signal inside a predetermined time window.
The sensor device of the present invention is particularly adapted for the measurement of material levels in process vessels and storage vessels, but is not thereto limited. It is understood that the sensor device may be used for measurement of other process variables such as flow, composition, dielectric constant, moisture l0 content, etc. In the specification and claims, the term 'vessel' refers to pipes, chutes, bins, tanks, reservoirs, or any other storage vessels. Such storage vessels may also include fuel tanks, and a host of automotive or vehicular fluid storage systems or reservoirs for engine oil, hydraulic fluids, brake fluids, wiper fluids, coolant, power steering fluid, transmission fluid and fuel.
Brief Description of the Drawings The invention will be explained in more detail with reference to the following drawings, in which:
Fig. 1a shows a schematic illustration of a first embodiment of the device according to the invention, Fig. lb shows a schematic illustration of a second embodiment of the device according to the invention, Fig. lc shows a schematic illustration of a third embodiment of the device according to the invention, Fig. 2 is a diagram which shows the interface signal amplitude as a function of time for various media, Fig. 3 is a graph which shows the change of the signal amplitude of the echo signals for various media, Fig. 4 is a graph which shows the change of the interface signal differential amplitude of the echo signals for various media, and 3o Fig. 5 shows a block diagram of a preferred embodiment of the device according to the invention.
Detailed Description of Preferred Embodiments Fig. 1a shows a schematic illustration of a first embodiment of the device according to the invention. The medium 9 whose limit level is intended to be detected is located in the vessel 8. The level measuring device, that is to say the TDR
sensor 1, is mounted in an opening in wall 12 of the roof 13 of the vessel 8. TDR is, moreover, the abbreviation for _Time _Domain _Reflectometry, which is normally used for the measuring method in which radio-frequency measuring signals are guided along a conductive element 6 in order to determine a limit or continuous level of a medium 9 October 16, 2000 in a vessel 8. The measuring signals (S) and the echo signals (R), which are radio-frequency pulses, are represented in stylized form in Fig. 1a. The measuring signals (S) are generated in the signal-generating unit 2 and are coupled onto the conductive element 6 via the coupling unit 3. Owing to the sudden impedance change upon the , transition from the coupling unit 3 (D fiducial launcher) to the conductive element 6, a portion of the measuring signal is reflected at the fiducial launcher 3 (See Fig. 2).
Referring to Figs. 1a and 2, the free end 7 of the TDR sensor 1 is shown not in contact with the medium 9. Since the electromagnetic field which is coupled to the measuring signal fills a certain three-dimensional area around the conductive element 6, a further peak (an echo signal) occurs in addition to the reflection at the free end 7 (end of-line reflection as shown in Fig. 2). This additional echo signal is caused by the reflection of the measuring signal on the surface 10 of the medium 9. This echo signal is clearly measurable as long as the free end 7 is in contact with the medium 9 or the distance between the free end 7 of the conductive element 6 and the surface 10 of the medium 9 is not greater than a maximum distance which is defined exactly in advance. While the fiducial launcher 3 peak (signal) and the end-of-line peak (signal) represent system-dependent echo signals, the echo signal reflected from the surface 10, which represents the fact that the medium 9 has reached the limit level in the vessel 8, is the so-called useful echo signal (See Fig. 2).
2o The useful echo signal is received by a receiving unit 4 and processed by an evaluation unit 5. While the signal -generating unit 2, the receiving unit 4, and the processing unit S could be any suitable well known units, in the preferred embodiment such units are those described in U.S. Patents 5,841,666 and U.S. Patents 5,884,231, the disclosures of which are hereby incorporated by reference.
Fig. lb shows a schematic illustration of a second embodiment of the device according to the invention. This second variant differs from the embodiment shown in Fig. 1a only in that, in this case, the free end 7 of the conductive element 6 terminates with its front flush with the coupling unit 3. One consequence of this configuration of the TDR sensor 1 can clearly be seen in Fig. 3: the end-of-line peak and the useful 3o echo signal occur virtually simultaneously, and interfere.
Fig. lc shows a schematic illustration of a third embodiment of the device according to the invention. This embodiment differs from the variant shown in Fig. lb only in that the TDR sensor 1 is mounted in the side wall 12 of the vessel 8 in which the medium 9 is located.
As will be discussed further the embodiments of the inventions shown in Figs.
la, lb and 1c are useful as switches. The switch is activated when the conductive element 6 either comes in contact with the medium 9 or the surface 10 of the medium 9 is within a distance which is predetermined and discussed later.
g EH 370 CA
October 16, 2000 In the graph shown in Fig. 2, the signal amplitudes of echo signals (S) without any medium (dotted lines), with oil as the medium (dashed line) and with water as the medium (solid line) are shown as a function of time. The signals shown in Fig.
LIMIT LEVEL OF A MEDIUM IN A VESSEL
Field of the Invention The invention relates to a device and a method for determining a limit level of a medium in a vessel.
Background of the Invention Capacitive measuring devices or vibration systems are used to detect the limit level of liquids or granular solids in vessels. In addition to such limit level detectors, 1o which signal that a predetermined level has been reached as soon as they come into contact with the medium to be measured, measuring systems exist which operate without making contact and, as the measuring radiation, use ultrasound waves, microwaves - or in particularly critical applications - radioactive radiation.
The known systems have been proven in practice, but cannot be used in all possible applications. Capacitive measuring devices and vibration systems come into direct contact with the medium to be measured. If they are used to detect corrosive media, then they must be very highly resistant to corrosion. Furthermore, deposits on the measuring devices lead to inaccurate measurement results. Their use is problematic if the level of different media, having different electrical characteristics, 2o is intended to be measured.
The application options of the sensors which are known are limited by the temperature and pressure conditions at the measurement point. For example piezo-ceramics which are used in vibration systems irreversibly lose their characteristic properties as soon as the ambient temperature exceeds a specific value, the Curie temperature, which depends on the respective material.
Those measuring devices which operate on the basis of ultrasound waves are also severely dependent on the temperature. Temperature compensation is absolutely essential here in order to obtain reliable measurement results. Ultrasound sensors are also highly dependent on the composition of the gas area located above the medium;
3o in vacuum conditions, or if the pressures in the gas area are high, they cannot be used.
It should furthermore be mentioned that the sensitivity of ultrasound sensors is also influenced by the noise level in the environment.
In many fields of use, for example in the petrochemical, chemical and foodstuffs industries, high-precision measurements are required of the level of liquids or granular solids in vessels (tanks, silos, etc.). For this reason sensors are increasingly being used in which short electromagnetic radio-frequency pulses or continuous microwaves are coupled onto a conductive, elongated element, for example a rod probe or a cable probe, and are introduced by means of the conductive element into the vessel in which the medium is stored.
October 16, 2000 From the physical point of view, this measuring method uses the effect that a proportion of the radio-frequency pulses or microwaves being propagated is reflected on the boundary surface between two different media, for example air and oil or air and water, as a result of the sudden change (discontinuity) in the dielectric constants of the two media, and this reflection is passed via the conductive element back into the receiving device. The reflected portion of the radio-frequency pulses or microwaves in this case becomes greater the greater the difference in the dielectric constants of the two media. The time of flight of the reflected portion of the radio-frequency pulses or microwaves allows the distance to the boundary surface to be 1o determined. If the height of the empty vessel is known it is possible to calculate the level of the medium in the vessel.
Sensors with guided radio-frequency signals (pulses or waves) are distinguished from sensors which emit radio-frequency pulses or waves freely (free-field microwave systems or 'real radar systems') by having considerably less attenuation. The reason for this is that the power flows in an entirely controlled manner along the rod or cable probe, or the conductive element. Furthermore, sensors using guided radio-frequency signals have a higher measurement quality in the near field than freely emitting sensors.
The advantage of sensors using guided radio-frequency signals is, furthermore, 2o the high accuracy and reliability of the level measurement. This is based on the fact that measurement using guided measuring signals is largely independent of the product properties of the medium (moisture, dielectric constant, change of medium), the vessel structure (materials, geometry) or the other operating conditions (dust, deposits, and angle of the granular solids).
Until now, it has not been known for such measuring systems with guided measuring signals to be used as limit level detectors.
The invention is based on the object of proposing a method and a device which allow a predetermined limit level of a medium in a vessel to be detected with high reliability.
3o A first embodiment of the inventive method achieves the object in that a radio-frequency measuring signal is coupled onto a conductive element of a predetermined length and is guided along the conductive element, the measuring signal is reflected as a system-dependent echo signal in those regions of the conductive element in which there is a sudden change in the characteristic impedance, the measuring signal is reflected as a useful echo signal when the free end of the conductive element is located in the immediate vicinity of the surface of the medium, or in contact with the medium, and the fact that the medium has reached the predetermined level in the vessel is determined on the basis of the relative position of the useful echo signal and ' October 16, 2000 at least one system-dependent echo signal, or on the basis of the relative position of two system-dependent echo signals.
According to an advantageous embodiment of the method according to the invention, use is made of the system-dependent echo signal of the signal which occurs upon the transition of the coupling of the measuring signal onto the conductive element (~fiducial launcher). Additionally or alternatively, use is made of the system-dependent echo signal of the signal which is reflected at the free end of the conductive element ('tJend-of-line peak). Furthermore, it is proposed to make use of an additional impedance which is integrated in the coupling unit and produces a 1o system-dependent echo signal. A further alternative is provided by setting a reference zero signal at the same moment when the measurement signal is triggered.
In the case of the method according to the invention, it is thus not absolutely essential for the conductive element to come into contact with the medium to be detected. This variant of the method described above thus also has the abovementioned advantages of measurement methods which make no contact. At the same time, the method according to the invention has the advantage over those measuring methods in which the measuring signals are emitted freely into space that the influence of external interference variables is largely excluded. This preferred variant of the method according to the invention operates particularly well, moreover, 2o when the medium has a high dielectric constant.
According to a further development of the method according to the invention, the fact that the predetermined level has been reached is output as soon as there occurs inside a predetermined time window a useful echo signal which has an opposite sign to the peak of the fiducial launcher signal or of the end-of-line peak signal.
This type of identification of the predetermined level is, of course, highly advantageous since it is based on a simple yes/no question, which can be implemented technically without any problems, for example by means of a threshold value detector. There is no need for complex evaluation methods based on the time of flight of the measuring signals.
Furthermore, one advantageous embodiment of the method according to the invention is the fact that the maximum or minimum level has been reached is output as soon as the end-of-line peak signal occurs inside a predetermined time window.
This embodiment can be used only when the conductive element is immersed in the medium. As soon as this is the case, the position of the end-of-line peak changes (owing to the different times of flight of the measuring signals outside and inside the medium or to an amplitude change due to partial or complete signal absorption in conductive media) with respect to the constant position of the peak which occurs owing to the reflection of the measuring signal upon the transition from the coupling unit to the conductive element.
q EH 370 CA
October 16, 2000 The object is also achieved by the following alternative of the inventive method for determining a limit level of a medium in a vessel. A radio-frequency measuring signal is coupled onto a conductive element of a predetermined length and is guided along the conductive element; the measuring signal is reflected as a system-s dependent echo signal in those regions of the conductive element in which there is a sudden change in the characteristic impedance; the measuring signal is reflected as a useful echo signal when the free end of the conductive element is located in the immediate vicinity of the surface of the medium, or in contact with the medium, and the fact that the medium has reached the predetermined level in the vessel is to determined on the basis of the amplitude change of one system-dependent echo signal, especially on the basis of the amplitude change of the end-of-line peak. Under specific process conditions and depending upon the proximity of the process material to the sensor/probe tip, the end-of-line peak may appear as any value across a spectrum of various positive and negative amplitudes. Critical to the detection then, is to monitor 15 that peak for any change of amplitude.
The object is furthermore achieved by the following alternative embodiment of the method according to the invention. A radio-frequency measuring signal is coupled onto a conductive element of a predetermined length and is guided along the conductive element; the measuring signal is reflected in each case as an echo signal in 2o those regions on the conductive element in which there is a sudden change in the characteristic impedance; a first echo signal and a second echo signal are determined for different levels; a differential signal is then formed from the first echo signal and the second echo signal, and the fact that a predetermined limit level of the medium has been reached in the vessel is determined with the aid of the position of the peak or 25 of the peaks of the differential signal or with the aid of the amplitude change of the peak or the peaks of the differential signal. It has been found that this variant of the method according to the invention is highly advantageous when it is necessary to determine the level of a medium having a relatively low dielectric constant.
According to a development of the embodiment of the method according to 3o the invention described above, the first echo signal is preferably determined when the free end of the conductive element is located in the immediate vicinity of the surface of the medium or is in contact with the medium, while the second echo signal is determined when the free end of the conductive element is not located in the immediate vicinity of the surface of the medium or is not in contact with the medium.
35 One advantageous embodiment of the method according to the invention envisages that the fact that the predetermined level has been reached is output as soon as the differential signal occurs in a time window in which the fiducial launcher peak and/or the end-of-line peak occur/occurs when there is no medium in the immediate vicinity of or in contact with the conductive element.
October 16, 2000 One preferred (since it is simple to implement) embodiment of the method according to the invention provides that the fact that the predetermined level has been reached is output when the amplitude of the useful echo signal or a peak of the differential signal is greater than or equal to a predetermined threshold value.
The device according to the invention comprises a signal-generating unit, a coupling unit, a conductive element, a receiving unit and an evaluation unit, the signal-generating unit generating radio-frequency measuring signals, the coupling unit coupling a measuring signal onto a conductive element of a predetermined length, the conductive element guiding the measuring signal, the measuring signal in each case 1o experiencing reflections as a system-dependent echo signal in those regions of the conductive element in which there is a sudden change in the characteristic impedance, the measuring signal experiencing reflections as a useful echo signal when the conductive element is in the immediate vicinity of the surface of the medium or is in contact with the medium, and the evaluation unit outputting the fact that a predetermined level of the medium has been reached in the vessel when the useful echo signal or a first system-dependent echo signal occurs inside a predetermined time window with reference to the system-dependent echo signal or a second system-dependent echo signal.
Furthermore, the object is achieved by the following variant of the device according to the invention. The device once again comprises a signal-generating unit, a coupling unit, a conductive element, a receiving unit and an evaluation unit, the signal-generating unit generating radio-frequency measuring signals, the coupling unit coupling a measuring signal onto a conductive element of a predetermined length, the conductive element guiding the measuring signal, the measuring signal in each case being reflected as an echo signal in those regions of the conductive element in which there is a sudden change in the characteristic impedance, and the receiving unit/evaluation unit determining a first echo signal and a second echo signal in the case of different levels, forming a differential signal from the first echo signal and the second echo signal, and determining the fact that the predetermined limit level of the 3o medium has been reached in the vessel with the aid of the position of the peak of the differential signal.
According to a preferred embodiment of both device variants according to the invention, the length of the conductive element is selected such that the peak of the fiducial launcher and the end-of-line peak overlap one another at least partially. The conductive element itself may be either a Goubau conductor or a Sommerfeld conductor.
One advantageous development of the inventive device variants envisages that the free end of the conductive element terminates with its front flush with the inner surface of a wall of the vessel or with the outer surface of the coupling unit.
October 16, 2000 It is advantageous and cost-effective if a comparator or discriminator circuit is used to identify the limit level of the medium in the vessel, which comparator or discriminator circuit identifies and outputs the change in sign of the echo signal upon the occurrence of the useful echo signal or the differential signal inside a predetermined time window.
The sensor device of the present invention is particularly adapted for the measurement of material levels in process vessels and storage vessels, but is not thereto limited. It is understood that the sensor device may be used for measurement of other process variables such as flow, composition, dielectric constant, moisture l0 content, etc. In the specification and claims, the term 'vessel' refers to pipes, chutes, bins, tanks, reservoirs, or any other storage vessels. Such storage vessels may also include fuel tanks, and a host of automotive or vehicular fluid storage systems or reservoirs for engine oil, hydraulic fluids, brake fluids, wiper fluids, coolant, power steering fluid, transmission fluid and fuel.
Brief Description of the Drawings The invention will be explained in more detail with reference to the following drawings, in which:
Fig. 1a shows a schematic illustration of a first embodiment of the device according to the invention, Fig. lb shows a schematic illustration of a second embodiment of the device according to the invention, Fig. lc shows a schematic illustration of a third embodiment of the device according to the invention, Fig. 2 is a diagram which shows the interface signal amplitude as a function of time for various media, Fig. 3 is a graph which shows the change of the signal amplitude of the echo signals for various media, Fig. 4 is a graph which shows the change of the interface signal differential amplitude of the echo signals for various media, and 3o Fig. 5 shows a block diagram of a preferred embodiment of the device according to the invention.
Detailed Description of Preferred Embodiments Fig. 1a shows a schematic illustration of a first embodiment of the device according to the invention. The medium 9 whose limit level is intended to be detected is located in the vessel 8. The level measuring device, that is to say the TDR
sensor 1, is mounted in an opening in wall 12 of the roof 13 of the vessel 8. TDR is, moreover, the abbreviation for _Time _Domain _Reflectometry, which is normally used for the measuring method in which radio-frequency measuring signals are guided along a conductive element 6 in order to determine a limit or continuous level of a medium 9 October 16, 2000 in a vessel 8. The measuring signals (S) and the echo signals (R), which are radio-frequency pulses, are represented in stylized form in Fig. 1a. The measuring signals (S) are generated in the signal-generating unit 2 and are coupled onto the conductive element 6 via the coupling unit 3. Owing to the sudden impedance change upon the , transition from the coupling unit 3 (D fiducial launcher) to the conductive element 6, a portion of the measuring signal is reflected at the fiducial launcher 3 (See Fig. 2).
Referring to Figs. 1a and 2, the free end 7 of the TDR sensor 1 is shown not in contact with the medium 9. Since the electromagnetic field which is coupled to the measuring signal fills a certain three-dimensional area around the conductive element 6, a further peak (an echo signal) occurs in addition to the reflection at the free end 7 (end of-line reflection as shown in Fig. 2). This additional echo signal is caused by the reflection of the measuring signal on the surface 10 of the medium 9. This echo signal is clearly measurable as long as the free end 7 is in contact with the medium 9 or the distance between the free end 7 of the conductive element 6 and the surface 10 of the medium 9 is not greater than a maximum distance which is defined exactly in advance. While the fiducial launcher 3 peak (signal) and the end-of-line peak (signal) represent system-dependent echo signals, the echo signal reflected from the surface 10, which represents the fact that the medium 9 has reached the limit level in the vessel 8, is the so-called useful echo signal (See Fig. 2).
2o The useful echo signal is received by a receiving unit 4 and processed by an evaluation unit 5. While the signal -generating unit 2, the receiving unit 4, and the processing unit S could be any suitable well known units, in the preferred embodiment such units are those described in U.S. Patents 5,841,666 and U.S. Patents 5,884,231, the disclosures of which are hereby incorporated by reference.
Fig. lb shows a schematic illustration of a second embodiment of the device according to the invention. This second variant differs from the embodiment shown in Fig. 1a only in that, in this case, the free end 7 of the conductive element 6 terminates with its front flush with the coupling unit 3. One consequence of this configuration of the TDR sensor 1 can clearly be seen in Fig. 3: the end-of-line peak and the useful 3o echo signal occur virtually simultaneously, and interfere.
Fig. lc shows a schematic illustration of a third embodiment of the device according to the invention. This embodiment differs from the variant shown in Fig. lb only in that the TDR sensor 1 is mounted in the side wall 12 of the vessel 8 in which the medium 9 is located.
As will be discussed further the embodiments of the inventions shown in Figs.
la, lb and 1c are useful as switches. The switch is activated when the conductive element 6 either comes in contact with the medium 9 or the surface 10 of the medium 9 is within a distance which is predetermined and discussed later.
g EH 370 CA
October 16, 2000 In the graph shown in Fig. 2, the signal amplitudes of echo signals (S) without any medium (dotted lines), with oil as the medium (dashed line) and with water as the medium (solid line) are shown as a function of time. The signals shown in Fig.
2 can occur when the conductive element 6 is either in contact with the medium 9 or within the predetermined distance from the surface 10 of medium 9. If there is no medium y in the vessel 8, then a relatively strong negative peak occurs after a short time, reflecting the proportion of the signal which occurs at the transition from the coupling unit 3 (fiducial launcher) to the conductive element 6. As can be seen from Fig. 2, neither the position nor the amplitude of this so-called fiducial launcher signal changes during filling of the vessel 8. This peak thus represents a system-dependent echo signal for the respectively used TDR sensor 1. Owing to the fact that this does not vary with regard to the medium or the respective level of the medium 9 in the vessel 8, the fiducial launcher is used as a reference signal for the useful echo signal, or for a further system-dependent echo signal. The useful echo signal occurs as soon as a medium 9 is located in the vessel 8.
As can be seen from the amplitude profile of the echo signal, which is not influenced by the presence of a medium 9 (i.e., dotted lines), the second system-dependent echo signal is the end-of-line peak (signal). The end-of-line peak (signal) reflects the proportion of the signal which is reflected at the free end 7 of the 2o conductive element 6. In contrast to the fiducial launcher, the end-of-line peak (signal) is not a variable which is dependent exclusively on the respectively used TDR
sensor 1. In fact, when covered by the medium 9 both the position and the amplitude of the end-of-line peak are influenced by the medium 9 whose limit level is intended to be detected. The reason why the end-of-line peak occurs at different times (See Fig. 2) with different media is the different propagation velocity of the measuring signal (S) in different media 9.
One variant of the method according to the invention uses the variation in the time at which the useful echo signal and/or the end-of-line peak (signal) occurs. If the useful echo signal and/or the end-of-line peak (signal) appears inside one or more 3o defined time windows where the reference signal is in each case the system-dependent fiducial launcher peak (signal) then this is a clear indication that the limit level has been reached.
Fig. 3 shows a graph which illustrates the change of the signal amplitude of the echo signals for different types of media 9. A TDR sensor 1 having a short conductive element 6 is used in this case. Owing to the short length of the conductive element 6, the end-of-line peak (signal) for no medium and the useful echo signal for a medium having a high dielectric constant (e.g., water) virtually coincide in time. As shown in Fig. 3, if there is no medium 9 in the vicinity of the TDR sensor 1, then there is only one, pronounced, negative end-of-line peak (signal) in the g EH 370 CA
October 16, 2000 time/amplitude profile of the echo signal. If a medium 9 with a high dielectric constant, for example water, is located in the vicinity of the TDR sensor 1, then a positive peak appears around the time of the end-of-line peak, as the result of the useful echo signal and the end-of-line peak overlapping one another.
The second variant of the method according to the invention uses the effect described above to determine the limit level. This second variant operates particularly reliably, moreover, when a medium 9 having a high dielectric constant is located in the vessel 8. If a positive peak appears in the time window 20 in which the negative end-of-line peak normally occurs, then this is a clear indication that the medium 9 in 1o the vessel 8 has reached the limit level.
As the signal profile for oil as the medium shows, this inversion effect does not occur with a medium 9 having a relatively low dielectric constant. In order to allow the method according to the invention to be used in a case such as this as well, the echo signal is in this case not used as such, but rather the difference between the echo signal when the medium 9 is present, and the echo signal without any medium 9.
Fig. 4 shows the resultant rate of change of the signal difference amplitude of the end-of-line peak (signal) in air and the useful echo signal for different media 9.
The solid curve shows the profile of the difference between the signals when the useful echo signal is being influenced by water as the medium 9. The dashed line 2o shows the corresponding difference between the signals in the presence of oil as the medium 9. With no medium present the difference would be a straight line through the zero voltage point (i.e., no amplitude). Both when detecting the level of water and when detecting the level of oil, there is a pronounced peak in a time window 20 in which the end-of-line peak normally appears with the opposite sign (See Fig.
As can be seen from the amplitude profile of the echo signal, which is not influenced by the presence of a medium 9 (i.e., dotted lines), the second system-dependent echo signal is the end-of-line peak (signal). The end-of-line peak (signal) reflects the proportion of the signal which is reflected at the free end 7 of the 2o conductive element 6. In contrast to the fiducial launcher, the end-of-line peak (signal) is not a variable which is dependent exclusively on the respectively used TDR
sensor 1. In fact, when covered by the medium 9 both the position and the amplitude of the end-of-line peak are influenced by the medium 9 whose limit level is intended to be detected. The reason why the end-of-line peak occurs at different times (See Fig. 2) with different media is the different propagation velocity of the measuring signal (S) in different media 9.
One variant of the method according to the invention uses the variation in the time at which the useful echo signal and/or the end-of-line peak (signal) occurs. If the useful echo signal and/or the end-of-line peak (signal) appears inside one or more 3o defined time windows where the reference signal is in each case the system-dependent fiducial launcher peak (signal) then this is a clear indication that the limit level has been reached.
Fig. 3 shows a graph which illustrates the change of the signal amplitude of the echo signals for different types of media 9. A TDR sensor 1 having a short conductive element 6 is used in this case. Owing to the short length of the conductive element 6, the end-of-line peak (signal) for no medium and the useful echo signal for a medium having a high dielectric constant (e.g., water) virtually coincide in time. As shown in Fig. 3, if there is no medium 9 in the vicinity of the TDR sensor 1, then there is only one, pronounced, negative end-of-line peak (signal) in the g EH 370 CA
October 16, 2000 time/amplitude profile of the echo signal. If a medium 9 with a high dielectric constant, for example water, is located in the vicinity of the TDR sensor 1, then a positive peak appears around the time of the end-of-line peak, as the result of the useful echo signal and the end-of-line peak overlapping one another.
The second variant of the method according to the invention uses the effect described above to determine the limit level. This second variant operates particularly reliably, moreover, when a medium 9 having a high dielectric constant is located in the vessel 8. If a positive peak appears in the time window 20 in which the negative end-of-line peak normally occurs, then this is a clear indication that the medium 9 in 1o the vessel 8 has reached the limit level.
As the signal profile for oil as the medium shows, this inversion effect does not occur with a medium 9 having a relatively low dielectric constant. In order to allow the method according to the invention to be used in a case such as this as well, the echo signal is in this case not used as such, but rather the difference between the echo signal when the medium 9 is present, and the echo signal without any medium 9.
Fig. 4 shows the resultant rate of change of the signal difference amplitude of the end-of-line peak (signal) in air and the useful echo signal for different media 9.
The solid curve shows the profile of the difference between the signals when the useful echo signal is being influenced by water as the medium 9. The dashed line 2o shows the corresponding difference between the signals in the presence of oil as the medium 9. With no medium present the difference would be a straight line through the zero voltage point (i.e., no amplitude). Both when detecting the level of water and when detecting the level of oil, there is a pronounced peak in a time window 20 in which the end-of-line peak normally appears with the opposite sign (See Fig.
3).
Thus, if a positive peak occurs inside a time window 20 around the end-of-line peak (See Fig. 3), then this is once again a clear indication that the medium 9 in the vessel 8 has reached the limit level. In order to improve the reliability of the detection results, the invention furthermore provides that the limit level is indicated only when the echo signal additionally exceeds a predetermined threshold value 22 inside the 3o defined time window 20 (See Fig. 4).
Fig. 5 shows a block diagram of a preferred embodiment of the device according to the invention. The device according to the invention can be produced technically very easily and cost-effectively and is included in the receiving unit 5. It is sufficient to confirm whether a peak or an inversion of the peak of the echo signal does or does not occur inside a defined time window 20. If a positive peak appears in the time window 20, then this is a clear indication that the medium 9 in the vessel 8 has reached the limit level. In terms of circuitry, the echo signal is passed to the input of a comparator or discriminator circuit 11 or of a threshold value detector.
A signal which appears at the output of the comparator or discriminator circuit 11 or of the October 16, 2000 threshold value detector is either 1 or U. A 1 indicates that the respective limit level to be monitored has been reached.
Thus, if a positive peak occurs inside a time window 20 around the end-of-line peak (See Fig. 3), then this is once again a clear indication that the medium 9 in the vessel 8 has reached the limit level. In order to improve the reliability of the detection results, the invention furthermore provides that the limit level is indicated only when the echo signal additionally exceeds a predetermined threshold value 22 inside the 3o defined time window 20 (See Fig. 4).
Fig. 5 shows a block diagram of a preferred embodiment of the device according to the invention. The device according to the invention can be produced technically very easily and cost-effectively and is included in the receiving unit 5. It is sufficient to confirm whether a peak or an inversion of the peak of the echo signal does or does not occur inside a defined time window 20. If a positive peak appears in the time window 20, then this is a clear indication that the medium 9 in the vessel 8 has reached the limit level. In terms of circuitry, the echo signal is passed to the input of a comparator or discriminator circuit 11 or of a threshold value detector.
A signal which appears at the output of the comparator or discriminator circuit 11 or of the October 16, 2000 threshold value detector is either 1 or U. A 1 indicates that the respective limit level to be monitored has been reached.
Claims (24)
1. Method for determining a limit level of a medium (9) in a vessel (8), comprising the steps of transmitting a radio-frequency measuring signal along a conductive element (6) of a predetermined length, receiving a system-dependent echo signal reflected from a region of the conductive element (6) in which there is a sudden change in the characteristic impedance, receiving a useful echo signal reflected from a surface (10) of the medium (9) when a free end of the conductive element (6) is located at least in the immediate vicinity of the surface (10) of the medium (9), and determining whether the medium (9) has reached a predetermined level in the vessel (8) by comparing the system-dependent echo signal with at least one of the useful echo signal and another system dependent echo signal.
2. Method according to Claim 1, wherein the other system dependent echo signal is a fiducial launcher signal which occurs upon the transition of the measuring signal from the coupling unit (3) (~fiducial launcher) onto the conductive element (6), and the system dependent signal is an end-of-line peak signal which is reflected at the free end (7) of the conductive element (6).
3. Method according to Claim 1, wherein the step of determining whether the predetermined limit level has been reached occurs inside a predetermined time window when the useful echo signal has an opposite sign to the peak of at least one of the system dependent echo signals.
4. Method according to Claim 2, wherein the step of determining whether the predetermined limit level has been reached occurs inside a predetermined time window when the useful echo signal has an opposite sign to the peak of at least one of the system dependent echo signals.
5. Method according to Claim 1, wherein the predetermined level is determined as soon as the end-of-line peak signal occurs inside a predetermined time window.
6. Method according to Claim 2, wherein the predetermined level is determined as soon as the end-of-line peak signal occurs inside a predetermined time window.
7. Method according to Claim 3, wherein the predetermined level is determined as soon as the end-of-line peak signal occurs inside the predetermined time window.
8. Method according to Claim 4, wherein the predetermined level is determined as soon as the end-of-line peak signal occurs inside the predetermined time window.
9. Method for determining a limit level of a medium (9) in a vessel (8), comprising the steps of transmitting a radio-frequency measuring signal along a conductive element (6) of a predetermined length, receiving a first system-dependent echo signal reflected from a region of the conductive element (6) in which there is a sudden change in the characteristic impedance, receiving a useful echo signal reflected from a surface (10) of the medium 9 when a free end of the conductive element (6) is located at least in the immediate vicinity of the surface (10) of the medium (9), receiving a second system dependent echo signal reflected from the free end of the conductive element (6), and determining whether the medium (9) has reached the predetermined level in the vessel (8) by detecting an amplitude change of the second dependent echo signal reflected from the free end of the conductive element (6).
10. Method for determining a limit level of a medium (9) in a vessel (8), comprising the steps of transmitting a radio-frequency measuring signal along a conductive element (6) of a predetermined length, receiving a first and a second echo signal reflected from a region on the conductive element (6) in which there is a sudden change in the characteristic impedance, forming a differential signal from the first echo signal and the second echo signal, and determining whether a predetermined limit level of the medium (9) has been reached in the vessel (8) using at least one of the position of at least one peak of the differential signal and the amplitude change of at least one peak of the differential signal.
11. Method according to claim 9, wherein the first echo signal occurs when the free end (7) of the conductive element (6) is located at least in the immediate vicinity of the surface (10) of the medium (9), and the second echo signal occurs when the free end (12) of the conductive element (6) is not located in the immediate vicinity of the surface (10) of the medium (9).
12. Method according to claim 10, wherein the fact that the predetermined level of the medium has been reached is determined as soon as the differential signal occurs in a time window in which the at least one of the first and second echo signals occurs when there is no medium (9)in the immediate vicinity of or in contact with the conductive element (6).
13. Method according to Claim 1, wherein the fact that the predetermined level of the medium has been reached is determined when the amplitude of the useful echo signal is at least equal to a predetermined threshold value.
14. Method according to Claim 9, wherein the fact that the predetermined level of the medium has been reached is determined when the amplitude of the useful echo signal is at least equal to a predetermined threshold value.
15. Method according to Claim 10, wherein the fact that the predetermined level of the medium has been reached is determined when a peak of the differential signal is at least equal to a predetermined threshold value.
16. Device for determining a limit level of a medium (9) in a vessel (8), comprising a signal-generating unit (2), a coupling unit (3), a conductive element (6), a receiving unit (4) and an evaluation unit (5), the signal-generating unit (2) generating radio-frequency measuring signals, the coupling unit (3) coupling a measuring signal onto a conductive element (6) of a predetermined length, the conductive element (6) guiding the measuring signal, and wherein the measuring signal in each case experiencing reflections as a system-dependent echo signal in those regions of the conductive element (6) in which there is a sudden change in the characteristic impedance, the measuring signal experiences reflections as a useful echo signal when the conductive element (6) is at least in the immediate vicinity of the surface (10) of the medium (9), and the evaluation unit (5) determines that a predetermined level of the medium (9) has been reached in the vessel (8) when at least one of the useful echo signal and a first system-dependent echo signal occurs inside a predetermined time window with reference to at least one of the first system-dependent echo signal and a second system-dependent echo signal.
17. Device for determining a limit level of a medium (9) in a vessel (8), comprising a signal-generating unit (2), a coupling unit (3), a conductive element (6), a receiving unit (4) and an evaluation unit (5), the signal-generating unit (2) generating radio-frequency measuring signals, the coupling unit (3) coupling a measuring signal onto a conductive element (6) of a predetermined length, the conductive element (6) guiding the measuring signal, and wherein the measuring signal in each case is reflected as an echo signal in those regions of the conductive element (6) in which there is a sudden change in the characteristic impedance and the evaluation unit (5) determines a first echo signal and a second echo signal in the case of different levels, forming a differential signal from the first echo signal and the second echo signal and determines the fact that the predetermined limit level of the medium (9) has been reached in the vessel (8) with the aid of the position of a peak of the differential signal.
18. Device according to Claim 17, wherein the length of the conductive element (6) is selected such that the peak of the first and second system dependent echo signals overlap one another at least partially.
19. Device according to Claim 16, wherein the conductive element (6) is one of at least a Goubeau conductor, a Sommerfeld conductor, and a coax cable comprising at least one of a conductive element and a separate shielding and at least two conductive elements having a predetermined distance from each other.
20. Device according to Claim 17, wherein the conductive element (6) is one of at least a Goubeau conductor, a Sommerfeld conductor, and a coax cable comprising at lest one of a conductive element and a separate shielding and at least two conductive elements having a predetermined distance from each other.
21. Device according to Claim 16, wherein a free end (7) of the conductive element (6) terminates with its front flush with at least one of an inner surface of a wall (12) of the vessel (8) and an outer surface of the coupling unit (3).
22. Device according to Claim 17, wherein a free end (7) of the conductive element (6) terminates with its front flush with at least one of an inner surface of a wall (12) of the vessel (8) and an outer surface of the coupling unit (3).
23. Device according to Claim 16, further including a discriminator circuit (11) which outputs a change in sign of the echo signal upon the occurrence of the useful echo signal inside a predetermined time window.
24. Device according to Claim 17, further including a discriminator circuit (11) which outputs a change in sign of the echo signal upon the occurrence of the differential signal inside a predetermined time window.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US47342799A | 1999-12-29 | 1999-12-29 | |
| US09/473,427 | 1999-12-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2325174A1 true CA2325174A1 (en) | 2001-06-29 |
Family
ID=23879479
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002325174A Abandoned CA2325174A1 (en) | 1999-12-29 | 2000-11-06 | Method and device for determining the limit level of a medium in a vessel |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP1128169A1 (en) |
| JP (1) | JP2001194211A (en) |
| CA (1) | CA2325174A1 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7113125B2 (en) | 2004-12-16 | 2006-09-26 | International Business Machines Corporation | Method for measuring material level in a container using RFID tags |
| US8276443B2 (en) | 2007-02-08 | 2012-10-02 | Krohne Messetechnik GmbH & Co. KG | Method of using a level meter employing the radar principle |
| CN103328939A (en) * | 2011-01-24 | 2013-09-25 | Vega格里沙贝两合公司 | Phase-based tracking |
| US10113901B2 (en) | 2015-02-11 | 2018-10-30 | Vega Grieshaber Ag | Method for evaluating a TDR limit level switch |
| US10704948B2 (en) | 2016-06-14 | 2020-07-07 | Vega Grieshaber Kg | Reflection microwave barrier |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2002027349A2 (en) * | 2000-09-27 | 2002-04-04 | Endress + Hauser Gmbh + Co. Kg | Method for detecting the limit state of a material, and device therefor |
| SE0403165D0 (en) | 2004-12-23 | 2004-12-23 | Saab Rosemount Tank Radar Ab | A radar level gauge system |
| DE102007005619A1 (en) * | 2007-01-31 | 2008-08-07 | Krohne S.A. | Level measuring device for measuring level of medium in container, has connection device including coupling device for microwave signal, where coupling device works as container closure |
| DE102007010627B4 (en) * | 2007-03-02 | 2014-03-20 | KROHNE Meßtechnik GmbH & Co. KG | level meter |
| DE102008016829A1 (en) | 2008-04-01 | 2009-10-08 | KROHNE Meßtechnik GmbH & Co. KG | Level switch and sensor element for a level switch |
| DE102010040262A1 (en) * | 2010-09-03 | 2012-03-08 | Endress & Hauser Meßtechnik GmbH & Co. KG | Arrangement for detecting separation layers of e.g. fat in container to control process flow in automation technology in e.g. food industry, has measuring devices with wave guides that are vertically and horizontally arranged in container |
| DE102015100415A1 (en) | 2015-01-13 | 2016-07-14 | Krohne Messtechnik Gmbh | Device for determining the level of a medium |
| EP3054271B1 (en) * | 2015-02-03 | 2017-06-28 | VEGA Grieshaber KG | Limit level switch with integrated position sensor |
| DE102020124299A1 (en) * | 2020-09-17 | 2022-03-17 | Endress+Hauser SE+Co. KG | Calibration of modular level gauges |
| CN112881480B (en) * | 2021-01-14 | 2022-12-02 | 中国农业大学 | Corn moisture nondestructive testing method and device |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3783112D1 (en) * | 1986-09-24 | 1993-01-28 | Cannonbear Inc | SENSOR AND METHOD FOR DETECTING THE LEAKAGE LEVEL AND FLOW. |
| US5609059A (en) * | 1994-12-19 | 1997-03-11 | The Regents Of The University Of California | Electronic multi-purpose material level sensor |
| US5827985A (en) * | 1995-12-19 | 1998-10-27 | Endress + Hauser Gmbh + Co. | Sensor apparatus for process measurement |
| EP0943103A4 (en) * | 1996-11-22 | 2000-08-23 | Berwind Corp | Material level sensing |
| DE19817378A1 (en) * | 1998-04-20 | 1999-10-21 | Siegfried Hillenbrand | Filling level measuring system for monitoring filling level in container and material level is determined across reflection signals of electromagnetic radiation |
-
2000
- 2000-10-16 EP EP00122521A patent/EP1128169A1/en not_active Withdrawn
- 2000-11-06 CA CA002325174A patent/CA2325174A1/en not_active Abandoned
- 2000-12-25 JP JP2000393487A patent/JP2001194211A/en active Pending
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7113125B2 (en) | 2004-12-16 | 2006-09-26 | International Business Machines Corporation | Method for measuring material level in a container using RFID tags |
| US8276443B2 (en) | 2007-02-08 | 2012-10-02 | Krohne Messetechnik GmbH & Co. KG | Method of using a level meter employing the radar principle |
| CN103328939A (en) * | 2011-01-24 | 2013-09-25 | Vega格里沙贝两合公司 | Phase-based tracking |
| CN103328939B (en) * | 2011-01-24 | 2016-01-20 | Vega格里沙贝两合公司 | Based on the tracking of phase place |
| US10113901B2 (en) | 2015-02-11 | 2018-10-30 | Vega Grieshaber Ag | Method for evaluating a TDR limit level switch |
| US10704948B2 (en) | 2016-06-14 | 2020-07-07 | Vega Grieshaber Kg | Reflection microwave barrier |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2001194211A (en) | 2001-07-19 |
| EP1128169A1 (en) | 2001-08-29 |
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