CA2314027A1 - Waveguide for a microwave fill-level measuring device - Google Patents
Waveguide for a microwave fill-level measuring device Download PDFInfo
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- CA2314027A1 CA2314027A1 CA002314027A CA2314027A CA2314027A1 CA 2314027 A1 CA2314027 A1 CA 2314027A1 CA 002314027 A CA002314027 A CA 002314027A CA 2314027 A CA2314027 A CA 2314027A CA 2314027 A1 CA2314027 A1 CA 2314027A1
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- waveguide
- unit
- conductors
- conductor
- carrier element
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/12—Supports; Mounting means
- H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
- H01Q1/225—Supports; Mounting means by structural association with other equipment or articles used in level-measurement devices, e.g. for level gauge measurement
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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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
- H01Q13/08—Radiating ends of two-conductor microwave transmission lines, e.g. of coaxial lines, of microstrip lines
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Thermal Sciences (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
Abstract
A waveguide for a fill-level measuring device to determine the fill level of a material in a container is proposed, which is not affected by internally mounted obstacles in the container, the inactive length of which is easily adjustable, and which can be easily cleaned from deposits or sediments.
It is particullarly useful in applications of the food industry and in relatively flat containers.
The waveguide is comprised of a probe unit (130) with at least one signal conductor (119) and two shielded conductors (131a, 131b), which are surrounded by carrier element (132), and a connecting unit (110) with a signal connector for connection of the conductors (119, 131a, 131b) with an electronic measuring circuit generating the microwave signals.
The Waveguide is mechanically attached to or on the container by means of an attachment unit (140).
It is particullarly useful in applications of the food industry and in relatively flat containers.
The waveguide is comprised of a probe unit (130) with at least one signal conductor (119) and two shielded conductors (131a, 131b), which are surrounded by carrier element (132), and a connecting unit (110) with a signal connector for connection of the conductors (119, 131a, 131b) with an electronic measuring circuit generating the microwave signals.
The Waveguide is mechanically attached to or on the container by means of an attachment unit (140).
Description
May 25, 2000 WAVEGUIDE FOR A MICROWAVE FILL-LEVEL MEASURING DEVICE
FIELD OF THE INVENTION
S The present invention relates to a waveguide for a fill level measuring device to determine the fill level of a material in a container by means of guided microwave pulse signals. In particular, the invention relates to a waveguide of a microwave fill level measuring device having a probe unit which is immersed in the material being measured, measurement signals are transmitted along the probe towards the material, and echo signals are reflected and returned along the probe.
BACKGROUND OF THE INVENTION
In order to determine the fill level of a material, microwave pulsed signals are generated in an electronic measuring circuit connected to a waveguide and are directed to the waveguide, usually along a cable connection, preferably a coaxial cable. The cable is connected to a connecting unit of the waveguide so that the signals are fed into the waveguide and are emitted along a probe unit towards the material to be measured. An upper surface or boundary surface of the material marking the fill level reflects the pulsed signals, which are then returned as so-called echo signals along the probe unit of the waveguide to the fill level measuring device. By means known to a person of ordinary skill in the art, the echo signals are superimposed on the transmitted microwave signals, and from the total signal formed in this manner, the elapsed time between the transmission of the microwave signals and the arrival of the echo signals is determined. This time is a measure of the propagation time of the microwave signals from the fill level measuring device to the surface of the material and back, and if the propagation speed of the signals is known, this time can be used to determine the distance traveled by the signals and to determine the fill level to be measured. This type of measurement of the fill level is based on a measurement of the transit time of guided microwave pulsed signals and is also known under the concept of TDR (Time Domain Reflectometry).
A probe unit of the waveguide immersed into the material is composed of at least one so-called conductor. Hereinafter, the concept of "conductor" will be used for a conductor May 25, 2000 made of any electrically conducting material, preferably metal, along which the pulse signals used for measurement will travel and/or which is used to guide the signals.
The concept of "conductor" in this sense can be both "signal" conductors, also called "hot"
conductors, and "shielded conductors," whereby a field generated by high-frequency pulse signals builds up between the conductors. Due to the high-frequency signals, the terms "signal conductor" and "shielded conductor" refer only to an instantaneous condition. They are not meant in the usual sense of electrical engineering, but rather are used here to better differentiate the individual conductors from each other. These designations are suggested, for example, by the designation of signal conductor and shielded conductor of the coaxial cable, with which the measured signals are guided to the conductors of the waveguide. A single-conductor waveguide, as explained herein, is composed only of one signal conductor. If necessary, and depending on the application, a probe unit of a waveguide can have any particular number of signal conductors and shielded conductors.
The accuracy of the measurement of the fill level will depend on the type of injection of the microwave signal and on the shape of the waveguide. Essential criteria for a preferred design of a waveguide are:
- impedance adjustment of the electronic measuring circuit by means of the signal injection to the probe unit;
- ratio between signal power transmitted to one reflecting boundary surface and power of the echo signals reflected therefrom; and - field gradient of the microwave signals in the radial direction around the probe unit.
The first criterion in the above list determines whether and to what extent interfering reflections occur in the region of the signal injection.
The second criterion determines a kind of global sensitivity of the waveguide, and depends essentially on the materials used for the waveguide. It denotes what amount of energy of the microwave signals will be available at the surface of the material for the signals reflected therefrom, and whether and how well the useful echo used for determining the fill level can be identified even in case of interference signals.
The first and second criteria determine the so-called block distance which denotes that particular initial length of the waveguide after the signal injection, on which no reasonable detection of the desired useful echo signal can occur without disproportionate expense.
FIELD OF THE INVENTION
S The present invention relates to a waveguide for a fill level measuring device to determine the fill level of a material in a container by means of guided microwave pulse signals. In particular, the invention relates to a waveguide of a microwave fill level measuring device having a probe unit which is immersed in the material being measured, measurement signals are transmitted along the probe towards the material, and echo signals are reflected and returned along the probe.
BACKGROUND OF THE INVENTION
In order to determine the fill level of a material, microwave pulsed signals are generated in an electronic measuring circuit connected to a waveguide and are directed to the waveguide, usually along a cable connection, preferably a coaxial cable. The cable is connected to a connecting unit of the waveguide so that the signals are fed into the waveguide and are emitted along a probe unit towards the material to be measured. An upper surface or boundary surface of the material marking the fill level reflects the pulsed signals, which are then returned as so-called echo signals along the probe unit of the waveguide to the fill level measuring device. By means known to a person of ordinary skill in the art, the echo signals are superimposed on the transmitted microwave signals, and from the total signal formed in this manner, the elapsed time between the transmission of the microwave signals and the arrival of the echo signals is determined. This time is a measure of the propagation time of the microwave signals from the fill level measuring device to the surface of the material and back, and if the propagation speed of the signals is known, this time can be used to determine the distance traveled by the signals and to determine the fill level to be measured. This type of measurement of the fill level is based on a measurement of the transit time of guided microwave pulsed signals and is also known under the concept of TDR (Time Domain Reflectometry).
A probe unit of the waveguide immersed into the material is composed of at least one so-called conductor. Hereinafter, the concept of "conductor" will be used for a conductor May 25, 2000 made of any electrically conducting material, preferably metal, along which the pulse signals used for measurement will travel and/or which is used to guide the signals.
The concept of "conductor" in this sense can be both "signal" conductors, also called "hot"
conductors, and "shielded conductors," whereby a field generated by high-frequency pulse signals builds up between the conductors. Due to the high-frequency signals, the terms "signal conductor" and "shielded conductor" refer only to an instantaneous condition. They are not meant in the usual sense of electrical engineering, but rather are used here to better differentiate the individual conductors from each other. These designations are suggested, for example, by the designation of signal conductor and shielded conductor of the coaxial cable, with which the measured signals are guided to the conductors of the waveguide. A single-conductor waveguide, as explained herein, is composed only of one signal conductor. If necessary, and depending on the application, a probe unit of a waveguide can have any particular number of signal conductors and shielded conductors.
The accuracy of the measurement of the fill level will depend on the type of injection of the microwave signal and on the shape of the waveguide. Essential criteria for a preferred design of a waveguide are:
- impedance adjustment of the electronic measuring circuit by means of the signal injection to the probe unit;
- ratio between signal power transmitted to one reflecting boundary surface and power of the echo signals reflected therefrom; and - field gradient of the microwave signals in the radial direction around the probe unit.
The first criterion in the above list determines whether and to what extent interfering reflections occur in the region of the signal injection.
The second criterion determines a kind of global sensitivity of the waveguide, and depends essentially on the materials used for the waveguide. It denotes what amount of energy of the microwave signals will be available at the surface of the material for the signals reflected therefrom, and whether and how well the useful echo used for determining the fill level can be identified even in case of interference signals.
The first and second criteria determine the so-called block distance which denotes that particular initial length of the waveguide after the signal injection, on which no reasonable detection of the desired useful echo signal can occur without disproportionate expense.
May 25, 2000 The third criterion determines whether and how much the fill level measuring device will respond to deposits or sediments on the probe unit.
In the simplest design, a waveguide of this kind has a probe unit with one individual signal conductor which can be a rod or a steel cable. A waveguide of this kind is also known as a "Sommerfeld conductor."
If the conductor is coated with a dielectric layer, usually a plastic film, then we call this a "Goubau conductor." A Sommerfeld conductor is available from the applicant under the designation "Levelflex." The great advantage of the single-conductor waveguide is that it can be of any length, due to its simple mechanical structure.
In spite of its simple mechanical structure, the single-conductor waveguide is not suitable for all applications. The electrical and magnetic fields used for the level measurements forms between the single conductor of the probe unit and a container wall, for example, so that the field around the waveguide shows a relatively large scattering. Signal injection (and feedback) of signals into the (or from the) single-conductor probe unit are relatively difficult to attain, since a significant portion of the signal energy is reflected from the signal injection or other changes in the geometry of the waveguide.
Other obstacles in the vicinity of the single-conductor waveguide, e.g., support pipes and internal structures in the container, which are measured by the field, can likewise impede the identification of the actual fill level measurement signal or make it entirely impossible.
This is especially true in the vicinity of a short pipe which is used to attach the waveguide to the container. In such a region, no fill level can be measured without disproportionate expense, but rather only starting at a certain distance away from it, which is called the "block distance" as referenced above.
Since a considerable portion of the signal energy in the single-conductor waveguide is consumed to build up the extensive field, i.e., is radiated off, only a small portion of the signal energy is available for a measurement of the fill level. In addition, the emitted energy can lead to undesirable harmonic effects in the attachment pipe due to multiple reflections.
At the present time, there is still no satisfactory way to blank out the interfering echo signals of the attachment pipe from the actual useful signal in a single-conductor waveguide.
Another known form of a waveguide has a probe unit with a signal conductor and a shielded conductor in a coaxial array. A usually rod-shaped signal conductor is May 25, 2000 concentrically surrounded by a usually tubular shielded conductor, so that the field generated by the microwave signals forms only in the usually narrow annulus between the signal conductor and the shielded conductor. The material penetrating the annulus causes the echo signal desired for determination of the fill level.
Coaxial waveguides are characterized by an effective signal injection. Since the field produced by the microwave measuring signal on the region of the annulus between the conductors is limited, no undesirable emission effects occur. There is no danger of interfering interactions with pipes or other internal structures in the tank.
The block distance is small and the function of the coaxial waveguide is not dependent on its installed position.
In modern waveguides, the smallest possible outer diameter is desirable, so that the residual annulus between the signal conductor and shielded conductor is very small in this kind of coaxial waveguide. The sensitivity to sediments or deposits of the material being measured in the annulus is quite large and can lead to an erroneous measured signal. Also, viscous materials, even if they only briefly fill the annulus or adhere to the signal conductor on the inside of the shielded conductor, are not suitable for coaxial waveguides. The material being measured must be of low viscosity.
The narrower the annulus of the coaxial waveguide, the more difficult it is to clean sediments or build-up of the material being measured. Due to the formation of residues and the associated danger to hygiene, coaxial conductors are not used today in the food industry.
As mentioned above, in coaxial waveguides the measuring signal is conducted between the signal conductor and the shielded conductor surrounding it, and the material penetrating into the annulus between the conductors generates the useful signal. Therefore, it is possible to seal off (by a suitable means) the annulus in a region near the connection portion of the waveguide and to block it off against the penetrating material.
For example, the annulus can be filled in the desired region by a suitable plastic, so that in the filled section, the involved length of the probe unit will not be available for measurements. This desired shift in the top measurement point for the fill level away from the attachment of the waveguide to the container, is also called the "inactive length" of the waveguide.
In WO-A 98/05931 another waveguide is described for a fill-level measuring device, in which two or more conductors located essentially in a common plane are used as a probe unit. The material to be measured is located around the conductors and between them.
May 25, 2000 The probe unit of this fill-level measuring device is composed of a "U-shaped"
conductor. Of particular interest is the field building up by the measurement signals between the parallel and mutually connected conductors. This construction represents a kind of compromise between a single-wire and coaxial waveguide and in a functional regard combines their advantages. However, for longer lengths of the probe unit and in moving media spacers are needed between the conductors in order to avoid disturbances in the field or short circuits due to bending or twisting of the conductor. These spacers or supports between the conductors act as reflectors for the measurement signals and lead to undesirable, interfering echoes. In addition, between the parallel conductors (and in particular also on the spacers) deposits or sediments can form which, in turn, cause undesirable, interfering echoes.
Another example of a waveguide with several conductors running in a common plane in the probe unit is described in U.S. Patent 4,807,471. In this case, the probe unit consists of paired, mutually associated conductors, and the conductors of at least one such conductor pair are electrically short-circuited. A disadvantage of this waveguide is that a signal conductor and a shielded conductor must be used in pairs, so that the signals on the conductors are in counterphase. At least one signal conductor is electrically connected to a shielded conductor by means of a PIN diode, and its function depends on the precise spacing of the mutually parallel conductors, and with a large length waveguide, this function must be assured by spacers between the signal conductor and shielded conductor. In turn, these spacers offer attachment points for undesirable deposits between the conductors, which then interfere with the measurement signal.
It is therefore the objective of the present invention to specify a waveguide for a fill-level measuring device, which is distinguished by a simple construction, which combines the advantages of the single wire and known multiple wire waveguides, such that it shows no interaction with container internal structures, its inactive length is adjustable in a simple manner, and it can be cleaned in a simple manner from deposits or sediments.
SUMMARY OF THE INVENTION
To achieve these objectives, the present invention includes a waveguide for a fill-level measuring device to determine the fill level of a material in a container by means of conducted microwave pulsed signals. The waveguide is partially immersed in the material to May 25, 2000 be measured, and is comprised of:
- a probe unit which includes -- at least three electrical conductors, -- at least one being a signal conductor and the remainder being a shielded conductor, and -- at least one carrier element which at least partially surrounds the conductors, - a connecting unit with a signal connector for connection of the conductors with an electronic measuring circuit generating the microwave signals, and - an attachment unit for mechanical attachment of the waveguide to or on the container.
In one embodiment of the waveguide according to the present invention, the carrier element is made of plastic.
In another embodiment of the waveguide, the signal conductor and/or the shielded conductor are made of electrically conducting plastic.
In another embodiment of the invention, the signal conductor and/or the shielded conductor are made of metal.
Additional embodiments of the invention include various cross-sectional shapes of the probe unit of the waveguide.
The invention is based on the basic idea of encasing multiple conductors, which are in an essentially parallel arrangement with each other and are insensitive to interfering influences, in a probe unit of a waveguide in such a manner that deposits or sediments between the conductors can be prevented and that, moreover, the probe unit can be cleaned in a simple manner. Due to its design, the waveguide according to the present invention is simple and can be reliably attached.
An additional advantage of the invention is that, due to the special configuration of the signal injection (or feedback) of the measuring signals and the potential for specific impedance adjustment, the inactive length of the waveguide can be adjusted in a desirable manner by a simple means. Therefore, the waveguide can be designed short enough to be suitable for measurements even in flat containers in which formerly no measurements could be carried out with microwave or radar fill-level measuring devices.
Another advantage of the invention is that it offers versatile configuration potentials May 25, 2000 for the probe unit in conjunction with different arrangements of the conductor. The criteria mentioned above, which determine, for example, the global sensitivity of the waveguide, can be optimized in a desirable manner with the invention for a particular application. For instance, through suitable selection of the number of conductors and of the material of the carrier element of the probe unit, the ratio of microwave energy between the interior and exterior of the probe unit can be established, so that the interference susceptibility of the waveguide to sediment can be adjusted as a function of the particular material to be measured. In addition, the waveguide can have a shape determined by the geometry of the container or by the material to be measured. The probe unit, which is immersed in the material to be measured, can take on any particular length.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be explained in greater detail based on embodiments which are illustrated in the figures. The same parts are referred to using the same reference numbers in all the figures; if needed for greater clarity, reference numbers already mentioned will be left out of the subsequent figures.
Figure 1 shows a longitudinal cross section of a first embodiment of a waveguide according to the invention;
Figure 2 shows a cross section of the probe unit of the waveguide shown to Figure 1;
Figure 3 shows a second embodiment of the waveguide according to the present invention;
Figure 4 shows a side view of the waveguide shown in Figure 3 with inner edges drawn in;
Figure 5 shows a cross section of a probe unit of a third embodiment of a waveguide according to the present invention;
Figure 6 shows a longitudinal cross section of a fourth embodiment of a waveguide according to the present invention;
Figure 7 shows a cross section of the probe unit of the waveguide shown in Figure 6;
Figure 8 shows a longitudinal cross section of the waveguide shown in Figure 6 from a different perspective;
Figure 9 shows a cross section of a probe unit of a fifth embodiment of a waveguide May 25, 2000 according to the present invention; and Figure 10 shows a cross section of a probe unit of a sixth embodiment of a waveguide according to the present invention.
S DETAILED DESCRIPTION OF THE INVENTION
A waveguide 100 according to the present invention and illustrated in Figure 1 features a connecting unit 110, a probe unit 130 and an attachment unit 140 for attachment of the waveguide 100 to or in a container (not shown), where the fill level of the material located in the container is to be determined.
The connecting unit 110 is composed of an outer and essentially cylindrical-shaped housing 112 as illustrated in Figure 1, whose head opening 113 is sealed off by a sealing unit 114. A plug 115 is attached to the sealing unit 114 and engages a corresponding drilled hole or connection opening 117 in the sealing unit 114. The plug 115 can, for example, be a commercial plug, preferably a BNC-plug. The plug 115 could also be threaded, so that it can be screwed into a corresponding inner threading in the connection opening 117 in the sealing unit 114. Of course, other types of attachment of the plug 115 to the sealing unit 114 are also possible, provided a mechanically secure and tight connection of the plug 115 to the sealing unit 114 is ensured.
The sealing unit 114 is preferably attached in the outer housing 112. For example, the sealing unit 114 could include an outer threading for engagement with a corresponding inner threading of the housing 112. Alternatively, other connection methods can be used provided that it securely attaches the sealing unit 114 in the housing 112, and if necessary, seals the housing 112.
The housing 112, the sealing unit 114 and the plug 115 are preferably made of metal.
But they can also be manufactured from other suitable materials, e.g., plastic. It must be taken into account that the sealing unit 114 must guide the high frequency, measurement signals provided at the plug 115, to conductors 131a and 131b located in the probe unit 130.
The ability to guide or conduct the high frequency signals then also requires a sealing unit 114 of plastic or a plug 115 of plastic.
A cable 116 located at the back of the plug 115, for example a coaxial cable, connects the waveguide 100 to an electronic measuring circuit (not shown). Measuring signals May 25, 2000 generated in the electronic measuring circuit are supplied along a "hot wire"
of the coaxial cable 116 to a contact pin 115a, which is in direct contact with a preferably rod-shaped signal conductor 119 in the probe unit 130. The contact pin llSa is surrounded in the interior of the sealing unit 114 by a cone 118, and thus is isolated from the sealing unit 114 which is connected to a shielded conductor of the coaxial cable 116. The cone 118 is preferably made of plastic, but it can also be made of another suitable material.
In the interior of the housing 112, or more precisely in the part of the head opening 113 located opposite the plug 115 when viewed in the direction of the attachment unit 140, is a head unit 120 of a carrier element 132 which adjoins the sealing unit 114.
The head unit 120 is mounted in a correspondingly shaped region of the head opening 113 of the housing 112 below the sealing unit 114. The head unit 120 is a component of the carrier element 132, in which the signal conductor 119 and the shielded conductors 131a and 131b are embedded.
The carrier element 132 is made of a dielectric material, for example, a PEEK, PPS or PTFE-plastic. Additional suitable materials are, for example, ECTFE, ETFE, FEP, PCTFE, PFA, PVDF, PVF, PVC, and in the food industry, carrier elements of PTFE, PCTFE and PFA-plastic are preferred.
The signal conductor 119 extends from a region of the probe unit 130 located opposite the sealing unit 114, through the cone 118 and out beyond the head unit 120 as far as the contact pin 115a of the plug 115. In the probe unit 130, the signal conductor 119 is surrounded along its entire length by the carrier element 132, and thus is isolated from the two shielded conductors 131a and 131b positioned parallel to it in the carrier element 132 as shown in the embodiment of Figure 1.
The terms "signal conductor" and "shielded conductor," as mentioned previously, are not being used in the usual sense of electrical engineering, but rather are used here for better differentiation of the individual conductors from each other. These designations refer to the signal conductor and the shielded conductor of the coaxial cable 116 through which the measuring signals are transmitted to the waveguide. In the embodiment, this coaxial arrangement for the conductors 119, 131a and 131b is retained, so the signal conductor 119 can be passed through for connection to the contact pin 115a between the shielded conductors 131a and 131b. For this purpose, in the head unit 120 of the probe unit 130, the shielded conductors 131a and 131b are connected with a crown-shaped coupling unit 121.
The May 25, 2000 coupling unit 121 is connected to an interior, front side 114a of the sealing unit 114. Thus, the shielded conductors 131a and 131b in the probe unit 130 are connected, through the coupling unit 121 and the sealing unit 114, to the shielded conductor of the coaxial cable 116.
In the embodiment of the waveguide 100 shown in Figure 1, the coupling unit 121 has a ring-shaped base unit illustrated by a cylindrical unit 121a, which extends out into two peak-like protrusions 121b and 121c. The cylindrical base unit 121a and the protrusions 121b and 121c together form the crown shape of the coupling unit 121, the peaks of which are connected to the shielded conductors 131a and 131b. This particular and preferred design of the coupling unit 121 can be produced very easily from a tubular-shaped component having the desired base unit with slanting sections extending therefrom which are tapered from outside to inside along the longitudinal axis of the tubular component. For the case where more than two shielded conductors are provided for the waveguide, crown-shaped coupling units 121 can be produced in a similar manner with the desired number of peaks for connection to the shielded conductors.
Furthermore, in contrast to the configuration of Figure 1, it is possible to control the inactive length of the waveguide 100 by changing the shape of the coupling unit 121, in particular changing the shape of its base unit 121a. For example, the base unit 121a of the coupling unit 121 can be extended in the direction of the probe unit 130 through the attachment unit 140, so that the signal conductor 119 is coaxially surrounded there by the base unit 121a. This enclosed region of the signal conductor 119 will not be available for a measurement and determines the inactive length. Alternatively, the invention also makes it possible to obtain a very short inactive length of the waveguide by, for example, forming the coupling unit 121 as a thin ring which is positioned transverse to the longitudinal axis of the shielded conductors 131a and 131b and joins them together.
The signal conductor 119, the shielded conductors 131a and 131b and the coupling unit 121 are made of electrically conducting material, preferably of metal.
But other electrically conducting materials could be used.
The probe unit 130 illustrated in Figure 1 is one particular embodiment of the waveguide 100 according to the invention. It can be tailored to the application and the container, for example, it can be made longer or of a different geometric shape. Also the attachment of the waveguide 100 can play a role in this tailoring. As a simplification, and to May 25, 2000 underscore the versatile utility of the waveguide 100, a simple attachment unit 140 is illustrated in Figure 1 having an outer threading 141 which engages a corresponding, inner threading of a suitable short pipe of the container. In addition, other types of attachment of the waveguide 100 are also possible, such as flange or plug-in connections, provided that they ensure a mechanically dependable and, if necessary, tight attachment of the waveguide 100 to or in the container.
As shown in Figure 2, the carrier element 132 of the waveguide 100 according to Figure 1 has an essentially oval cross-sectional shape. The shielded conductor 131a, 131b and the centrally positioned signal conductor 119 are clearly shown. Some advantages of the oval cross-sectional shape is that it provides sufficient mechanical stability, and it requires relatively little material for the carrier element 132 and has low power losses along the probe unit 130. The oval shaped probe unit 130 can also be easily cleaned and is suitable, especially when made of appropriate plastic, for use in the food industry. The probe unit 130 with this oval cross section can be manufactured in any particular length without great additional manufacturing expense.
Figure 3 shows a second embodiment of a waveguide 200 according to the present invention. The waveguide 200 is designed, similar to the waveguide 100 according to Figure 1 with a connecting unit 210, an attachment unit 240 and a probe unit 230, in which two shielded conductors 231a and 231b and also a signal conductor 219 are provided.
A coaxial cable can be connected to a sealing unit 214 that can be screwed into the housing of the connecting unit 210, similar to the embodiment of Figure 1. The measuring signals being guided along the coaxial cable.
In contrast to the waveguide 100 according to Figures 1 and 2, the probe unit 230 has a carrier element 232 with a rhomboidal cross section. Figure 3 shows a crown-shaped coupling unit 221 having protrusions 221a and 221b which are connected with the shielded conductors 231a and 231b. Like the embodiment shown in Figure 1, the coupling unit 221 is connected with the sealing unit 214, so that the shielded conductors 231a and 231b attached to the coupling unit 221 are in contact with a shielded conductor of the coaxial cable. The connection of the signal conductor 219 to a signal conductor of the coaxial cable is also preferably designed similar to the embodiment in Figure 1. The attachment unit corresponds in shape and function to the attachment unit 140 of Figure 1.
May 25, 2000 The carrier element 232 includes a thickened portion 230a towards the coupling unit 221 which covers the peaks of the protrusions 221a and 221b of the coupling unit 221. This ensures a dependable mechanical protection of the shielded conductors 231a and 231b attached thereto. If necessary, the coupling unit 221 can be encased by a thin plastic tube (not shown) so that it is not directly exposed to the material being measured.
Figure 4 shows a side view of the waveguide 200 with dashed lines indicating the interior edges of components. In the connecting unit 210 is shown the sealing unit 214 with an opening or bushing for a plug 215 which includes a contact pin 215a that plugs into a corresponding bushing of the signal conductor 219. The plug 215 could be, for example, a BNC-plug. The signal conductor 219 and also the carrier element 232 are composed of several parts for reasons of manufacture and assembly. Figure 4 also shows a cone 218 isolating the signal conductor 219 in the region of the connecting unit 210 from the shielded conductors 231a and 231b (see Figure 3), and from the coupling unit 221 with its protrusions 221a and 221b. However, only the protrusion 221a connected to the shielded conductor 231a is shown in Figure 4 due to the side view.
Figure 5 shows a cross-sectional view of a probe unit 330 of a third embodiment of the waveguide according to the invention. A signal conductor 319 and also two shielded conductors 331a and 331b are embedded in a carrier element 332, which is preferably made of one of the above mentioned plastics. The conductors have a rectangular cross section in contrast to the conductors discussed above. If a probe unit 330 with small dimensions is required, then with this embodiment, strips of metal can be used as conductors so that the probe unit 330 can be manufactured at low cost as a kind of flat ribbon cable.
Flat probe units 330 according to the embodiment shown in Figure 5 are suitable for assembly in the vicinity of straight container walls, where very little space is available in the interior of the container due to other internal structures.
The other parts of the waveguide, such as the connecting unit and the coupling unit, correspond in shape and function to the embodiments shown in Figures 1, 2, 3 or 4.
A fourth embodiment of the invention is presented in Figures 6, 7 and 8. In contrast to the embodiments described above which have three conductors in the probe unit, in this embodiment a waveguide 400 with a probe unit 430 has a carrier element 432 in which there are two embedded signal conductors 419a and 419b and also two shielded conductors 431a May 25, 2000 and 431b. In addition, a connecting unit 410 of the waveguide 400 is configured differently than that of the waveguides according to Figures 1-4.
The essential difference is in the basic conception of the waveguide 400, which is provided for a special sealing of the carrier element 432 in an attachment unit 440.
The carrier element 432 has a star-shaped cross section, as illustrated in Figure 7, in a region separated from the connecting unit 410. The carrier element 432 is flared out in the attachment unit 440 into a separate carrier element unit 432a. A double cone 418, preferably made of plastic, is attached to the carrier element 432 in the connecting unit 410. A Y-shaped bridge unit 419c, preferably made of metal, joins the signal conductors 419a and 419b. The Y-shaped bridge unit 419c is surrounded by the separate carrier element unit 432a and extends into the double cone 418. The separate carrier element unit 432a and extends into the double cone 418 isolate the bridge unit 419c from shielded conductor extensions 431c and 431d, which are also preferably made of metal.
In a housing 412 of the connecting unit 410 there is a cone mount 418a, preferably made of metal, for the double cone 418, which is electrically connected to the shielded conductor extensions 431c and 431d. A sealing unit 414, which is equipped with a plug bushing (as described above) for a plug connected to a coaxial cable, is securely joined by means of a threaded connection 414b to the cone mount 418a. The sealing unit 414, in contrast to the previously described embodiments of the invention, is not rigidly attached to the housing 412, but rather can be displaced therein within certain limits.
The shielded conductor extensions 431c and 431d are surrounded in the region of the attachment unit 440 by a plastic casing 450. The casing 450 covers the shielded conductor extensions 431c and 431d with respect to the material being measured. The casing 450, for example, is manufactured for applications in the food industry from cold-flowing plastic, preferably Teflon or similar material, and continues through the interior of the attachment unit 440 out to the housing 412 of the connecting unit 410. In case the material of the casing 450 begins to flow and the clamping of the separate carrier element unit 432a and the shielded conductor extensions 431c and 431d in the attachment unit 440 decreases, there is a danger of minor leaks to the interior of the housing 412. However, the invention is designed to handle this situation through the use of an easily tensioned coil spring 452 in the interior of ' EH 367 CA
May 25, 2000 the housing 412 which is provided during installation of the sealing unit 414.
The spring 452 acts on the conical mount 418a and pulls it together with the shielded conductor extensions 431c and 431d attached thereto into the attachment unit 440. A slight conicity of the shielded conductor extensions 431c and 431d, shown in Figures 6 and 8, limits their stroke and prevents the sealing unit 414 from exiting the housing 412.
Figures 9 and 10 show additional embodiments of various cross sections of probe units and carrier elements which illustrate the versatile utility of the invention.
In Figure 9 there is an essentially round probe unit 530 of a fifth embodiment of the waveguide with four conductors presented in cross section. In a carrier element 532, which is preferably made of one of the plastics mentioned above, two signal conductors 519a and 519b and also two shielded conductors 531a and 531b are embedded with their edges engaged in corresponding recesses of the carrier element 532. They can be isolated from the outside, that is from the material, by an appropriate plastic casing.
In one particularly simple embodiment, the conductors 519a, 519b, 531a and 531b can be attached in the form of metal strips externally on a cylindrical carrier element 532 and attached in place there by an additional casing such as, for example, a plastic tube.
The other parts of the waveguide, such as the connecting unit and the Y-shaped bridge unit, have a similar structure and function to the embodiments according to Figures 6-8.
Figure 10 shows a cross section of an essentially rectangular probe unit 630 of a sixth embodiment of the waveguide with four conductors. In a carrier element 632, which is preferably made of one of the plastics mentioned above, there are two embedded signal conductors 619a and 619b and also two shielded conductors 631a and 631b, whose edges, at the corners here, are mounted into corresponding recesses of the carrier element 632. They can be externally isolated from the material, for example, by means of a corresponding plastic casing.
Here too, the conductors 519a, 519b, 531a and 531b can be attached, for example in the form of kinked or otherwise pre-shaped metal strips, externally on the edges of the rod-like carrier element 532 and fixed in place by an additional casing such as a plastic tube.
The other parts of the waveguide, such as the connecting unit and the Y-shaped bridge unit, have a similar structure and function to the embodiments according to Figures 6-8.
The particular advantage of the probe unit illustrated in Figure 10 is that the May 25, 2000 conductors can be relatively large and the edge spacing between them can be kept relatively small. With this structure the global sensitivity of the waveguide can be optimized in a simple manner.
]5
In the simplest design, a waveguide of this kind has a probe unit with one individual signal conductor which can be a rod or a steel cable. A waveguide of this kind is also known as a "Sommerfeld conductor."
If the conductor is coated with a dielectric layer, usually a plastic film, then we call this a "Goubau conductor." A Sommerfeld conductor is available from the applicant under the designation "Levelflex." The great advantage of the single-conductor waveguide is that it can be of any length, due to its simple mechanical structure.
In spite of its simple mechanical structure, the single-conductor waveguide is not suitable for all applications. The electrical and magnetic fields used for the level measurements forms between the single conductor of the probe unit and a container wall, for example, so that the field around the waveguide shows a relatively large scattering. Signal injection (and feedback) of signals into the (or from the) single-conductor probe unit are relatively difficult to attain, since a significant portion of the signal energy is reflected from the signal injection or other changes in the geometry of the waveguide.
Other obstacles in the vicinity of the single-conductor waveguide, e.g., support pipes and internal structures in the container, which are measured by the field, can likewise impede the identification of the actual fill level measurement signal or make it entirely impossible.
This is especially true in the vicinity of a short pipe which is used to attach the waveguide to the container. In such a region, no fill level can be measured without disproportionate expense, but rather only starting at a certain distance away from it, which is called the "block distance" as referenced above.
Since a considerable portion of the signal energy in the single-conductor waveguide is consumed to build up the extensive field, i.e., is radiated off, only a small portion of the signal energy is available for a measurement of the fill level. In addition, the emitted energy can lead to undesirable harmonic effects in the attachment pipe due to multiple reflections.
At the present time, there is still no satisfactory way to blank out the interfering echo signals of the attachment pipe from the actual useful signal in a single-conductor waveguide.
Another known form of a waveguide has a probe unit with a signal conductor and a shielded conductor in a coaxial array. A usually rod-shaped signal conductor is May 25, 2000 concentrically surrounded by a usually tubular shielded conductor, so that the field generated by the microwave signals forms only in the usually narrow annulus between the signal conductor and the shielded conductor. The material penetrating the annulus causes the echo signal desired for determination of the fill level.
Coaxial waveguides are characterized by an effective signal injection. Since the field produced by the microwave measuring signal on the region of the annulus between the conductors is limited, no undesirable emission effects occur. There is no danger of interfering interactions with pipes or other internal structures in the tank.
The block distance is small and the function of the coaxial waveguide is not dependent on its installed position.
In modern waveguides, the smallest possible outer diameter is desirable, so that the residual annulus between the signal conductor and shielded conductor is very small in this kind of coaxial waveguide. The sensitivity to sediments or deposits of the material being measured in the annulus is quite large and can lead to an erroneous measured signal. Also, viscous materials, even if they only briefly fill the annulus or adhere to the signal conductor on the inside of the shielded conductor, are not suitable for coaxial waveguides. The material being measured must be of low viscosity.
The narrower the annulus of the coaxial waveguide, the more difficult it is to clean sediments or build-up of the material being measured. Due to the formation of residues and the associated danger to hygiene, coaxial conductors are not used today in the food industry.
As mentioned above, in coaxial waveguides the measuring signal is conducted between the signal conductor and the shielded conductor surrounding it, and the material penetrating into the annulus between the conductors generates the useful signal. Therefore, it is possible to seal off (by a suitable means) the annulus in a region near the connection portion of the waveguide and to block it off against the penetrating material.
For example, the annulus can be filled in the desired region by a suitable plastic, so that in the filled section, the involved length of the probe unit will not be available for measurements. This desired shift in the top measurement point for the fill level away from the attachment of the waveguide to the container, is also called the "inactive length" of the waveguide.
In WO-A 98/05931 another waveguide is described for a fill-level measuring device, in which two or more conductors located essentially in a common plane are used as a probe unit. The material to be measured is located around the conductors and between them.
May 25, 2000 The probe unit of this fill-level measuring device is composed of a "U-shaped"
conductor. Of particular interest is the field building up by the measurement signals between the parallel and mutually connected conductors. This construction represents a kind of compromise between a single-wire and coaxial waveguide and in a functional regard combines their advantages. However, for longer lengths of the probe unit and in moving media spacers are needed between the conductors in order to avoid disturbances in the field or short circuits due to bending or twisting of the conductor. These spacers or supports between the conductors act as reflectors for the measurement signals and lead to undesirable, interfering echoes. In addition, between the parallel conductors (and in particular also on the spacers) deposits or sediments can form which, in turn, cause undesirable, interfering echoes.
Another example of a waveguide with several conductors running in a common plane in the probe unit is described in U.S. Patent 4,807,471. In this case, the probe unit consists of paired, mutually associated conductors, and the conductors of at least one such conductor pair are electrically short-circuited. A disadvantage of this waveguide is that a signal conductor and a shielded conductor must be used in pairs, so that the signals on the conductors are in counterphase. At least one signal conductor is electrically connected to a shielded conductor by means of a PIN diode, and its function depends on the precise spacing of the mutually parallel conductors, and with a large length waveguide, this function must be assured by spacers between the signal conductor and shielded conductor. In turn, these spacers offer attachment points for undesirable deposits between the conductors, which then interfere with the measurement signal.
It is therefore the objective of the present invention to specify a waveguide for a fill-level measuring device, which is distinguished by a simple construction, which combines the advantages of the single wire and known multiple wire waveguides, such that it shows no interaction with container internal structures, its inactive length is adjustable in a simple manner, and it can be cleaned in a simple manner from deposits or sediments.
SUMMARY OF THE INVENTION
To achieve these objectives, the present invention includes a waveguide for a fill-level measuring device to determine the fill level of a material in a container by means of conducted microwave pulsed signals. The waveguide is partially immersed in the material to May 25, 2000 be measured, and is comprised of:
- a probe unit which includes -- at least three electrical conductors, -- at least one being a signal conductor and the remainder being a shielded conductor, and -- at least one carrier element which at least partially surrounds the conductors, - a connecting unit with a signal connector for connection of the conductors with an electronic measuring circuit generating the microwave signals, and - an attachment unit for mechanical attachment of the waveguide to or on the container.
In one embodiment of the waveguide according to the present invention, the carrier element is made of plastic.
In another embodiment of the waveguide, the signal conductor and/or the shielded conductor are made of electrically conducting plastic.
In another embodiment of the invention, the signal conductor and/or the shielded conductor are made of metal.
Additional embodiments of the invention include various cross-sectional shapes of the probe unit of the waveguide.
The invention is based on the basic idea of encasing multiple conductors, which are in an essentially parallel arrangement with each other and are insensitive to interfering influences, in a probe unit of a waveguide in such a manner that deposits or sediments between the conductors can be prevented and that, moreover, the probe unit can be cleaned in a simple manner. Due to its design, the waveguide according to the present invention is simple and can be reliably attached.
An additional advantage of the invention is that, due to the special configuration of the signal injection (or feedback) of the measuring signals and the potential for specific impedance adjustment, the inactive length of the waveguide can be adjusted in a desirable manner by a simple means. Therefore, the waveguide can be designed short enough to be suitable for measurements even in flat containers in which formerly no measurements could be carried out with microwave or radar fill-level measuring devices.
Another advantage of the invention is that it offers versatile configuration potentials May 25, 2000 for the probe unit in conjunction with different arrangements of the conductor. The criteria mentioned above, which determine, for example, the global sensitivity of the waveguide, can be optimized in a desirable manner with the invention for a particular application. For instance, through suitable selection of the number of conductors and of the material of the carrier element of the probe unit, the ratio of microwave energy between the interior and exterior of the probe unit can be established, so that the interference susceptibility of the waveguide to sediment can be adjusted as a function of the particular material to be measured. In addition, the waveguide can have a shape determined by the geometry of the container or by the material to be measured. The probe unit, which is immersed in the material to be measured, can take on any particular length.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be explained in greater detail based on embodiments which are illustrated in the figures. The same parts are referred to using the same reference numbers in all the figures; if needed for greater clarity, reference numbers already mentioned will be left out of the subsequent figures.
Figure 1 shows a longitudinal cross section of a first embodiment of a waveguide according to the invention;
Figure 2 shows a cross section of the probe unit of the waveguide shown to Figure 1;
Figure 3 shows a second embodiment of the waveguide according to the present invention;
Figure 4 shows a side view of the waveguide shown in Figure 3 with inner edges drawn in;
Figure 5 shows a cross section of a probe unit of a third embodiment of a waveguide according to the present invention;
Figure 6 shows a longitudinal cross section of a fourth embodiment of a waveguide according to the present invention;
Figure 7 shows a cross section of the probe unit of the waveguide shown in Figure 6;
Figure 8 shows a longitudinal cross section of the waveguide shown in Figure 6 from a different perspective;
Figure 9 shows a cross section of a probe unit of a fifth embodiment of a waveguide May 25, 2000 according to the present invention; and Figure 10 shows a cross section of a probe unit of a sixth embodiment of a waveguide according to the present invention.
S DETAILED DESCRIPTION OF THE INVENTION
A waveguide 100 according to the present invention and illustrated in Figure 1 features a connecting unit 110, a probe unit 130 and an attachment unit 140 for attachment of the waveguide 100 to or in a container (not shown), where the fill level of the material located in the container is to be determined.
The connecting unit 110 is composed of an outer and essentially cylindrical-shaped housing 112 as illustrated in Figure 1, whose head opening 113 is sealed off by a sealing unit 114. A plug 115 is attached to the sealing unit 114 and engages a corresponding drilled hole or connection opening 117 in the sealing unit 114. The plug 115 can, for example, be a commercial plug, preferably a BNC-plug. The plug 115 could also be threaded, so that it can be screwed into a corresponding inner threading in the connection opening 117 in the sealing unit 114. Of course, other types of attachment of the plug 115 to the sealing unit 114 are also possible, provided a mechanically secure and tight connection of the plug 115 to the sealing unit 114 is ensured.
The sealing unit 114 is preferably attached in the outer housing 112. For example, the sealing unit 114 could include an outer threading for engagement with a corresponding inner threading of the housing 112. Alternatively, other connection methods can be used provided that it securely attaches the sealing unit 114 in the housing 112, and if necessary, seals the housing 112.
The housing 112, the sealing unit 114 and the plug 115 are preferably made of metal.
But they can also be manufactured from other suitable materials, e.g., plastic. It must be taken into account that the sealing unit 114 must guide the high frequency, measurement signals provided at the plug 115, to conductors 131a and 131b located in the probe unit 130.
The ability to guide or conduct the high frequency signals then also requires a sealing unit 114 of plastic or a plug 115 of plastic.
A cable 116 located at the back of the plug 115, for example a coaxial cable, connects the waveguide 100 to an electronic measuring circuit (not shown). Measuring signals May 25, 2000 generated in the electronic measuring circuit are supplied along a "hot wire"
of the coaxial cable 116 to a contact pin 115a, which is in direct contact with a preferably rod-shaped signal conductor 119 in the probe unit 130. The contact pin llSa is surrounded in the interior of the sealing unit 114 by a cone 118, and thus is isolated from the sealing unit 114 which is connected to a shielded conductor of the coaxial cable 116. The cone 118 is preferably made of plastic, but it can also be made of another suitable material.
In the interior of the housing 112, or more precisely in the part of the head opening 113 located opposite the plug 115 when viewed in the direction of the attachment unit 140, is a head unit 120 of a carrier element 132 which adjoins the sealing unit 114.
The head unit 120 is mounted in a correspondingly shaped region of the head opening 113 of the housing 112 below the sealing unit 114. The head unit 120 is a component of the carrier element 132, in which the signal conductor 119 and the shielded conductors 131a and 131b are embedded.
The carrier element 132 is made of a dielectric material, for example, a PEEK, PPS or PTFE-plastic. Additional suitable materials are, for example, ECTFE, ETFE, FEP, PCTFE, PFA, PVDF, PVF, PVC, and in the food industry, carrier elements of PTFE, PCTFE and PFA-plastic are preferred.
The signal conductor 119 extends from a region of the probe unit 130 located opposite the sealing unit 114, through the cone 118 and out beyond the head unit 120 as far as the contact pin 115a of the plug 115. In the probe unit 130, the signal conductor 119 is surrounded along its entire length by the carrier element 132, and thus is isolated from the two shielded conductors 131a and 131b positioned parallel to it in the carrier element 132 as shown in the embodiment of Figure 1.
The terms "signal conductor" and "shielded conductor," as mentioned previously, are not being used in the usual sense of electrical engineering, but rather are used here for better differentiation of the individual conductors from each other. These designations refer to the signal conductor and the shielded conductor of the coaxial cable 116 through which the measuring signals are transmitted to the waveguide. In the embodiment, this coaxial arrangement for the conductors 119, 131a and 131b is retained, so the signal conductor 119 can be passed through for connection to the contact pin 115a between the shielded conductors 131a and 131b. For this purpose, in the head unit 120 of the probe unit 130, the shielded conductors 131a and 131b are connected with a crown-shaped coupling unit 121.
The May 25, 2000 coupling unit 121 is connected to an interior, front side 114a of the sealing unit 114. Thus, the shielded conductors 131a and 131b in the probe unit 130 are connected, through the coupling unit 121 and the sealing unit 114, to the shielded conductor of the coaxial cable 116.
In the embodiment of the waveguide 100 shown in Figure 1, the coupling unit 121 has a ring-shaped base unit illustrated by a cylindrical unit 121a, which extends out into two peak-like protrusions 121b and 121c. The cylindrical base unit 121a and the protrusions 121b and 121c together form the crown shape of the coupling unit 121, the peaks of which are connected to the shielded conductors 131a and 131b. This particular and preferred design of the coupling unit 121 can be produced very easily from a tubular-shaped component having the desired base unit with slanting sections extending therefrom which are tapered from outside to inside along the longitudinal axis of the tubular component. For the case where more than two shielded conductors are provided for the waveguide, crown-shaped coupling units 121 can be produced in a similar manner with the desired number of peaks for connection to the shielded conductors.
Furthermore, in contrast to the configuration of Figure 1, it is possible to control the inactive length of the waveguide 100 by changing the shape of the coupling unit 121, in particular changing the shape of its base unit 121a. For example, the base unit 121a of the coupling unit 121 can be extended in the direction of the probe unit 130 through the attachment unit 140, so that the signal conductor 119 is coaxially surrounded there by the base unit 121a. This enclosed region of the signal conductor 119 will not be available for a measurement and determines the inactive length. Alternatively, the invention also makes it possible to obtain a very short inactive length of the waveguide by, for example, forming the coupling unit 121 as a thin ring which is positioned transverse to the longitudinal axis of the shielded conductors 131a and 131b and joins them together.
The signal conductor 119, the shielded conductors 131a and 131b and the coupling unit 121 are made of electrically conducting material, preferably of metal.
But other electrically conducting materials could be used.
The probe unit 130 illustrated in Figure 1 is one particular embodiment of the waveguide 100 according to the invention. It can be tailored to the application and the container, for example, it can be made longer or of a different geometric shape. Also the attachment of the waveguide 100 can play a role in this tailoring. As a simplification, and to May 25, 2000 underscore the versatile utility of the waveguide 100, a simple attachment unit 140 is illustrated in Figure 1 having an outer threading 141 which engages a corresponding, inner threading of a suitable short pipe of the container. In addition, other types of attachment of the waveguide 100 are also possible, such as flange or plug-in connections, provided that they ensure a mechanically dependable and, if necessary, tight attachment of the waveguide 100 to or in the container.
As shown in Figure 2, the carrier element 132 of the waveguide 100 according to Figure 1 has an essentially oval cross-sectional shape. The shielded conductor 131a, 131b and the centrally positioned signal conductor 119 are clearly shown. Some advantages of the oval cross-sectional shape is that it provides sufficient mechanical stability, and it requires relatively little material for the carrier element 132 and has low power losses along the probe unit 130. The oval shaped probe unit 130 can also be easily cleaned and is suitable, especially when made of appropriate plastic, for use in the food industry. The probe unit 130 with this oval cross section can be manufactured in any particular length without great additional manufacturing expense.
Figure 3 shows a second embodiment of a waveguide 200 according to the present invention. The waveguide 200 is designed, similar to the waveguide 100 according to Figure 1 with a connecting unit 210, an attachment unit 240 and a probe unit 230, in which two shielded conductors 231a and 231b and also a signal conductor 219 are provided.
A coaxial cable can be connected to a sealing unit 214 that can be screwed into the housing of the connecting unit 210, similar to the embodiment of Figure 1. The measuring signals being guided along the coaxial cable.
In contrast to the waveguide 100 according to Figures 1 and 2, the probe unit 230 has a carrier element 232 with a rhomboidal cross section. Figure 3 shows a crown-shaped coupling unit 221 having protrusions 221a and 221b which are connected with the shielded conductors 231a and 231b. Like the embodiment shown in Figure 1, the coupling unit 221 is connected with the sealing unit 214, so that the shielded conductors 231a and 231b attached to the coupling unit 221 are in contact with a shielded conductor of the coaxial cable. The connection of the signal conductor 219 to a signal conductor of the coaxial cable is also preferably designed similar to the embodiment in Figure 1. The attachment unit corresponds in shape and function to the attachment unit 140 of Figure 1.
May 25, 2000 The carrier element 232 includes a thickened portion 230a towards the coupling unit 221 which covers the peaks of the protrusions 221a and 221b of the coupling unit 221. This ensures a dependable mechanical protection of the shielded conductors 231a and 231b attached thereto. If necessary, the coupling unit 221 can be encased by a thin plastic tube (not shown) so that it is not directly exposed to the material being measured.
Figure 4 shows a side view of the waveguide 200 with dashed lines indicating the interior edges of components. In the connecting unit 210 is shown the sealing unit 214 with an opening or bushing for a plug 215 which includes a contact pin 215a that plugs into a corresponding bushing of the signal conductor 219. The plug 215 could be, for example, a BNC-plug. The signal conductor 219 and also the carrier element 232 are composed of several parts for reasons of manufacture and assembly. Figure 4 also shows a cone 218 isolating the signal conductor 219 in the region of the connecting unit 210 from the shielded conductors 231a and 231b (see Figure 3), and from the coupling unit 221 with its protrusions 221a and 221b. However, only the protrusion 221a connected to the shielded conductor 231a is shown in Figure 4 due to the side view.
Figure 5 shows a cross-sectional view of a probe unit 330 of a third embodiment of the waveguide according to the invention. A signal conductor 319 and also two shielded conductors 331a and 331b are embedded in a carrier element 332, which is preferably made of one of the above mentioned plastics. The conductors have a rectangular cross section in contrast to the conductors discussed above. If a probe unit 330 with small dimensions is required, then with this embodiment, strips of metal can be used as conductors so that the probe unit 330 can be manufactured at low cost as a kind of flat ribbon cable.
Flat probe units 330 according to the embodiment shown in Figure 5 are suitable for assembly in the vicinity of straight container walls, where very little space is available in the interior of the container due to other internal structures.
The other parts of the waveguide, such as the connecting unit and the coupling unit, correspond in shape and function to the embodiments shown in Figures 1, 2, 3 or 4.
A fourth embodiment of the invention is presented in Figures 6, 7 and 8. In contrast to the embodiments described above which have three conductors in the probe unit, in this embodiment a waveguide 400 with a probe unit 430 has a carrier element 432 in which there are two embedded signal conductors 419a and 419b and also two shielded conductors 431a May 25, 2000 and 431b. In addition, a connecting unit 410 of the waveguide 400 is configured differently than that of the waveguides according to Figures 1-4.
The essential difference is in the basic conception of the waveguide 400, which is provided for a special sealing of the carrier element 432 in an attachment unit 440.
The carrier element 432 has a star-shaped cross section, as illustrated in Figure 7, in a region separated from the connecting unit 410. The carrier element 432 is flared out in the attachment unit 440 into a separate carrier element unit 432a. A double cone 418, preferably made of plastic, is attached to the carrier element 432 in the connecting unit 410. A Y-shaped bridge unit 419c, preferably made of metal, joins the signal conductors 419a and 419b. The Y-shaped bridge unit 419c is surrounded by the separate carrier element unit 432a and extends into the double cone 418. The separate carrier element unit 432a and extends into the double cone 418 isolate the bridge unit 419c from shielded conductor extensions 431c and 431d, which are also preferably made of metal.
In a housing 412 of the connecting unit 410 there is a cone mount 418a, preferably made of metal, for the double cone 418, which is electrically connected to the shielded conductor extensions 431c and 431d. A sealing unit 414, which is equipped with a plug bushing (as described above) for a plug connected to a coaxial cable, is securely joined by means of a threaded connection 414b to the cone mount 418a. The sealing unit 414, in contrast to the previously described embodiments of the invention, is not rigidly attached to the housing 412, but rather can be displaced therein within certain limits.
The shielded conductor extensions 431c and 431d are surrounded in the region of the attachment unit 440 by a plastic casing 450. The casing 450 covers the shielded conductor extensions 431c and 431d with respect to the material being measured. The casing 450, for example, is manufactured for applications in the food industry from cold-flowing plastic, preferably Teflon or similar material, and continues through the interior of the attachment unit 440 out to the housing 412 of the connecting unit 410. In case the material of the casing 450 begins to flow and the clamping of the separate carrier element unit 432a and the shielded conductor extensions 431c and 431d in the attachment unit 440 decreases, there is a danger of minor leaks to the interior of the housing 412. However, the invention is designed to handle this situation through the use of an easily tensioned coil spring 452 in the interior of ' EH 367 CA
May 25, 2000 the housing 412 which is provided during installation of the sealing unit 414.
The spring 452 acts on the conical mount 418a and pulls it together with the shielded conductor extensions 431c and 431d attached thereto into the attachment unit 440. A slight conicity of the shielded conductor extensions 431c and 431d, shown in Figures 6 and 8, limits their stroke and prevents the sealing unit 414 from exiting the housing 412.
Figures 9 and 10 show additional embodiments of various cross sections of probe units and carrier elements which illustrate the versatile utility of the invention.
In Figure 9 there is an essentially round probe unit 530 of a fifth embodiment of the waveguide with four conductors presented in cross section. In a carrier element 532, which is preferably made of one of the plastics mentioned above, two signal conductors 519a and 519b and also two shielded conductors 531a and 531b are embedded with their edges engaged in corresponding recesses of the carrier element 532. They can be isolated from the outside, that is from the material, by an appropriate plastic casing.
In one particularly simple embodiment, the conductors 519a, 519b, 531a and 531b can be attached in the form of metal strips externally on a cylindrical carrier element 532 and attached in place there by an additional casing such as, for example, a plastic tube.
The other parts of the waveguide, such as the connecting unit and the Y-shaped bridge unit, have a similar structure and function to the embodiments according to Figures 6-8.
Figure 10 shows a cross section of an essentially rectangular probe unit 630 of a sixth embodiment of the waveguide with four conductors. In a carrier element 632, which is preferably made of one of the plastics mentioned above, there are two embedded signal conductors 619a and 619b and also two shielded conductors 631a and 631b, whose edges, at the corners here, are mounted into corresponding recesses of the carrier element 632. They can be externally isolated from the material, for example, by means of a corresponding plastic casing.
Here too, the conductors 519a, 519b, 531a and 531b can be attached, for example in the form of kinked or otherwise pre-shaped metal strips, externally on the edges of the rod-like carrier element 532 and fixed in place by an additional casing such as a plastic tube.
The other parts of the waveguide, such as the connecting unit and the Y-shaped bridge unit, have a similar structure and function to the embodiments according to Figures 6-8.
The particular advantage of the probe unit illustrated in Figure 10 is that the May 25, 2000 conductors can be relatively large and the edge spacing between them can be kept relatively small. With this structure the global sensitivity of the waveguide can be optimized in a simple manner.
]5
Claims (8)
1. Waveguide for a fill-level measuring device to determine the fill level of a material in a container by means of conducted microwave pulsed signals, said waveguide is partially immersed in the material to be measured, and is comprised of:
- a probe unit which includes -- at least three electrical conductors, -- at least one being a signal conductor and the remainder being a shielded conductor, and -- at least one carrier element which at least partially surrounds the conductors, - a connecting unit with a signal connector for connection of the conductors with an electronic measuring circuit generating the microwave signals, and - an attachment unit for mechanical attachment of the waveguide to or on the container.
- a probe unit which includes -- at least three electrical conductors, -- at least one being a signal conductor and the remainder being a shielded conductor, and -- at least one carrier element which at least partially surrounds the conductors, - a connecting unit with a signal connector for connection of the conductors with an electronic measuring circuit generating the microwave signals, and - an attachment unit for mechanical attachment of the waveguide to or on the container.
2. The waveguide of claim 1 having the carrier element made of plastic.
3. The waveguide of claim 1 or 2 having the signal conductor and/or the shielded conductor made of electrically conductive plastic.
4. The waveguide of claim 1 or 2 having the signal conductor and/or the shielded conductor made of metal.
5. The waveguide of one of the claims 1 through 4 having the carrier element of an essentially oval cross-sectional shape.
6. The waveguide of one of the claims 1 through 4 having the carrier element of an essentially polygonal cross-sectional shape.
7. The waveguide of one of the claims 1 through 4 having the carrier element of an essentially star-shaped cross-section.
8. The waveguide of one of the claims 1 through 4 having the carrier element of an essentially round cross-sectional shape.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP99113686.2 | 1999-07-15 | ||
| EP99113686A EP1069649B1 (en) | 1999-07-15 | 1999-07-15 | Waveguide for a level measuring device operating with microwaves |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2314027A1 true CA2314027A1 (en) | 2001-01-15 |
Family
ID=8238594
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002314027A Abandoned CA2314027A1 (en) | 1999-07-15 | 2000-07-13 | Waveguide for a microwave fill-level measuring device |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1069649B1 (en) |
| JP (1) | JP3423674B2 (en) |
| CA (1) | CA2314027A1 (en) |
| DE (1) | DE59912561D1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3301413A1 (en) * | 2016-09-30 | 2018-04-04 | Rosemount Tank Radar AB | Guided wave radar level gauge system for interface measurement |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004104629A1 (en) * | 2003-05-23 | 2004-12-02 | Siemens Milltronics Process Instruments Inc. | Cable mechanism for a remote mounted radar-based level measurement system |
| DE102004033033A1 (en) | 2004-07-07 | 2006-02-09 | Vega Grieshaber Kg | Level measurement antenna arrangement for radar level gauges |
| DE102005042646A1 (en) * | 2005-09-07 | 2007-03-08 | Endress + Hauser Gmbh + Co. Kg | Device for detecting and monitoring the level of a medium in a container |
| DE102006003742A1 (en) * | 2006-01-25 | 2007-08-02 | Endress + Hauser Gmbh + Co. Kg | Device for determining and monitoring filling level of medium in tank, has dielectric filling body that comprises hermetically sealed recess volume in its inerior one, and antenna with antenna coupling-in region is also provided |
| DE102007061573A1 (en) | 2007-12-18 | 2009-06-25 | Endress + Hauser Gmbh + Co. Kg | Device for determining and / or monitoring at least one level of at least one medium in a container according to a travel time measurement method and / or a capacitive measurement method |
| EP2154495B1 (en) | 2008-08-15 | 2013-05-22 | Sick Ag | TDR sensor and measuring method |
| DE102010001273A1 (en) * | 2009-12-30 | 2011-07-07 | Endress + Hauser GmbH + Co. KG, 79689 | Device with coaxial construction |
| JP6059454B2 (en) * | 2012-06-22 | 2017-01-11 | 株式会社キーエンス | Liquid level measuring device |
| FR3013447B1 (en) * | 2013-11-15 | 2016-01-01 | Valeo Sys Controle Moteur Sas | DEVICE FOR MEASURING LIQUID LEVEL |
| TWI486560B (en) * | 2013-11-25 | 2015-06-01 | Finetek Co Ltd | Cable level temperature sensor |
| US11555731B2 (en) | 2017-11-14 | 2023-01-17 | Rochester Sensors, Llc | TDR transducer with boomerang waveguide |
| WO2019110103A1 (en) * | 2017-12-07 | 2019-06-13 | Vega Grieshaber Kg | Limit level sensor and method for operating same |
| EP3647745B1 (en) * | 2018-10-29 | 2023-07-05 | Rochester Sensors, LLC | Tdr transducer |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4240445A (en) * | 1978-10-23 | 1980-12-23 | University Of Utah | Electromagnetic energy coupler/receiver apparatus and method |
| US4503384A (en) * | 1982-04-28 | 1985-03-05 | General Motors Corporation | Microwave probe for measurement of dielectric constants |
| AU5510098A (en) * | 1996-11-22 | 1998-06-29 | Berwind Corporation | Material level sensing |
-
1999
- 1999-07-15 EP EP99113686A patent/EP1069649B1/en not_active Expired - Lifetime
- 1999-07-15 DE DE59912561T patent/DE59912561D1/en not_active Expired - Lifetime
-
2000
- 2000-07-12 JP JP2000211645A patent/JP3423674B2/en not_active Expired - Fee Related
- 2000-07-13 CA CA002314027A patent/CA2314027A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3301413A1 (en) * | 2016-09-30 | 2018-04-04 | Rosemount Tank Radar AB | Guided wave radar level gauge system for interface measurement |
| CN107884035A (en) * | 2016-09-30 | 2018-04-06 | 罗斯蒙特储罐雷达股份公司 | Radar level gauge system and the method for determining the interface material position in storage tank |
| US10184820B2 (en) | 2016-09-30 | 2019-01-22 | Rosemount Tank Radar Ab | Guided wave radar level gauge system for interface measurement |
Also Published As
| Publication number | Publication date |
|---|---|
| EP1069649B1 (en) | 2005-09-14 |
| JP3423674B2 (en) | 2003-07-07 |
| DE59912561D1 (en) | 2005-10-20 |
| JP2001066177A (en) | 2001-03-16 |
| EP1069649A1 (en) | 2001-01-17 |
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