News Column

Patent Issued for Potential Separation for Filling Level Radar

May 14, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Fehrenbach, Josef (Haslach, DE); Schultheiss, Daniel (Hornberg, DE); Griessbaum, Karl (Muehlenbach, DE), filed on December 17, 2009, was published online on April 29, 2014.

The assignee for this patent, patent number 8711049, is Vega Grieshaber KG (Wolfach, DE).

Reporters obtained the following quote from the background information supplied by the inventors: "For reasons relating to measuring technology and for reasons of safety the potential of the electrical supply line of a radar sensor should be separate from the potential of the filling level container, which is often made of metal. This can for example lead to a reduction in the noise effects in measuring, and to a reduction in the susceptibility to interference of the measuring signals. Furthermore, such insulation leads to improved safety, for example in relation to the avoidance of fires that can occur as a result of a short circuit or a defect in the electrical supply or in the electronics of the filling level radar. Undesired spark-over could, for example, lead to ignition or damage of the contents.

"WO 2005/038414 relates to a method and a device to insulate a filling level radar. In this arrangement the electrical insulator is arranged so as to be transverse in relation to an open end of a waveguide. The other end of the waveguide feeds the aerial. In this arrangement the insulator extends continuously over the entire cross section of the waveguide."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "According to an exemplary embodiment of the present invention, a filling level radar for determining a filling level in a tank is provided, the filling level radar comprising a first waveguide and a second waveguide. Between the two waveguides a separation element is positioned which is adapted for galvanically, i.e. electrically insulating the first waveguide from the second waveguide. The separation element comprises a tubular section coaxially aligned with the first waveguide and the second waveguide.

"The tubular section has a longitudinal axis which is identical to the longitudinal axis of the first and second waveguides and serves as a creepage path.

"According to another exemplary embodiment of the present invention, the tubular section of the separation element has an axial length which is about four times larger than a thickness of the separation element. For example, the axial length of the tubular section is about 2 mm and the thickness of the separation element is, at least in most regions of the separation element, about 0.5 mm.

"According to another exemplary embodiment of the present invention, the first waveguide has a first inner diameter, the second waveguide has a second inner diameter and the tubular section of the separation element has a third inner diameter which is smaller than the first in a diameter and the second in a diameter.

"According to another exemplary embodiment of the present invention, the separation element is adapted for being inserted into the second waveguide, wherein the separation element comprises a nose section and wherein the second waveguide comprises a groove section. The nose section engages the groove section when the separation element is inserted into the second waveguide thus forming a releasable connection between the separation element and the second waveguide after insertion.

"Furthermore, according to another exemplary embodiment of the present invention, an antenna for a filling level meter for transmitting or receiving electromagnetic waves is provided. The antenna comprises a second waveguide and a separation element to connect the second waveguide to an external first waveguide of the filling level meter and to insulate the second waveguide from the first waveguide galvanically, i.e. electrically. Furthermore, the separation element comprises a tubular section coaxially aligned with the first waveguide and the second waveguide.

"According to another embodiment of the present invention a filling level radar with potential separation to determine a filling level in a tank is stated, the filling level radar comprising an antenna for transmitting and/or receiving electromagnetic waves, a feed device for feeding the electromagnetic waves to the antenna, and a separation element for insulating the feed device from the antenna, wherein the separation element comprises a recess in longitudinal direction of the feed device, and wherein the separation element comprises a region of overlap for overlapping in longitudinal direction at least the feed device or the antenna.

"By designing the separation element with a recess in longitudinal direction of the feed device, for example unimpeded or uninfluenced propagation of the electromagnetic waves within the feed device, and from the feed device to the antenna (and back), may be ensured. In the case of a feed device with round cross section the separation element may for example be ring shaped, while in the case of a feed device with rectangular cross section the separation element may be rectangular (with a rectangular recess that corresponds to the inner circumference of the feed device in longitudinal direction (i.e. in the direction of propagation of the waves).

"According to a further embodiment of the present invention the feed device comprises a first waveguide and a radiation source, wherein the radiation source is designed to generate the electromagnetic waves, and wherein the first waveguide is designed to guide the electromagnetic waves from the radiation source to the antenna.

"According to a further embodiment of the present invention the filling level radar further comprises a second waveguide that is connected to the antenna, wherein the separation element is arranged between the first waveguide and the second waveguide.

"According to this embodiment of the present invention insulation is provided between a first waveguide and a second waveguide. In this way the antenna may be insulated from the first waveguide; however, when viewed locally, such insulation is not in place directly between the first waveguide and the antenna, but instead at a distance from the antenna, namely between the first waveguide and a second waveguide that is connected to the antenna.

"According to a further embodiment of the present invention a connection between the separation element and the feed device, or between the separation element and the second waveguide, or (for example if there is no second waveguide) between the separation element and the antenna, is designed such that the feed device is rotatably held relative to the antenna.

"In this way it is for example possible to provide rotatability between the sensor housing with installed circuit and the antenna subassembly. This improves the flexibility of the filling level radar because changing environmental conditions or installation conditions can often require other sensor housing positions.

"Furthermore, depending on interfering installations in containers, e.g. baffles, which also generate reflections apart from those of the contents' surface, and which thus make measuring more difficult, it may be advantageous that the polarisation of the electromagnetic wave that is transmitted by the antenna can be rotated. By means of such polarisation rotation, certain interfering reflections may be minimised so that in this way measuring of the contents becomes more reliable and more accurate. If merely the complete filling level sensor is rotated in its installed position, in the case of sensors with flange attachments this would mean that all installation screws of the flange would have to be undone, and in accordance with the hole division of the flange said flange would have to be rotated for example in 90.degree. or 60.degree. steps. This does not support any fine adjustment of the polarisation beyond the incremental steps predefined by the hole division.

"In the case of sensors with a screw thread, the polarisation rotation has to take place by corresponding rotation of the screw thread, which while it is possible at the required fine adjustment, can however pose problems in relation to the sealing function of the thread.

"By means of the rotatability between the separation element and the feed device, or between the separation element and the antenna, which rotatability has been proposed in the present invention, polarisation rotation may take place without the need for rotating the antenna, which normally establishes a firm mechanical connection with the flange or the screw thread. With the position of the flange attachment or of the screw thread unchanged, the polarisation by rotation of the feed device, if need be coupled with the sensor housing, may be rotated at the desired fine adjustment, without installation effort and without impeding the tightness of the container.

"According to a further embodiment of the present invention the cross section of the first waveguide differs from that of the second waveguide.

"In this way it is for example possible for the separation element to make possible expansion of the diameter of the waveguide in that the separation element, for example, bridges the difference between the diameter of the first waveguide and the diameter of the second waveguide.

"According to a further embodiment of the present invention the filling level radar further comprises a cross-section adaptor between the first waveguide and the second waveguide or the antenna in the region of the separation element, wherein the first waveguide in relation to the frequency of the signals to be transmitted is monomode-dimensioned, and wherein the second waveguide or the antenna is multimode-capable. This characteristic directly results from the ratio of waveguide diameter to wavelength of the transmitted microwave signals. In this arrangement the cross-section adaptor is dimensioned in such a way that in the second waveguide or in the antenna it generates no higher modes or only insignificantly higher modes than the fundamental mode.

"According to this embodiment of the present invention the insulation of the first waveguide of the antenna or of a second waveguide can be combined with a cross-section adapter.

"In this way it may for example be possible to reduce the sensitivity to condensate droplets as a result of the comparatively large diameter of the second waveguide or of the antenna, while in spite of multimode capability of the second waveguide or of the antenna no echoes that falsify the measuring signals occur any longer while at the same time insulation between the first waveguide and the antenna is ensured.

"According to a further embodiment of the present invention the cross-section adapter and the separation element are designed in the form of a tight connection between the first waveguide and the second waveguide or between the first waveguide and the antenna.

"In this way materials conveyance between a tank on the side of the antenna and the outside environment on the side of the waveguide may be prevented. Thus, it may for example be possible to avoid corrosion or other damage or destruction of the filling level radar above the antenna or above the second waveguide. Furthermore, in this way any unwanted feed-in of solid, liquid or gaseous materials into the tank may be prevented.

"According to a further embodiment of the present invention the antenna is designed as a horn antenna, parabolic antenna or bar antenna. In this way it is possible to separate different antennae from the potential of the first waveguide.

"According to a further embodiment of the present invention the waveguide is designed as a round waveguide or a rectangular waveguide.

"According to a further embodiment of the present invention a region of overlap is provided between the first waveguide and the second waveguide and/or the antenna, wherein the first waveguide is insulated from the second waveguide and/or from the antenna in the region of overlap by means of the separation element. The first waveguide is designed to transmit a signal with a wavelength of .lamda., while the length of the region of overlap is .lamda./4 in longitudinal direction.

"The above is used for electrically matching the transition region in which potential separation takes place. Normally, interrupting the metal wall of the waveguide unfavourably affects the high-frequency characteristics of the waveguide. By means of a so-called .lamda./4-transformer mutual impedance matching of the two separate waveguides can be improved. An open-circuited stub line with a length of .lamda./4 transforms a short circuit to its input. The region of overlap with the separation element that is arranged in between acts as such an open-circuited stub line. The open circuit in the direction of the outer jacket of the waveguide is transformed as a short circuit into the region of the inner jacket of the waveguide. The high-frequency-like short circuit at this direct-voltage-like nonconducting seam position favours onward transmission of the microwaves, thus causing a reduction in interfering reflections.

"According to a further embodiment of the present invention the connection between the separation element and the feed device, or between the separation element and the second waveguide, or (if there is no second waveguide) between the separation element and the antenna, is constructed in the form of a plug-type connection so that the feed device can be unplugged from the antenna or from the second waveguide.

"By designing the arrangement with a disconnectable connection, through which the entire top part of the filling level radar can be unplugged from the antenna or from the lower (second) waveguide, the electronics together with the first waveguide may in a simple manner be deinstalled, i.e. replaced. This may improve the flexibility of the arrangement, in particular in the case of repair or maintenance.

"According to a further embodiment of the present invention the separation element is designed for electrically insulating the feed device from the antenna. For example, the separation element is dimensioned such that adequate electrical insulation up to a specified maximum voltage is ensured.

"Furthermore, according to another embodiment of the present invention, the separation element is designed to thermally insulate the feed device from the antenna. This can in particular, for example, be advantageous if the thermal conditions in the interior of the tank are to be kept constant and are to be insulated against thermal influences from the outside.

"Likewise, in the case where the temperatures in the container are extreme it may be advantageous to largely keep these temperatures away from the electronics so as not to risk influencing the function, or even failure of the electronics as a result of such temperatures.

"For the purpose of electrical insulation the separation element may comprise a dielectric.

"According to a further embodiment of the present invention the separation element is designed as a dielectric barrier that comprises a layer of rigid dielectric material.

"According to a further embodiment of the present invention an antenna for transmitting and/or receiving electromagnetic waves is stated, wherein the antenna comprises a separation element to insulate the antenna from a feed device, wherein the feed device is designed to feed the electromagnetic waves to the antenna, and wherein the separation element comprises a recess in longitudinal direction of the waveguide.

"Such an antenna may be used as a modular component for a filling level radar, wherein insulation between the antenna and the electronics is ensured.

"According to a further embodiment of the present invention the feed device comprises a first waveguide and a radiation source, wherein the radiation source is designed to generate the electromagnetic waves, and wherein the first waveguide is designed to guide the electromagnetic waves from the radiation source to the antenna.

"According to a further embodiment of the present invention a method for potential separation for a filling level radar is provided, wherein feeding electromagnetic waves to an antenna takes place by way of a feed device. Furthermore, the electromagnetic waves are transmitted and/or received by an antenna. Moreover, the feed device is insulated from the antenna by means of a separation element, wherein the separation element comprises a recess in longitudinal direction of the feed device.

"In this way a method may be provided by which potential separation between, on the one hand, an (upper) feed device and electronics that are connected to said feed device, and, on the other hand, to a (lower) antenna is made possible, wherein the insulation has no influence on the signal line.

"According to a further embodiment of the present invention the electromagnetic waves are guided by a first waveguide of the feed device and a second waveguide, which is connected to the antenna, wherein the separation element is arranged between the first waveguide and the second waveguide.

"In this way insulation of the first waveguide from the second waveguide may be achieved. In this arrangement the insulation may not depend on the antenna.

"Further embodiments of the present invention are disclosed in the subordinate claims."

For more information, see this patent: Fehrenbach, Josef; Schultheiss, Daniel; Griessbaum, Karl. Potential Separation for Filling Level Radar. U.S. Patent Number 8711049, filed December 17, 2009, and published online on April 29, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=64&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=3171&f=G&l=50&co1=AND&d=PTXT&s1=20140429.PD.&OS=ISD/20140429&RS=ISD/20140429

Keywords for this news article include: Electronics, Vega Grieshaber KG, Electrical Insulation.

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Source: Electronics Newsweekly