Patent Description:
Radar level gauge systems are in wide use for measuring filling levels in tanks. Radar level gauging is generally performed either by means of noncontact measurement, whereby electromagnetic signals are radiated towards the product contained in the tank, or by means of contact measurement, often referred to as guided wave radar (GWR), whereby electromagnetic signals are guided towards and into the product by a probe. The electromagnetic signals are reflected at the surface of the product, and the reflected signals are received by a receiver or transceiver comprised in the radar level gauge system. Based on the transmitted and reflected signals, the distance to the surface of the product can be determined.

More particularly, the distance to the surface of the product is generally determined based on the time between transmission of an electromagnetic signal and receipt of the reflection thereof in the interface between the atmosphere in the tank and the product contained therein. In order to determine the actual filling level of the product, the distance from a reference position to the surface is determined based on the above-mentioned time (the so-called time-of-flight) and the propagation velocity of the electromagnetic signals.

While measuring the filling level of a liquid product may be rather straight-forward, it is more challenging to evaluate a solid product, because the surface of the product may be non-flat and/or non-horizontal. Therefore, the highest level of the solid product may not be directly below the antenna of a radar level gauge system of the non-contacting type.

In view of this characteristic of solid products, it is known to scan the transmit signal from the transceiver of the radar level gauge system across the surface of the product, either by mechanically tilting the antenna of the radar level gauge, or by directing the emitted beam using phase array techniques. <CIT> describes examples of both of these scanning methods.

However, both of these basic scanning methods have drawbacks. Mechanical tilting of the antenna requires a relatively costly and bulky mechanical arrangement, and phase array techniques may make it difficult to transmit sufficient power to get a reliable evaluation result.

DE <NUM><NUM><NUM> A1 discloses a radar-based level measuring device with a first quasi-optical device, which is designed to adjust the focusing, the filtering, a beam offset and/or the beam path of the radar transmission signal towards the product in a variable manner. The quasi-optical device comprises a round holder that is rotatable about an axis, which can be rotated by a drive unit with a stepper motor, piezo-drive or an arrangement with a magnet and a spring according to the clockwork principle. Alternatively, the quasi-optical device may be displaced linearly.

<CIT> describes a radar beam deflection unit for a radar level indicator, wherein the different main emission directions of the antenna are generated using at least one prism which lies in the beam path of the level indicator and is rotated.

<CIT> describes a scanning radar system for e.g. a blast furnace, having a microwave reflector mounted to a rotatable material-directing chute, and a non-scanning antenna, wherein as the chute moves, the surface of the product is scanned.

<CIT> describes a fill level sensor using the radar principle, having a dielectric antenna with at least one supply element and at least one lens formed of a dielectric material. The dielectric antenna has an outer component and a spherical inner component that may be rotated, changing the main direction of radiation, thereby allowing for several measurements of different areas of the surface of the product.

In view of the above, a general object of the present invention is to provide for improved determination of a topographic property of a product, in particular a solid product.

According to a first aspect of the present invention, it is provided a radar level gauge system for determining a topographic property of a product, the radar level gauge system comprising a transceiver for generating, transmitting and receiving electromagnetic signals; a signal transfer element coupled to the transceiver and configured to emit an electromagnetic transmit signal from the transceiver in an emission direction; a propagating member arranged and configured to propagate the transmit signal towards the surface of the product, and to propagate a reflection signal resulting from reflection of the transmit signal at the surface of the product back towards the transceiver, the propagating member being movably arranged in relation to the signal transfer element and configured to deflect the transmit signal from the signal transfer element to a plurality of different propagation directions, each propagation direction corresponding to a position of the propagating member in relation to the signal transfer element in a plane perpendicular to the emission direction; an elastic system coupled to the signal transfer element and to the propagating member, and arranged to define at least one property of an oscillating movement of one of the propagating member and the signal transfer element in relation to the other one of the propagation member and the signal transfer element, the oscillating movement being restricted from taking place in the emission direction; an actuator arranged to initiate the oscillating movement and processing circuitry coupled to the transceiver and configured to determine the topographic property based on the transmit signal and the reflection signal.

The "transceiver" may be one functional unit capable of transmitting and receiving electromagnetic signals, or may be a system comprising separate transmitter and receiver units.

It should be noted that the processing circuitry may be provided as one device or several devices working together.

The present invention is based upon the realization that various topographic properties of a solid product can be determined without detailed knowledge about the scanning direction at all times.

The present inventors have further realized that such scanning with only limited control of the scanning direction can be achieved in a cost-efficient and compact manner, without significantly reducing the transmitted power, by providing a propagating member that can redirect the transmit signal depending on the relative positioning of the propagating member and the signal transfer element, and providing for an oscillating relative movement between the signal transfer element and the propagating member.

Hereby, predictable scanning of the surface of the product can be achieved by simple and cost-efficient means. The scanning pattern across the surface of the product can be determined by selection of the properties of the elastic system. In embodiments, the elastic system may be configured to allow tuning of its properties, providing for tuning of the scanning pattern.

To prevent changes in in the beam shape of the transmit signal, the oscillating movement of the propagating member in relation to the signal transfer element is advantageously restricted from taking place in the emission direction, so that the oscillating movement can substantially only take place in a plane perpendicular to the emission direction.

In embodiments where a two-dimensional scanning pattern is desired, the elastic system may define a first eigenfrequency of a first component of the oscillating movement and a second eigenfrequency, different from the first eigenfrequency, of a second component of the oscillating movement.

According to a second aspect of the present invention, it is provided a method of determining a topographic property of a product using a radar level gauge system comprising a transceiver; a signal transfer element coupled to the transceiver; a propagating member movably arranged in relation to the signal transfer element and configured to deflect an electromagnetic signal from the signal transfer element depending on a position of the propagating member in relation to the signal transfer element; an elastic system coupled to the signal transfer element and to the propagating member; an actuator; and processing circuitry coupled to the transceiver, the method comprising: generating, by the transceiver, an electromagnetic transmit signal; emitting, by the signal transfer element, the transmit signal in an emission direction; propagating, by the propagating member, the transmit signal towards a surface of the product; propagating, by the propagating member, a reflection signal resulting from reflection of the transmit signal at the surface of the product, back towards the transceiver; receiving, by the transceiver, the reflection signal; oscillating, by the elastic system and the actuator, one of the propagating member and the signal transfer element in relation to the other one of the propagating member and the signal transfer element in a plane perpendicular to the emission direction, the oscillating movement being restricted from taking place in the emission direction, while the transmit signal is propagated towards the surface of the product and the reflection signal is propagated back towards the transceiver; and determining, by the processing circuitry, the topographic property of the product based on a timing relation between the transmit signal and the reflection signal.

In summary, the present invention thus relates to a radar level gauge system for determining a topographic property of a product, comprising a transceiver; a signal transfer element coupled to the transceiver and configured to emit an electromagnetic transmit signal from the transceiver in an emission direction; a propagating member for propagating the transmit signal towards the surface of the product and a reflection signal back towards the transceiver, the propagating member being movably arranged in relation to the signal transfer element and configured to deflect the transmit signal; an elastic system coupled to the signal transfer element and to the propagating member, and arranged to define at least one property of an oscillating movement of the propagating member in relation to the signal transfer element; an actuator arranged to initiate the oscillating movement; and processing circuitry coupled to the transceiver for determining the topographic property based on the transmit signal and the reflection signal.

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing a currently preferred embodiment of the invention, wherein:.

<FIG> schematically illustrates a radar level gauge system <NUM> according to an example embodiment of the present invention installed at a tank <NUM> containing a solid product <NUM>. As is schematically indicated in <FIG>, the solid product <NUM> has a non-flat surface topography, and the radar level gauge system <NUM> is configured to determine a topographic property of the product <NUM>, which may, for example, be a maximum, minimum or average level of the product <NUM>.

To this end, the radar level gauge system <NUM> according to embodiments of the present invention is controllable to deflect the transmit signal ST to hit different locations <NUM> on the surface of the product <NUM>. As is schematically indicated in <FIG>, a reflection signal SR resulting from reflection of the transmit signal ST at the surface of the product <NUM> is returned to the radar level gauge system <NUM>. This allows the radar level gauge system <NUM> to determine the distance to different positions on the surface of the product, which in turn allows determination of the above-mentioned topographic property.

Referring now to <FIG>, which is a schematic block-diagram of the radar level gauge system <NUM> in <FIG>, the radar level gauge system <NUM> comprises a transceiver <NUM>, a signal transfer element <NUM>, a propagation member <NUM>, an elastic system <NUM>, an actuator <NUM>, processing circuitry <NUM>, and a communication interface <NUM>.

The transceiver <NUM> is configured to generate, transmit and receive electromagnetic signals, advantageously microwave signals, in a, per se, known manner. As will be well-known to one of ordinary skill in the relevant art, the transceiver may, for example, operate using pulsed signals and/or a frequency sweep.

The signal transfer element <NUM> is coupled to the transceiver <NUM> and configured to emit the above-mentioned transmit signal ST in an emission direction <NUM>. The signal transfer element <NUM> may also capture the reflection signal SR and provide the reflection signal SR to the transceiver <NUM>.

The propagating member <NUM> is arranged and configured to propagate the transmit signal ST towards the surface of the product <NUM> and to propagate the reflection signal SR back towards the transceiver <NUM>, via the signal transfer element <NUM>. The propagating member <NUM> is movably arranged in relation to the signal transfer element <NUM>, and is configured to deflect the transmit signal ST from the signal transfer element <NUM> to a plurality of different propagation directions, each propagation direction corresponding to a position of the propagating member <NUM> in relation to the signal transfer element <NUM> in a plane perpendicular to the emission direction <NUM>.

The elastic system <NUM> is coupled to the signal transfer element <NUM> and to the propagating member <NUM>, and is arranged to define at least one property of an oscillating movement of the propagating member <NUM> in relation to the signal transfer element <NUM>.

In this context, it should be noted that movement of the propagating member <NUM> in relation to the signal transfer element <NUM> includes movement of one or both of the propagating member <NUM> and the signal transfer element <NUM>, as long as there is relative movement therebetween.

The actuator <NUM> is arranged to at least initiate the oscillating relative movement, between the propagating member <NUM> and the signal transfer element <NUM>.

The processing circuitry <NUM> is coupled to the transceiver <NUM> and configured to determine the above-mentioned topographic property of the product <NUM> based on the transmit signal ST and the reflection signal SR. In particular, the topographic property may be determined based on a series of timing relations between the transmit signal ST and the reflection signal SR while the above-mentioned relative oscillating movement is taking place, so that the transmit signal ST is deflected in different directions. A distance between a reference position at the radar level gauge system and the surface of the product <NUM> may then be determined for the different locations <NUM> on the surface of the product <NUM> mentioned above with reference to <FIG>.

The communication from/to the radar level gauge system <NUM> via the communication interface <NUM> may be wireless communication, or may take place over an analog and/or digital wire-based communication channel. For instance, the communication channel may be a two-wire <NUM>-<NUM> mA loop and signals indicative of distances to the different locations <NUM> on the surface of the product <NUM> may be communicated by providing a currents corresponding to the distances on the two-wire <NUM>-<NUM> mA loop. Digital data may also be sent across such a <NUM>-<NUM> mA loop, using the HART protocol. Furthermore, pure digital communication protocols such as Modbus or Foundation Fieldbus may be used.

A first example embodiment of the radar level gauge system <NUM> in <FIG> will now be described with reference to <FIG>.

<FIG> is a schematic partial view of the radar level gauge system <NUM> facing the product <NUM> as seen along the emission direction <NUM>. In the partly structural and partly conceptual illustration in <FIG>, the transceiver <NUM> is realized as a microwave IC mounted on a carrier structure <NUM> in the form of a microwave circuit board, and the signal transfer element <NUM> comprises a patch formed in the carrier structure <NUM> and connected to a signal output (not shown) of the transceiver <NUM>. The propagating member <NUM> is, in this example configuration, provided in the form of a microwave lens which at least partly has an ellipsoid shape.

In <FIG>, the elastic system is conceptually indicated as comprising a first spring element <NUM> and a second spring element <NUM>. The first spring element <NUM> defines a first eigenfrequency ω<NUM> of a first component of the oscillating movement of the propagating member <NUM> in relation to the signal transfer element <NUM> in a first direction (the x-direction in <FIG>), and the second spring element <NUM> defines a second eigenfrequency ω<NUM> of a second component of the oscillating movement of the propagating member <NUM> in relation to the signal transfer element <NUM> in a second direction (the y-direction in <FIG>). Any elastic system for which the oscillating movement is restricted to a plane (the xy-plane) perpendicular to the emission direction <NUM> can be functionally represented by the first spring element <NUM> and the second spring element <NUM> in <FIG>.

In the example configuration in <FIG>, the actuator <NUM> is indicated as a controllable actuator that is coupled between the carrier structure <NUM> and the propagating member <NUM>. It should be noted that the actuator <NUM> does not have to be coupled to both the carrier structure <NUM> and the propagating member <NUM> to initiate the oscillating movement, but that the actuator <NUM> could, for example, be coupled to the carrier structure <NUM> and arranged and controllable to provide impulses to the propagating member <NUM>. Furthermore, the actuator <NUM> could alternatively be coupled between the elastic system <NUM> and a stationary structure, such as the carrier structure <NUM> in <FIG>.

<FIG> is a simplified side view of the radar level gauge system <NUM> in <FIG> that is mainly intended to illustrate an example configuration and arrangement of the propagating member <NUM> in relation to the signal transfer element <NUM>. In this example configuration and arrangement, the propagating member <NUM> is an ellipsoidal microwave lens with a first focal point <NUM> and a second focal point <NUM>. As is schematically illustrated in <FIG>, the signal transfer element <NUM> is arranged in the first focal point <NUM>, in the absence of the above-described relative oscillating movement.

As mentioned above, the relative oscillating movement will result in deflection, in this case through refraction, of the transmit signal ST (and the reflection signal SR). <FIG> shows the propagating member <NUM> being displaced to the left (and/or the signal transfer element <NUM> being displaced to the right) as compared to the situation in <FIG>, resulting in deflection of the transmit signal ST to the left in relation to the emission direction <NUM>, so that a different location <NUM> on the surface of the product <NUM> is hit by the transmit signal ST. <FIG> shows the propagating member <NUM> being displaced to the right (and/or the signal transfer element <NUM> being displaced to the left) as compared to the situation in <FIG>, resulting in deflection of the transmit signal ST to the right in relation to the emission direction <NUM>, so that a different location <NUM> on the surface of the product <NUM> is hit by the transmit signal ST.

<FIG> schematically illustrate different example configurations of the elastic system <NUM> coupled to the signal transfer element <NUM> and to the propagating member <NUM> in the first example embodiment of the radar level gauge system <NUM> described above. <FIG> are views of the radar level gauge system <NUM> as seen along the emission direction <NUM> from the product <NUM> side.

In the first example configuration in <FIG>, the elastic system <NUM> comprises a spring wire <NUM>, that is coupled to the carrier structure <NUM> and to the propagating member <NUM>. The spring wire <NUM> is configured to define a first eigenfrequency ω<NUM> of a first component of the oscillating movement of the propagating member <NUM> in relation to the signal transfer element <NUM> in a first direction (the x-direction), and a second eigenfrequency ω<NUM> of a second component of the oscillating movement of the propagating member <NUM> in relation to the signal transfer element <NUM> in a second direction (the y-direction). The oscillating movement is restricted to the xy-plane by the configuration of the spring wire <NUM> and/or by a restricting structure (not shown in <FIG>).

To illustrate one of many possible alternatives to the spring wire <NUM> in <FIG> shows that the elastic system <NUM> instead comprises a sheet metal structure <NUM> that has been shaped to provide the desired properties of the oscillating movement.

<FIG> schematically show a radar level gauge system <NUM> according to a second example embodiment of the present invention, where the propagating member <NUM> comprises a parabolic reflector. The parabolic reflector has a focal point, and the elastic system is configured in such a way that the signal transfer element <NUM> is arranged in the focal point in the absence of the relative oscillating movement, when the system is at rest.

Also for this embodiment of the radar level gauge system <NUM>, the relative oscillating movement will result in deflection, in this case through reflection, of the transmit signal ST (and the reflection signal SR). <FIG> shows the signal transfer element <NUM> being displaced to the left, resulting in deflection of the transmit signal ST to the right in relation to the emission direction <NUM>, so that a different location <NUM> on the surface of the product <NUM> is hit by the transmit signal ST. <FIG> shows the signal transfer element <NUM> being displaced to the right, resulting in deflection of the transmit signal ST to the left in relation to the emission direction <NUM>, so that a different location <NUM> on the surface of the product <NUM> is hit by the transmit signal ST.

Although it is indicated in <FIG> that the signal transfer element <NUM> is being displaced, it could be possible to instead displace the propagation member <NUM>, or both the signal transfer element <NUM> and the propagation member <NUM>.

To get a desired coverage of the surface of the product <NUM>, it may be desirable to configure the elastic system <NUM> to define different first ω<NUM> and second ω<NUM> eigenfrequencies. <FIG> are simulations of scanning patterns obtainable for different configurations of the elastic system <NUM> comprised in the radar level gauge system <NUM> according to embodiments of the present invention. In <FIG>, the ratio between the first ω<NUM> and second ω<NUM> eigenfrequencies is <NUM>, in <FIG>, the ratio is <NUM>, and in <FIG>, the ratio is <NUM>.

Claim 1:
A radar level gauge system (<NUM>) for determining a topographic property of a product (<NUM>), the radar level gauge system comprising:
a transceiver (<NUM>) for generating, transmitting and receiving electromagnetic signals;
a signal transfer element (<NUM>) coupled to the transceiver and configured to emit an electromagnetic transmit signal from the transceiver in an emission direction (<NUM>);
a propagating member (<NUM>) arranged and configured to propagate the transmit signal towards the surface of the product, and to propagate a reflection signal resulting from reflection of the transmit signal at the surface of the product back towards the transceiver, the propagating member (<NUM>) being movably arranged in relation to the signal transfer element (<NUM>) and configured to deflect the transmit signal from the signal transfer element to a plurality of different propagation directions, each propagation direction corresponding to a position of the propagating member in relation to the signal transfer element in a plane perpendicular to the emission direction;
an elastic system (<NUM>) coupled to the signal transfer element and to the propagating member, and arranged to define at least one property of an oscillating movement of one of the propagating member and the signal transfer element in relation to the other one of the propagating member and the signal transfer element, the oscillating movement being restricted from taking place in the emission direction (<NUM>);
an actuator (<NUM>) arranged to initiate the oscillating movement; and
processing circuitry (<NUM>) coupled to the transceiver (<NUM>) and configured to determine the topographic property based on the transmit signal and the reflection signal.