Fill-level measuring device

Abstract

Disclosed is a fill-level measuring device for determining the fill level in a container. The device comprises: a radar module for determining a distance to the surface of the filling material; a 3D camera for capturing at least one region of the surface of the filling material; and an evaluation circuit that is designed to measure a maximum distance and a minimum distance from the captured distance values and to determine the fill level on the basis of the distance, providing that the distance is smaller than the maximum distance value and greater than the minimum distance value. As a result of the redundancy or the verification provided by the 3D camera of the distance calculated by the radar module, the fill-level measuring device according to the invention is therefore more reliable with regard to the miscalculation of an incorrect fill level.

Claims

1. A system for determining a fill level of a filling material located in a container, the system comprising: a radar module which is designed to emit a radar signal in the direction of the filling material and to determine a distance from a surface of the filling material on the basis of a reflected radar signal; a 3D camera which is designed to determine a plurality of distance values on the basis of a recording of at least one region of the surface of the filling material as a function of corresponding positions within the region; and an evaluation circuit configured to: determine a maximum distance value and a minimum distance value from the plurality of distance values; and determine the fill level using the distance when the distance is less than the maximum distance value and greater than the minimum distance value.

2. The fill-level measuring device according to claim 1, wherein the evaluation circuit is further configured to output a first warning signal when the distance determined by the radar module is less than the minimum distance value or greater than the maximum distance value.

3. The fill-level measuring device according to claim 2, wherein the evaluation circuit is further configured to output the first warning signal and/or a further warning signal when the minimum distance value is less than a corresponding value at a predefined maximum level.

4. The fill-level measuring device according to claim 2, wherein the evaluation circuit is further configured to: calculate a difference value by subtracting the minimum distance value from the maximum distance value; and output the first warning signal and/or a further warning signal when the difference value exceeds a predefined maximum range.

5. The fill-level measuring device according to claim 1, wherein the evaluation circuit is designed to determine a scatter from the plurality of distance values of a selected section of the region of the recording, and wherein the evaluation circuit is configured to determine a roughness of the surface of the filling material from the determined scatter.

6. The fill-level measuring device according to claim 1, wherein the radar module is designed to emit the radar signal at a frequency of at least 75 GHz.

7. The fill-level measuring device according to claim 1, wherein the radar module is designed to determine the distance from the surface of the filling material by the FMCW method or by the pulse propagation method.

8. The fill-level measuring device according to claim 1, wherein the 3D camera is designed to generate a grayscale image of the surface of the filling material in the region in which the 3D camera determines the plurality of distance values.

9. The fill-level measuring device according to claim 1, wherein the evaluation circuit is designed to detect a contour on the basis of the recording within the region if along the contour a discontinuity is detected between the distance values on the two sides of the contour.

10. The fill-level measuring device according to claim 9, wherein the evaluation circuit is designed to detect a movement and/or a displacement of the contour.

11. The fill-level measuring device according to claim 9, wherein the evaluation circuit is designed to determine an internal cross-section, including an internal cross-sectional area, of the container on the basis of the detected contour.

12. The fill-level measuring device according to claim 1, wherein the evaluation circuit is designed to determine an orientation of the fill-level measuring device with respect to a vertical, when a flat plane is determined on the basis of the recording within the region.

13. A method for determining a fill level of a filling material located in a container, the method comprising: providing a system for determining the fill level of the filling material located in the container, the system including: a radar module which is designed to emit a radar signal in the direction of the filling material and to determine a distance from a surface of the filling material on the basis of a reflected radar signal; a 3D camera which is designed to determine a plurality of distance values on the basis of a recording of at least one region of the surface of the filling material as a function of corresponding positions within the region; and an evaluation circuit configured to: determine a maximum distance value and a minimum distance value from the plurality of distance values; and determine the fill level using the distance when the distance is less than the maximum distance value and greater than the minimum distance value; determining a distance to the surface of the filling material on the basis of a reflected radar signal emitted by the radar module in the direction of the filling material; ascertaining a plurality of distance values on the basis of a recording of a 3D camera of at least one region of the surface of the filling material; determining a maximum distance value and a minimum distance value from the plurality of distance values by means of an evaluation circuit; and determining the fill level by means of the distance by the evaluation unit when the distance is less than the maximum distance value and greater than the minimum distance value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail with reference to the following figures. The following is shown:

(2) FIG. 1 shows a schematic representation of a fill-level measuring device according to the present disclosure on a container with a filling material,

(3) FIG. 2 shows a top view of the filling material from the perspective of the fill-level measuring device according to the present disclosure, and

(4) FIG. 3 shows different measured values depending on different measurement conditions.

DETAILED DESCRIPTION

(5) For understanding the invention, FIG. 1 shows an arrangement of the fill-level measuring device 1 according to the invention on a flanged connection of a container 2, as is generally customary for radar-based fill-level measuring devices. In the container 2 there is a filling material 3, whose level L is to be determined by the fill-level measuring device 1. For this purpose, the fill-level measuring device 1 is mounted on the container 2 at a known installation height h above the filling material 3. In this case, the container 2 can be more than 100 m high, depending on the type.

(6) The fill-level measuring device 1 is aligned and fastened to the container 2 in such a way that it continuously, cyclically or also acyclically emits a radar signal S.sub.R in the direction of the surface of the filling material 3, doing so by means of a radar module 11. As a result of the reflection of the radar signal S.sub.R at the filling material surface, the radar module 11 of the fill-level measuring device 1 receives the reflected radar signal S.sub.R as a function of the distance D.sub.R=h−L to the filling material surface after a corresponding running time.

(7) As a rule, the fill-level measuring device 1 is connected via an interface, such as “PROFIBUS”, “HART” or “Wireless HART”, to a higher-level unit 4, such as a process control system. In this way, the fill-level value L can be transmitted, for example in order to control the flow or discharge of the container 2 if necessary. However, other information about the general operating state of the fill-level measuring device 1 can also be communicated.

(8) If the radar module 11 operates by the pulse radar method, the radar signal S.sub.R will be radar pulses possibly periodically emitted, so that the distance D.sub.R and thus the fill level L can be determined directly on the basis of the pulse propagation time between emission of the pulse and the reflected pulse-shaped radar signal S.sub.R.

(9) In the case of FMCW radar, the radar signal S.sub.R is a continuous signal, but with a temporally defined modulated frequency. Accordingly, the propagation time and thus the distance D.sub.R or the fill level L when implementing the FMCW method can be determined on the basis of the instantaneous frequency difference between the currently received radar signal S.sub.R and the radar signal S.sub.R emitted at the same time. With both radar methods, it is possible according to the prior art to resolve the fill level L already with an accuracy in the sub-micron range under ideal conditions (well-reflecting filling material 3, flat filling material surface, no obstacles such as stirrers or other internals in the signal path of the radar signal S.sub.R). Even in the case of rough or wrinkled filling material surfaces or a dusty atmosphere, a reliable measurement of the fill level L at a point on the filling material surface is possible by means of the radar methods described above.

(10) However, periodic measurement of the fill level L by means of the radar methods described above comes up against its limits when the surface of the filling material 3 is not flat. This can occur in particular in the case of bulk material 3 of filling material, for example when bulk cones form during filling of the container 2. When the filling material 3 is being pumped out, depressions can occur on the filling material surface. Since the fill level is determined by means of the radar module 11 only periodically at a point on the surface of the filling material 3, this can lead to an erroneous interpretation of the fill level L. For example, an emptying operation can be stopped when an empty container 2 has been detected by the radar module 11 even though filling material 3 is still present at the edge of the container interior. In the opposite case, when the container 2 is full, it may happen that a filling operation is not stopped even though a maximum filling level L.sub.max at one location on the filling material surface has already been exceeded, because this was not detected by the radar module 11.

(11) According to the invention, the fill-level measuring device 1 shown in FIG. 1 therefore comprises a 3D camera 12 in addition to the radar module 11 for emitting and receiving the radar signal S.sub.R. Analogously to the radar module 11, the 3D camera 12 is arranged and oriented in such a way that a recording R.sub.3D can be recorded by means of the 3D camera 12 of the surface of the filling material 3 or at least of an area of the surface. In this case, as can be seen from the top view of the filling material surface in FIG. 2, the recording R.sub.3D is composed of a multiplicity of distance values d.sub.i,j as a function of corresponding pixels or positions [i, j] which are present within the recorded region [m; n].

(12) In principle, the additional determination of the distance values by the 3D camera increases the redundancy of the fill-level measuring device 1: The distance values can be compared to the distance D.sub.R determined by the radar module 11. For this purpose, the maximum distance value d.sub.max and the minimum distance value d.sub.min can be determined from the distance values of the 3D camera. If the distance D.sub.R is less than the maximum distance value of d.sub.max and greater than the minimum distance value of d.sub.min (shown in section (a) of FIG. 3), this can be interpreted as verification of the distance D.sub.R determined by the radar module. If the verification is unsuccessful, i.e. the distance D.sub.R determined by the radar module 11 is less than the minimum distance value of d.sub.min or greater than the maximum distance value of d.sub.max (shown in section (b) in FIG. 3), the fill-level measuring device 1 may for example output a first warning signal s.sub.f1 to the higher-level unit 4. The reason for this may be, for example, that the radar module is not receiving the radar signal S.sub.R, which is produced as echo from the filling material surface, but rather an unwanted echo such as, for example, a multiple reflection.

(13) This type of verification can be applied both to flat and non-flat filling material surfaces. In general, the ability to verify the ascertained fill level L represents an advantageous property of the fill-level measuring device 1 since it is potentially possible to meet one of the required specifications with regard to functional safety, for example, the IEC 61508 standard. In many applications, compliance with corresponding standards is in turn a precondition for permitting the fill-level measuring device 1 to be used for the corresponding application.

(14) In the fill-level measuring device 1 shown in FIG. 1, an evaluation circuit 13 is provided for verification of the distance D.sub.R and compares the distance values with the distance D.sub.R determined by the radar module 11 for this purpose. In this case, the evaluation circuit 13 can be realized, for example, as a microcontroller, in which the distance values and the distance D.sub.R can be retrieved from the radar module 11 or the 3D camera via corresponding inputs. On the output side, the evaluation circuit 13 can be connected to the higher-level unit 4 in order to transmit the corresponding first warning signal s.sub.f1, for example in the case of unsuccessful verification.

(15) In the recording R.sub.3D of the filling material surface shown in FIG. 2, a situation is shown in which the filling material surface is not flat, but has a bulk material cone (see also FIG. 1). The bulk material cone or the profile of the filling material surface is shown in the form of contour lines. Accordingly, the minimum distance d.sub.min detected by the 3D camera is located at the tip of the bulk material cone. In an alternative interpretation of FIG. 2, the contour lines of the filling material surface can also represent a depression funnel, so that the maximum distance d.sub.max ascertained by the 3D camera 12 represents the deepest point of the depression.

(16) Even in the case of a flat surface, for example in the case of liquid filling materials 2, advantageous synergy effects are possibly produced by the additional 3D camera 12: For example, the evaluation circuit 13 can be designed to determine the orientation of the fill-level measuring device 1 relative to the vertical. This can be calculated, for example, by mathematically defining a plane and determining its normal vector within the region of [m; n] of the recording R.sub.3D on the basis of the distance values d.sub.i,j. Since the resulting plane is horizontal for liquid fill materials 3, the normal vector corresponds to the vertical. Since an exactly vertical alignment of the radar module 11 is advantageous on account of the optimum reception of the reflected radar signal S.sub.R, the determination of the orientation relative to the vertical is appropriate above all during installation of the fill-level measuring device 1. For example, the current orientation of the vertical could be displayed during installation of the fill-level measuring device 1 on its display or on a display of a peripheral device.

(17) In addition to the pure verification of the determined distance D.sub.R, the recording R.sub.3D of the distance values d.sub.i,j offers further synergy effects: Further irregular states in the container 2 can be detected by further analysis of the distance values d.sub.i,j: with the aid of the difference value Δd between the maximum distance value of d.sub.max and the minimum distance value of drain and/or the absolute position of minimal distance value of d.sub.min and maximum distance value d.sub.max (with respect to the container height h) it can thus be concluded for example that there is a possible bulk material cone, a depression funnel or deposits of the filling material 3 on the wall of the container 2. In this case, a corresponding warning signal s.sub.f1, . . . , s.sub.fn can be generated, in particular when the difference value Δd over a predefined maximum range Δd.sub.max. (shown schematically in FIG. 3, section (c)) is exceeded. Furthermore, a gradient or inclination of the filling material surface between the locations of the two distance values d.sub.i,j corresponding to this could be calculated, for example on the basis of the difference value Δd, in order for example to be able to determine the taper of any bulk material cone.

(18) If the 3D camera is designed for this purpose, at least in those situations in which a warning signal s.sub.fn is output, it can additionally record a grayscale image of the region [m; n] of the filling material surface that can be provided for examining the particular situation (on the display of the fill-level measuring device 1 or for example also on a display of an external mobile radio device). FIG. 2 does not show that the recording R.sub.3D in FIG. 2 also encompasses the inner cross-section of the container 2. In such a case, the evaluation circuit 13 could be designed, for example, to determine the internal cross-section on the basis of the recording R.sub.3D. In this case, the internal cross-section as such can be detected in that the evaluation circuit within the recording R.sub.3D searches for a corresponding contour within the recording R.sub.3D. In this case, a “contour” is defined in that a predefined discontinuity, that is to say a “kink” or a jump, of the corresponding distance values d.sub.i,j between the two sides of the contour can be determined along the contour.

(19) In this connection, a jump between two distance values possibly separated by a contour, can be mathematically detected in the simplest case by the difference value of these distance values exceeding a predefined value. By contrast, the determination of a “kink” between two distance values between which the contour runs is less trivial: For this purpose, the distance values which in each case lie further outwardly in relation to the contour can also be included in such a way that the change or the “gradient” between them is to be calculated. In this case, an abrupt change in the slope between two distance values refers to the course of a contour between them. Corresponding analytical or numerical methods, which can be implemented in the evaluation circuit 13 for this purpose, are sufficiently known.

(20) If the internal cross-section of the container 2 is determined in this way, on the basis of this the internal cross-sectional area of the container 2 can be deduced. This in turn can be used to calculate the volume which the filling material 3 actually occupies in the container 2 on the basis of the determined distance values d.sub.i,j (or on the basis of the distance D.sub.R determined by the radar module 11 if the filling material 3 has a flat surface). This offers the advantage that, in the calculation of the volume, any change in the internal cross-section of the container 2 can also be taken into account with the height h. It goes without saying that this type of volume calculation can be applied not solely in the case of circular internal cross-sections, as shown in FIG. 2.

(21) When a contour is detected by the evaluation circuit 13, the contour can be assigned not solely to the inner cross-section of the container 2. If perturbations such as stirrers or inlets/outlets are present in the container 2 within the recording R.sub.3D, these can also appear as contours in the recording R.sub.3D. In the case of rotating agitators, a moving contour could be assigned correspondingly. In this way, for example, a distance value D.sub.R measured by radar module 11, which corresponds to distance values d.sub.i,j enclosed by the contour, can be classified as erroneous.

(22) If the evaluation circuit 13 can carry out a contour recognition, there is a further possible application in addition to the detection of disturbances and the determination of the container internal cross-section: When the fill-level measuring device 1 is attached to a round connection, such as for example a flange (see FIG. 1) a possibly detected contour can also be assigned to the flange opening. Those distance values d.sub.i,j which are assigned to the contour can serve to determine the distance D.sub.R by the radar module 11: The radar signal S.sub.R received after reflection, which has a time- and thus a distance-dependence both in the case of pulse radar and FMCW methods, can thus only be evaluated below the distance values d.sub.i,j corresponding to the flange in order to block out interfering components of the received radar signal S.sub.R from this region.