METHOD FOR DETERMINING THE FILL LEVEL OF A FILLING MATERIAL IN A CONTAINER

Abstract

The present disclosure relates to a method for safe and exact ascertaining of fill level of a fill substance located in a container by means of an ultrasonic, or radar-based, fill level measuring device. In such case, the method is distinguished by the feature that the evaluation curve created based on the reflected received signal is differently greatly smoothed as a function of measured distance. To achieve this, the evaluation curve can be specially filtered, depending on the application. In this way, noise fractions and disturbance echoes can be efficiently suppressed, without unnecessarily limiting the accuracy of the fill level measurement.

Claims

1-8. (canceled)

9. A method for ascertaining fill level of a fill substance located in a container using a fill level measuring device, the method comprising: transmitting a transmitted signal in a direction of the fill substance; receiving a received signal that is dependent on a measured distance; creating an evaluation curve based at least on the received signal; smoothing the evaluation curve using at least one filtering method; and determining the fill level based on the smoothed evaluation curve, wherein the evaluation curve is differently greatly smoothed as a function of measured distance.

10. The method as claimed in claim 9, wherein the transmitted signal is an ultrasonic signal.

11. The method as claimed in claim 9, wherein the transmitted signal is a radar signal transmitted according to the Frequency Modulated Continuous Wave (FMCW) method or according to the pulse travel time method.

12. The method as claimed in claim 9, wherein the at least one filtering method is a low-pass filtering, an average value filtering, a moving average value filtering, a maximum value filtering, and/or a moving maximum value filtering.

13. The method as claimed in claim 9, wherein in at least one portion of the measured distance, a filtering method is implemented which differs from a filtering method in an adjoining portion.

14. The method as claimed in claim 12, for the case in which an average value filtering and/or a maximum value filtering are/is applied as a filtering method, the average value filter and/or the maximum value filter is designed with a window width, which changes as a function of measured distance.

15. The method as claimed in claim 14, wherein the window width is changed linearly or non-linearly, including exponentially and/or logarithmically, with the measured distance, and/or wherein the window width is set to be constant in at least two different portions of the measured distance with mutually differing widths.

16. The method as claimed in claim 9, wherein the measured distance is divided into a near region, a middle region, and a far region, wherein the smoothing in the near region and in the far region is set lower compared with the middle region.

17. A fill level measuring device, comprising: a transmitting unit, which is designed to transmit a transmitted signal; a receiving unit, which is embodied to receive a received signal; and an evaluation unit, wherein the evaluation unit is designed: based at least the received signal, to create an evaluation curve; to smooth the evaluation curve differently as a function of measured distance; and based on the smoothed evaluation curve, to determine a fill level.

Description

[0028] The invention will now be explained based on the appended drawing, the figures of which show as follows:

[0029] FIG. 1 a typical arrangement of a fill level measuring device,

[0030] FIG. 2 an unsmoothed evaluation curve, as well as an evaluation curve smoothed by maximum value filtering, and

[0031] FIG. 3 different variants for smoothing the evaluation curve as a function of measured distance.

[0032] For providing a general understanding of the invention, FIG. 1 shows a typical arrangement of an ultrasonic, or radar-based, fill level measuring device 1 on a container 2. Located in the container 2 is a fill substance 3, whose fill level L is to be determined by the fill level measuring device 1. In this regard, the fill level measuring device 1 is placed on the container 2 at a known installed height h above the container floor. In such case, the container 2 can, depending on application, be more than 100 m tall. Independently of the implemented measuring principle (ultrasound, pulse radar, FMCW), the fill level measuring device 1 includes as basic functional blocks: [0033] a transmitting unit (for ultrasound, for example, a correspondingly operated piezo element; in the case of radar above 70 GHz, for example, a semiconductor-based, primary radiator), which is designed to transmit the sent, or transmitted, signal S.sub.HF, [0034] a receiving unit for receiving the corresponding, received signal R.sub.HF, and [0035] an evaluation unit, which is designed based on the received signal R.sub.HF to create and to smooth an evaluation curve, and based on that to determine the fill level L.

[0036] As a rule, fill level measuring device 1 is connected via a bus system, for instance, a “PROFIBUS”, “HART” or “wireless HART” bus system, to a superordinate unit 4, for example, a process control system. In this way, on the one hand, information concerning the operating state of the fill level measuring device 1 can be communicated. Also information concerning fill level L can be transmitted, in order, in given cases, to control flows incoming to the container 2.

[0037] As evident from FIG. 1, the fill level measuring device 1 is so arranged on the container 2 that it transmits radar- or ultrasonically based, transmitted signals S.sub.HF in the direction of the surface of the fill substance 3. After reflection on the fill substance surface, the fill level measuring device 1 receives the reflected received signals R.sub.HF after a travel time t. In such case, the travel time t depends on the measured distance d, i.e. the distance h-L to the fill substance surface.

[0038] For ascertaining the fill level L, the received signal R.sub.HF is registered in the form of an evaluation curve A(d). To the extent that the fill level measuring device 1 works based on ultrasound, the evaluation curve A(d) corresponds directly to the amplitude curve of the received signal R.sub.HF as a function of time (and, thus, as a function of the measured distance d). In the case of the pulse radar principle, the evaluation curve A(d) is, due to the high pulse frequency of the fill level measuring device 1, as a rule, created by undersampling the received signal R.sub.HF. To the extent that the FMCW method is implemented in the fill level measuring device 1, the evaluation curve is created by mixing the transmitted signal S.sub.HF with the received signal R.sub.HF. As shown in FIG. 2, the end result is that the evaluation curve A(d) provides the amplitude of the received signal as a function of measured distance, independently of the implemented measuring principle.

[0039] FIG. 1 shows schematically that the fill substance 3 is present in the form of a bulk good with a corresponding bulk-good cone. Accordingly, the corresponding evaluation curve A(d) shown in FIG. 2 is quite noisy. From the unfiltered evaluation curve A(d) it is, consequently, under these conditions not possible with sufficient safety correctly to figure out that amplitude maximum of the evaluation curve A(d), which was brought about by reflection of the transmitted signal S.sub.HF on the fill substance surface. For this reason, a filter-based smoothing of the evaluation curve A(d) is, as a rule, required for determining the fill level L. FIG. 2 shows, thus, supplementally, the evaluation curve A(d) smoothed per maximum value filtering and following average value formation. In comparison with a low-pass filtering, this offers the advantage that no loss, or no lessening, of amplitude is effected thereby.

[0040] As can be seen in FIG. 2, there results from the maximum value filtering a curve, which roughly follows the local maxima of the unfiltered evaluation curve A(d). In such case, the more the filtering (which means, in such case, the greater the window width, over which the maximum values are averaged), the greater small local maxima are masked out.

[0041] FIG. 2 shows, moreover, that, based on the smoothed evaluation curve A(d), the fill level L can be associated with a local maximum. A very highly accurate determining of the fill level value L is, however, not possible in such case, due to the greatly smoothed maximum. According to the invention, it is, consequently, provided that the evaluation curve A(d) is smoothed differently as a function of measured distance, thus, with different filtering strengths. For this, there are, such as shown in FIG. 3, various possibilities for putting this into practice.

[0042] A first possibility for measured distance-dependent smoothing is to divide the measured distance into different portions I, II, III and to set in each of the portions I, II, II, in each case, a constant filtering strength, wherein the filtering strength differs from that of the adjoining portion I, II, III. This potential type of implementation is shown in curve (a) of FIG. 3. Alternatively or supplementally, it is also an option so to set the filtering that the filtering strength continuously changes, at least in one of the portions I, II, III. In this connection, curve (b) of FIG. 3 shows a linear change of the filtering strength. As shown by curve (c), however, also any other type of continuous change, such as logarithmic, exponential, etc., can be implemented.

[0043] In the case of all the curves (a, b, c) shown in FIG. 3, the smoothing strengths in the near region I and in the far region III (in each case, with reference to the fill level measuring device 1) are lower compared with the middle region II of the measured distance d. This strategy of weakening the smoothing in the near region I and in the far region III (and, thus, strengthening the smoothing in the middle region II) is especially suitable for determining the fill level L according to the invention in a safe and yet exact manner: Especially in the near region I and in the far region III, the received signal R.sub.HF can be disturbed by parasitic multi-echoes, container floor echoes or device internal echoes.

[0044] Besides changing the filtering strength, i.e. the strength of the smoothing, another variant for implementing the invention provides that mutually differing filter types are used in different portions I, II, III of the measured distance. With referenced to FIG. 3, this means, for example, that the evaluation curve A(d) is smoothed in the middle region II by means of a low-pass filtering, while in the other portions I, III a maximum value filtering is implemented. In such case, the strength of the smoothing in the case of maximum value- or average value filtering is increased by increasing the window width. In the case of low-pass filtering, the filtering strength is correspondingly set by the attenuation, or damping, factor of the lowpass filter.

LIST OF REFERENCE CHARACTERS

[0045] 1 fill level measuring device [0046] 2 container [0047] 3 fill substance [0048] 4 superordinate unit [0049] A(d) evaluation curve [0050] d measured distance [0051] R.sub.HF received signal [0052] F fill level [0053] h installed height [0054] S.sub.HF transmitted signal [0055] I, II, III portions