Method for determining the fill level of a fill substance located in a container

Abstract

A method for determining the fill level of a fill substance located in a container. The method, which is based on the pulse travel time principle, is distinguished by the fact that extra-range echos can be recognized. For this, the method includes two method portions, in which microwave pulses are transmitted in the direction of the surface of the fill substance with different repetition rates in measuring cycles following one after the other. In each method portion, travel times are ascertained. The fill level is ascertained based on the first travel time and/or based on the second travel time, to the extent that they approximately agree. Otherwise, it is assumed that such echo pulses concern extra-range echos. Thus, by means of the method of the invention, it can be assured for pulse radar-based fill-level measurements that extra-range echos do not result in erroneous fill level values.

Claims

1. A method for determining fill level of a fill substance located in a container, comprising the steps as follows: in a first method step with a first repetition rate in measuring cycles following one after the other, a first microwave pulse with a first center frequency is transmitted in the direction of the surface of the fill substance, after transmitting the first microwave pulse, at least one first echo pulse received, wherein a first travel time between transmission of the first microwave pulse and receipt of the at least one first echo pulse is ascertained; and, in a second method step with a second repetition rate in measuring cycles following one after the other, a second microwave pulse with a second center frequency is transmitted in the direction of the surface of the fill substance, after transmitting the second microwave pulse, at least one second echo pulse is received, wherein a second travel time between transmission of the second microwave pulse and receipt of the at least one second echo pulse is ascertained, wherein, to the extent that said first travel time and said second travel time approximately agree, the fill level is ascertained based on said first travel time and/or based on said second travel time.

2. The method as claimed in claim 1, wherein: at least in one measuring cycle of said first method step, the first microwave pulse is transmitted with a predefined delay, which corresponds approximately to the reciprocal of twice the first center frequency; and/or at least in one measuring cycle of said second method step, the second microwave pulse is transmitted with a predefined delay, which corresponds approximately to the reciprocal of twice the second center frequency.

3. The method as claimed in claim 2, wherein: for the case, in which, in multiple measuring cycles of said first method step and/or of said second method step, the microwave pulse is transmitted delayed, in which measuring cycle the first microwave pulse and/or the second microwave pulse are/is transmitted delayed is randomly controlled.

4. The method as claimed in claim 1, wherein: said first method step and said second method step are performed simultaneously.

5. The method as claimed in claim 1, wherein: said first method step and said second method step are performed alternately.

6. A fill-level measuring device for determining fill level of a fill substance located in a container, comprising: a pulse producing unit for producing with a first repetition rate a first microwave pulse with a first center frequency in measuring cycles following one after another, as well as for producing with a second repetition rate a second microwave pulse with a center frequency in measuring cycles following one after another, a transmitting/receiving unit for transmitting the first microwave pulse and the second microwave pulse in the direction of the surface of the fill substance, as well as for receiving the at least one first echo pulse and/or the at least one second echo pulse after transmitting the first microwave pulse and the second microwave pulse; and an evaluation unit for ascertaining a first travel time between transmission of the first microwave pulse and receipt of the at least one first echo pulse, for ascertaining a second travel time between transmission of the second microwave pulse and receipt of the at least one second echo pulse, as well as for for ascertaining fill level based on said first travel time and/or based on said second travel time to the extend that said first travel time and said second travel time approximately agree.

7. The fill-level measuring device as claimed in claim 6, wherein: said pulse producing unit includes a delay unit for delay of the emitting of the first microwave pulse and/or of the second microwave pulse.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained based on the appended drawing, the figures of which show as follows:

(2) FIGS. 1a, and 1b are two schematic representations of transmitted microwave pulses and resulting received echo pulses as a function of time;

(3) FIG. 2 is a first embodiment of a fill level measuring device for performing the method of the invention; and

(4) FIG. 3 is a second embodiment of a fill level measuring device for performing the method of the invention.

DETAILED DISCUSSION IN CONJUNCTION WITH THE DRAWINGS

(5) FIGS. 1a and 1b illustrate the functional principle of the method of the invention for determining the fill level L of a fill substance 2 located in a container 1.

(6) The method is distinguished by the fact that extra-range echos are recognized as such. A fundamental feature of the method is that microwave pulses S.sub.1, S.sub.2 are transmitted with at least two different repetition rates f.sub.R1, f.sub.R2. In this connection, FIGS. 1a and 1b show the transmitted microwave pulses S.sub.1, S.sub.2 as well as associated, received echo pulses E.sub.1, E.sub.2 as a function of time, wherein the signal strengths [S.sub.1, S.sub.2, E.sub.1, E.sub.2] are plotted on the ordinate.

(7) Two different cases are considered in FIGS. 1a and 1b: In the first case, the echo pulses E.sub.1, E.sub.2 are extra-range echos (shown as dashed lines). In the second case, the echo pulses E.sub.1, E.sub.2 are fill substance echos (shown as solid lines), such as required for determining the fill level L from the reflection of the microwave pulses S.sub.1, S.sub.2 on the surface of the fill substance 2.

(8) In FIG. 1a, the microwave pulses S.sub.1 are transmitted with a first repetition rate f.sub.R1. A first travel time t.sub.1 can be associated with each of the echo pulses E.sub.1. In contrast therewith, in FIG. 1b, the microwave pulses S.sub.2 are transmitted with a slower, second repetition rate f.sub.R2. Also in this case, a second travel time t.sub.2 can be associated with the echo pulses E.sub.2. As can be seen by comparing FIGS. 1a and 1b, in the case of the echo pulses E.sub.2, which result from reflection of the microwave pulse S.sub.2 on the surface of the fill substance 2, the second travel time t.sub.2 does not change in comparison with the first travel time t.sub.1. The behavior is different in the case of the extra-range echos: the second travel time t.sub.2 is less compared with the first travel time t.sub.1. This effect is attributed to the fact that the travel time t.sub.0 of extra-range echos remains constant with reference to the next to last microwave pulse S.sub.1, S.sub.2, not, however, with reference to the last microwave pulse S.sub.1, S.sub.2.

(9) According to the invention, it is thus detected whether an echo pulse E.sub.1, E.sub.2 is an extra-range-echo by comparing the first travel time t.sub.1 and the second travel time t.sub.2 with one another. When the first travel time t.sub.1 and the second travel time t.sub.2 do not agree, then the echo is an extra-range echo. Otherwise, it can be assumed from the comparison that an extra-range echo is not involved, so that the fill level L is determined based on the equal travel times t.sub.1, t.sub.2.

(10) FIG. 2 shows a very simple embodiment of a fill level measuring device for performing the method of the invention. It includes a pulse producing unit 3 for producing the microwave pulses S.sub.1, S.sub.2. As known from the state of the art, serving for this is a first pulse generator 31 and a first high-frequency oscillator 33, which has a predetermined center frequency f.sub.m in the GHz-region. In order to be able to transmit the microwave pulses S.sub.1 S.sub.2 with different repetition rates f.sub.R1, f.sub.R2, the pulse producing unit 3 includes a frequency divider 32. With this, a predetermined repetition rate f.sub.R of the pulse generator 31 is variably divided down in such a manner that sequentially in alternation two different repetition rates f.sub.R1, f.sub.R2 get set. In the case of this embodiment, the microwave pulses S.sub.1, S.sub.2 of both method portions are produced by the same pulse producing unit 3. Therefore, it is only possible to perform the first method portion and the second method portion of the method of the invention alternatingly.

(11) In the scope of the invention, however, any other method for production of microwave pulses S.sub.1, S.sub.2 with different repetition rates f.sub.R1, f.sub.R2 can be used. This could be achieved, for example, by another pulse producing unit supplementally to the illustrated pulse producing unit 3. In such case, an option would be that two high-frequency oscillators with mutually differing center frequencies f.sub.M1, f.sub.M2 are implemented. In this case, an option would be that the first method portion and the second method portion of the method of the invention are performed at the same time.

(12) In the case of the fill-level measuring device shown in FIG. 2, one transmitting/receiving unit 4 serves for transmitting and receiving both the microwave pulses S.sub.1, S.sub.2 and the echo pulses E.sub.1, E.sub.2. For this, the transmitting/receiving unit 4 includes a transmitting/receiving separator, duplexer or directional coupler 41 as well as an antenna 42. Instead of the one antenna 42, another option is to use a plurality of antennas for separate sending and receiving. In such case, the transmitting/receiving separator, duplexer or directional coupler 41 would not be required.

(13) Serving for ascertaining the fill level L based on the travel times t.sub.1, t.sub.2 is an evaluation unit 5. It includes a microcontroller 51 for A/D conversion of the echo pulses E.sub.1, E.sub.2 as well as for calculating the travel times t.sub.1, t.sub.2.

(14) FIG. 2 shows only signal paths. Control paths, for example, for operating of the first pulse generator 31 and/or the first frequency divider 32 by the microcontroller 51 are not shown for reasons of perspicuity.

(15) FIG. 3 shows a further development of the fill level measuring device shown in FIG. 2. In the case of the fill-level measuring device shown in FIG. 3, a sampling and a therewith connected time expansion of the echo pulses E.sub.1, E.sub.2 occurs according to the state of the art, in order to facilitate the ascertaining of the travel times t.sub.1, t.sub.2 based on a resulting intermediate frequency signal IF. The sampling occurs in a mixer 56 by a sampling signal, which is produced analogously to the microwave pulses S.sub.1, S.sub.2 by a reference pulse generator 52, a second frequency divider 53 and a second high-frequency oscillator 54. In such case, it is necessary for performing the method of the invention that the first frequency divider 32 and the second frequency divider 53 have the same divisor.

(16) The fill-level measuring device shown in FIG. 3 includes, moreover, two delay units 34, 55. They serve to delay the transmission of the individual microwave pulses S.sub.1, S.sub.2 or the sampling signal, as the case may be, by a half wavelength (with reference to the center frequency f.sub.M of the high-frequency oscillators 33, 54). In such case, advantageously, it is controlled randomly, whether the microwave pulses S.sub.1, S.sub.2 and the sampling signal are delayed, By this additional measure, the signal strength of the extra-range echos E.sub.1, E.sub.2 can be lessened up to 20 dB, without that the signal strength of the echo pulses E.sub.1 E.sub.2 resulting from reflection of the microwave pulse S.sub.1, S.sub.2 on the surface of the fill substance 2 is reduced. Also in the case of this measure, it is necessary that the two delay units 34, 55 are operated concordantly. This means that either the two delay units 34, 55 instantaneously delay the transmission of the microwave pulses S.sub.1, S.sub.2, or neither of the two is delayed. Alternatively to the embodiment shown in FIG. 3, an option would be that the delay units 34, 55 are arranged between the frequency dividers 32, 53 and the high-frequency oscillators 33, 54.

(17) This measure, which serves for reducing the signal strength of extra-range echos E.sub.1, E.sub.2, could also be applied in the case of the embodiment of the fill level measuring device shown in FIG. 2. In this case, the extra effort would be limited to only a single delay unit in the pulse producing unit 3.