Method for Increasing a Quality of Sampled Receive Signals and Measuring Device for Time Domain Reflectometry

Abstract

A method for increasing a quality of sampled receive signals includes: generating a plurality of sampling signal repetition rates with a running variable; determining a receive signal repetition rate associated with each of the sampling signal repetition rates; generating a receive signal sequence consisting of the receive signals; generating a sampling signal sequence consisting of the sampling signals; generating a mixed signal sequence; low-pass filtering the mixed signal sequence; determining a quality indicator of the low-pass filtered mixed signal sequence; selecting a quality indicator which exceeds a predetermined quality threshold from the determined quality indicators; and using the sampling signal repetition rate and the receive signal repetition rate associated therewith. A related measuring device is also disclosed.

Claims

1. A method for increasing a quality of sampled receive signals with a signal processing device having a controller, a receive signal generator for generating receive signals with an upper receive signal cut-off frequency f.sub.E,G, a sampling signal generator for generating sampling signals, a mixer and a low-pass filter with a low-pass cut-off frequency f.sub.T,G, the method comprising: the congroller generating a set I⊂ and a plurality of sampling signal repetition rates f.sub.A,W,i with a running variable i for all i∈I; the controller determining a receive signal repetition rate associated with each of the sampling signal repetition rates f.sub.A,W,i with a factor c=f.sub.E,G/(f.sub.E,G−f.sub.T,G) either according to f.sub.A,W,i≈c.Math.f.sub.A,W,i or according to f.sub.E,W,i≈1/c.Math.f.sub.A,W,i with f.sub.E,W,i≠f.sub.A,W,i; wherein the steps generating a receive signal sequence consisting of the receive signals in that the receive signal generator is triggered with the receive signal repetition rate f.sub.E,W,i by the controller; generating a sampling signal sequence consisting of the sampling signals in that the sampling signal generator is triggered with the sampling signal repetition rate f.sub.A,W,i by the controller; generating a mixed signal sequence in that the receive signal sequence and the sampling signal sequence are mixed with one another by the mixer; low-pass filtering the mixed signal sequence by the low-pass filter; and determining a quality indicator of the low-pass filtered mixed signal sequencers by the controller; are executed for all i∈I; the controller then selecting a quality indicator which exceeds a predetermined quality threshold from the determined quality indicators; and subsequently using the sampling signal repetition rate f.sub.A,W,i and the receive signal repetition rate f.sub.E,W,i associated therewith.

2. The method according to claim 1, wherein a start sampling signal repetition rate f.sub.A,W,0 and an interpolation factor N∈{≥3} are predetermined, wherein a new set I={i:i∈{1, . . . , N}.Math.I and (i+N)∈} is determined, and wherein then the sampling signal repetition rates according to f.sub.A,W,i=f.sub.A,W,0 (1+(i−1)/N) are determined only for i for all i∈I.

3. The method according to claim 1, wherein a start sampling signal repetition rate f.sub.A,W,0 and an interpolation factor N∈{≥3 and N∈} are predetermined, wherein a new set I={i:i∈{1, . . . . N}.Math.I} is determined and then the sampling signal repetition rates according to f.sub.A,W,i=f.sub.A,W,0 (1+(i−1)/N) are determined only for i for all i∈I.

4. The method according to claim 1, wherein each of the receive signals is a pulse and/or each of the sampling signals is/are Dirac pulses.

5. The method according to claim 1, wherein each of the quality indicators is a signal-to-noise ratio of the low-pass filtered mixed signal sequence.

6. The method according to claim 1, wherein the receive signal generator has a transmit signal generator for generating and transmitting transmit signals and a measuring probe; wherein the measuring probe is designed for guiding the transmit signals and the receive signals and for generating the receive signals by reflection of the transmit signals at a transition of the measuring probe to a medium; and wherein the transmit signals are generated and transmitted by the transmit signal generator, wherein the transmit signals are first guided by the measuring probe to the transition at which the receive signals are generated by reflection, and then the receive signals are guided back via the measuring probe).

7. A measuring device for time domain reflectometry, comprising: a signal processing device having a controller, a receive signal generator for generating receive signals with an upper receive signal cut-off frequency f.sub.E,G, a sampling signal generator for generating sampling signals, a mixer and a low-pass filter with a low-pass cut-off frequency f.sub.T,G; wherein the receive signal generator has a transmit signal generator for generating and transmitting transmit signals and a measuring probe; wherein the measuring probe is designed for guiding the transmit signals and the receive signals and for generating the receive signals by reflection of the transmit signals at a transition of the measuring probe to a medium; wherein the controller is designed to generate a set I⊂ and a plurality of sampling signal repetition rates f.sub.A,W,i with a running variable i for all i∈I; and determine a receive signal repetition rate associated with each of the sampling signal repetition rates f.sub.A,W,i with a factor c=f.sub.E,G/(f.sub.E,G−f.sub.T,G) either according to f.sub.E,W,i≈c.Math.f.sub.A,W,i or according to f.sub.E,W,i≈1/c.Math.f.sub.A,W,i with f.sub.E,W,i≠f.sub.A,W,i, wherein the controller is further designed for all i∈I; generate a receive signal sequence consisting of the receive signals by triggering the receive signal generator with the receive signal repetition rate f.sub.E,W,i; generate a sampling signal sequence consisting of the sampling signals by triggering the sampling signal generator with the sampling signal repetition rate f.sub.A,W,i; determine a quality indicator from a mixed signal sequence low-pass filtered by the low-pass filter, wherein the mixed signal sequence is generated by the mixer by mixing the receive signal sequence and the sampling signal sequence; and wherein the controller is further designed to then select, from the determined quality indicators, a quality indicator which exceeds a predetermined quality threshold, and to subsequently use the sampling signal repetition rate f.sub.A,W,i and the receive signal repetition rate f.sub.E,W,i associated therewith.

8. The measuring device according to claim 7, wherein at least one of: a start sampling signal repetition rate f.sub.A,W,0 and an interpolation factor N∈{≥3} are predetermined, wherein a new set I={i:i∈{1, . . . , }⊂I and (i+N)∈} is determined, and wherein then the sampling signal repetition rates according to f.sub.A,W,i=f.sub.A,W,0 (1+(i−1)/N) are determined only for i for all i∈I; a start sampling signal repetition rate f.sub.A,W,0 and an interpolation factor N∈{≥3 and N∈} are predetermined, wherein a new set I={i:i∈{1, . . . , N}⊂I} is determined and wherein then the sampling signal repetition rates according to f.sub.A,W,i=f.sub.A,W,0 (1+(i−1)/N) are determined only for i for all i∈I; each of the receive signals is a pulse and/or each of the sampling signals is/are Dirac pulses; each of the qualify indicators is a signal-to-noise ratio of the low-pass filtered mixed signal sequence; the receive signal generator has a transmit signal generator for generating and transmitting transmit signals and a measuring probe; the measuring probe is designed for guiding the transmit signals and the receive signals and for generating the receive signals by reflection of the transmit signals at a transition of the measuring probe to a medium; and the transmit signals are generated and transmitted by the transmit Signal generator, wherein the transmit signals are first guided by the measuring probe to the transition at which the receive signals are generated by reflection, and then the receive signals are guided back via the measuring probe.

9. The measuring device according to claim 7, wherein the measuring device is a level measuring device and the measuring probe is a level measuring probe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In detail, there is a plurality of possibilities for designing and further developing the method and the measuring instrument. For this, reference is made to the following description of a preferred embodiment in conjunction with the drawings.

[0045] FIG. 1 illustrates an embodiment of a measuring device for time domain reflectometry.

[0046] FIG. 2 illustrates an embodiment of a signal processing device of the measuring device.

[0047] FIG. 3 illustrates examples of signal waveforms of the signal processing device over time.

DETAILED DESCRIPTION

[0048] FIG. 1 shows a measuring device 1 for time domain reflectometry and FIG. 2 shows an embodiment of a signal processing device 2 of the measuring device 1. FIG. 3 represents signals of the signal processing device 2 over time. The representation of the signals over time is qualitative. In particular, the representation of time is not to scale.

[0049] The signal processing device 2 has a controller 3, a receive signal generator 4, a sampling signal generator 5 for generating sampling signals s.sub.A, namely in the form of Dirac pulses, a mixer 6 and a low-pass filter 7 with a low-pass cut-off frequency f.sub.T,G=8 kHz. The receive signal generator 4 is designed to generate receive signals s.sub.E with an upper receive signal cut-off frequency f.sub.E,G=2 GHz.

[0050] The receive signal generator 4 has a transmit signal generator 8 for generating and transmitting transmit signals s.sub.S, namely in the form of Dirac pulses, a coupler 9 and a measuring probe 10. Each of the transmit signals s.sub.S is a Dirac pulse, and therefore each of the receive signals s.sub.E is also a Dirac pulse. The measuring probe 10 is partially immersed in a medium 11. The medium 11 has a fill level in a container which is not shown. The measuring probe 10 is configured to guide the transmit signals s.sub.S and the receive signals s.sub.E and to generate the receive signals by reflection of the transmit signals at a transition 12 between the measuring probe 10 and the medium 11. Accordingly, in this embodiment, the measuring device 1 is a level measuring device and the measuring probe 10 is a level measuring probe.

[0051] The controller 3 is designed to generate a set I⊂ and a plurality of sampling signal repetition rates f.sub.A,W,i with a running variable i for all i∈I and, in this embodiment, to determine a receive signal repetition rate associated with each of the sampling signal repetition rates f.sub.A,W,i according to f.sub.E,W,i=(f.sub.A,W,i.Math.f.sub.E,G)/(f.sub.E,G−f.sub.T,G) with f.sub.E,W,i>f.sub.A,W,i.

[0052] Further, the controller 3 is designed to determine for all i∈I a receive signal sequence S.sub.E,F,i consisting of the receive signals s.sub.E by triggering the receive signal generator 4 with the receive signal repetition rate f.sub.E,W,i, a sampling signal sequence S.sub.A,F,i consisting of the sampling signals s.sub.A by triggering the sampling signal generator 5 with the sampling signal repetition rate f.sub.A,W,i, and a quality indicator Q.sub.i from a mixed signal sequence sM,i low-pass filtered by the low-pass filter 7. Here, the mixed signal sequence sM,i is generated by the mixer 6 by mixing the receive signal sequence S.sub.E,F,i and the sampling signal sequence S.sub.A,F,i with each other. Each of the quality indicators Q.sub.i is a signal-to-noise distance of the low-pass filtered mixed signal sequence, which is also referred to as s.sub.F,i.

[0053] During operation of the measuring device 1, the controller 3 triggers both the receive signal generator 4 and the sampling signal generator 5. Triggering the receive signal generator 4 triggers the transmit signal generator 8. To transmit a receive trigger signal s.sub.E,T at the receive signal repetition rate f.sub.E,W,i from the controller 3 to the transmit signal generator 8, there is a receive trigger signal path 13 between the controller 3 and the transmit signal generator 8. The receive trigger signal s.sub.E,T is generated by the controller 3 and triggers the transmit signal generator 8. To transmit a sampling trigger signal s.sub.A,T at the sampling signal repetition rate f.sub.A,W,i from the controller 3 to the sampling signal generator 5, there is a sampling trigger signal path 14 between the controller 3 and the sampling signal generator 5. The sampling trigger signal s.sub.A,T is generated by the controller 3 and triggers the sampling signal generator 5.

[0054] Further, there is a signal path 15 between the signal generator 8 and the measuring probe 10. The transmit signals s.sub.S are transmitted from the transmit signal generator 8 to the measuring probe 10 via the signal path 15 and the receive signals s.sub.E are transmitted in the opposite direction. The coupler 9 decouples the receive signals s.sub.E from the signal path 15 and guides them to the mixer 6. There is a sampling signal path 16 between the sampling signal generator 5 and the mixer 6 for the transmission of the sampling signals s.sub.A from the sampling signal generator 5 to the mixer 6. There is a mixer signal path 17 for the transmission of the mixer signal sequence s.sub.M from the mixer 6 to the low-pass filter 7. The controller 3 determines the quality indicators Q.sub.i from the low-pass filtered mixer signal sequence 5F. There is a low-pass signal path 18 from the low-pass filter 7 to the controller 3 for transmission of the low-pass filtered mixed signal sequence 5F.

[0055] During operation, the measuring device 1 executes a method for increasing a quality of sampled receive signals with the following steps indicated by bullet dashes: [0056] A set I⊂ and a plurality of sampling signal repetition rates f.sub.A,W,i with a running variable i for all i∈I are generated by the controller. Namely, a starting sampling signal repetition rate f.sub.A,W,0=1 MHz and an interpolation factor N∈{≥3} are given. Then, a new set I={i:i∈{1, . . . , N}.Math.I and (i+N)∈} is determined and then the sampling signal repetition rates are determined according to f.sub.A,W,i=f.sub.A,W,0 (1+(i−1)/N) for i∈I. [0057] A receive signal repetition rate associated with each of the sampling signal repetition rates f.sub.A,W,i is determined by the controller according to f.sub.E,W,i=(f.sub.A,W,i.Math.f.sub.E,G)/(f.sub.E,G−f.sub.T,G) with f.sub.E,W,i>f.sub.A,W,i. [0058] In this step, the following sub-steps indicated by bullet dots are executed for all i∈I: [0059] The transmit signal generator 8 of the receive signal generator 4 is triggered by the controller 3 with the receive signal repetition rate f.sub.E,W,i. For this purpose, the controller 3 generates a receive trigger signal sequence s.sub.E,T consisting of the receive trigger signals S.sub.E,T,F,i and routes it via the receive trigger signal path 13 to the receive signal generator 4 and in this to the transmit signal generator 8. The receive trigger signal sequence s.sub.E,T consisting of the receive trigger signals S.sub.E,T,F,i is shown in FIG. 3a. The transmit signal generator 8 generates and outputs the transmit signals s.sub.S, which form the transmit signal sequence S.sub.S,F,i, triggered by the triggering. Each of the transmit signals s.sub.S is a Dirac pulse. The transmit signal sequence S.sub.S,F,i consisting of the transmit signals s.sub.S is shown in FIG. 3b. The transmit signals s.sub.S are guided from the transmit signal generator 8 to the measuring probe 10 via the signal path 15 and reflected in the measuring probe 10 at the transition 12, thus generating the receive signals 5E. Thus, each of the receive signals s.sub.E is also a Dirac pulse. A time interval between one of the transmit signals s.sub.S and the receive signal s.sub.E generated by this transmit signal is Δt and represents a transit time of the signals, from which the controller 3 determines a fill level of the medium 11. The receive signals s.sub.E propagate in the opposite direction to the propagation direction of the transmit signals s.sub.S. The receive signals s.sub.E are decoupled from the signal path 15 by the coupler 9 and guided to the mixer 6. In this way, the receive signal sequence S.sub.E,F,i consisting of the receive signals s.sub.E is generated. The receive signal sequence S.sub.E,F,i consisting of the receive signals s.sub.E is shown in FIG. 3c. [0060] The controller 3 triggers the sampling signal generator 5 with the sampling signal repetition rate f.sub.A,W,i For this, a sampling trigger signal sequence s.sub.A,T consisting of the sampling trigger signals s.sub.A,T,F,i is generated by the controller 3 and guided to the sampling signal generator 5 via the sampling trigger signal path 14. The sampling trigger signal sequence s.sub.A,T consisting of the sampling trigger signals S.sub.A,T,F,i is shown in FIG. 3d. The sampling signal generator 5 generates and outputs the sampling signals s.sub.A, which form the sampling signal sequence s.sub.A,F,i, triggered by the triggering. Each of the sampling signals is a Dirac pulse. The sampling signals are guided from the sampling signal generator 5 to the mixer 6 via the sampling signal path 16. The sampling signal sequence S.sub.A,F,i consisting of the sampling signals s.sub.A is shown in FIG. 3e. [0061] The mixer 6 mixes the receive signal sequence S.sub.E,F,i and the sampling signal sequence S.sub.A,F,i with each other. This generates the mixed signal sequence s.sub.M,i. The mixed signal sequence is guided via the mixed signal path 17 from the mixer 6 to the low-pass filter 7. [0062] The mixed signal sequence s.sub.M,i is low-pass filtered by the low-pass filter 7. The low-pass filtered mixed signal sequence s.sub.F,i is guided via the low-pass signal path 18 from the low-pass filter 7 to the controller 3. The low-pass filtered mixed signal sequence s.sub.F,i is shown in FIG. 3f. [0063] The quality indicator Q.sub.i of the low-pass filtered mixed signal sequence s.sub.F,i is determined by the controller. [0064] The controller selects a quality indicator Q.sub.i from the determined quality indicators that exceeds the specified quality threshold. Then, the sampling signal repetition rate and receive signal repetition rate associated with this quality indicator are used.

[0065] The individual signals in the signal sequences shown in FIGS. 3a, 3b, 3c, 3d and 3e are spaced further apart in time than is shown in the figures. Accordingly, the temporal representation of the signal sequences is not to scale. The signals of the signal sequences shown in FIGS. 3b, 3c and 3e are Dirac pulses. Accordingly, the representation of the signals is not true to scale.

[0066] For I={1, 2, 3, 4} and N=4, the following results:

[0067] The new set I is {i:i∈{1, . . . , 4}.Math.I and (i+4)∈}={i:1, 3}, since only for i∈{1, 3} according to (i+N) prime numbers arise, namely {5, 7}.

[0068] The first sampling signal repetition rate is f.sub.A,W,1=1,000,000 Hz and the first receive signal repetition rate is f.sub.E,W,1=1,000,004 Hz. The second sampling signal repetition rate is f.sub.A,W,3=1,500,000 Hz and the second receive signal repetition rate is f.sub.E,W,3=1,500,006 Hz.

[0069] In practice, however, sets I with more elements and larger interpolation factors N are usually used, for example I={1, 2, 3, 4, . . . , 60} and N=60. With these, the following results:

[0070] The new set I is {i:i∈{1, . . . , 60}.Math.I and (i+60)∈}={i:1, 7, 11, . . . }. Further, only the subset {i:1, 7, 11} of I is used. The prime numbers belonging to this subset are {61, 67, 71}.

[0071] The first sampling signal repetition rate is f.sub.A,W,1=1,000,000 Hz and the first receive signal repetition rate is f.sub.E,W,1=1,000,004 Hz. The second sampling signal repetition rate is f.sub.A,W,7=1,100,000 and the second receive signal repetition rate is f.sub.E,W,7=1,100,004.4 Hz. The third sampling signal repetition rate is f.sub.A,W,11=1,166,666.7 Hz and the third receive signal repetition rate is f.sub.E,W,11=1,166671.3 Hz.

[0072] Just using this subset of I is sufficient to be able to mask out an interference signal with near certainty, since an interference signal with a frequency f.sub.D with a frequency spacing of 61.Math.67.Math.71.Math.1 MHz=290.177.Math.1 MHz is present for all three elements of I.