Method and device for determining distance values

Abstract

The invention relates to a method for determining distance values, comprising: emitting a transmit signal having at least one transmit pulse and receiving a receive signal having at least one receive pulse; measuring at least one pulse propagation time on the basis of the transmit signal, the receive signal and a periodic time reference signal; and determining a distance value on the basis of the pulse propagation time; wherein measuring the pulse propagation time comprises determining at least one signal portion duration, which represents at least one part of the pulse propagation time, as a function of a plurality of different reference times distributed over a period length of the time reference signal.

Description

[0001] Method and device for determining distance values

[0002] The present invention relates to a method and a device for determining distance values ​​based on pulse transit times.

[0003] The goal is to improve the measurement of distance values ​​based on pulse time-of-flight by increasing measurement accuracy without sacrificing measurement speed. At the same time, the cost of the required hardware should be kept as low as possible.

[0004] It is therefore an object of the invention to determine distance values ​​with higher measurement accuracy at the same or higher measurement speed.

[0005] The problem is solved by the subject matter of the independent claims.

[0006] A method for determining a distance value comprises at least the following steps: transmitting a transmitted signal with at least one transmitted pulse and receiving a received signal with at least one received pulse; measuring at least one pulse transit time based on the transmitted signal, the received signal, and a periodic time reference signal; and determining a distance value based on the pulse transit time; wherein measuring the pulse transit time comprises determining at least one signal section duration, which represents at least a portion of the pulse transit time, as a function of a plurality of mutually different reference times distributed over a period length of the time reference signal.

[0007] In an exemplary embodiment of the invention, the interval between a transmitted pulse and a received pulse, which together form an evaluation signal, is measured multiple times by repeatedly determining at least one signal segment duration elapsed between the transmitted and received pulses based on time-delayed versions of the evaluation signal. The time delays between the individual versions are always smaller than the period length of the time reference signal ("clock") used for the measurement, so that the reference times selected for the delays are distributed over a period length of the time reference signal. In this way, the measurement accuracy within a period length can be improved.

[0008] Preferably, a respective signal section duration is determined as the sum of predetermined reference time durations ("delay times") by delaying and sampling the signal sections using several delay elements connected in series, which together form a so-called delay line. The signal sections are thus each processed using a time-to-digital converter (TDC) to obtain the signal section durations as a digital value. The signal delays caused by the delay elements must be distinguished from the delays previously implemented to form the multiple signal sections. Advantageously, several TDCs can be used in parallel to determine several signal section durations in parallel.

[0009] The signal section durations obtained for the delayed signal sections are preferably averaged by summing the signal section durations and dividing them by the number of summands. The pulse transit time measured on this basis is more accurate than a conventional measurement based on just one signal section. It should be understood that forming the delayed signal sections does not improve the noise-related measurement error because a signal delay does not influence the noise signal component. However, the measurement error resulting from digitizing the measured signal section durations, i.e., from using TDCs, can be significantly reduced by the method according to the invention. A particular advantage of the method is that the measurement accuracy can be improved even for a single transmission pulse without impairing the measurement speed.This is achieved by systematically recording and improving the digital measurement accuracy within one period length of the time reference signal, i.e. in the subperiod range, by repeatedly determining the signal section duration, as further described below.

[0010] Embodiments of the invention are disclosed in the description, the figures and the claims.

[0011] According to one embodiment, the signal section duration is determined based on an evaluation signal that represents a time interval or a time difference between the at least one transmitted pulse and the at least one received pulse. In other words, the evaluation signal comprises the time information regarding the position of the transmitted pulses and the received pulses. Consequently, the evaluation signal can be used to determine, in particular, the transmission time of a transmitted pulse, the reception time of a received pulse, and the time interval between them. The time interval between a respective transmitted pulse and an associated received pulse corresponds to the pulse transit time of the transmitted pulse.

[0012] Preferably, the evaluation signal is used to determine the

[0013] The signal section duration for at least some of the reference times is evaluated in parallel, in particular by using multiple TDCs in parallel. The signal section duration can thus be determined efficiently and at high speed. The TDCs can generally each have several linked delay elements to successively delay and sample the evaluation signal by a predetermined reference time period.

[0014] According to a further embodiment, the signal section duration is determined based on multiple separate versions of the evaluation signal. For example, an associated version of the evaluation signal can be generated for each reference time, wherein the versions differ from one another depending on the reference times. In particular, the versions can each be shifted by a constant delay time, so that the respective start times of the versions are distributed over a period length of the time reference signal ("clock"). The individual shifted versions are evaluated at least partially in parallel, in particular by multiple TDCs, in order to increase the evaluation speed.

[0015] The multiple versions of the evaluation signal are preferably generated depending on the reference times distributed within a period. For example, the versions can be shifted relative to one another depending on the reference times. The individual versions can then be evaluated independently of the reference times using the periodic time reference signal in order to determine a signal section duration for each version. For this purpose, several preferably identical time measuring elements, e.g. TDCs, can advantageously be used. Alternatively, the multiple versions of the evaluation signal can be generated independently of the reference times. For example, the versions can be identical copies of the evaluation signal, which are, however, evaluated depending on the reference points in order to determine the signal section durations. The evaluation of the versions can again advantageously take place in parallel.

[0016] To generate the different versions depending on the reference times, the evaluation signal can be shifted several times in succession by a predetermined constant time interval. The reference times thus differ by an integer multiple of the predetermined time interval. In this way, the reference times can be evenly distributed over a period length.

[0017] Alternatively, in the case of identical versions of the evaluation signal, it is conceivable to shift the time reference signal ("clock") multiple times by the predetermined time interval. In this way, shifted versions of the time reference signal can be created, which are used to determine the signal section durations. For example, each version of the evaluation signal can be evaluated depending on the time reference signal, which is shifted by a multiple of the predetermined time interval according to the assigned reference time.

[0018] According to a further embodiment, the signal section duration represents a time duration of a signal section of the evaluation signal. The signal section can directly represent the pulse propagation time, i.e. the distance between a transmitted pulse and an associated received pulse, or a portion of the pulse propagation time. In particular, the signal section can have a length that corresponds to a partial period, i.e. a portion of a full period of the time reference signal. The signal section can therefore be formed by a section of the evaluation signal that cannot be measured over an entire period length and therefore requires a finer measurement resolution. For example, the signal section can be limited by a transmitted pulse and the subsequent end point of a full period of the time reference signal. Alternatively, the signal section can be limited by a received pulse and the preceding start point of a full period of the time reference signal.

[0019] The signal section is preferably a coherent section of the evaluation signal, ie the section is not composed of separate sections.

[0020] The signal section duration is preferably determined as the sum of several predetermined reference time periods ("delay times"), each of which is shorter than the period length of the time reference signal ("clock"). For this purpose, the signal can be shifted and sampled several times by one of the reference time periods, starting from the first boundary of the signal section until the expiration of one period of the time reference signal. This measurement principle is preferably implemented by several delay elements ("delay line") connected in series, with each delay element causing a signal delay by a predetermined reference time period.

[0021] The pulse transit time is generally measured based on a first signal section duration, in particular by determining a sum of predetermined reference time durations (delay times), each of which is shorter than the period length and thus performs a "fine measurement." Furthermore, at least one second signal section duration can be determined, which forms a further part of the pulse transit time and is included in the measurement of the pulse transit time. For example, the second signal section duration can be determined by a coarse measurement by determining the second signal section duration as an integer multiple of a second reference time duration. The second reference time duration is preferably formed by the period length of the time reference signal. For example, the second signal section duration can be determined by counting entire clock pulses or periods of the time reference signal.The measurement of the second signal section duration is therefore coarser than the measurement of the first signal section duration.

[0022] The interval between the successive reference times for forming the delayed signal samples is preferably constant. The reference times can be distributed evenly or equidistantly over the period length, e.g., by forming the delayed signal samples with similar time delay elements.

[0023] As described above, the signal section duration is determined multiple times in order to capture the measurement accuracy within a period length and to determine the pulse transit time with greater accuracy. For this purpose, the signal section duration is preferably determined for each of the reference times (e.g., for each delayed signal acquisition) with a first resolution. The signal section durations determined for the individual reference times are then combined using a statistical calculation rule in order to determine the signal section duration with a second resolution that is higher than the first resolution. The first resolution can be defined in particular by the aforementioned predetermined reference time periods ("delay times"), the sum of which is used to determine an individual signal section duration.The calculation rule preferably includes summing the signal segment durations determined for the various reference times and dividing them by the number of summands. The resolution can be improved in this way depending on the number of signal segment durations determined. In general, the resolution can be improved by up to 1 / N if N signal segment durations are determined for a single transmitted pulse.

[0024] The resolution for a single determined signal section duration is, for example, 2.4 mm. This resolution can be improved to 2.4 / 20, i.e., approximately 0.12 mm, by determining 20 signal section durations. This assumes that the period length of the time reference signal is 1.667 ns and the reference times for the individual signal section durations are evenly distributed over a period length, i.e., the distance between the reference times is 1667 ps / 20, i.e., approximately 83.35 ps. For comparison: By performing N repeated measurements, the measurement accuracy can usually only be improved by 1 / N 1 / 2 be improved.

[0025] The statistical calculation rule does not have to be applied directly to the signal segment durations. For example, it is possible to first measure a respective pulse transit time for each reference time point based on the signal segment duration and, if necessary, additional signal segment durations. Then, the pulse transit times obtained for the various reference times can be summed and divided by the number of summands.

[0026] According to a further embodiment, to measure a single pulse transit time, several signal section durations are determined and subtracted from one another. For example, a first signal section duration represents the time duration from a transmitted pulse to the beginning of the next period of the time reference signal. A second signal section duration represents the time duration between a received pulse and the end of the preceding period of the time reference signal. The second signal section duration can advantageously be subtracted from the first signal section duration in order to compensate for a systematic measurement error when measuring the partial period length. For this purpose, the first and second signal section durations can each be determined in the manner according to the invention as a function of several reference times that are equidistant from one another.By calculating the difference between the first and second signal segment durations, the systematic distance between the reference times can be compensated. The number of whole periods of the time reference signal that lie between the first and second signal segment durations can be added to this difference to obtain the pulse transit time.

[0027] According to a further embodiment, the signal section duration is determined as a function of a control parameter. This enables automatic switching between different methods for determining the signal section duration. For example, the signal section duration can generally be determined as a function of the multiple reference times if the control parameter has a predetermined value. Otherwise, the signal section duration is not determined as a function of the multiple reference times.

[0028] It has been shown that determining the signal section duration based on multiple reference times leads to particularly good results when the signal-to-noise ratio (SNR) is comparatively high. This can be taken into account, for example, by automatically determining the control parameter based on a signal quality that represents the SNR of the received signal. In this way, the determination of the signal section duration can advantageously be adaptively adjusted to the SNR. Thus, even under variable usage conditions, accurate results can always be achieved with maximum speed and accuracy.

[0029] For example, the signal section duration can be determined based on a single reference time when the SNR falls below a predetermined threshold. The control parameter can have the value 0 in this case, for example, and the value 1 otherwise.

[0030] In order to be able to determine the signal section duration and, in particular, the pulse transit time with high speed and accuracy even at low SNR values, a preferred approach is to transmit multiple transmit pulses at a high repetition rate in order to obtain a large number of receive pulses as repeat measurements. For this purpose, the transmit signal can generally comprise multiple transmit pulses, which are advantageously transmitted in a transmit pulse sequence comprising multiple transmit pulse groups, with the transmit pulse spacing between consecutive transmit pulses within a transmit pulse group being less than a predetermined maximum pulse transit time.

[0031] According to a further embodiment, the different reference times correspond to several mutually different signal times of the evaluation signal, which are independent of the transmitted pulses and / or received pulses. The signal times are determined as a function of the periodic time reference signal ("clock"), in particular such that the signal times are evenly distributed over a period of the time reference signal. The exact determination of the signal times is thus independent of the transmitted pulses and / or received pulses.A further aspect of the disclosure relates to a device for determining distance values, wherein the device comprises at least the following: a transmitter-receiver arrangement for transmitting a transmission signal with at least one transmission pulse and receiving a reception signal with at least one reception pulse; and a measuring device configured to carry out the method according to one of the described embodiments.

[0032] According to one embodiment, the measuring device comprises a multiprocessor system and a field programmable gate array (FPGA) with several cascaded delay elements and logic gates. The delay elements are each adapted to delay the evaluation signal by a predetermined reference time period.

[0033] Preferably, the FPGA has several groups of delay elements, each of which has several delay elements connected in series and together forms a respective delay line. The signal sections of the evaluation signal, which are delayed depending on the various reference times, are each processed and sampled in parallel with a delay line to determine the signal section duration to be measured as the sum of the predetermined reference time periods. The signal section duration can thus be measured as a digital value.

[0034] According to a preferred embodiment, the measuring device is designed as a single-chip system, meaning all components of the measuring device are combined on a single chip. This promotes high measurement speed and low manufacturing costs. Advantageously, additional electronic components of the device, such as the transmitters and receivers of the transceiver arrangement, can also be integrated on the chip to make the device as a whole particularly compact and lightweight.

[0035] The invention is described below purely by way of example with reference to the drawings, wherein further advantageous features and embodiments are disclosed.

[0036] The figures show in detail:

[0037] Fig. 1 is a block diagram of a method for determining a distance value based on an evaluation signal;

[0038] Fig. 2 is a block diagram of a method for determining a distance value based on several evaluation signals;

[0039] Fig. 3 is a schematic timing diagram illustrating a determination of a signal section duration as a function of a first reference time;

[0040] Fig. 4 is a schematic timing diagram illustrating a determination of a signal section duration as a function of a second reference time;

[0041] Fig. 5 is a schematic timing diagram illustrating an alternative determination of a signal section duration as a function of a second reference time.

[0042] An evaluation signal is received by a receiver 12 and fed to a first evaluation unit 10 via an input interface 14. The evaluation signal represents a transmitted signal with at least one transmitted pulse and a received signal with multiple received pulses, which are reflected and received in a measurement environment after the transmitted signal has been previously transmitted. The evaluation signal is evaluated to measure the pulse transit times between a transmitted pulse and a received pulse.

[0043] The evaluation signal is evaluated, among other things, with the aid of a plurality of time measuring elements TDC 1 , TDC 2 , TDC 3 , ... , TDCN, where the number of time measuring elements is, for example, N = 20. Each time measuring element TDC is adapted to determine a pulse transit time on the basis of the evaluation signal at high speed as the sum of several predetermined reference time periods. For this purpose, the time measuring elements TDC are each designed as a time-to-digital converter (TDC) with several delay elements connected in series, which each delay the evaluation signal by one of the reference time periods. The reference time periods can be essentially the same, but can also be different from one another. Further features of the functioning of the time measuring elements TDC are explained with reference to Fig. 3.

[0044] Each time measuring element receives a separate version of the evaluation signal for evaluation. For this purpose, several versions of the evaluation signal are generated by delaying the evaluation signal using several delay elements D1, D2, DN-1, each by a predetermined time offset. The time offset is constant for all delay elements D and amounts to 1 / N multiplied by the predetermined reference time period. The reference time period is defined as the period length of a reference time signal, which is used to determine the pulse transit time. For the example case of N = 20, the time offset is 1 / 20 of the period length, i.e., each delay element D delays the respective input signal by 1 / 20 of the period length. The first time measuring element TDC1 receives the evaluation signal as an unchanged version, i.e., without prior delay, see Fig. 1.The second timing element TDC2 receives a version of the evaluation signal, which is delayed by the delay element D1 by the predetermined time offset. The third timing element TDC3 receives another version of the evaluation signal, which is delayed by the delay elements D1 and D2 by twice the time offset. The Nth timing element TDCN receives as input a version of the evaluation signal, which is delayed (N1) times by the time offset. In this way, multiple versions of the evaluation signal with different reference times are provided.

[0045] The versions of the evaluation signal are each evaluated with an associated TDC timing element to measure a respective pulse transit time. From a statistical perspective, minor differences between the respective pulse transit times are to be expected, which are due to the different reference times and the limited measurement accuracy of the timing elements.

[0046] The pulse transit times determined by the TDC timing elements are summed using an adder 16 and applied with a factor to determine an arithmetic mean of the pulse transit times. To do this, the sum is multiplied by a factor equal to 1 / N, i.e., for N=20, the factor is 1 / 20. It is understood that the arithmetic mean can also be determined by other methods, and comparable statistical calculation rules can be used.

[0047] The pulse transit time averaged in this way is statistically more accurate by 1 / N than the pulse transit time determined using a single time measuring element TDC, provided that the noise of the received signal is negligibly small.

[0048] The averaged pulse transit time is processed with noise suppression 20 to exclude unwanted measurement results caused by noise from further processing.

[0049] The averaged pulse transit time is forwarded via an output interface 22 to a second evaluation unit 24 to convert the pulse transit times into distance values. For this purpose, half the pulse transit time is multiplied by the speed of light.

[0050] The method described above for determining an averaged pulse transit time based on multiple versions of an evaluation signal can be expanded by evaluating several different evaluation signals in parallel. For this purpose, the available N timing elements can be divided into several groups, each processing one of the evaluation signals to obtain an averaged pulse transit time. Each evaluation signal is evaluated based on multiple versions of the evaluation signal. However, due to the reduced number of timing elements per averaged pulse transit time, a smaller number of versions of the evaluation signal are used for each evaluation signal.

[0051] The evaluation signals are each received by an associated receiver, which is generally shown in Fig. 2 as the m-th receiver 26 (m=1, 2, ..., M). The following assumes two evaluation signals as an example (M=2). The first evaluation signal, m=1, is applied via the input interface 14 to the delay elements D1,..., Dk-1 (k <N) jeweils um den vorbestimmten Zeitversatz verzögert, um mehrere Fassungen des ersten Auswertungssignals mit voneinander verschiedenen Bezugszeitpunkten zu bilden. Die Fassungen werden mittels der Zeitmesselemente TDC1 , TDCk ausgewertet, um pro Zeitmesselement eine Pulslaufzeit zu erhalten. Nachdem für das erste Auswertungssignal jeweils k Pulslaufzeiten ermittelt wurden, werden diese in dem Addierer aufsummiert und durch die Anzahl der Summanden k geteilt. Dies erfolgt z.B. durch Multiplikation mit dem Faktor 1 / k in dem Mulitplizierer 18.

[0052] The second evaluation signal, m=2, is delayed in parallel with the first evaluation signal, m=1, by the delay elements Dk, ..., DN-1, each by the predetermined time offset, in order to form several versions of the second evaluation signal with different reference times. The multiple versions are evaluated with the timing elements TDCk+1, ..., TDCN, in order to obtain a pulse transit time for each timing element. The pulse transit times (Nk) thus determined are in turn summed in the adder and divided by the number of summands (Nk). This is done, for example, by multiplying by the factor 1 / (Nk) in the multiplier 18.

[0053] It should be understood that, in general, M evaluation signals are evaluated in parallel with subsets of the N available timing elements TDC. Optionally, a control device 28 is provided, which is adapted to connect the input interface 14 to the mth receiver 26 in each case in order to feed the mth evaluation signal to the assigned subset of timing elements TDC and to ensure the group-wise averaging of the pulse transit times. The various evaluation signals are thus based on different received signals.

[0054] The control device 28 may generally have a predetermined

[0055] A control input is received that controls the group-wise distribution of the timing elements (TDC). This is based on the consideration that the number of pulse transit times determined per received evaluation signal can advantageously be variably adjusted depending on the current measurement conditions, e.g., the SNR.

[0056] The following describes the measurement of a pulse transit time using a time measuring element TDC with reference to the schematic timing diagram in Fig. 3.

[0057] The pulse transit time is measured between a transmitted pulse 34 and a subsequent received pulse 36. The two pulses 34 and 36 together form an evaluation signal.

[0058] The transmit pulse 34 and the receive pulse 36 are each shown as rectangular pulses, with the pulse transit time defined as the duration between the rising edges of the transmit pulse 34 and the receive pulse 36. The rising edges occur at signal times ts1 and ts2. However, other definitions for the pulse transit time are also possible.

[0059] The measurement of the pulse transit time is carried out on the basis of a periodic square wave signal 32 with a period length TR1 and a reference time period TR2, wherein the reference time period TR2 is smaller than the period length TR1.

[0060] To measure the pulse transit time, integer multiples of the period length TR1 and integer multiples of the reference period TR2 are determined. First, the number of 38 whole period lengths TR1 between the rising edges of the transmit pulse 34 and the receive pulse 36 is counted. Second, a first signal section duration TS1 between the signal times ts1 and t1 and a second signal section duration TS2 between the signal times ts2 and t2 are measured as integer multiples of the reference period TR2.

[0061] The first signal section duration TS1 corresponds to the time duration between the rising edge of the transmitted pulse 34 and the beginning of the next time period TR1 of the square-wave signal 32. The second signal section duration TS2 corresponds to the time duration between the rising edge of the received pulse 36 and the beginning of the subsequent time period TR1 of the square-wave signal 32, see Fig. 3.

[0062] The signal section duration TS1 is measured as a multiple of the reference time period TR2 by successively shifting the evaluation signal by the reference time period TR2 with the transmission pulse 34. The integer multiple of the reference time period TR2 determined in this way is indicated in Fig. 3 by reference numeral 40.

[0063] Analogous to the signal section duration TS1, the signal section duration TS2 is also measured as a multiple of the reference time duration TR2. The integer multiple of the reference time duration TR2 is indicated in Fig. 3 for the signal section duration TS2 by reference numeral 42.

[0064] The pulse transit time is the sum of the multiple of the period length TR1 (reference number 38) and the first multiple of the reference time period TR2 (reference number 40) minus the second multiple of the reference time period TR2 (reference number 42).

[0065] It should be understood that the signal section durations TS1 and TS2 determined with a time measuring element TDC are each measured as a function of only one reference time t1 or t2.

[0066] With reference to Fig. 4, the following describes how the shifting of the evaluation signal by a delay element D affects the measurement of the pulse transit time by a time measuring element TDC. Pulses 44 and 46 shown in Fig. 4 represent the shifted evaluation signal, with pulses 44 and 46 corresponding to pulses 34 and 36 with a time shift to the right. By processing this shifted version of the evaluation signal, pulses 44 and 46 are evaluated as a function of the reference times t3 and t4, respectively, in order to measure the signal section durations TS3 and TS4, each as an integer multiple of the reference time duration TR2.

[0067] Due to the shift, the signal section durations TS3 and TS4 are each shorter than the signal section durations TS1 and TS2. However, the differences (TS1-TS2) and (TS3-TS4) are equal without taking the measurement error into account, so the shift is compensated. In Fig. 4, the signal times ts1 and ts2 of pulses 34 and 36 from Fig. 3 are shown as dashed lines.

[0068] By averaging the pulse transit times measured in this way, the measurement accuracy of the pulse transit time is improved, as described in connection with Fig. 1 and 2.

[0069] As an alternative to shifting the evaluation signal, it is conceivable to shift the square-wave signal 32. For this purpose, the delay elements D can, in deviation from Fig. 1 and Fig. 2, be designed to successively delay the square-wave signal 32 for the timing elements TDC2 to TDCN, so that each of these timing elements receives a separate, shifted version of the square-wave signal. In other words, the timing element TDC2 is operated on the basis of a square-wave signal that is shifted by the predetermined time offset compared to the "previous" square-wave signal used for the timing element TDC1. The square-wave signal used for the timing element TDC3 is delayed again by a time offset, and so on.

[0070] Fig. 5 illustrates the case of a shift in the square-wave signal. The square-wave signal 48 shown there corresponds to a shifted version of the square-wave signal 32 from Fig. 3 and Fig. 4. The evaluation signal with pulses 34 and 36, however, is unchanged, i.e., not shifted. Due to the shift in the square-wave signal, the signal section durations TS3 and TS4 are measured as a function of the same reference times t3 and t4 as in Fig. 4. For comparison, the different reference times t1 and t2 from Fig. 3 are shown in dashed lines in Fig. 5.

[0071] LIST OF REFERENCE SYMBOLS

[0072] 10 First evaluation unit

[0073] 12 recipients

[0074] 14 Input interface

[0075] 16 adders

[0076] 18 multipliers

[0077] 20 Noise Reduction

[0078] 22 Output interface

[0079] 24 Second evaluation unit

[0080] 26 m receiver

[0081] 28 Control device

[0082] 30 control parameters

[0083] 32 Reference time signal

[0084] 34 transmission pulse

[0085] 36 Receive pulse

[0086] 38 Multiple of the first reference period

[0087] 40 multiples of the second reference period

[0088] 42 Multiple of the second reference period

[0089] 44 transmission pulse

[0090] 46 Receive pulse

[0091] D Delay elements

[0092] TDC timing elements t1, t2, t3, t4 reference times ts1, ts2 signal times ts3, ts4 signal times

[0093] TS1 , TS2 signal durations

[0094] TS3, TS4 signal durations

[0095] TR1 First reference period

[0096] TR2 Second reference period

Claims

PATENT CLAIMS 1. A method for determining a distance value, the method comprising: - transmitting a transmission signal with at least one transmission pulse (34) and receiving a reception signal with at least one reception pulse (36); - measuring at least one pulse transit time based on the transmitted signal, the received signal and a periodic time reference signal (32, 48); - Determining a distance value on the basis of the pulse transit time; wherein measuring the pulse transit time comprises determining at least one signal section duration (TS1, TS2, TS3, TS4) which represents at least a portion of the pulse transit time, and wherein the signal section duration (TS1, TS2, TS3, TS4) is determined as a function of a plurality of mutually different reference times (t1, t2, t3, t4) which are distributed over a period length (TR1) of the time reference signal (32, 48).

2. The method according to claim 1, wherein the signal section duration (TS1, TS2, TS3, TS4) is determined on the basis of an evaluation signal which represents the time interval between the at least one transmission pulse and the at least one reception pulse, in particular wherein the evaluation signal for determining the signal section duration (TS1, TS2, TS3, TS4) is evaluated in parallel for at least some of the reference times (t1, t2, t3, t4).

3. Method according to claim 2, wherein the signal section duration (TS1, TS2, TS3, TS4) on the is determined on the basis of several separate versions of the evaluation signal, in particular wherein the several versions for determining the signal section duration (TS1, TS2, TS3, TS4) are at least partially evaluated in parallel.

4. The method according to claim 3, wherein the plurality of versions of the evaluation signal for determining the signal section duration (TS1, TS2, TS3, TS4) are generated as a function of the reference times and evaluated independently of the reference times, or wherein the plurality of versions of the evaluation signal for determining the signal section duration (TS1, TS2, TS3, TS4) are generated independently of the reference times and evaluated as a function of the reference points.

5. The method according to one of claims 2 to 4, wherein the signal section duration (TS1, TS2, TS3, TS4) represents a time duration of a signal section of the evaluation signal, wherein the signal section duration (TS1, TS2, TS3, TS4) is determined as a sum of several predetermined reference time durations (TR2), each of which is smaller than the period length (TR1) of the time reference signal (32, 48).

6. Method according to one of the preceding claims, wherein a distance between the reference times is smaller than the period length (TR1) of the time reference signal (32, 48).

7. Method according to one of the preceding claims, wherein the signal section duration (TS1, TS2, TS3, TS4) is determined for each of the reference times with a first resolution (TR2), and wherein the for the reference times (t1, t2, t3, t4) determined signal section durations are combined using a statistical calculation rule in order to determine the signal section duration (TS1, TS2, TS3, TS4) with a second resolution which is higher than the first resolution (TR2).

8. The method according to one of the preceding claims, wherein the signal section duration is formed by a first signal section duration (TS1, TS3) which is determined as a function of a first reference time (t1) and a second reference time (t3), wherein a second signal section duration (TS2, TS4) is determined as a function of a third reference time (t2) and a fourth reference time (t4), wherein a first distance between the first reference time (t1) and the second reference time (t3) is equal to a second distance between the third reference time (t2) and the fourth reference time (t4), and wherein, in order to measure the pulse transit time, a difference between the first signal section duration (TS1, TS3) and the second signal section duration (TS2, TS4) is formed in order to compensate for the first distance and / or the second distance.

9. Method according to one of the preceding claims, wherein the determination of the signal section duration (TS1, TS2, TS3, TS4) is carried out as a function of a control parameter, wherein the signal section duration (TS1, TS2, TS3, TS4) is determined as a function of the plurality of reference times (t1, t2, t3, t4) if the control parameter has a predetermined value, and wherein otherwise the signal section duration (TS1, TS2, TS3, TS4) not dependent on the multiple reference times (t1, t2, t3, t4).

10. The method according to claim 9, wherein a signal quality is determined which represents a signal-to-noise ratio of the received signal, and wherein the control parameter has the predetermined value as a function of the signal quality.

11. Method according to claim 9 or 10, wherein, if the control parameter does not have the predetermined value, the signal section duration (TS1, TS2, TS3, TS4) is determined as a function of only one reference time.

12. Method according to one of the preceding claims, wherein a first signal section duration (TS1) and a second signal section duration (TS2) are determined in parallel or sequentially as a function of the plurality of reference times (t1, t2, t3, t4).

13. Method according to one of the preceding claims, wherein the plurality of reference times (t1, t2, t3, t4) represent a plurality of, preferably at least 10, mutually different signal times, and wherein the signal times are preferably independent of the transmission pulse (34) and / or a reception pulse (36), or wherein the signal times are determined as a function of the time reference signal (32).

14. Device for determining a distance value, comprising: - a transmitter-receiver arrangement for transmitting a transmitting a signal with at least one transmit pulse (34) and receiving a receive signal with at least one receive pulse (36); and - a measuring device which is arranged to carry out the method according to one of the preceding claims.

15. The device according to claim 14, wherein the measuring device comprises a multiprocessor system and a field programmable gate array with a plurality of delay elements connected in series and logical links.

16. Device according to claim 14 or 15, characterized in that the measuring device is designed as a single-chip system.

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