Method for using radar device and radar device
By employing Chirp-Z transform and narrow-frequency spectrum analysis in frequency-modulated continuous wave radar, the problems of high energy demand and insufficient accuracy in existing technologies are solved, enabling high-precision range determination in low-energy environments.
Patent Information
- Application Number
- CN202510593247.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-05-08
- Filing Date
- 2025-05-08
- Publication Date
- 2025-11-11
AI Technical Summary
Existing frequency-modulated continuous wave radars have high energy requirements and insufficient accuracy when determining the distance between radar equipment and objects, which affects the application effect.
An improved approach is adopted, which reduces energy requirements while maintaining the accuracy of distance determination by determining the maximum spectral value within a coarse frequency range and then using the Chirp-Z transform for fine spectral analysis within a narrow frequency range.
While reducing the energy requirements of radar equipment, it maintains or improves the accuracy of distance determination and is suitable for continuous operation in low-energy environments.
Smart Images
Figure CN120928331A_ABST
Abstract
Description
Technical Field
[0001] This invention relates, in one aspect, to a method for determining the distance between a radar device and an object using a frequency-modulated continuous wave radar. In another aspect, this invention also relates to a radar device for determining the distance between a radar device and an object using a frequency-modulated continuous wave radar. Background Technology
[0002] A radar device is typically a device that generates and emits transmitted signals, receives reflected signals caused by the transmitted signals at an object, and evaluates the reflected and / or transmitted signals. The reflected signal is the echo of the transmitted signal at the object. The transmitted signal, and therefore the reflected signal, is an electromagnetic wave with a frequency within the radar frequency range. The evaluation provides at least information about the object. This information may include, for example, the distance or velocity between the radar device and the object.
[0003] Regardless, radar equipment includes an antenna assembly and a control unit. The antenna assembly has an antenna for transmitting a transmitted signal and an antenna for receiving a reflected signal, or a transmitting antenna for transmitting a transmitted signal and a receiving antenna for receiving a reflected signal. The control unit is configured to generate a transmitted signal and transmit it through the antenna assembly, as well as to receive reflected signals through the antenna assembly and evaluate the reflected and / or transmitted signals.
[0004] This method and radar equipment involve frequency-modulated continuous wave radar. Therefore, the frequency of the transmitted signal is modulated. Thus, it is neither a pulse radar nor an unmodulated continuous wave radar. Frequency-modulated continuous wave radar is also abbreviated as FMCW radar. This abbreviation stands for frequency-modulated continuous wave radar.
[0005] When this type of method is executed during the operation of this type of radar equipment, the following method steps are performed:
[0006] - Generate an FM transmission signal and transmit the transmission signal through an antenna device.
[0007] - Receive the reflected signal caused by the emitted signal at the object through an antenna device.
[0008] - The transmitted and reflected signals are mixed together to form a mixed signal, and the spectrum of the mixed signal is determined. The mixed signal has beats.
[0009] - Determine the spectral maximum value and the spectral maximum frequency of the spectral maximum value in the spectrum. The beat rate is essentially determined by the spectral maximum value and the spectral maximum frequency.
[0010] - Determine the distance between the radar equipment and the target using the maximum frequency in the spectrum. The maximum frequency in the spectrum corresponds to the distance.
[0011] These method steps, as well as other method steps, are in principle performed by the control device. The method steps are referred to as steps below.
[0012] It is known from existing technology that the spectrum of a mixed signal can be determined using the Fast Fourier Transform (FFT).
[0013] The Fourier coefficients S of the FFT k Determine using the following formula:
[0014] Where k = 0, 1, 2, ..., N-1
[0015] In the above formula, s n These are time-discrete measurements of the mixed signal. These measurements are taken by the control device. N is the number of measurements.
[0016] Belongs to the Fourier coefficient S k Fourier frequency f k Determine using the following formula:
[0017] in
[0018] In this formula, f s It is the sampling frequency, which is used by the control device to discretely measure the measured value s in a time-discrete manner. n Perform sampling.
[0019] Its related Fourier frequency f k Fourier coefficient S at point k These are spectral lines. The spectral frequency step size of two successive spectral lines is Δf = f s / N. For k=0, the spectral line with the lowest Fourier frequency and located at the lower limit frequency f is obtained. min,FFT = at f0 = 0, and for k = N / 2, the spectral line with the highest Fourier frequency is obtained and is at the upper limit frequency f. max,FFT =f N / 2 = at fs / 2.
[0020] Therefore, the spectrum starts from the lower limit frequency f. min,FFT Extending to the upper limit frequency f max,FFT And it is formed by spectral lines, where each spectral line is composed of Fourier coefficients S. k and Fourier frequency f kCharacterization. The spectrum, in principle, has the shape of a Gaussian bell curve in terms of frequency. The spectrum formed by FFT has a number of 1+N / 2 spectral lines.
[0021] The maximum frequency of the spectral maximum is determined with an accuracy of spectral frequency step size Δf. Typically, the accuracy of determining the maximum frequency, and therefore the distance to the radar equipment and object determined using the maximum frequency, is not precise enough for the application. However, the accuracy of determining the maximum frequency can be improved through various methods. Accuracy is improved if the determined maximum frequency is closer to the actual maximum frequency, which is the frequency at which the spectral maximum value is located.
[0022] This method involves interpolation between spectral lines, and using interpolation, the maximum frequency of the spectrum can be determined with greater precision.
[0023] According to another method, zeros are added to the measured values before determining the spectrum to reduce the frequency step size Δf. The added zeros are evaluated as measured values, and thus also increase N. Due to the reduced frequency step size, the determined maximum frequency of the spectrum has greater accuracy. Methods that increase the number of measured values of the mixed signal used to determine the spectrum are not considered here.
[0024] According to another method, the spectrum of a mixed signal is determined using the Chirp-Z transform. The Chirp-Z transform is abbreviated as CZT.
[0025] CZT's Fourier coefficients S k Determine using the following formula:
[0026] Where k = 1, 2, ..., M-1
[0027] Alternatively, the Fourier coefficients S of CZT can be calculated using the following formula. k :
[0028] Where k = 0, 1, 2, ..., M-1
[0029] In the two formulas above, s n Again, these are time-discrete measurements of a mixed signal, and N is the number of measurements. M is the number of Fourier frequencies. It is optional and, for example, pre-given.
[0030] In the formula above, A is determined according to the following formula:
[0031]
[0032] The W in the above formula is determined according to the following formula:
[0033]
[0034] f min It is the lower limit frequency of the spectrum, and f max This is the upper limit frequency of the spectrum. Compared to other methods described for determining the maximum frequency of the spectrum based on FFT, this method improves the accuracy of the maximum amplification.
[0035] If the application requires the highest possible accuracy in determining the maximum frequency of the spectrum and therefore implements the above method using CZT of the radar equipment, the disadvantage of this type of method is the high energy requirement of the radar equipment in determining the distance between the radar equipment and the object when the method is executed. Summary of the Invention
[0036] Therefore, the objective of this invention is to describe a method and a radar device of this type, wherein the energy requirement for determining the distance is reduced when the method is performed without affecting the accuracy of the distance determination.
[0037] This task is solved by the method according to claim 1. This method modifies this type of method and is therefore also a frequency-modulated continuous wave radar. The modified method includes the following steps:
[0038] The following sub-steps are performed in the first step:
[0039] - Generates and emits frequency-modulated transmission signals.
[0040] - Receive the reflected signal caused by the transmitted signal at the object.
[0041] - The transmitted signal and the reflected signal are mixed together to form a mixed signal.
[0042] In the second step, the following sub-steps are performed:
[0043] - Determine the approximate spectrum of the mixed signal within a coarse frequency range.
[0044] - Determine the maximum spectral value in the rough spectrum.
[0045] - Determine the coarse maximum frequency of the spectrum value within the coarse frequency range.
[0046] In the third step, considering the maximum frequency of the coarse spectrum, a frequency range is determined on the one hand, and the number of spectral frequencies within that frequency range is also determined on the other hand. Here, the quotient of the frequency range and the number yields the target spectral frequency step size. The maximum frequency of the coarse spectrum is located within the frequency range, and the frequency range is smaller than the coarse frequency range. Preferably, the frequency range is as narrow as possible around the maximum frequency of the coarse spectrum.
[0047] In the fourth step, the fine spectrum of the mixed signal within a frequency range having that number of spectral frequencies is determined using the Chirp-Z Transform (CZT). Compared to the FFT, the CZT allows for the selection of both the frequency range and the number of spectral frequencies within that range, independent of the number of measurements.
[0048] In the fifth step, the fine-grained maximum frequency of the spectral maximum value within the frequency range is determined. This is determined with the precision of the target spectral frequency step size. For example, the target spectral frequency step size is pre-defined according to the application.
[0049] In the sixth step, the distance between the radar device and the object is determined using the maximum frequency of the fine spectrum. Preferably, this distance is displayed to the user.
[0050] The radar equipment performing this method typically has a control unit and an antenna unit. The steps of the method are executed by the control unit, which, as previously described, transmits signals and receives reflected signals through the antenna unit.
[0051] Compared to existing methods that also utilize CZT, this method requires less energy from the radar equipment without compromising the accuracy of range determination. The lower energy requirement stems from the fact that CZT is used only within a specific frequency range, and this frequency range is smaller than a coarse frequency range.
[0052] This method can be designed and improved in various ways. Here, these steps are also performed by radar equipment, preferably by a control device.
[0053] In the first design of this method, the first step is first re-executed. Then, in a step, considering the previously determined fine-spectrum maximum frequency, the frequency range is determined again on the one hand, and the number of spectral frequencies within that frequency range is determined again on the other hand. Here, the quotient of the frequency range and the number again yields the target spectral frequency step size. This step is a modified third step, in which the previously determined fine-spectrum maximum frequency is considered instead of the coarse-spectrum maximum frequency. Specifically, the fine-spectrum maximum frequency is considered such that it lies within that frequency range. Then, the fourth step is re-executed. Then, the spectral maximum value is searched in the fine spectrum. If the spectral maximum value is found, the fine-spectrum maximum frequency of that spectral maximum value in the fine spectrum is determined, and the sixth step is re-executed.
[0054] Suitable for this design is to execute the method continuously. During continuous execution, the distance between the radar device and the target is also continuously determined, i.e., updated at regular time intervals. The second step is not performed here, therefore the coarse spectrum is not re-determined. Thus, only CZT is still used in this frequency range, which further reduces energy requirements.
[0055] If the maximum spectral value is not found in the design scheme, several alternative design schemes can be derived to still find the maximum spectral value.
[0056] In the first alternative design scheme, the first step is first repeated. Then, in a step, considering the previously determined maximum frequency of the fine spectrum, the frequency range is determined again on the one hand, and the number of spectral frequencies within the frequency range is determined again on the other hand. Preferably, the frequency range is larger than the previously determined frequency range. Here, the quotient of the frequency range and the number yields a spectral frequency step size larger than the target spectral frequency step size. This step is a modified third step, wherein, in particular, the quotient must not exceed the target spectral frequency step size, but is larger. Then, the fourth step is repeated. Then, the maximum spectral value is searched in the fine spectrum. If the maximum spectral value is found, the fine spectrum maximum frequency of the maximum spectral value within the frequency range is determined, and the third, fourth, fifth, and sixth steps are repeated. By repeating the third, fourth, fifth, and sixth steps, the target spectral frequency step size is set again, and the distance is determined with the accuracy of the target spectral frequency step size.
[0057] In an improved version of the above design, if the maximum spectral value is not found again, the steps according to the aforementioned design are repeated. Preferably, the frequency range is expanded.
[0058] In the second alternative design, the first step is first repeated. Then, considering the previously determined maximum frequency of the fine spectrum, a frequency range different from the previously determined frequency range is determined, and the number of spectral frequencies within that frequency range that differs from the previously determined number is also determined. Preferably, the frequency range is larger than the previously determined frequency range. Here, the quotient of the frequency range and the number yields the target spectral frequency step size. This step is a modified third step. Then, the fourth step is repeated. The maximum spectral value is then searched for in the fine spectrum. If the maximum spectral value is found, the fine spectrum maximum frequency of that maximum spectral value within the frequency range is determined, and the sixth step is repeated. Steps three, four, and five do not need to be repeated because the target spectral frequency step size has already been set, and therefore the distance is determined with the precision of the target spectral frequency step size.
[0059] In an improved version of the above design, if the maximum spectral value is not found, the steps according to the above design are repeated. Preferably, the frequency range is increased.
[0060] In the third alternative design scheme, steps two, three, four, five, and six are repeated. Preferably, this design scheme is executed only if a maximum spectral value was not found when executing the first and / or second alternative design schemes. This is because in the case of the third alternative design scheme, step two is executed again, where a coarse spectrum of the mixed signal is determined, which implies additional energy requirements.
[0061] If a maximum spectral value has been found and the distance has been determined in one of the alternative design schemes, then the first design scheme of the method is preferably re-executed. If no maximum spectral value is found in any of the alternative design schemes, then the method according to claim 1 is re-executed. Therefore, the method is executed continuously, and the radar device executing the method is also in continuous operation.
[0062] In another design of this method, the frequency range and the number of spectral frequencies are determined by additionally taking into account previously determined distances. By additionally considering previously determined distances, a narrower frequency range around the maximum frequency of the actual spectrum is determined.
[0063] In another design of this method, the rate of change of the previously determined distance is determined, and the number of frequency ranges and spectral frequencies is determined with respect to said rate. By additionally considering the rate, a narrower frequency range around the maximum frequency of the actual spectrum is determined.
[0064] In one design of this method, a coarse spectrum of the mixed signal is determined using an FFT. The FFT is suitable for determining a coarse spectrum because it generates signals between 0 and f. S The spectrum is located within a frequency range between / N. The maximum spectral value representing the distance lies within this frequency range in every case. Therefore, using FFT allows us to roughly determine the actual maximum frequency of the maximum spectral value, i.e., the coarse maximum frequency.
[0065] In another design, a coarse frequency range is determined using the bandwidth of the transmitted signal and / or a pre-given maximum velocity between the radar device and the object.
[0066] In another design, the transmitted signal is generated at a frequency that increases or decreases over a transmission interval Δt. The transmission interval is the duration for which the transmitted signal is emitted. Preferably, the increasing frequency has a constant slope over time within the transmission interval. This type of transmitted signal can be generated in a simple manner and results in high accuracy in determining the distance to the object.
[0067] In an improved version of the above design scheme of this method, the frequency range is defined by an upper frequency f. max and lower limit frequency f min Limitation. The upper limit frequency f max The predetermined maximum distance d between the radar device and the object is determined. max The emission interval Δt is proportional to the product of the reciprocal of the speed of light, 1 / c0. The speed of light is the speed of light in a vacuum. Therefore, the applicable equation is:
[0068]
[0069] Preferably, the upper limit frequency is determined as the product of the maximum distance, the emission interval, the reciprocal of the speed of light, and a factor of 2. Therefore, the applicable frequency is:
[0070]
[0071] In this design scheme, the lower limit frequency f min The predetermined minimum distance d between the radar equipment and the object is determined. min The product of the emission interval Δt and the reciprocal of the speed of light, 1 / c0, is proportional. Therefore, it applies to:
[0072]
[0073] Preferably, the lower limit frequency is determined as the product of the minimum distance, the emission interval, the reciprocal of the speed of light, and a factor of 2. Therefore, the applicable frequency is:
[0074]
[0075] As already mentioned, a maximum distance d is preset for the radar equipment, i.e., the control device. max and minimum distance d min These maximum and minimum distances are relevant to the corresponding application of the method and can be easily determined. The maximum and minimum distances are preferably stored in the control device.
[0076] In an improved version of the above design, the divisor (the speed of light c0 divided by twice the bandwidth B of the transmitted signal) is first determined, along with a pre-given maximum speed v between the radar device and the object. max The distance change Δd between the radar device and the object is determined by summing the products of the two successive transmissions of the transmitted signal and the time interval T between them. Therefore, the applicable method is:
[0077]
[0078] Furthermore, the maximum distance d is determined by adding the product of the weighting factor k and the distance variation Δd to a previously determined distance d between the radar equipment and the target. max Therefore, the applicable terms are:
[0079] d max =d+k·Δd
[0080] Furthermore, the minimum distance d is determined by subtracting the product of the weighting factor k and the distance change Δd from the previously determined distance d between the radar device and the object. min Therefore, the applicable terms are:
[0081] d max =dk·Δd
[0082] Furthermore, a weighting factor is selected between 1 and 2. A maximum speed v is pre-defined for the radar equipment, i.e., the control unit. max The maximum speed is related to the specific application of the method and can be easily determined.
[0083] This task is solved not only by the aforementioned methods but also by the radar device according to claim 15. The radar device is constructed to perform one of the aforementioned methods. For this purpose, the radar device specifically includes a control device and an antenna device.
[0084] In one design of radar equipment, the radar equipment is a field device. Preferably, the radar equipment is a level measuring device or a level switch. If the radar equipment is a level measuring device or a level switch, the object is a medium, and the level of the medium in the container should be measured or monitored. The distance then corresponds to the level of the medium in the container. Because the level changes only slowly with respect to the time interval T between two successive transmissions of the transmitted signal, this method is particularly suitable for applications in level measuring devices and level switches.
[0085] In another design, the radar device has a current loop interface and is further configured for communication via said current loop interface and for feeding electrical energy from the current loop solely through said current loop interface. This method is particularly suitable for radar devices of this design. Because the power extractable from the current loop is so low that it is insufficient to safely perform methods known from the prior art. In the case of the method described herein, the energy required for each determination of distance during continuous operation is low, thus ensuring reliable operation when the radar device is fed solely from the current loop. In a preferred improvement, the radar device is a level measuring device or a level switch as described previously. Attached Figure Description
[0086] Numerous possibilities for designing and improving the method and the radar device are given in detail. For this purpose, reference is made not only to the dependent claims of the independent claims but also to the following description of preferred embodiments taken in conjunction with the accompanying drawings. In the drawings,
[0087] Figure 1 Showing radar equipment and objects,
[0088] Figure 2 The flowchart of the method is shown.
[0089] Figure 3 The transmitted and reflected signals are shown over time.
[0090] Figure 4a The rough spectrum of the mixed signal is shown, and
[0091] Figure 4b The fine spectrum of the mixed signal is shown. Detailed Implementation
[0092] Figure 1 A radar device 1 and an object 2 are shown. In this embodiment, the radar device 1 is a level measuring device, and the object 2 is a medium having a level in a container 3. The radar device 1 is configured to continuously determine the distance d between the radar device 1 and the object 2. In this embodiment, the distance d corresponds to the level of the medium in the container 3.
[0093] Radar device 1 has a control unit 4, an antenna unit 5, and a current loop interface 6. Antenna unit 5 has a transmitting antenna 7 and a receiving antenna 8. Radar device 1 is configured to communicate via the current loop interface 6 and to be powered solely from a current loop via the current loop interface 6. The radar device is connected to a current loop 9 via the current loop interface 6. During operation, radar device 1 communicates via the current loop 9 and is powered solely from the current loop. Communication specifically includes continuously transmitting over a distance d.
[0094] The control device 4, and thus the radar device 1, are configured to perform the methods described below. Figure 2 A flowchart showing the method executed by control device 4 is provided.
[0095] In step 101, the following sub-steps are performed:
[0096] In the first sub-step 101a of the first step 101, a frequency modulation transmission signal 10 is generated. Figure 3 The transmitted signal 10 is shown over time. The transmitted signal 10 is generated here at an increasing frequency f over the transmission interval Δt. More precisely, the frequency f increases from f1 to f2. The increasing frequency f has a constant slope within the transmission interval Δt. The frequency f lies within the radar frequency range. The transmitted signal 10 has a bandwidth B = f2 - f1.
[0097] In the second sub-step 101b, a transmission signal 10 is transmitted through the transmitting antenna 7 of the antenna device 5. Figure 1 The propagation of the transmitted signal 10 in the direction toward the object 2 is shown, and the transmitted signal is an electromagnetic wave.
[0098] In the third sub-step 101c, the receiving antenna 8 of the antenna device 5 receives the reflected signal 11 caused by the transmitted signal 10 at the object 2, and the reflected signal is also an electromagnetic wave. Figure 1 This illustrates the propagation of the reflected signal 10 in the direction toward radar device 1, and Figure 3 The reflected signal 10 over time is shown.
[0099] In the fourth sub-step 101d, the transmitted signal 10 and the reflected signal 11 are mixed together to form a mixed signal. The reflected signal 11 is delayed by a delay time t compared to the transmitted signal 10. M See Figure 3 The mixed signal has a beat frequency f. M The beat rate. Beat frequency f M and delay time t M They correspond to each other. Therefore, it is possible to use the beat frequency f in addition to the speed of light c0. M The actual distance d is determined precisely.
[0100] In step 102, the following sub-steps are performed:
[0101] In the first sub-step 102a of the second step 102, a coarse spectrum of the mixed signal within a coarse frequency range is determined using FFT. Here, the Fourier coefficients S k,FFT Determine using the following formula:
[0102] Where k = 0, 1, 2, ..., N-1
[0103] In the above formula, k is the running index, and s n These are time-discrete measurements of the mixed signal. These are also measured by control device 4. N is the number of measurements.
[0104] Belongs to the Fourier coefficient S k,FFT Fourier frequency f k，FFT Determine using the following formula:
[0105] in
[0106] In this formula, f s The sampling frequency is used by control device 4 to measure the mixed signal s in a time-discrete manner. n Perform sampling.
[0107] Figure 4a The diagram schematically illustrates spectral lines 12 of a coarse spectrum determined using FFT. Each of the spectral lines 12 is represented by a Fourier coefficient S. k,FFT (Entered there as Sk) and its related Fourier frequency f k，FFT (Enter f there) k The approximate frequency step size of the two successive spectral lines is determined to be Δf. FFT =f s / N. The spectral line 12, which has the lowest Fourier frequency, is at the lower limit frequency f. min,FFT =f0=0, and for k=N / 2, the spectral line 12 with the highest Fourier frequency is obtained, and it is at the upper limit frequency f. max,FFT =f N / 2 =f s / 2 places.
[0108] The approximate frequency range starts from the lower limit frequency f. min,FFT Extending to the upper limit frequency f max,FFT The rough spectrum, in principle, has the shape of a Gaussian bell curve in terms of frequency.
[0109] In the second sub-step 102b, the spectral maximum value 13 is determined in the coarse spectrum. This determination reveals that the spectral maximum value 13 is located at a Fourier frequency f. k-1,FFT Spectral line 12 and having a Fourier frequency f k，FFT The spectral lines are between 1 and 2.
[0110] In the third sub-step 102c, the coarse maximum frequency of the spectral maximum value 13 within the coarse frequency range is determined. This determination yields the Fourier frequency f. k，FFT The closest value to the maximum spectral value is 13. Therefore, the approximate maximum frequency of the spectrum is f. k，FFT .
[0111] In the third step 103, on the one hand, the maximum frequency f around the rough spectrum is determined. k，FFT The frequency range is to be as narrow as possible, and on the other hand, the number M of spectral frequencies within the frequency range is determined. The frequency range is limited by a lower frequency f. min and upper limit frequency f max Limitations. In this embodiment, f min =f k-1,FFT , and f max =f k，FFT The maximum spectral value of 13 lies within this frequency range. Around the maximum frequency f of the approximate spectrum... k，FFT The narrowness of the frequency range here is due to the spectral frequency step size Δf in terms of resolution. FFT Limitations. Furthermore, the frequency range (f) max -f min The quotient is formed by the quantity M. This quotient is the target frequency step size Δf. Therefore, the applicable values are:
[0112]
[0113] The quantity M is determined here to be such that the target spectral frequency step Δf yields a distance d with a certain accuracy, which is sufficient for the application.
[0114] In step 104, the mixed signal is determined in a frequency range having a number of M spectral frequencies, i.e., at f, when using CZT. min and f max The fine spectrum between them. Here, the Fourier coefficients S k Determine using the following formula:
[0115] Where k = 1, 2, ..., M-1
[0116] In the above formula, k is the running index, and s nAgain, N represents the time-discrete measurements of the mixed signal, and N is again the number of measurements. The run index k associated with FFT differs from the run index k associated with CZT.
[0117] In the above formula, A is determined according to the following formula:
[0118]
[0119] The W in the above formula is determined according to the following formula:
[0120]
[0121] f s It is a known sampling frequency. Figure 4b The spectral line 12 is schematically shown as a fine spectrum determined using CZT.
[0122] In step 5, 105, the fine-grained maximum frequency of the spectral maximum value 13 is determined within the frequency range. This determination yields the frequency f. k-1 The closest value to the maximum spectral value is 13. Therefore, the maximum frequency of the fine spectrum is f. k-1 .
[0123] In step 6.106, the maximum frequency f of the fine spectrum is used. k-1 The distance d between radar device 1 and object 2 is determined under the following conditions. The maximum frequency of the spectrum, 13, represents the beat rate. In an ideal situation, the maximum frequency f of the fine spectrum is... k-1 Corresponding to beat frequency f M The purpose of this method is to apply a frequency sufficiently close to the beat frequency f. M Determine the maximum frequency f of the fine spectrum k-1 .
[0124] In step 7.107, the following sub-steps are performed:
[0125] In the first sub-step 107a of the seventh step 107, the first step 101 is re-executed, wherein the first sub-step 101a is preferably omitted.
[0126] In the second sub-step 107b, considering the previously determined fine-spectrum maximum frequency f k-1 In this case, the frequency range is determined again, and the frequency range is again subject to the upper limit frequency f. max and lower limit frequency f min The limitation is further defined, and on the other hand, the number M of spectral frequencies within the frequency range is determined again, wherein the quotient of the frequency range and the number M yields the target spectral frequency step size Δf.
[0127] In the third sub-step 107c, the fourth step 104 is executed again.
[0128] In the fourth sub-step 107d, the maximum spectral value 13 is searched in the fine spectrum, and the maximum spectral value is also found here.
[0129] In the fifth sub-step 107e, the fine spectral maximum frequency of the spectral maximum value 13 in the frequency range is determined, and the sixth step 106 is re-executed.
[0130] In step 7, the method is continuously executed by radar device 1, and each execution provides the current distance d between radar device 1 and object 2, i.e., the current level of the medium in container 3.
[0131] After initially determining the distance d between radar device 1 and object 2, the frequency range is determined as follows, wherein the frequency range is subject to the upper limit frequency f as explained above. max and lower limit frequency f min limit.
[0132] The upper limit frequency is determined according to the following formula:
[0133]
[0134] The lower frequency limit is determined according to the following formula:
[0135]
[0136] In the two formulas above, d max It is the maximum distance between radar device 1 and object 2, and d min This refers to the minimum distance. In this embodiment, the maximum and minimum distances correspond to the maximum and minimum levels of the medium in container 3, i.e., object 2.
[0137] Maximum distance d max When using a previously determined distance d, the following formula is used to determine it:
[0138] d max =d+k·Δd
[0139] Minimum distance d min Similarly, using the previously determined distance d, it is determined according to the following formula:
[0140] d max =dk·Δd
[0141] In the two formulas above, Δd is the distance change between radar device 1 and object 2, and k is a weighting factor, which is chosen between 1 and 2.
[0142] The distance change Δd is determined according to the following formula:
[0143]
[0144] In the above formula, B is the bandwidth of the transmitted signal 10, and v max It is the pre-given maximum speed between the radar equipment and the object, and T is the time interval between two successive transmissions of the transmitted signal 10.
[0145] The above determination of the frequency range after first determining the distance d has also been used in alternative design schemes to first determine the distance d, since the initial value of the distance d has been given in advance.
[0146] Figure Labels
[0147] 1. Radar equipment
[0148] 2. Object
[0149] 3. Container
[0150] 4. Control device
[0151] 5. Antenna device
[0152] 6. Current loop interface
[0153] 7. Transmitting antenna
[0154] 8. Receiving antenna
[0155] 9. Current loop
[0156] 10. Transmit signal
[0157] 11. Reflected signal
[0158] 12. Spectral lines
[0159] 13. Maximum value of the spectrum.
Claims
1. A method for determining the distance (d) between a radar device (1) and an object (2) by means of a frequency-modulated continuous wave radar, using a radar device (1). The first step includes the following sub-steps: generating and transmitting a frequency-modulated transmission signal (10); receiving a reflected signal (11) caused by the transmission signal (10) at the object (2); and mixing the transmission signal (10) and the reflected signal (11) into a mixed signal. Then, in the second step, a sub-step is performed: determining the approximate frequency range (f min,FFT f max,FFT The coarse spectrum of the mixed signal in the coarse spectrum, the maximum spectral value (13) in the coarse spectrum, and the maximum spectral value (13) in the coarse frequency range (f) min,FFT f max,FFT The coarse maximum frequency (f) in the spectrum k，FFT ), Then, in the third step, considering the maximum frequency (f) of the rough spectrum k，FFT In the case of determining the frequency range (f) min f max And on the other hand, it is determined in the frequency range (f) min f max The number of spectral frequencies (M) in the spectrum, wherein the frequency range (f) max -f min The quotient of the quantity (M) yields the target frequency step size (Δf) of the spectrum. Then, in the fourth step, the frequency range (f) of the mixed signal with a number (M) spectral frequencies is determined using the Chirp-Z transform. min f max The fine spectrum in ) Then, in the fifth step, the maximum spectral value (13) is determined in the frequency range (f) min f max The fine spectrum maximum frequency (f) in ) k-1 ),and Then, in the sixth step, the maximum frequency of the fine spectrum (f) is used. k-1 In the case of ), the distance (d) between the radar device (1) and the object (2) is determined.
2. The method of claim 1, wherein the first step is re-executed. Then, in one step, the previously determined fine-spectrum maximum frequency (f) is considered. k-1 In this case, the frequency range (f) is determined again. min f max ), and on the other hand, determine again the number (M) of spectral frequencies within the frequency range, wherein the frequency range (f max -f min The quotient of the quantity (M) yields the target frequency step size (Δf). Then, step four is repeated. Then, the maximum spectral value (13) is found in the refined spectrum, and If a spectral maximum value (13) is found, then the spectral maximum value (13) is determined to be within the frequency range (f). min f max Find the maximum frequency of the fine spectrum within the range, and then repeat step six.
3. The method according to claim 2, wherein if the maximum spectral value (13) is not found, the first step is re-executed. Then, in one step, considering the previously determined fine-spectrum maximum frequency (f) k-1 In this case, the frequency range (f) is determined again. min f max And on the other hand, it is determined again in the frequency range (f) min f max The number of spectral frequencies (M) in the spectrum, wherein the frequency range (f) max -f min The quotient of the quantity (M) yields a frequency step size greater than the target frequency step size (Δf). Then, step four is repeated. Then, the maximum spectral value (13) is found in the refined spectrum. If a spectral maximum value (13) is found, then the spectral maximum value (13) is determined to be within the frequency range (f). min f max The fine spectrum maximum frequency in ) is then used to re-execute steps three, four, five, and six.
4. The method of claim 3, wherein if no maximum spectral value (13) is found, the step of claim 3 is repeated, and wherein the frequency range (f) is preferably amplified. min f max ).
5. The method according to claim 2, wherein if the maximum spectral value (13) is not found, the first step is repeated. Then, the previously determined fine-spectrum maximum frequency (f) is considered. k-1 In the case of ), on the one hand, the frequency range (f) is determined from the previously determined frequency range. min f max Different frequency ranges, and on the other hand, determining the number of spectral frequencies in said frequency ranges that differ from a previously determined number (M), wherein the quotient of said frequency range and said number yields the target spectral frequency step size (Δf). Then, step four is repeated. Then, the maximum spectral value (13) is found in the refined spectrum. If the maximum spectral value (13) is found, the fine maximum frequency of the maximum spectral value (13) in the frequency range is determined, and step six is repeated.
6. The method of claim 5, wherein if no maximum spectral value (13) is found, the step of claim 5 is repeated, and wherein the frequency range (f) is preferably amplified. min f max ).
7. The method according to any one of claims 2 to 6, wherein if the maximum spectral value (13) is not found, the second step, the third step, the fourth step, the fifth step and the sixth step are re-executed.
8. The method according to any one of claims 2 to 7, wherein the frequency range (f) is determined by additionally taking into account a previously determined distance (d). min f max ) and the number of spectral frequencies (M).
9. The method according to any one of claims 2 to 8, wherein the rate of change of the previously determined distance (d) is determined, and the number of frequency ranges and spectral frequencies is determined in addition to taking the rate of change into account.
10. The method according to any one of claims 1 to 9, wherein the coarse spectrum is determined when using FFT.
11. The method according to any one of claims 1 to 10, wherein a predetermined maximum velocity (V) is used between the bandwidth (B) of the transmitted signal (10) and / or the radar device (1) and the object (2). max Determining the coarse frequency range (f) in the case of ) min,FFT f max,FFT ).
12. The method according to any one of claims 1 to 11, wherein the transmitted signal (10) is generated at a frequency (f) that increases or decreases over the transmission interval (Δt), wherein preferably the increasing frequency (f) has a constant slope over time within the transmission interval (Δt).
13. The method of claim 12, wherein the frequency range is subject to an upper frequency limit (f). max ) and lower limit frequency (f min )limit, The upper limit frequency (f) max The distance (d) between the radar device (1) and the object (2) is determined to be the pre-given maximum distance (d) between them. max The product of the emission interval (Δt) and the reciprocal of the speed of light (c0) is proportional. The lower limit frequency (f) min The distance (d) between the radar device (1) and the object (2) is determined to be a pre-given minimum distance (d) between them. min The product of the emission interval (Δt) and the reciprocal of the speed of light (c0) is proportional. Preferably, the upper limit frequency (f) max The maximum distance (d) was determined to be the maximum distance. max The product of the emission interval (Δt), the reciprocal of the speed of light (c0), and a factor of 2, and Preferably, the lower limit frequency (f) min The minimum distance (d) was determined to be the minimum distance. min The product of the distance between the light rays (Δt), the reciprocal of the speed of light (c0), and the factor 2.
14. The method according to claim 13, wherein a predetermined maximum velocity (v) between the radar device (1) and the object (2) is determined by dividing the speed of light (c0) by twice the bandwidth (B) of the transmitted signal (10). max The distance change (Δd) between the radar device (1) and the object (2) is determined by summing the product of the two successive transmissions of the transmitted signal (10) and the time interval (T). The maximum distance (d) is determined by adding the product of the weighting factor (k) and the distance change (Δd) to a previously determined distance (d) between the radar device (1) and the object (2). max ), The minimum distance (d) is determined by subtracting the product of the weighting factor (k) and the distance change (Δd) from the previously determined distance (d) between the radar device (1) and the object (2). min ),and The weighting factor (k) is selected between 1 and 2.
15. A radar device (1) for determining the distance between a radar device (1) and an object (2) by means of a frequency-modulated continuous wave radar, characterized in that, The radar device (1) is configured to perform the method according to any one of claims 1 to 14.
16. The radar device (1) according to claim 15, characterized in that, The radar device (1) is a field device, preferably a level measuring device or a level switch.
17. The radar device (1) according to claim 15 or 16, characterized in that, The radar device (1) has a current loop interface (6) and is configured to communicate through the current loop interface (6) and to be fed electrical energy from the current loop (9) solely through the current loop interface (6).