RU2661488C1 - Method of the distance measurement - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to the field of measurement technology, in particular to measuring distance in a near frequency radar of industrial use, for example in level gauges. This result is achieved due to the fact that a linear connection of middle frequency of the difference signal with the measured distance is used for measurement. Decrease in the error in measuring the distance is ensured by a decrease in the distortion of the difference frequency signal (DFS) by the parasitic frequency modulation (FM), which is caused by frequency dispersion in the waveguide of the antenna-waveguide tract (AWT). Reduction of distortions is carried out by setting the necessary FM law. Necessary FM law depends on the length of the AWT waveguide and on the distance between the antenna and the object under control, so the process of it’s determination is iterative, but rapidly converging.

EFFECT: achieved technical result of the invention is a decrease in the measurement error of the distance caused by frequency dispersion in the AWT.

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Description

The invention relates to the field of measuring technology, in particular to measuring the distance in the near frequency radar of industrial applications, for example, in closed tanks when measuring the liquid level by converting the measured distance from the measuring device to the surface of the liquid in the filling level.

To achieve high accuracy, measurements in rangefinders with frequency modulation try to provide the largest possible frequency tuning range ΔF for frequency modulation (FM) [1, p. 274]. A prerequisite for high measurement accuracy is the linear law of frequency change during FM.

In many cases, for example, at high temperatures, in hazardous areas, radiation exposure, and a number of other factors, only the absence of mechanical contact with the probed object allows you to perform a distance measurement operation and automate the measurement process. However, under such adverse conditions, it is necessary, using the waveguide, to spread the signal generation and processing unit from the antenna installed in the control zone rather far. In this case, the distance from the antenna to the probed objects is subject to measurement. Due to the frequency dispersion of electromagnetic waves in the waveguide, spurious frequency modulation (FFM) of the probe waves occurs even with a linear FM transmitter. Moreover, the measurement error increases significantly in the presence of spurious amplitude modulation (PAM) of the probing signal and the presence of many objects probed simultaneously with the controlled objects. Often, one of the objects is useful, and the rest are considered to be interference, which cause an increase in the error of distance measurement when moving a useful object past the interfering one even in favorable conditions without the MFD. The presence of FFM and PAM lead to a significant increase in such an error.

To reduce the error, various methods of refining the measurement results are used. In particular, there is a known radar method for measuring distance, based on spectral analysis of the RF system with subsequent refinement of the measurement results at an additional stage of processing the RF system, during which the reference signal is formed, its parameters are varied and used to calculate the distance when the spectrum parameters of the reference signal are closest to the parameters RF spectrum [2]. However, distortions of the signal spectrum due to frequency dispersion lead to measurement errors by all known methods [3, 4, 5].

Reducing the influence of spurious frequency modulation is proposed in an iterative method of generating a probing adaptive frequency-modulated signal for a rangefinder with periodic frequency modulation [6], which is a prototype, the cycle of which includes the formation of periodic modulating voltage, generating and exciting probe waves, receiving, after the propagation time, reflected echo waves, mixing them with part of the power of the sounding waves, extracting the difference frequency signal, measuring the duration of instantaneous periods of the difference frequency signal for signal processing interval, which is part of the modulation period. In subsequent measurement cycles, corrective voltage is generated to reduce the difference between the average and instantaneous values of the duration of the periods to a given control level.

If there is no interference, then, to obtain the correcting modulation voltage, and to measure the distance to the probed surface, echo waves reflected from the probed surface are used

In the presence of interference, the above version of the method is not applicable.

Therefore, under the conditions of interference when several objects are simultaneously probed to form a probing adaptive frequency-modulated signal for a rangefinder with periodic frequency modulation, one part of the power of the probing waves is emitted through the measuring channel in the direction of the probed objects and wave echoes from the probed objects are used to measure the distance to them, and the second part of the power of the sounding waves excite the reference channel, made in the form of a piece of feeder line, and use reflected from the end f The core line echoes the signal to obtain the correct modulation voltage.

The formation of the periodic modulation voltage U _mod (t) is performed by generating digital samples of U _mod (t _j ) at fixed times t _j , converting them into discrete analog samples and low-pass filtering, while generating digital samples of the modulating voltage U _{mod, k} (t _j ) at the k-th modulation period is performed recursively in accordance with the voltage U _{mod, k-1} (t _j ) at the previous (k-1) -th period and the correcting voltage ΔU _k (t _j ) obtained taking into account the non-uniformity of the instantaneous periods of the difference signal frequencies:

- корректирующее напряжение;Where:

- corrective voltage;

- постоянный коэффициент, равный средней крутизне нарастания модулирующего напряжения;

- a constant coefficient equal to the average steepness of the rise of the modulating voltage;

U _m - the amplitude of the modulating voltage;

T _m - modulation period;

- относительное изменение периода сигнала разностной частоты;

- the relative change in the period of the signal of the differential frequency;

ΔT _p (t _i ) = T _pi -T _cf - the deviation of the period of the signal of the differential frequency from the average value;

- средний период сигнала разностной частоты;

- the average period of the differential frequency signal;

N is the number of crossings of the zero level signal of the differential frequency for the processing interval,

moreover, the values of η (t) at intermediate points t _j between the moments when the signal crosses the differential frequency of the zero level t _{i are} calculated using interpolation formulas.

It is possible to generate digital samples of the modulating voltage at the intersection points of the zero level with a differential frequency signal in the kth modulation period U _{mod, k} (t _i ) by rearranging on the time axis similar samples of the (k-1) th period using the formulas:

and at the intermediate points of the modulation period using interpolation.

The cited method can be implemented by a device [7] containing a digital signal processing circuit, an antenna-waveguide device, a controlled radio-frequency signal generator, a frequency synthesizer with two inputs and one output, a directional coupler with one input and two outputs, a mixer with two inputs and one output, a series-connected filter, a preliminary analog processing circuit, an analog-to-digital converter, a control circuit with one input and two outputs. In this case, the input of the controlled generator of the radio frequency signal is connected to the output of the frequency synthesizer, the inputs of which are connected, respectively, with the first output of the controlled generator of the radio frequency signal and the first output of the digital signal processing circuit, and the output of the controlled generator of the radio frequency signal is connected to a series-connected power divider and directional coupler, the first output of which is connected to the input of the antenna-waveguide device. The inputs of the mixer are connected, respectively, with the second output of the power divider and with the second output of the directional coupler, and the output is connected to series-connected controlled filters. The output of the second controlled filter is connected to a preliminary analog processing circuit, the output of which is connected to the input of the analog-to-digital converter, and the output of the analog-to-digital converter is connected to the input of the digital signal processing circuit. The input of the control circuit is connected to the second output of the digital signal processing circuit, and its two outputs are connected to the second inputs of the respective controlled filters.

In the last cited method, when probing one or more objects, the modulation law does not change. But when probing several objects, some of which may play the role of interference, the reference channel is used, made in the form of a piece of the feeder line, in which there is also dispersion, however, the degree of distortion of the signal by spurious frequency modulation in the reference channel cannot coincide with the distortion of the signal by spurious frequency modulation in the measuring channel. As a result, an error arises again, caused by both the dispersion in the measuring channel and the combined effect of dispersion, PAM, and interference.

The technical result of the invention is to reduce the error of distance measurement both due to the influence of frequency dispersion in the waveguide of the antenna-waveguide path, and because of the combined effect of frequency dispersion, PAM and the mutual influence of probed objects, each of which plays the role of interference in measuring distances to other objects.

The technical result is achieved by the fact that in the method of measuring distance by a radio range finder with periodic discrete frequency modulation of the probe radio waves, the measurement cycle of which includes:

generating a radio frequency signal with periodic discrete frequency modulation with known values of the initial ƒ ₀ and final frequencies, the frequency modulation range Δƒ, the modulation period and the number of discrete samples of the frequency M;

formation and emission of radio waves in the direction of the probed objects;

the allocation of part of the generated radio frequency signal;

reception, after the propagation time, of the echo waves and the formation of the reflected signal from them;

mixing it with the selected part of the generated radio frequency signal;

the allocation of low-frequency components of the resulting signal and the allocation of them the signal of the differential frequency (RMS), containing information about the distances to the controlled objects;

analogue processing of RFs;

analog-to-digital conversion of the RF system;

calculation of the difference frequency corresponding to the reflection from one of the monitored objects from the number of probed;

calculating the distance to the controlled object from the known propagation velocity of the radio waves and the differential frequency of the RMS;

changing the law of frequency modulation;

carry out the following additional set of actions in compliance with the following conditions.

In each measurement cycle, with the exception of the first measurement result of the distance R to one controlled object, the known length of the waveguide of the antenna-waveguide path L and the critical frequency of the waveguide ƒ _cr , the law of frequency modulation is changed and used in the next cycle of measuring the distance to this controlled object.

In this case, the measurement of the distance to other controlled objects is sequentially performed with other modulation laws.

In the first measurement cycle, the signal is generated with a frequency modulation law defined by discrete frequency samples частоты (m) with current numbers m, in accordance with the expression

;

;

;

.Where

;

;

;

.

, где R_н=R/L, и при превышении модуля разности

заранее заданной величины Δ в следующих циклах измерений сигнал генерируют с законом частотной модуляции, определенным дискретными отсчетами частоты в соответствии с выражениемThe measured distance determines the difference

where R _n = R / L, and when exceeding the modulus of the difference

of a predetermined value Δ in the next measurement cycles, the signal is generated with the law of frequency modulation determined by discrete frequency samples in accordance with the expression

ниже заранее заданной величины Δ сигнал генерируют с законом частотной модуляции, определенным дискретными отсчетами частоты в соответствии с предыдущим выражением.while decreasing the modulus of the difference

below a predetermined value Δ, a signal is generated with a frequency modulation law determined by discrete frequency samples in accordance with the previous expression.

Using discrete samples of frequency ƒ (m), a signal with digital samples of frequency ƒ _c (m) is generated.

The analysis of the prior art, including a search by patent and scientific and technical sources of information, and identifying sources containing information about analogues of the claimed invention, allows us to establish that the applicant has not found technical solutions characterized by features identical to all the essential features of the claimed invention. The definition from the list of identified analogues of the prototypes of the method made it possible to identify a set of essential (with respect to the technical result perceived by the applicant) distinctive features in the claimed objects set forth in the claims. Therefore, the claimed technical solution meets the requirement of "novelty" under the current law. Information about the fame of the distinguishing features in the totality of the characteristics of the known technical solutions with the achievement of the same as the claimed method and device, there is no positive effect. Based on this, it was concluded that the proposed technical solution meets the criterion of "inventive step".

A comparison of the features of the known and proposed methods for analyzing the inventive step shows a significant difference between the conditions, the modes of operations on electrical signals (both continuous and in the form of digital samples), which are characterized by amplitude, frequency and phase.

In addition, the conditions and modes of implementing the set of actions are interconnected with the dimensions of the antenna-waveguide device of the radio range finder and the measured distance.

These differences lead to the appearance of qualitatively new properties of the claimed method - the ability to accurately measure distances to controlled objects with distortion of the IF signals caused by dispersion, and PAM.

The essence of the proposed method is illustrated using a structural diagram of one of the possible radio range finders, schematically depicted in FIG. 1 by the spectra depicted in FIG. 2, FIG. 3, the graphs depicted in FIG. four.

In FIG. 2 shows a spectrum of a three-frequency signal in the presence of a waveguide and a linear law of frequency modulation.

In FIG. Figure 3 shows the spectrum of the same three-frequency signal in the presence of a waveguide, measuring the distance to an object with an average difference frequency and the law of frequency modulation ƒ (m) in the second measurement cycle.

In FIG. 4 shows the error in measuring the distance to one controlled object in the presence of a waveguide and interfering reflection from the antenna.

A radio range finder with frequency modulation of the probe radio waves (Fig. 1) contains: a controllable generator of a radio frequency signal (UGRS) 1 with one input and two outputs; Digital Signal Processing (DSP) 2 with three outputs and one input; antenna waveguide device (AVU) 3; power divider (DM) 4 with one input and two outputs; directional coupler (NO) 5 with one input and two outputs; mixer 6 with two inputs and one output; frequency synthesizer (MF) 7 with one output and two inputs; filter 8; pre-analog processing circuit (SPAO) 9; analog-to-digital converter (ADC) 10 with two inputs and one output.

The output of the midrange 7 is connected to the input of the UGRS 1. The inputs of the midrange 7 are connected, respectively, with the first output of the UGRS 1 and with the first output of the SSCOS 2. The output of the UGRS 1 is connected to series-connected DM 4 and NO 5, and the first output of HO 5 is connected to the AVU 3 The second outputs DM 4 and HO 5 are connected, respectively, with the first and second inputs of the mixer 6, the output of which is connected to the input of the filter 8. The output of the filter 8 is connected to the series-connected SPAO 9 and ADC 10, and the output of the ADC 10 and its second input are connected , respectively, with the first input and the second output of the alarm system 2. The third output of the alarm system 2 is nformatsionnym yield of DME.

The antenna АВУ 3 can be made, for example, in the form of an axisymmetric conical horn.

The filter 8 can be made in the form of a well-known [8, p. 93-129] high-pass filter or band-pass filter.

The practical implementation of the device is not difficult and is carried out on the basis of widely distributed electronic elements, for example, those produced by ANALOG DEVICES, MOTOROLA, MICRONETICS, PERE-GRINE, etc.

Using a radio range finder with frequency modulation of the probing radio waves, the distance measuring method is as follows.

Part of the generated RF signal with periodic frequency modulation in the form of a sequence of RF signals with known values of the initial ƒ ₀ and final frequencies, the frequency modulation range Δƒ, the modulation period and the number of discrete samples of the frequency M, from UGRS 1 (Fig. 1), controlled by MF 7, through DM 4 and HO 5 it enters the antenna of the AVU 3, which generates directional radiation in the direction of the probed objects. After reflection from the probed objects, the echo waves are received by the antenna АВУ 3 and converted into a reflected signal, which through НО 5 is supplied to the second input of the mixer 6. As a heterodyne signal, the selected part 4 of the generated signal is used as the local oscillator, which is fed to the first input of the mixer 6. The output signal of the mixer 6 it is filtered by filter 8 and from the first output it enters the input of SPAO 9, where it is processed by a given gain and additional suppression of high-frequency components. As a result, the low-frequency components of the resulting signal are distinguished, from which the information component of the RMS u _and (t, τ _R ), which contains information about the distances to the controlled objects, is extracted. The information component of the UHF u _and (t, τ _R ) are used to calculate the distance. At the same time, it may also contain components created by reflections from controlled and interfering objects, which lead to measurement errors.

The selected informational component of the RMS u _and (t, τ _R ) through the ADC 10 is fed to the first input of the RNC 2. Using SCLR 2, all actions on the RL components are performed, the synthesizer of the MF 7 is set by setting discrete frequency codes, and the ADC 10 is synchronized.

Using digital samples u _qi (m, τ _R ), (where m = 0, ..., M - 1; M is the number of samples) of the information component of the UHF u _and (t, τ _R ) using SCR 2, the spectrum S _and (τ _R ). This spectrum is distorted by spurious frequency modulation due to frequency dispersion in the waveguide, and its shape depends on the length of the waveguide of the antenna-waveguide path, spurious amplitude modulation and the presence of interference. Then, the center frequency of the spectrum is calculated, for example, by the frequency of its maximum, the distance R is calculated and recorded in the memory of SCE 2 according to the known propagation velocity of the radio waves and the calculated center frequency of the spectrum.

Using the calculated distance R and a priori information recorded in the memory of SCOS 2 and a priori information about the waveguide length of the antenna-waveguide path L, the critical waveguide frequency ƒ _cr , the initial frequency ƒ ₀ and the frequency modulation range Δƒ, according to one of the above expressions for ƒ (m), depending from the ratio of the calculated distance R to the waveguide length of the antenna-waveguide path L, the necessary frequency modulation law ƒ (m) and its digital samples ƒ _c (m) are calculated. The codes corresponding to the digital samples of the frequencies ƒ _c (m), from one of the outputs of the SSCOS 2 control the frequency synthesizer MF 7, with which the frequency of generation of the UGRS 1 is set close to ƒ (m).

The choice of a controlled object is carried out using the well-known method of measuring ranges to several targets [9] p. 236, implemented on the basis of digital spectrum analysis [9] p. 240, which in this case is performed, for example, by sequentially processing part of the samples of the discrete spectrum of the superficial frequency ( processing in the spectral window), starting from the first count. The number of processed samples corresponds to the value of the resolution element of the used signal with frequency modulation (for example, 3 samples). Then, sequential discrete movement of the processed portion of the spectrum is performed by the value of one resolution element. The selected part of the samples of the discrete spectrum is processed under the condition that the maximum sample in this part of the spectrum exceeds a predetermined threshold level. In this case, the spectral window is set symmetrically with respect to the detected maximum reference.

After measuring, in accordance with the claimed method, the distances to the first selected object, continue further sequential movement of part of the selected samples (spectral window) until the entire spectrum of the RMS is processed and the distances to all controlled objects are measured.

The distortion of the RHF spectrum S (x) is illustrated in FIG. 2, which shows the normalized amplitude spectrum of a three-frequency superfine frequency, calculated using the discrete Fourier transform [1]. In the calculations, we used: the normalized waveguide length x _L = 2ΔƒL / s equal to 20 (here c is the speed of light); normalized distances to three controlled objects x _R = 2ΔƒR / c, equal to 0, 20 and 40, respectively; diameter of a circular waveguide 25 mm; ƒ ₀ = 8.5 GHz and the modulation range Δ _f = 3 GHz is used; x = FT is the normalized current frequency F is the cyclic frequency of the frequency response, T is the duration of the time interval corresponding to a monotonic change in frequency with frequency modulation. The spectrum is normalized to the amplitude value of the spectrum, not distorted by the dispersion. Taking into account the frequency dispersion in the waveguide of the antenna-waveguide path, the normalized frequencies of the spectrum maxima corresponding to the components of the RMS from the three monitored objects are about 27 bin, 47 bin, and 67 bin.

In FIG. Figure 3 shows that, as a result of implementing the method of measuring the distance for one of the monitored objects, for example, an object that creates an RMS term with a frequency of about 47 bins, the law of frequency modulation ƒ (m) using SCR 2 and MF 7 is set such that in this term The RFM disappears in the IFM, while in the components of the RFM with other frequencies (in the given example with the frequencies of 27 bin and 67 bin), the IFM is not completely suppressed and the spectrum becomes undistorted only for the controlled object that creates the term of the RFM with the frequency of 47 bin. As a result, you can accurately determine the distance to this controlled object. After measuring the distance to one controlled object, measurements are successively carried out to other controlled objects with different modulation laws and with similar sets of actions.

The effect of interfering reflection from the antenna on the magnitude of the error in measuring the distance over the spectrum of the signal with the IFM obtained by modeling the measurement process is shown in FIG. 4 (curve 11). The signal u (m) with amplitude U was formed on the basis of the expression

when the distance changes from 0 to 1.5 m. The noise-signal ratio q = 0.2. The waveguide length is 5 m. In calculating the spectrum, the Blackman weight function was used [10, 11]. Given a constant bias, the maximum value of the error is about 0.25 m.

The same figure shows the measurement error for the same q, but when implementing the inventive method of measuring distance (curve 12). In this case, the maximum error value is about 0.0062 m. In the above example, the total error reduction is 40 times, and the oscillating component of the error decreases by 18 times.

INFORMATION SOURCES

1. Atayants B.A., Davydochkin V.M., Yezersky V.V., Parshin B.C., Smolsky S.M. Precision short-range radar systems for industrial applications. M .: Radio engineering. 2012.512 p.

2. Davydochkin V.M., Parshin B.C. Distance measurement with a level meter with frequency modulation of the emitted signal in the presence of interfering reflections of low intensity. // Proceedings of the Russian NTO RES named after Popova Series: Digital signal processing and its application. 8th International Conference Vol. VIII - 2. Moscow. 2006.S. 530-533.

3. US patent No. 5546088 08/13/1996.

4. US patent No. 6107957 08/22/2000.

5. US patent No. 5504490 A, G01S 13/08, from 02.04. 1996.

6. RF patent No. 2234716. A method of generating a probing frequency-modulated signal for a rangefinder with periodic frequency modulation / Atayants B.A., Ezersky V.V., Baranov I.V., Bolonin V.A., Davydochkin V.M., Kagalenko B.V. Publ. 08/20/2004.

7. RF patent No. 2234688. A method of measuring the distance to the probed material, its electrophysical parameters (options), a device for its implementation and a calibration method. Atayants B.A., Ezersky V.V., Baranov I.V., Bolonin V.A., Davydochkin V.M., Kagalenko B.V., Pronin V.A. Published on 08.20.2004.

8. A.J. Peyton, W. Walsh. Analog electronics on operational amplifiers. (Translated from English): M .: BINOM, 1994.352 s.

9. Bakulev P.A. Radar systems. Textbook for high schools. - M .: Radio engineering. 2004.320 s.

10. Davydochkina S.V. Weight functions for adaptive harmonic analysis of finite-state oscillatory processes // Collection of scientific works of the faculty of Ryazan State Agrotechnological University named after P.A. Kostycheva. Ryazan, 2008.S. 78-81.

11. Dvorkovich V.P., Dvorkovich A.V. Window functions for harmonic signal analysis M .: Technosphere, 2014. - 112 p.

Claims (10)

1. A method of measuring distance with a radio range finder with periodic discrete frequency modulation of the probe radio waves, the measurement cycle of which includes: generating a radio frequency signal with periodic discrete frequency modulation with known values of the initial ƒ ₀ and final frequency, the frequency modulation range Δƒ, the modulation period and the number of discrete samples of the frequency M ; formation and emission of radio waves in the direction of controlled objects; the allocation of part of the generated radio frequency signal; reception, after the propagation time, of the echo waves and the formation of the reflected signal from them; mixing it with the selected part of the generated radio frequency signal; isolating the low-frequency components of the resulting signal and extracting from them a difference frequency signal (RMS) containing information about the distances to the controlled objects, analog processing of the RMS, analog-to-digital conversion of the RMS, calculating the difference frequency corresponding to the reflection from one of the monitored objects, calculating the distance from known the propagation velocity of the radio waves and the differential frequency of the frequency difference, a change in the law of frequency modulation, characterized in that in each measurement cycle with the exception of The result of measuring the distance R to one controlled object, the known length of the waveguide of the antenna-waveguide path L and the critical frequency of the waveguide ƒ _cr, change the law of frequency modulation and use it in the next cycle of measuring the distance to this controlled object. 2. The method according to p. 1, characterized in that in the first measurement cycle the signal is generated with a frequency modulation law defined by discrete samples of frequency ƒ (m) with current numbers m, in accordance with the expression

, where a = Δƒ / ƒ ₀ ; b = ƒ _cr / ƒ ₀ ;

;

, and when the module exceeds the difference

, where R _n = R / L, of a predetermined value Δ in the following measurement cycles, the signal is generated with a frequency modulation law defined by discrete frequency samples in accordance with the expression

, while decreasing the modulus of the difference

below a predetermined value Δ, a signal is generated with a frequency modulation law determined by discrete frequency samples in accordance with the previous expression. 3. The method according to p. 1, characterized in that the discrete samples of the frequency ƒ (m) generate a signal with digital samples of the frequency ƒ _c (m). 4. The method according to p. 1, characterized in that the selection of one of the monitored objects is performed by processing a portion of the samples of the discrete spectrum of the RF system around the expected position of the object, corresponding to the value of one resolution element of the used signal with frequency modulation, and sequential discrete movement of the processed portion of the spectrum by one permission element, starting from the first countdown. 5. The method according to p. 1, characterized in that the processing of the selected part of the samples of the discrete spectrum is carried out when the maximum sample in this part exceeds the predetermined threshold level.

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