RU2436117C1 - Method of measuring distance from radiator to controlled medium - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: existing methods of measuring distance are based on differential frequency signal (DFS) analysis. In the disclosed method, distance is determined from the measured values of probing frequency at two time instants corresponding to DFS zeroes, separated from each other by a whole number of DFS half-periods. This enables to lower the required frequency deviation of the probing signal. Two versions of the present method are disclosed.

EFFECT: measuring distance with minimisation of the required frequency tuning range.

2 cl, 2 dwg

Description

The invention relates to the field of near location and, in particular, to level meters of a controlled environment. A known method of measuring distance [1], which is an analogue, consists in the fact that a frequency-modulated signal is emitted in the direction of the medium being monitored, a signal reflected from the medium is received, by converting the probe and reflected signals on the mixer, a difference frequency signal (RMS) is received, and a difference signal is measured the frequency by which the measured distance is calculated.

The disadvantage of this method is the presence of a discrete measurement error, the value of which may turn out to be unacceptably large. An increase in the accuracy of measuring the distance in this case is possible due to an increase in the frequency deviation, but if high accuracy is required, the magnitude of the necessary deviation may turn out to be technically unrealizable.

Also known are methods of measuring the distance to a controlled environment [2, 3], which are analogues and reduce discrete error. They are based on various methods of extracting distance information from the RFS. So, in [2], in order to reduce the discrete error, the time moments of the appearance of characteristic points (for example, zeros of the difference frequency signal) are determined, the accumulation of the values of the weight function corresponding to the characteristic points of the RMS and calculation of the distance taking into account the values of the weight function.

In the method [3], the distance is measured by emitting a frequency-modulated signal in the direction of the medium being monitored, receiving a reflected signal, receiving an RF system, generating two pulsed signals when the radiation frequency coincides with two specified reference frequencies, measuring the duration of the interval between these signals, maintaining this interval constant by comparing it with the reference time interval and the necessary changes in the amplitude of the symmetrical triangular modulation voltage, forming I pulsed signals corresponding to the extremes of the RMS, changes in the sign of the derivative of the modulating triangular voltage at the moment of the appearance of one of these pulses after the radiation frequency reaches one of the two values of the reference frequencies, the measurement of the difference frequency during the measurement interval, selected so as to reduce the discrete error of measuring the distance to Wednesday.

Analogs [2, 3] have disadvantages; higher frequency tuning ranges are required, since the processing methods implemented in them require a sufficiently large number of characteristic points of the RMS for a given modulation period; the second drawback is the dependence of the measurement error on the nonlinearity of the modulation characteristic.

There is also a known method of measuring distance [4], which is a prototype in which the nonlinearity of the modulation characteristic for the error in measuring the distance is taken into account based on the moments of appearance of characteristic points of the RMS. The disadvantage of this method is that its effectiveness depends on the number of characteristic points of the RF system. At small distances, their number decreases, which makes it necessary to increase the frequency range.

Thus, both the analogues [2, 3] and the prototype [4] implement methods for processing the difference frequency signal, which requires an increase in the frequency tuning range.

The technical problem is the development of a method for measuring distance with the minimum required frequency tuning range.

1. In the first embodiment, the technical problem is solved as follows. In the direction of the medium being monitored, a frequency-modulated signal with a symmetric modulation characteristic is emitted, a signal reflected from the medium is received, by mixing it with a probing signal, a difference frequency signal is obtained, the number of half-periods m of the difference frequency signal on the modulation half-period is determined from zero values, the start time of the first half-period of the RPS is measured - t _n , measured the end time m of the half-period - t _{n + m} , measured the frequency of the probe signal at times t _n , t _{n + m} - f _n , f _{n + m} , and the measured distance it is calculated by the formula (ascending branch of the modulation characteristic):

where ν is the speed of electromagnetic waves.

Formula (1) is obtained from the following considerations. Phase difference between the probing and reflected signals

where θ is the phase of the reflection coefficient, which very little depends on the frequency.

For some f _n

where n is an unknown integer corresponding to the zero value of the difference frequency signal.

Similarly, for f _{n + m}

± - correspond to the ascending and descending branches of the modulation characteristic.

Under the assumption that θ _n = θ _{n + m} , we obtain (1).

The error in determining R will ultimately be determined by the measurement error f _{n + m} , f _n . We will proceed from the natural assumption that the errors are independent, equal and normally distributed, then

Expression (2) allows us to evaluate the relationship between the mean square values of δf and δR:

, приходим к выражениюDue to the fact that

we arrive at the expression

, которую надо иметь достаточно большой на периоде модуляции несущей. Это достигается за счет увеличения диапазона перестройки частоты, которая составляет 500÷700 МГц.In the analogues and prototype, the smoothing of the measurement error depends on the number of characteristic points of the RMS, from value

, which must be large enough during the period of carrier modulation. This is achieved by increasing the frequency tuning range, which is 500 ÷ 700 MHz.

It can be seen from (3) that δR is independent of m; therefore, the frequency deviation is chosen to ensure the necessary accuracy regardless of the value of m, which makes it possible to do with a smaller frequency deviation. If we assume that the measured distance lies within 1 ÷ 30 m, af _{n + m} -f _n = 150 MHz, then in accordance with (3) we have:

R = 1 m, δR = 0.94 · 10 ^-6 δf [cm], δf - [Hz];

R = 30 m, δR = 2.22 · 10 ^-5 δf.

Obviously, the frequency tuning range is 2Δf> f _{n + m} -f _n . For these estimates, we can take 2Δf = 200 MHz, while the accuracy of measuring the frequency δf can be of the order of 10 ⁵ Hz. Averaging over several periods of modulation can improve the given estimates.

2. According to the second option, the technical problem is solved as follows.

по которым вычисляется расстояние по формулеIn the direction of the medium being monitored, a frequency-modulated signal with a symmetric modulation characteristic is emitted, a signal reflected from the medium is received, by mixing it with a probing signal, a difference frequency signal is obtained, the number of half-periods m of the difference frequency signal on the modulation half-period is determined from zero values, the start time of the first half-period of the RPS is measured - t _n , measured the end time m of the half-cycle - t _{n + m} , the frequency of the probing signal is reduced on the mixer using a constant frequency signal from f ₀ , which coincides with the central frequency of the probing signal. At the mixer output, the frequency of the converted signal over the interval of the half-period of modulation T _M / 2 varies from Δf to zero. Next, the converted signal is fed to the amplifier. The passband ΔF is selected from the condition ΔF≥ν / 4R _min (if ν = 3 · 10 ⁸ m / s, R _min = 1 m, then ΔF≥75 MHz), so that the center frequency of the amplifier will be Δf-ΔF / 2. From the output of the amplifier, the signal is supplied to the measurement unit at moments t _n , t _{n + m} frequencies

by which the distance is calculated by the formula

This option simplifies the procedure and improves the accuracy of frequency measurement. Expression (3) in this embodiment takes the form:

The proposed method for measuring distance has a set of operations performed with probing and reflected signals, which are unknown for methods and devices for this purpose. It follows that the inventive method meets the criterion of "novelty."

The inventive step can be estimated based on the following features of the proposed method.

1. The proposed method requires less frequency deviation, because its accuracy does not depend on the number of characteristic points of the RMS, which takes place in analogues [2, 3] and prototype [4].

и от их разности (суммы), расстояние неизменно, дискретная ошибка δR=c/8Δf, требующая для ее уменьшения специальных способов обработки СРЧ, отсутствует.2. From formulas (3) and (5) it follows that the error in determining the distance by the proposed method depends only on the accuracy of the frequency measurement

and from their difference (sum), the distance is invariable, there is no discrete error δR = c / 8Δf, which requires special methods for processing the RMS to reduce it.

.3. The nonlinearity of the modulation characteristic greatly increases the measurement error if the distance is measured by the frequency of the difference signal, i.e. in all known FM level gauges, in the proposed method, the influence of nonlinearity is minimized, determined by the increase in measurement error

.

These differences do not follow explicitly from available sources, which allows us to conclude that the claimed method meets the criterion of "inventive step".

Possible structural diagrams of the two proposed embodiments of the proposed method are shown in figure 1, a), b). Blocks included in the device: 1 - transceiver microwave module; 2 - modulator; 3 - block processing system of the RF; 4, 5 - transmitting and receiving antennas; 6 - directional coupler; 7 - frequency measurement unit; 8 - microprocessor; 9 - indicator; 10 - shear frequency generator; 11 - converter and frequency amplifier. The operation of the schemes is as follows. At the modulating input of the transceiver microwave module 1 from the modulator 2, a symmetrical triangular voltage is supplied, modulating the frequency of the transmitter. From the output of the transmitting part of unit 1, the signal through the directional coupler 6 is supplied to the transmitting antenna 4, from the second output of the directional coupler 6 the signal is supplied (according to the variant of FIG. 1, a) to the frequency measuring unit 7, according to the variant of FIG. 1, b - to the block conversion and amplification 11, the second input of which from the generator 10 is supplied with frequency oscillations f ₀ equal to the average frequency of the probing signal. From the output of block 11, the oscillations, the frequency of which does not exceed the deviation Δf of the probing signal, are fed to the frequency measuring unit 7. The signal reflected from the controlled medium is supplied to the receiving input of module 1 using the receiving antenna 5 3, where it is filtered, amplified, limited, turning into a sequence of rectangular pulses, which is fed to one of the inputs of the microprocessor 8. From the second output of the modulator 2, the pulse signal is applied to the microprocessor 8 s specifying half-periods of modulation. The microprocessor 8 at each half-period of modulation determines the number of half-periods of the RMS m, generates short pulse signals that coincide in time with the beginning of the first and end of the m-th periods of the RMS. These signals are fed to the frequency measurement unit, determining the moments when the measurement began. From the output of block 7, the measured frequency values are supplied to the microprocessor 8, where, in accordance with formulas (1) or (4), the distance is calculated. The calculation results are submitted to indicator 9.

The proposed method allows to measure the distance with a smaller deviation compared to methods based on the analysis of the differential frequency signal, which reduces the level of mismatch of the microwave path, and therefore reduces spurious amplitude modulation of the differential frequency signal, increasing the measurement accuracy t _n and t _{n + m} and, ultimately, the distance to the environment. Reducing the frequency deviation simplifies the implementation of FM, which is especially important for digital synthesis of the frequency of the probing signal. Important is the absence in the proposed method of a discrete error inversely proportional to the frequency deviation.

Bibliographic data

1. Theoretical foundations of radar. / Ed. J.D. Shirman. M .: Sov. Radio, 1970.560 s.

2. Application of Japan 30-1591, MKI G01S 13/34. / Inventions of the countries of the world. 1985. No.15.

3. RF patent No. 2151408, G01S 13/34.

4. RF patent No. 2234108 of 08/10/2004.

Claims (2)

1. The method of measuring the distance from the emitter to the controlled medium, including radiation in the direction of the medium of the radio signal with periodic frequency modulation, receiving the reflected signal, mixing it with the radiated signal and receiving the differential frequency signal, characterized in that on each modulation half-cycle the number of half-periods "m "difference-frequency signal is further determined start time t _n the first half cycle and the end time m-th half cycle t _{n + m,} measure the frequency of the signal f _n, f _{n + m,} the corresponding yk bound moments of time, and the distance is calculated by the formula:

ν is the speed of electromagnetic waves above the medium. 2. A method of measuring the distance from the emitter to the controlled medium, including radiation in the direction of the medium of the radio signal with periodic frequency modulation, receiving the reflected signal, mixing it with the radiated signal to obtain a difference frequency signal, mixing it with the carrier frequency of the probe signal, characterized in that each half-period of modulation determines the number of half-periods "m" of the differential frequency signal, then determine the start time of the first half-period t _n and the end time of the m-th half-period t _{n + m} , measure t is the frequency of the signal obtained by lowering the frequency of the probe signal by the magnitude of the carrier frequency at times t _n , t _{n + m} , and the distance is calculated by the formula:

Where

,

- the measured frequency of the low-frequency sounding signal; ν is the speed of electromagnetic waves above the medium.

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