JP3390673B2 - Water level measurement method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water level measuring method for measuring a distance from an antenna to a water surface by using radio waves to obtain a water level. 2. Description of the Related Art A conventional radio wave level meter using frequency-modulated radio waves receives radio waves radiated from the aerial to the water surface and receives the reflected radio waves. After the generated beat signal is filtered, frequency / voltage conversion processing is performed, and the distance from the voltage value obtained in the frequency / voltage conversion processing to the water surface, that is, the water level is calculated. According to the above-mentioned prior art, there is a problem that an erroneous water level may be output due to the influence of unnecessary frequency components due to multiple reflections occurring between the water surface and the antenna. Further, there is a problem that the disturbance of the radio wave generated by the wave on the water surface is reflected on the side wall surface of the well for measuring the water level and becomes an unnecessary frequency component, which causes a decrease in the S / N ratio of the beat signal and makes it difficult to accurately detect the water level. . SUMMARY OF THE INVENTION The present invention proposes a solution to this problem, in which the influence of unnecessary frequency components due to multiple reflections between the water surface and the antenna included in the beat signal is proposed. It is an object of the present invention to remove the influence of the disturbance of the radio wave generated by the wave on the water surface reflected on the side wall surface of the well for measuring the water level to become an unnecessary frequency component and to lower the S / N ratio of the beat signal. In order to achieve the above object, according to the present invention, there is provided a transmitter for generating a frequency-modulated high-frequency signal with a frequency shift width of FM modulation being ΔF. The frequency-modulated high-frequency signal from the transmitting unit is repeated toward the water surface via the circulator (the repetition frequency is f
m) An antenna that radiates and receives a reflected wave reflected from the water surface, a reflected wave received by the antenna is received through the circulator, and a high-frequency signal from the transmitting unit is transmitted through the circulator. Receiving part of the high-frequency signal radiated toward the water surface from the circulator and detecting a beat signal with the received reflected wave, and a signal for receiving the beat signal from the receiving part and processing it Water level does not change rapidly using radio wave level meter with processing unit
In the water level measurement method in the case, opposite from the water level data obtained before
The value of the optimum beat frequency calculated by
Give the adaptive filter an optimal passband
In the signal processing unit, data obtained by extracting a frequency component of the beat signal from the received beat signal by a fast Fourier transform process is provided to the adaptation filter, and thereafter, the beat signal obtained by processing with the adaptation filter is obtained. Of the beat signal, the frequency (fr) of the beat signal is extracted by discrete Fourier transform processing using the major frequency component of the extracted beat signal, and the following calculation is performed from the frequency of the extracted beat signal. It is characterized in that the distance (R) from the antenna to the water surface is obtained by the equation R = C (radio wave propagation velocity) · fr / (4 · ΔF · fm). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 shows an FM-C according to an embodiment of the present invention.
In the block diagram of the water level meter using W radar, 1 is a transmission unit,
Reference numeral 2 denotes a circulator, 3 denotes an antenna, 4 denotes a receiving unit, 5 denotes a signal processing unit, 6 denotes an operation unit, 7 denotes a display unit, 8 denotes a well, 9 denotes a water surface, 10 denotes a transmission wave, and 11 denotes a reflected wave. [0008] 1 is a transmission unit, which determines the frequency shift width of FM modulation.
A frequency-modulated high-frequency signal is generated as ΔF, and the frequency-modulated high-frequency signal, that is, a transmission wave, generated in the transmission unit 1 is supplied to the antenna 3 via the circulator 2 and travels from the antenna 3 to the water surface 9 of the well 8. The transmitted wave 10 repeats
(The repetition frequency is fm) . The reflected wave 11 reflected by the water surface 9 is received by the antenna 3 and is input to the receiver 4 via the circulator 2. The receiver 4 receives the frequency-modulated high-frequency signal generated by the transmitter 1, that is, a part of the transmission wave via the circulator 2, and a part of the transmission wave and the received reflected wave are mixed. The resulting beat signal is detected. The beat signal is amplified by the receiving unit 4 and then output to the signal processing unit 5. The signal processing unit 5 receives the beat signal, samples the beat signal, converts the beat signal into digital data by A / D conversion, and performs arithmetic operation. The spectrum of the frequency component is obtained by performing the fast Fourier transform by the processing. Since it contains frequency components as noise caused by reflected waves etc., in order to remove these frequency components as noise, use that the water level does not suddenly change in advance , that is, the water level does not change suddenly Place
In this case , the optimum beat frequency value obtained by back calculation from the water level data obtained previously is given to the adaptation filter of the signal processing unit 5 using the operation unit 6, and the spectrum of the frequency component obtained by the fast Fourier transform is obtained. Is processed by the adaptive filter to remove the above-described noise, and the frequency value of the beat signal obtained as a result of further performing the discrete Fourier transform processing using the maximum value of the frequency component obtained by this processing is referred to as FM-CW R = C · fr / (4 · ΔF · fm) R: distance from antenna to water surface C: radio wave propagation speed fr: frequency of beat signal ΔF: frequency shift width of FM modulation fm: frequency of FM modulation The distance to the water surface is calculated by substituting into the repetition frequency. Since C, ΔF, and fm are all known in the above formula, R can be obtained by substituting the value of fr. According to the present invention, the water level does not change rapidly.
In this case, the observed beat signal is converted to digital data and then subjected to a fast Fourier transform to give the optimum value obtained by calculating the beat frequency back from the already obtained water level to optimize the passband of the adaptive filter. By setting and performing adaptive filter processing, a reduction in the S / N ratio, that is, the influence of noise, caused by the above-described multiple reflection or disturbance of radio waves due to waves on the water surface and the wall of the well is removed, and accurate beats are obtained by discrete Fourier transform. The frequency can be detected, and an effect that an accurate water level can be calculated from the beat frequency is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a block diagram of a water level gauge using an FM-CW radar. [Description of Signs] 1 ... Transmission unit 2 ... Circulator 3 ... Antenna 4 ... Reception unit 5 ... Signal processing unit 6 ... Operation unit 7 ... Display unit 8 ... Well 9 ... Water surface 10 ... Transmission waves 11 ... Reflection

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 23/284 G01S 13/34 G01S 13/42

Claims (1)

(57) Claims: 1. A transmitting section for generating a frequency-modulated high-frequency signal with a frequency shift width of FM modulation being ΔF , and a frequency-modulated signal from the transmitting section. The high-frequency signal through the circulator toward the water surface (repeated frequency f
m) An antenna that radiates and receives a reflected wave reflected from the water surface, a reflected wave received by the antenna is received through the circulator, and a high-frequency signal from the transmitting unit is transmitted through the circulator. Receiving part of the high-frequency signal radiated toward the water surface from the circulator and detecting a beat signal with the received reflected wave, and a signal for receiving the beat signal from the receiving part and processing it Water level does not change rapidly using radio wave level meter with processing unit
In the case of the water level measurement method, the optimum beat frequency obtained by back calculation from the water level data obtained previously
Give the value of the number to the adaptive filter of the above signal processor and pass
The band is optimally set, and the signal processing unit applies data obtained by extracting the frequency component of the beat signal to the adaptation filter by the fast Fourier transform processing, and then applies the data to the adaptation filter. The main frequency component is extracted from the frequency components of the beat signal obtained by the processing, and the frequency (f) of the beat signal is obtained by discrete Fourier transform using the extracted main frequency component of the beat signal.
r) is extracted, and the distance (R) from the antenna to the water surface is obtained from the frequency of the extracted beat signal by the following formula: R = C (radio wave propagation speed) · fr / (4 · ΔF · fm) Water level measurement method.