RU2523104C1 - Ice-protected echo sounder - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: echo sounder includes a forward digital frequency synthesiser unit whose output is connected to the input of a transmitter, and the control input is connected to a microcontroller. By controlling radiation frequency, the forward digital frequency synthesiser unit enables to avoid the effect of varying parameters of the protective plate on the highest possible depth measured by the echo sounder.

EFFECT: avoiding the effect of varying parameters of the protective plate of the radiating surface of an electroacoustic transducer on the highest possible depth measured by the echo sounder by varying radiation frequency of the echo sounder.

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Description

The present invention relates to hydroacoustic systems for determining the depth and can be used in echo sounders with automatic adaptive detection of echo signals from the bottom and depth measurement and with ice protection of the emitting surface of the electro-acoustic transducer.

To protect the radiating surface of the sonar transducer in the conditions of ice navigation from mechanical damage by crushed ice, protective soundproof plates are used that can withstand the required specific pressure. For ships of classes Ice1 (LU1) protective plates are used from polymer materials, and for ships of classes Icebreaker 6 (LL6) .... Icebreaker 9 (LL9) LU9 - from metals (aluminum, titanium, steel), which must withstand specific pressure up to 100 kg / cm ² [1].

The protective plate is a partition whose resistance is different from the acoustic impedances of two media shared by it, and its acoustic impedance is greater than the acoustic impedance of the medium in which it resides.

The best passage of sound through the partition is possible, i.e. the transmittance of acoustic waves is 1, in the case when an integer number of half-waves λ / 2 fits into its thickness h, i.e. provided that h = n · λ / 2 (n = 1, 2, 3, ...) [2], [3]. The transmittance of acoustic waves τ (f) is determined [2]

$$\tau (f)=\mathrm{one}-{\left(K_p(f)\right)}^2,(\mathrm{one})$$

Where

, $$K_p(f)=\frac{(R_{\mathrm{one}}/R_2)-(R_2/R_{\mathrm{one}})}{\sqrt{\left[{\left(\frac{R_{\mathrm{one}}}{R_2}+\frac{R_2}{R_{\mathrm{one}}}\right)}^2+\mathrm{four}{\left[ctg\left(\frac{2\pi h}{\lambda }\right)\right]}^2\right]}}$$

,

λ = c ₂ / f _u ,

f _u - radiation frequency,

R ₁ = ρ ₁ c ₁ - acoustic resistance of the medium (water), ρ ₁ , c ₁ , specific gravity and speed of sound in water, respectively.

R ₂ = ρ ₂ c ₂ - acoustic resistance of the material of the partition (protective plate), ρ ₂ , c ₂ specific gravity and speed of sound in the material of the protective plate, respectively.

The protective plate is soundproof, i.e. the transmittance of acoustic waves is close to zero if an odd number of quarters of wavelengths fit into its thickness.

If the protective plate has a thickness less than half a wave, then the transmission of sound through it improves with a decrease in its thickness. It should be noted that with an increase in the specific density of the material of which the protective plate is made, the frequency bandwidth decreases in which the transmittance of acoustic waves through the protective plate is close to 1. For a fixed thickness of the protective plate with a change in the speed of sound in the material (for example, due to changes in the ambient temperature) of which the protective plate is made, the central frequency changes at which the transmittance of acoustic waves through the protective plate is equal to units . Thus, the protective plate is a narrow-band filter for acoustic waves, and the higher the acoustic resistance (product of specific gravity and sound velocity) of the material of which the protective plate is made in comparison with the acoustic resistance of water, the narrower the transmission band of acoustic waves and the stronger the dependence of the central position frequencies of the speed of sound with the material of the plate and its thickness. During operation, the speed of sound in the material of the plate changes depending on the ambient temperature, and the thickness of the plate can also change. These changes lead to a decrease in the transmittance of acoustic waves through the protective plate, and therefore to a decrease in the maximum measured depth with an echo sounder. Note that the protective plates are made of polycarbonate, have a lower acoustic impedance, the product (ρ · c), than metals, so their acoustic wavelength bandwidth is wider than that of any of the metals, but the metals have greater mechanical strength.

A classic example of an echo sounder with ice protection for the emitting surface of an electro-acoustic transducer is the Norwegian-made navigation sounder EN 250 Navigation Echo Sounder (SIMRAD, Kongsberg Maritime AS) [4]. The radiating surface of the electro-acoustic transducer is protected in this design by a polycarbonate plate.

The Norwegian company SKIPPER produces a navigation sonar GDS 101 [5]. It has the same specifications as EN250. To protect the radiating surface of the electro-acoustic transducer, it can be installed in a special tank of ice execution (ice protection Tank). A protective plate is additionally mounted to the tank. The tank itself is installed by inserting into the bottom of the tank. In the echo sounders EN 250, GDS 101, the radiation frequency is constant and does not depend on the properties of the protective plate of the emitting surface of the electro-acoustic transducer changing during operation of the echo sounder.

In the known echo sounder [6], which contains a synchronizer, a pulse generator, a piezoelectric vibrator, an amplifier, a detector, a threshold device, an indication unit, a time interval measuring device, an automatic gain control unit (VARU), a VARU unit allows stationary the amplitude of the echo signals, which varies with depth . However, the radiation frequency is constant, therefore, when used with a protective plate of the radiating surface of the electro-acoustic transducer, the maximum measured depth, determined by the radiation frequency, will depend on the physical parameters of the protective plate - thickness, specific gravity, sound velocity in the protective plate.

The closest set of features to the proposed echo sounder is the "Echo sounder" described in the patent [7], which contains a microcontroller, a display, a transmitter, an analog-to-digital converter, a receiver, an electro-acoustic transducer, a VARU unit.

This "Fishfinder" periodically emits sounding pulses and maintains the amplitude of the echo signal in the range, providing the maximum signal to noise ratio for a specific depth by stepwise radiation of power and selecting the minimum necessary gain of the receiver, and also automatically determines the beginning of the echo signal from the bottom.

However, during operation during operation of the echo sounder through the protective plate, this is not enough to ensure measurement of the maximum possible depth.

In this case, the maximum measured depth with an echo sounder will depend on the physical properties of the material of the protective plate - the thickness and speed of sound in the material of the protective plate, because in (1), ρ1, ρ2 are constant values; h, c1, c2 - variables that cannot be controlled. Thus, the disadvantage of the echo sounder [7] is the inability to measure the maximum possible depth due to changes in the physical parameters of the protective plate during its operation, which affect the value of the radiation frequency at which the transmittance of acoustic waves τ (f) is close to unity.

The objective of the invention is to eliminate the influence of changing parameters on the maximum possible depth, measured by an echo sounder.

The technical result of the invention is the compensation of changes in operating parameters of the echo sounder by adjusting the radiation frequency f _u in the automatic mode.

To ensure the specified technical result, the echo sounder with ice protection is made up of a microcontroller, a transmitter, a receiver, and an analog-to-digital converter, the output of which is connected to a microcontroller, as well as an electro-acoustic transducer connected to a transmitter and a receiver, also containing a display, the input of which is connected to the microcontroller , and a block of temporary automatic gain control, the input of which is connected to the microcontroller, and the transmitter is made with a step p by adjusting the power, the adjustment input of which is connected to the microcontroller, the receiver is made with two gain control inputs, the first adjustment input, which provides step-by-step gain control, is connected to the microcontroller, and the second adjustment input is connected to the output of the temporary automatic gain control block, also containing a direct digital synthesizer block frequency, the output of which is connected to the input of the transmitter, and the control input is connected to the microcontroller, while the electro-acoustic transducer installed inside the ship's hull in the protective tank filled with water, secured to the bottom of the vessel and separated from the environment protection plate.

New features in the proposed echo sounder is the introduction of a direct digital frequency synthesizer into the echo sounder, the output of which is connected to the transmitter input, and the control input is connected to the microcontroller. This allows direct control of the radiation frequency to compensate for its departure due to changes in the physical parameters of the protective plate during operation of the echo sounder. The essence of the invention is shown in FIG. 1 and FIG. 2, where FIG. 1 is a block diagram of a declared echo sounder, and FIG. 2 is an example of installing an electro-acoustic transducer relative to the bottom of a vessel.

Microcontroller 1 has five outputs and one input. The display input 6 is connected to the first output of the microcontroller, the input of the temporary automatic gain control unit 7 is connected to the second, the gain of the receiver 3 is adjusted stepwise to the third, the transmitter radiation power control input is 2, and the direct digital synthesizer frequency control input is fifth frequency 8, the output of which is connected to the input of the transmitter 2. To the input of the microcontroller 1 is connected the output of an analog-to-digital converter 4. The output of the temporary automatic gain control unit 7 is connected to Ode to control the gain of the receiver 3, the output of which is connected to the input of the analog-to-digital converter unit 4. The output of the transmitter 2 is connected to the inputs of the receiver 3 and the electro-acoustic transducer 5.

The electro-acoustic transducer 5 is installed in a tank 9, which is filled with a liquid medium - water 10. Tank 9 is fixed in the bottom of the vessel 12 and is closed by a protective plate 11, which is in contact with sea water 10.

It is known that at the speed of longitudinal waves in steel, depending on its grade, it varies from 5680 m / s to 6100 m / s and linearly depends on temperature [8]. It is also known that the transmittance of acoustic waves of a plate is equal to 1, if an integer number of half-waves λ / 2 fits into its thickness h, i.e. provided that h = n · λ / 2, (n = 1, 2, 3, ...) [2].

The influence of changes in the speed of sound in the material of the protective plate due to changes in ambient temperature and its thickness on the transmittance of acoustic waves of the plate can be eliminated by changing the frequency of radiation, which automatically compensates for changes in the speed of sound in the material of the protective plate due to changes in the ambient temperature and its thickness. Changes in the speed of sound in water due to changes in temperature have very little effect on the transmittance of the acoustic waves of the plate, so it is not considered. Also, changes in the specific gravity of water and plate material due to temperature changes have very little effect on the transmittance of the acoustic waves of the plate, therefore they are also not considered.

And so, according to (1), to compensate for the decrease in the speed of sound in the material of the protective plate, the radiation frequency should decrease, and with a decrease in the thickness of the protective plate, the radiation frequency should increase.

The proposed echo sounder works as follows.

The initial radiation frequency of the echo sounder f _u is constant, set by the microcontroller MK 1, based on the a priori known speed of sound C _PL in the material of the protective plate and its thickness h

, $$fu=\frac{\mathrm{FROM}Pl}{2\text{·}h}$$

,

wherein f _u should be approximately equal to the center frequency of the passband in the radiation of the sonar transducer.

At the initial moment of time, that is, at the time the echo sounder starts, the microcontroller MK 1 sets, by programming block 8 of the direct digital frequency synthesizer DDS, the radiation frequency equal to f _u , which is fed to the input of transmitter 2, the average value of the gain in receiver 3 at the first input gain control and the average value of the radiated power in the transmitter 2 at the input of the power control, also the minimum value of the gain at the second control input, determined by the time control unit eskoy STC gain control unit 7. Then, the MC 1 starts TVG unit 7 in synchronization with emission of the probe pulse through a transmitter electroacoustic transducer EMAT 5 Wednesday. The VARU 7 unit is proportional to the decrease in the amplitude of the echo signal, due to spatial attenuation, increases the gain of the receiver 3 at the second input of the gain control of the receiver 3, thereby the echo level is stationary within the dynamic range of the VARU 7 [9].

The received echo signal with the dynamic range compressed by the action of the Varu 7 from the output of the receiver 3 is digitized by an analog-to-digital converter ADC 4 and is entered into the MK 1 unit as an array of sequential samples. In block MK 1, a number of samples are distinguished from it, making up an echo signal from the bottom. Then block MK 1 determines from this series a reference corresponding to the maximum amplitude of the echo signal Am, and compares it with two values of А _n - the lower threshold and А _в - the upper threshold [7].

Further, if A _m <A _n , then the MK 1 block in subsequent radiation-reception cycles first increases the radiation power to maximum, and only then the gain of receiver 3 (so as not to increase the noise level at the output of the receiver), until the condition And _n <A _m ≤A _in .

If the radiation power and gain are maximum, and A _m <A _n , then in subsequent cycles the radiation-reception of the MC adjusts the radiation frequency - first, it increases the radiation frequency, and then reduces it to the condition A _n <A _m .

The range of variation of the radiation frequency δf in block DDS 8 is defined as

$$f_u\pm \delta f=({\mathrm{FROM}}_{Pl}\pm \delta {\mathrm{FROM}}_{Pl})/(h\pm \delta h),(2)$$

where δС _PL - the maximum deviation of the speed of sound in the plate material, taking into account changes in temperature and aging of the plate material from the initial value С _PL

δh - manufacturing tolerance on the thickness of the protective plate.

In (2), the signs should be chosen in different directions to calculate the maximum value of δf, while it should be borne in mind that the passband of the echo sounder antenna in reception and radiation should be greater than δf.

The change step when controlling the radiation frequency in the DDS 8 unit should not be chosen small, because this will lead to an increase in the regulation time of the radiation frequency, and should not be chosen large, because this can lead to the omission of the radiation frequency value corresponding to the maximum value of the transmittance of the acoustic waves of the protective plate and also to a decrease in the maximum possible measured depth.

The step of change when adjusting the radiation frequency in the DDS 8 unit should be chosen from the condition that the frequency dependence of the acoustic wave transmittance graphs of the plate, constructed according to (1) for two adjacent frequency values, overlap at the level of 0.975 or the acoustic wave transmittance graphs are built for two thickness of the plate or values of the speed of sound in it, which differ by the value of the error of their measurement.

Note that in each radiation-receive cycle, MK 1 detects the echo from the bottom according to the algorithm described in the patent [7] and calculates the depth and displays the numerical value of the depth on the display 6. The choice of the steps of the radiated power and gain values to reduce run time condition A _n <A _m ≤ A _in , for example, can be calculated by the method of steepest descent.

Then a new radiation-reception cycle begins, in which the described procedures for detecting an echo from the bottom, establishing its amplitude, calculating the depth and displaying it on display 6 are repeated, using the radiation frequency set above if A _n <A _m .

Thus, by changing the frequency of radiation in the DDS 8 unit, the MK 1 unit maintains the transmittance of acoustic waves through the protective plate close to 1, and thereby provides the measurement of the maximum possible depth with an echo sounder.

For practical implementation of the echo sounder, the Avalue EPI-QM57 microcontroller can be used as a microcontroller - a single-board EPIC computer of industrial design based on the Intel i7-620LE processor with a set of interfaces and an integrated electronic Flash disk for storing the echo sounder software.

As a transmitter, a pulse amplifier assembled according to a bridge circuit can be used, and by changing the supply voltage of the bridge output stage, the emitted transmitter power can be changed from 1 W to 200 W in steps of 6 dB; by changing the supply voltage of the output stage, the MK must control the 4-bit parallel code.

As a receiver, an amplifier can be used based on the AD600 IC - an amplifier with a voltage-varying gain in the range from 0 to 80 dB, which should be provided by the VARU 7 unit, and the AD7945 IC - a digital-to-analog converter that can stepwise change the receiver gain from 0 to 48 dB after 3 dB under the influence of an 8-bit code coming from the MK.

An LCD monitor with a VGA interface can be used as a display.

As an ADC 4, an AD7892-2-12-bit ADC with a parallel interface and a speed of 1.6 μs can be used.

VARU 7 can be implemented on the basis of a counter, the synchronization of which should be carried out by MK, sorting through the addresses of ROM in which the law of VARU is written; the ROM outputs must be connected to a digital-to-analog converter, which, in fact, generates a voltage-varying VARU from 0 to 2.5 V, which controls the gain of the receiver.

Block 8 of the DDS direct digital frequency synthesizer [10] can be implemented on the basis of ANALOG DEVICES AD9951 chip [11] - with a 32-bit phase battery, an output 14-bit DAC and 400 MHz clock frequency and a frequency resolution of 0.093 Hz. The value of the output frequency f _{u is} calculated by the formula

, $$fu=\frac{N\text{·}fc}{2^{32}}$$

,

where N is the binary frequency code;

f _c is a clock frequency of 400 MHz or less.

Block MK 1 at the control input of DDS 8 sets the frequency selection code - N and during the duration of the probe pulse allows the block DDS 8 to generate a sinusoidal voltage of frequency f _u.

The AD9951 direct digital frequency synthesizer (DDS) microcircuit generates a sinusoidal voltage at the output with the possibility of programmed control of its amplitude and a maximum resolution of 0.093 Hz.

The use of the radiation frequency setting during the operation of the echo sounder with the protection of the emitting surface of the electro-acoustic transducer allows its energy potential to be used to the fullest extent and thereby ensures the measurement of the maximum possible depth by the echo sounder.

The proposed echo sounder is fully automatic and does not require operator intervention. The advantage of the described echo sounder is also the ability to record in electronic form information about the measured depths in the coordinates of the depth-distance traveled for subsequent accurate reproduction on the display for analysis.

The increased accuracy of depth measurement and the automatic mode of operation, combined with the possibility of linking the measured depths to the geographical coordinates and time received from the GPS receiver, make it possible to use it as a navigation echo sounder on ice class vessels and where mechanical protection of the sonar transducer is necessary.

List of used information sources.

1. Appolonov E.M. et al. Calculation of ice load on the icebreaker bottom in extreme shallow water. Proceedings of the Central Research Institute. Academician A.N. Krylova, 2011, number 63, p. 5 ... 10.

2. Fedorov I.I. Echo sounders and other sonar products. Shipbuilding Course. Book 4, L .: 1960, p. 67 ... 71.

3. Shendorov E.L. Wave tasks of hydroacoustics. L. 1972, pp. 213 ... 216.

4. www.simrad.com / 164241ac_EN250_product_specific_lr.pdf.

5. www.skipper.no / GDS101_brochure.pdf.

6. Depth sounder. RF patent No. 2123191 of 1998.12.10, m. Cl. GO1S 15/00.

7. Depth sounder. RF patent No. 2241242, dated March 31, 2003, m. GO1S 15/00.

8. Physical quantities. Handbook edited by I.S. Grigoryeva et al. M, Energoatomizdat, 1991, p. 148.

9. Kobyakov, Yu.S. et al. Design of sonar fishing equipment. L., Shipbuilding, 1986, p. 141.

10. Gnatek Yu.R. Handbook of digital-to-analog and analog-to-digital converters. M, RADIO AND COMMUNICATION, 1982, pp. 255 ... 259.

11. www.analog.com, AD9951.pdf, p. 12.

Claims (1)

An ice protection sounder containing a microcontroller, a transmitter, a receiver, and an analog-to-digital converter in series, the output of which is connected to a microcontroller, as well as an electro-acoustic transducer connected to a transmitter and a receiver, also containing a display, the input of which is connected to a microcontroller, and a temporary automatic adjustment unit gain, the input of which is connected to the microcontroller, and the transmitter is made with step-by-step power control, the adjustment input of which is connected to to the microcontroller, the receiver is made with two gain control inputs, the first control input providing step-by-step gain control is connected to the microcontroller, and the second control input is connected to the output of the temporary automatic gain control unit, also containing a direct digital frequency synthesizer unit, the output of which is connected to the transmitter input and the control input is connected to the microcontroller, while the electro-acoustic transducer is installed inside the hull in a protective tank, filled m of water bonded to the bottom of the vessel and separated from the external environment by a protective plate.

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