RU2241242C1 - Echo sounder - Google Patents

Abstract

FIELD: hydro-acoustic depth measuring systems.

SUBSTANCE: device has serially connected microcontroller, transmitter, receiver and analog-digital converter, output of which is connected to microcontroller, and electro-acoustic converter connected to transmitter and receiver, and a display, input of which is connected to microcontroller, and block for temporary automatic adjustment of amplification, input of which is connected to microcontroller, and transmitter is made with stepped adjustment of power, input for adjustment of which is connected to microcontroller, transmitter is made with two inputs for amplification adjustment, first input provides for stepped adjustment of amplification and is connected to microcontroller, and second input is connected to output of block for temporary automatic amplification adjustment.

EFFECT: higher precision of depth measurements.

2 dwg

Description

The invention relates to sonar systems for determining depth, and can be used in echo sounders with automatic adaptive detection of echo signals from the bottom and depth measurement.

In the known echo sounder [L1], which contains a synchronizer, a pulse generator, a piezo 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 level of radiated power is constant and does not depend on depth, therefore, the signal-to-noise ratio at the input of the deciding device - a threshold device - will decrease with increasing depth due to an increase in the level of hydroacoustic interference, since the gain of the receiver under the influence of a VARU increases with depth, which will lead to to decrease the accuracy of measuring depth. The use of a non-adaptive threshold device in conditions of a changing noise level makes it difficult to correctly detect echo signals from the bottom.

The closest set of features to the proposed echo sounder is the "Acoustic distance measuring system" described in patent [L2], which contains a microprocessor, memory, a number of interfaces, a digital-to-analog converter, a display, a transmitter, a receiver, an analog-to-digital converter, and an electro-acoustic converter.

In this “Acoustic distance measuring system” constant power is periodically emitted by the transmitter, the receiver is made logarithmic, that is, its gain according to the logarithmic law depends on the amplitude of the input signal. The output signal from the receiver is digitized by an analog-to-digital converter, and fed to the microprocessor for the purpose of detecting the echo signal from the bottom and measuring the distance to it, using an adaptive detection threshold, the level of which depends on both the signal amplitude and the noise level, which allows you to confidently detect echo signals from the bottom against the background of interference of false signals.

However, constant power radiation and the logarithmic dependence of the gain do not fully compensate for the decrease in the amplitude of the echo signals with increasing depth, that is, they do not allow achieving the optimal signal-to-noise ratio for each specific depth and backscattering coefficient from the interface from the point of view of measurement error two media, and this does not allow to minimize the error of depth measurement due to the changing level of hydroacoustic noise [L4, p. 80, 81].

In the “Acoustic distance measuring system”, a point in the echo signal from the bottom is taken as the signal’s arrival time, where its amplitude is equal to the adaptive threshold without taking into account the steepness of the leading edge and the absolute amplitude of the echo signal from the bottom, and this leads to an additional error of depth measurement [L4 , p. 80, 81].

The objective of the invention is to increase the accuracy of measurements by reducing errors due to noise and the final value of the steepness of the echo signal front.

To solve this problem, an echo 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, and a display whose input is connected to the microcontroller, are inserted into it new features, namely: a temporary automatic gain control unit, the input of which is connected to the microcontroller, and the transmitter is made with step-wise power adjustment, stroke adjustment which is connected to the microcontroller, the receiver is provided with two gain control inputs, the first input of adjustment that provides a step gain control, connected to the microcontroller, and a second input connected to the output adjustment time automatic gain control block.

The essence of the invention is presented in figure 1, where:

1 - microcontroller (MK);

2 - transmitter;

3 - receiver;

4 - analog-to-digital Converter (ADC);

5 - electro-acoustic transducer (EAP);

6 - display;

7 - block temporary automatic gain control (VARU);

Figure 2 is an illustration of the operation of the echo sounder.

It is known [L4, p. 81] that when measuring depth, the accuracy of the measurement depends on errors due to noise and the final value of the steepness of the leading edge of the echo signal.

The influence of these errors can be reduced by introducing a VARU, which automatically compensates for the decrease in the echo amplitude with increasing depth by proportionally increasing the gain of the receiver, as well as keeping the echo amplitude in the range that provides the maximum signal to noise ratio for a specific depth by stepwise radiation of power and selecting the minimum necessary gain of the receiver, as well as by automatically detecting the beginning of the echo signal from the bottom.

It is known that during the propagation of signals in dispersion media, attenuation of the high-frequency components of the signal spectrum leads to its noticeable broadening, that is, to distortion of the shape of the echo signal and the extension of its fronts.

According to [L3, p. 240], it follows that as the reference point for counting the time of arrival of the echo signal, one should choose the moment of the first appearance of the echo signal, and at the point in time where the amplitude reaches its maximum value or passes through the zero mark.

The proposed echo sounder works as follows.

At the initial time, that is, at the time of starting the software, the MC sets the average value of the gain in the receiver at the first input of the gain control and the average value of the radiated power in the transmitter at the input of the power adjustment. Note that the minimum value of the radiation power should provide a measurement of shallow depths, and the maximum value of the limiting depths. Also, the minimum value of the gain set at the first input of the gain control taking into account the gain at the second input of the adjustment, determined by the VARU unit, should provide the measurement of the minimum depths, and the maximum value - the maximum depths for the echo sounder. Then, the MC starts the VARU block synchronously with the radiation of the probe pulse by the transmitter through the EAP to the medium. The VARU unit is proportional to the decrease in the amplitude of the echo signal, due to spatial attenuation, increases the gain of the receiver at the second input of the gain control of the receiver, thereby stationary the level of the echo signal within the dynamic range of the VARU [L5, p. 141].

The received echo signal with the dynamic range compressed under the influence of the automatic differential control valve from the receiver output is digitized by the ADC and introduced into the MC as an array of sequential samples. In MK, this initial array of samples is processed according to the algorithm described in the patent [L2], and a number of samples constituting an echo signal from the bottom are extracted from it. Then MK determines from this series a reference corresponding to the maximum amplitude of the echo signal Am (see Fig. 2), and compares it with the two values of an and Av.

The value of the voltage with the amplitude An is chosen from the condition of the minimum acceptable value of the signal / noise ratio and the level of acoustic noise at the input of the receiver.

An≥ q · Pn · ν · Kus.mah

where q is the minimum allowable signal to noise ratio;

P _n is the interference pressure at the receiver input;

ν - pressure sensitivity of the EAP;

Kus.mah - the maximum gain of the receiver, taking into account the action of the VARU.

The voltage value with the amplitude Av is selected from the conditions of unlimited amplitude of the echo signal in the output stage of the receiver and Av &γτ; An.

The ratio between two adjacent levels of radiated power Δ p must satisfy the condition

The ratio between two adjacent stages of the gain Δ at the first input of the gain control of the receiver must satisfy the condition

These conditions for the selection of Δ p and Δ y values ensure that the condition An &λτ; Am≤ Av.

Further, if Am &λτ; An, then the MK in subsequent radiation-reception cycles initially increases the radiation power to the maximum, and only then the gain of the receiver (so as not to increase the noise level at the output of the receiver), until the condition An &λτ; At≤ Av.

If Am &γτ; Av, then in subsequent cycles the MC radiation-reception first reduces the gain of the receiver at the first control input to the minimum, and only then the radiated transmitter power until the condition An &λτ; Am≤ Av.

Note that in each cycle the radiation-reception of the MC detects the echo signal from the bottom according to the algorithm described in the patent [L2], and the choice of the steps of the radiated power and the values of the gain to reduce the time for the fulfillment of the condition An &λτ; Am ≤ Av, for example, can be calculated by the steepest descent method, or by some other algorithm.

Further, if the condition An &λτ; Am ≤ Av, then MK starts the algorithm for determining the beginning of the echo signal from the bottom, that is, the determination of the corresponding sample A _n from the original array of samples according to the algorithm

A _n = A _i if A _i ≤ K ₁ · A _i-1 and A _i &λτ; K ₂ · A _{i + 1} , m≥ i≥ 1

where i is the reference number;

Ai is the amplitude of the i-th reference;

K - coefficient, K ₁ ≥ 1, K ₂ ≥ 1 provide detection of the beginning of the echo signal in the presence of noise;

m is the reference number corresponding to the maximum amplitude in the echo from the bottom.

That is, the MK enumerates the samples, starting from the number m, in the direction of decreasing the reference number until the inflection point of the echo signal is found (see Fig. 2), that is, the reference number n.

According to the statement [L2], and considering that the EAF is an electromechanical transducer with a finite Q factor Q, and the pressure of the probing signal created by it reaches a maximum in about Q periods of the frequency at which it operates, then at the time of arrival of the echo signal, you should choose exactly the point inflection of the leading edge of the echo from the bottom.

Then MK calculates the depth H from the bottom according to the formula

Н = (tАЦП · n) · Сзв / 2,

where tACP is the ADC conversion time;

Szv - the speed of sound in the medium;

n is the ADC reference number corresponding to the beginning of the echo from the bottom

and displays the numerical value of the depth on the display.

Then a new radiation-reception cycle begins, in which the described procedures for detecting the echo signal from the bottom, establishing its amplitude, determining its beginning, calculating the depth and displaying it on the display are repeated.

Thus, by changing the emitted transmitter power and the gain of the receiver, the MK keeps the amplitude of the echo signal from the bottom in the range of voltage amplitudes from An to Av, thereby ensuring a signal / noise ratio not lower than the minimum acceptable level and reduces the error in measuring depth due to noise, and also determines algorithmically the beginning of the echo signal from the bottom and thereby reduces the error in measuring depth due to the final value of the steepness of the leading edge of the echo signal from the bottom.

For practical implementation of an echo sounder, an AXIOM SBC 8360 microcontroller can be used as a microcontroller. It is a single-board 3.5-inch computer of industrial design on Intel's Celeron-1.1 GHz 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 based on the AD600 IC can be used - an amplifier with a variable voltage gain in the range from 0 to 80 dB, which should be provided by the VARU unit, and AD7945 IC - a digital-to-analog converter that can stepwise change the receiver gain from 0 up 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, the AD7892-2 IC can be used - a 12-bit full ADC with a parallel interface and a speed of 1.6 μs.

VARU 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.

The use of an adaptive detection threshold makes it possible to confidently detect an echo signal from the bottom under the conditions of pitching and noise on the ship due to the rotation of the screws and the operation of its mechanisms.

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 information in electronic form about the measured depths in the coordinates depth - the distance traveled for subsequent accurate reproduction on the display for analysis at any time scale.

The increased accuracy of depth measurement and the automatic mode of operation, combined with the ability to bind the measured depths to the geographical coordinates and time received from the GPS receiver, make it possible to use it as a measuring echo sounder.

Literature

1. Fishfinder. Patent 2123191 RU of 1998.12.10, GO 1 S 15/00, application No. 97111517/09 of 1997.07.02.

2. Acoustic distance measuring system. European patent A2 0340953, G 01 S 7/52, G 01 S 15/88.

3. The use of ultrasound in medicine. / Edited by C. Hill, M .: Mir, 1989, p. 240 (listing 5.2.2.2).

4. Khrebtov A.A. and other marine echo sounders. L .: Shipbuilding, 1982, p. 80, 81.

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

Claims (1)

An echo 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, and a display whose input is connected to a microcontroller, characterized in that a unit is inserted into it temporary automatic gain control, 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 krokontrolleru, the receiver is provided with two gain control inputs, the first input of adjustment that provides a step gain control is connected to the microcontroller, and a second input connected to the output adjustment time automatic gain control block.

Images