RU1840754C - Measuring method of ship's movement speed relative to ground - Google Patents

Abstract

FIELD: radio-engineering.

SUBSTANCE: invention refers to radio-engineering, and can be used when designing hydroacoustic logs meant for measuring ship's speed relative to ground. In order to reach the effect in measuring method of ship's speed relative to ground, which is based on measuring Doppler shift of frequency, proportionality factor between ship's movement speed relative to ground and Doppler shift of frequency is varied depending on ship's speed change.

EFFECT: improving measuring accuracy.

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Description

The invention relates to the field of sonar and can be used in the design of sonar lags designed to measure the speed of the ship relative to the ground. The main parameter of sonar lags is the accuracy of speed measurement. Theoretical and experimental studies have shown that the resulting error in the measurement of velocity is determined by both fluctuation and systematic errors. It was shown that the contribution of the systematic component to the resulting error is 40-50%. Later studies conducted when sailing a submarine in real conditions showed that the proportion of the systematic component in the total error can reach 70%. Thus, the exclusion of a systematic error from the measured velocity values is of paramount importance, the possibility of improving the accuracy of the sonar lags depends on the solution of this issue.

It is known that the systematic component of the measurement error can be reduced by calibrating the equipment and introducing appropriate corrections into it. Such calibration for sonar logs is carried out on a special measured mile. Calibration results determine lag coefficient

where K ₁ - lag coefficient,

V _et - the speed of the submarine on a measured mile, measured by means of standardization;

V _CR - the value of the speed measured by the lag.

The one lag coefficient value obtained from the calibration results can be manually entered into the lag equipment. In this case, the entered coefficient value is stored until the next calibration.

According to the existing method, lag calibration is carried out only at one speed value. As such a speed is selected, for example, the speed of the submarine V = 15 knots, as the most likely at the transitions. This calibration technique assumes that the lag coefficient in the mastered speed range is independent of speed.

However, an analysis of the experimental data available for the lag shows that the lag coefficient, even in the speed range of 5-15 knots, is not constant. So, for example, when calibrating the prototype lag, the dependence of the coefficient K ₁ on speed was obtained, shown in Fig. 1. Calibration was carried out at three fixed speeds of 5; 10; 15 nodes, and the values of the lag coefficient at each of the speeds are reliable, since they are obtained by statistical processing of a large series of measurements. A similar dependence of the coefficient K ₁ on speed was obtained earlier during sea trials of an experimental log sample. The resulting dependence of the coefficient K ₁ on speed is shown in Fig.2. Comparing the dependencies shown in figures 1 and 2, it is interesting to note almost the same slopes of the curves to the abscissa. A certain difference in the absolute values of the coefficients is explained by different designs of fairings and various signal processing schemes in the experimental and experimental samples of the lag.

Thus, the very fact of the presence of the dependence of the lag coefficient on speed can be considered experimentally confirmed. As already noted above, according to the existing method, the coefficient obtained for the speed V = 15 knots is taken into account in the lag equipment. From the point of view of the lag equipment, this means that the digital counter measuring the Doppler frequency operates with a constant measuring time corresponding to the lag coefficient for the speed V = 15 knots. In this case, an error is introduced fundamentally when the lag operates at other speeds. As indicated earlier, this error is δ ₁ = 0.85% for V = 5 nodes and δ ₂ = 0.44% for V = 10 nodes. Errors δ ₁ and δ _{2 are} commensurate in magnitude with the limiting errors of the lag. It is especially undesirable to have such an error at a speed of V = 5 knots, which is the most probable speed of the submarine when it is in a combat position.

The aim of the invention is the exclusion from the resulting error of speed measurement, that systematic component, which is due to the inconsistency of the lag coefficient in a wide range of speeds.

Improving the accuracy of measuring speed with a lag is achieved by the fact that the time of averaging (measuring) speed data in a digital lag counter changes as a function of the speed of the ship.

Description of the invention

The nature of the functional dependence connecting the change in the coefficient K ₁ with the change in speed, in the general case, can be different (the measurement of the coefficient K _{1 is} carried out during the calibration of the lag). So, for example, for the lag (as shown in figure 1) this dependence is almost linear.

In the general case, the introduction of this functional dependence in the lag equipment should be carried out using a special functional converter, the input of which receives information about the speed of the ship and the output of which gives a signal that controls the change in the measurement time in the counting path.

With a constant capacity of the time channel counter, a change in the counting time can be achieved either by changing the frequency of the time-generating local oscillator or by adding time to the channel input depending on the speed of a certain number of pulses.

Circuit Example

In the lag, the timing oscillator in the counter time channel is made according to the RC-generator circuit with the Wien bridge. To implement the proposed method, it is enough to connect the axis of the double potentiometer included in the Wien bridge circuit with the axis of the tracking system, working out the speed from the relative lag.

With a change in the speed of the ship, the frequency of the time-generating local oscillator will automatically change, and therefore the measurement time in the counter. With an appropriately phased system, a change in the measurement time completely compensates for errors caused by the inconsistency of the lag coefficient.

The necessary coefficient of proportionality between the change in speed and the change in the resistance value of the potentiometer can be provided by a reduction coefficient. The fact that the correction introduced in this case will be proportional not to the absolute but to the relative velocity is not significant at real flow velocities, since the corrections themselves are of the order of tenths of a percent and therefore entering them with an accuracy of even 10% will practically not lead to a deterioration in accuracy the proposed method.

If it is necessary to increase the accuracy of the correction input, one can use information about the longitudinal component of the absolute speed of the ship, which carries information about the longitudinal component of the current, as a speed sensor. A possible circuit solution is illustrated in figure 2. The Doppler frequency, proportional to the longitudinal component of the velocity, is converted in counter 1 to code V _x . The code of the longitudinal component of the velocity is converted in the converter 2 first into a constant voltage level, then in the converter 3 into the pulse repetition rate, which, through the matching circuit 4, are fed to the input of the counter time channel 7. The pulse from the fantastron 5 is received at the second input of the matching circuit 4, duration whose τ≡S determines the necessary scale relations. In this case, the number of pulses N≡V _x · S arrives at the summation circuit 6. A change in the pulse repetition rate at the input of the pulse time channel also leads to variations in the measurement time T _var and, therefore, to compensation for errors caused by the velocity dependence of the lag coefficient. For example, when the lag coefficient K _{1 is} increased by 1%, the frequency at the input of the time channel increases by 1%, the measurement time decreases by 1%, and thus the averaged values of the velocity components V _x and V _y do not contain errors due to an increase in the lag coefficient.

Positive effect

From an analysis of the available experimental data, we can conclude that the implementation of the proposed method will allow:

1) To increase the accuracy of the existing sonar lags in the speed range of 5-10 knots approximately 2-3 times.

2) Reduce the requirements for the rigidity of the fairings of acoustic lag antennas when operating in a wide range of submarine speeds.

Claims (1)

A method of measuring the speed of a ship relative to the ground, based on measuring the Doppler frequency shift, characterized in that, in order to improve the accuracy of measuring the speed of the ship relative to the ground, the proportionality coefficient between the speed of the ship relative to the ground and the Doppler frequency shift is changed depending on the change in the speed of the ship.

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