SU545949A1 - String gravimeter - Google Patents

Description

The invention of 5 is referred to instruments for measuring the force of gravity on an effective basis and can be used in marine geophysical surveys.

A gravimeter is known, the sensor of which consists of a vibrating conducting string, a weight made in the form of a lever, one end of which is attached to the body by means of intersecting springs, and an excitation magnet. The recording equipment is equipped with a special computer that calculates instantaneous values of gravity and averaged them for some time during measurements 1. The device’s disadvantages include extremely high sensitivity to interference, especially vibration, a complex non-linear dependence of the output frequency on acceleration, as a result the accuracy of the instrument is low (up to 10 mGl merestraction).

A gravimeter is known that contains an inertial mass suspended on a wire or tape of conductive material 2. In this gravimeter, an inertial mass is attached to the body. It is possible to carry out damping masses due to narrow gaps between it and the body. Such damping is clearly not enough to cause the instrument to resist vibration. The main disadvantage is that the dependence of the oscillation frequency

the strings from the accelerations acting on the device are not proportional, and this nonlinearity leads to systematic errors.

A string gravimeter is known, comprising a housing, a string, a working load placed in the field of a damping magitite, a driving magnet, plates connecting the load to the housing, an electronic excitation device: a vibrating string, and a recording device with a frequency meter 3.

The effects of this gravimeter are 51 non-linear communication of the output to the instantaneous value of the force of gravity, which under the action of large accelerations can lead to significant errors in the measurement results.

The purpose of the invention is to improve the measurement accuracy.

To do this, in the proposed gravimeter, the working load is made in the form of a roller, which is sequentially connected via a frequency meter, a digital high-pass filter and a code-to-analog converter with an electronic device and connected in parallel with a damping magnet winding.

Ia fng. 1 shows the proposed gravimeter; in fig. 2 is a block diagram of the electrical part of the gravimeter.

The gravimeter contains a body /, string 2 with

reinforced on her working load 3, made in the form of a coil. To prevent horizontal displacements, the load is attached to the body using plates 4. The string is placed in the gap of the exciting permanent magnet 5. The working load is located in the gap of the damping constant magnetite 6 with the winding 7. The upper end of the string is connected to the body or rigidly or through a spring .

The string is electrically connected with the electronic device, which is a string oscillator 8 with it (phpg 2). The output of the strings of the south autogenerator is connected to a frequency meter 9 and to a frequency detector. A frequency detector is a device that produces a voltage at the output, the value of which depends on the frequency of the input signal. This device can be made but any known analog circuit, however, to improve accuracy, it is advisable to use digital technology. In this case, the frequency meter is connected to a digital high-pass filter JO and a code-to-analog converter. The output of the converter is connected with the coil 3 and with the winding 7.

The gravimeter works as follows.

Under the influence of vertical accelerations, a variation of the string oscillation frequency occurs. The meter readings are taken accordingly. In order for the frequency changes of the string associated with the curve of the body not to be commenced, the readings of the measurement frequencies are sent to a digital high-pass filter with a cut at a frequency of about 0.01 Hz. The output signal of the filter is fed to the transducer, the code-log, the output of which is not exactly the same, the ipoporion of the filtered readings of the measured signals. The output voltage of the converter-code-analogue goes to the coil, through it, respectively, a current passes, which, interacting with the hp lem and the hogs of the damping magnet, creates a force that compresses the accelerating accelerations. Due to the effect of the described feedback, only small changes in frequency associated with the length of the imperfect process patterns remain. The systematic effects associated with nonlinearity of the characteristics of the gravimeter, while reduced to negligible velcpp. So prp

compensation of disturbances with a low accuracy of the norm of one gala systematic resolution of about 0.1 mGl.

Since the current passing through the coil has a demagnetizing effect on a permanent magnet, to increase the accuracy of the number system on a magnet, the magnetizing coil is distributed, connected to the output of the converter code in such a way that the field generated by it is equal and The opposite side is relative to the field of the compensation coil.

The positive effect of this is to reduce the level of interference on the string to a level where the nonlinearity of the string gravimeter does not cause any helium errors and, as a result, increases the accuracy of the measurements. At the same time, the string gravimeter retains all the positive qualities of a digital instrument. A small level of residual disturbances facilitates the last filtering shown.

Form} l and inventions

Gravimeter, containing body, string, working load, placed in the field

damping of its magnet, exciting magit, plastpps connecting the load with the case, an electronic device for exciting the oscillations of the line, and a recording device with a frequency meter, which is HI, and with the aim of improving the accuracy of 11 measurements, The working load is made in the form of a catuptc, which successively connects the yen through the measuring tube, digital high-pass filter and the code-to-analog converter with electronic device and

in parallel with the winding of the damping magpite.

Source information taken into account by irq ekertize:

1. Prospectus of Sokkisha Ltd. Proc. Ceod. Soe. Japan v. 9 1963 pp 571-576.

2. The patent of France L 1536427. cl G 01 V, 1968.

3. Inkjet gravimeter to measure gravity and sea. Lime USSR Academy of Sciences, sir. Geophysical .Y 3, 1959.

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