SU913310A1 - Wire gravimeter - Google Patents

Description

The invention relates to instruments for measuring gravity on a movable base and can be used in marine geophysical. filming.

Known string gravimeter, comprising a housing, a string, a working load placed in the field of a damping magnet, a driving magnet, plates connecting the load to the housing, an electronic device for exciting vibrations of the string and a recording device with frequency meters [1].

The disadvantages of this gravimeter are the non-linear connection of the output frequency with the instantaneous value of gravity, which under the action of large accelerations of interference can lead to significant errors in the measurement results.

Also known is a string gravimeter comprising a case, a string with a working load fixed on it, placed in the field of a damping magnet, a driving magnet, plates connecting the load to the case, an electronic device for exciting the vibrations of the string and registering the device, with the working load executing the GRAMMETER

2

not in the form of a coil, which is connected in series through a frequency meter, a digital filter of high hours

The latter and the code converter are analogous to an electronic device and are connected in parallel with the winding of the damping magnet. As a result, the positive quality of this gravel-0 meter is the reduction of the noise level on the string [2].

The disadvantages of this string. The gravimeter is a significant complication of the gravimeter in the electronic part, due to the introduction of an additional chain of interference correction on the string by using a digital filter with a low cut-off frequency (about 0.01 Hz) and a converter

__ code - high resolution log.

The purpose of the invention is to simplify the device without loss of accuracy.

The goal is achieved by the fact that the string gravimeter, comprising a body,

25 string with a working load reinforced on it, made in the form of a coil, a damping magnet with a winding, an excitation magnet, plates connecting the load to the body, registering the device with the meter often *

3

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You are equipped with a quartz plate with two current recordings, located at the point of attachment of the string with the case between the case and the string, so that its current collectors are connected to the inputs of the additionally installed charge amplifier, the outputs of which are connected to the coil.

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

The gravimeter includes a housing 1, a string 2 with a working load 3 mounted on it, 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 permanent magnet 5 and b with the winding 7. The upper end of the string is rigidly connected to the body 1 through a quartz converter 8. The output of the string oscillator 9, containing the string connected to the frequency meter 10 (Fig. 2). Current collectors 11 and 12 of the quartz transducer 8 are connected to the input of the charge amplifier 13, the outputs of which are connected to the coil 3 and the winding 7.

The gravimeter works as follows. at once.

Signal acting on said string is a mixture of the measured desired signal d _x, svyazannogb with a change of gravity, and interference d _n, has a broad frequency spectrum. Under the influence of these vertical accelerations, the strength of the mechanical tension of the string G, and, consequently, the frequency at the output of the string oscillator 9 (£ =, where w is the mass of the string, 2 is the length of the string), changes the readings of the frequency meter. In order that only changes in the frequency of the string associated with very slow changes in gravity (the useful signal) can be read on the reading device of the frequency meter 10, the interference signal must be filtered out. Quartz Converter 8, working under tension under the action of vertical accelerations of interference, at its output (current collectors 11 and 12) produces an electrical signal in the form of a charge, which is amplified in the charge amplifier 13 '; and in the form of current 1 is fed into the coil 3 located in the field of the damping magnet 6. In the coil 3, a force Ha = B1P (where B is the magnet induction, 2 is the length of turns) is proportional to the interference d и and directed against the additional force caused by the interference signal d _p . Thus, the disturbing force is compensated by the force of Ρβ. Due to the fact that quartz

Converter 8 has a frequency response similar to that of a first-order differentiator, the time constant of which can reach 100 s or more, such a high-pass filter with a charge amplifier at the output essentially replaces a circuit with a digital filter that is difficult to manufacture and set up and converter code output current. The transfer function of the quartz transducer 8 with charge amplifier 13 has the form

where 5 is the sensitivity of the quartz transducer 8 with charge amplifier 13;

Ф - filter time constant, where

δ = <3, | / So,

where <3 ,, is the piezoelectric constant;

C - own capacity of the piezoelectric transducer;

С _о - capacitance in the feedback circuit, charge amplifier;

= COP _C ,

where K - leakage resistance (1Ο ^Ί 10 ^ ohms).

When C = 10-100 pF, άη = 2.3.10 ' ^and C / n.

C = Co, sensitivity 5 is minimal (0.02-0.2) V / N. When the mass of the movable part gravimeter 200 g is 4-10 "® V / mGal. If d _n hindrance filtered mGal to 10, the minimum signal at the output of the charge amplifier 13 is 0.4 mV, which practically causes no difficulties in constructing such a circuit, A 10 mGal noise, when averaged in the frequency meter 10, leads to an error of less than 0.1 mGal. If necessary, the time constant 7 can be increased by increasing the capacitance Cf. a simultaneous decrease in sensitivity can be compensated for, for example, by choosing the piezoelectric effect leads to the expression for the charge

0 = P 0 / x

where is the length;

x is the width of the piezocrystal.

Since the current passing through the coil 3, has a demagnetizing effect on the permanent magnet, as in the prototype, to improve the accuracy of the compensation system on the magnet 5 is a biasing winding 7 connected to the output of the power amplifier 13 such

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in such a way that the field created by it is equal and directed in the opposite direction with respect to the field of the compensation coil.

The positive effect of this invention is a significant simplification of the structural gravimeter while maintaining its accuracy characteristics due to the inclusion of a quartz transducer. The vertical accelerations in charge from the side of the string attachment to the body.

Claims (1)

Claim A string gravimeter, comprising a housing, a string with a coil supported on it, made in the form of a coil, a damping magnet with a winding, a driving magnet, plates connecting the load to the housing, a recording device with a frequency meter which is identical to that in order to simplify device and improve measurement accuracy, it is equipped with a quartz transducer with two current collectors. located between the case and the string, while the current collectors are connected to the inputs of the additionally installed charge amplifier, the output of which pogo connected to the coil.