SU499542A1 - Device for determining gravimetric constant - Google Patents

Description

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The invention relates to the field of marine navigation instrumentation and can be used in apparatus measuring the acceleration of gravity on a moving base. A string gravimeter is known, which is a mass suspended on a thin vertical structure, the upper end of which is rigidly fixed. The string hangs between the two poles of a permanent magnet and vibrates in the transverse direction at the natural frequency of the st interaction between the voltage applied to the ends of the string and the magnetic field of the constant magnet. The frequency of transverse vibrations is determined by the internal tension of the string, and therefore depends on the acceleration of gravity g.

The string is an integral part of the resonant circuit, and its oscillations are maintained through an amplifier and feedback. The change in gravity g is fixed as the change in the natural frequency of the string oscillations.

To prevent rotation of the load around the axis of the string, the load is connected to the frame by means of thin horizontal legs or flat horizontal springs. To weaken the effect of alternating perturbing accelerations, the cavity of the device around the load is filled with a damping fluid.

Such an instrument only measures the effect of gravity in the vertical direction. The disadvantages of this device are the imperfection of the design and the lack of registration of horizontal accelerations of the device and its inclination.

To compensate for accelerations transverse to the direction of measurement, the proposed device for determining the gravimetric constant contains a platform whose axis of rotation coincides with the direction of measurement. On the platform, there are two electromagnets of horizontal magnetic suspension, which have central through holes in the rod of the magnetic conductors, through which strings pass, stretching the ferromagnetic mass. In the vertical direction, the ferromagnetic mass is held by two electromagnets of a vertical magnetic suspension.

The strings oscillate in the transverse direction with a frequency varying depending on the magnitude of the accelerations acting in the direction of the instrument axis (measurement direction). Gathering information about the magnitude of the current acceleration device - frequency.

The drawing shows the proposed device containing a spherical ferromagnetic mass 1 stretched on two pretensioned strings 2, sensors 3 of their transverse oscillations, and two pairs of electromagnets of magnetic suspension 4 and 5. Electromagnets of horizontal magnetic suspension have central through holes in the core of magnetic conductors and located on platform 6, perpendicular to the direction of measurement and rotating around this on the npaBvieHHH.

The strings have a tape profile, and they are attached to the rim of the platform through the piezoelectric elements of the vibrators 7, which excite the transverse vibrations of the strings.

The principle of operation of the device is as follows.

The signals of transverse vibrations of the strings 2 are removed by the sensor 3, amplified and, after doubling in frequency, arrive at the piezoelemeite of the vibrator 7, exciting the transverse oscillations in the strings.

As is well known, string oscillations in the transverse direction with a frequency / o can be caused by a longitudinal tension periodically varying with frequency 2 / o.

In this way, a positive feedback circuit is closed, providing stable transverse healing of the string at its own frequency.

Under the action of acceleration, which coincides with the direction of measurement, the same changes in the tension of both strings occur. However, their own frequencies are changed by equal amounts. The collection of useful information is carried out by an electronic circuit that determines the frequency and frequency of both strings with the same sign and magnitude. The same information serves as an input signal to control the vertical magnetic suspension.

In the negative feedback circuit for controlling the magnetic suspension, there are filtering and corrective circuits that transmit only signals at interference frequencies (for example, vibration frequencies, ship rocking, etc.). The vertical suspension thus compensates for the change in the simultaneous tension of the strings, caused only by the interference signals, and the suspension rigidity for the interference signals is maximum.

For useful signals that do not pass through the filter circuits, the stiffness of the vertical magnetic suspension is practically zero.

Thus, compensation for a change in the tension of the strings caused by the action of the useful signal does not occur and the tension can be measured by its simultaneous change in both strings.

When the platform 6 rotates around the measured direction (in the drawing, around

Z-axis. The projection of the transverse acceleration on the axis perpendicular to the measured direction (the direction of the strings) varies harmonically with the frequency of rotation 5 of the platform. Therefore, in order to eliminate the influence of transverse (horizontal) accelerations of the change in the useful signal with the frequency of rotation of the platform, they are passed through a smoothing device.

0 During acceleration, perpendicular to the direction of measurement (in the horizontal drawing), the tension of one string increases, the other decreases, causing an increase in the co-frequency of the transverse

5 vibrations of one string and the corresponding reduction - the other string. The extracted differential frequency serves as an input signal for controlling the horizontal magnetic suspension, the electromagnets of which create

0 force, compensating for the difference in the tension of the strings, and, consequently, the action of horizontal acceleration.

To register accelerations perpendicular to the direction of measurement, an electronic circuit is used to sense the difference frequency signal. The amplitude of this signal determines the magnitude of the lateral acceleration, and the phase shift determines the direction of action of this acceleration in the plane of the platform.

0 The proposed device can find much wider application than a conventional gravimeter, since it allows gravimetric measurements to be made in any given direction.

5 In addition, this device can be used to measure the travimetric forces on a movable base by inserting filter and correction circuits into a biaxial magnetic suspension, compensating for the effects of harmful signals, such as periodic horizontal and vertical emissions, (ship rolling, vibrations, etc.).

Claims (1)

Invention Formula A device for determining the gravimetric constant, containing a ferromagnetic mass stretched on two strings, sensors of their oscillation frequency and four electromagnets of a biaxial magnetic suspension, which, in order to compensate for accelerations transverse to the direction of measurement, contains a platform, the axis of rotation of which coincides with the direction of measurement, and on the platform there are two electromagnets having central through holes in the core of the magnetic cores through which the strings pass.