Geophysical field methods

The working principles of gravimeter

When changing the gravity force in two subsequent observation points, the pendulum which is sustained by the main spring, deviates to the certain angle relative to the equlibrium state (horizontal position of the pendulum), stretches the main spring and spins the quartz pendulant string, untill elastic force of the main spring and spinning moment are balancing the activity of the vertical component of gravitational force, herewith the pendulum index projecting to the instrument scale with the use of optic system on the instrument scale, changes its position relative to the zero point (scale center). By rotation of the micrometer screw, it is positioned the index into the zero state (pendulum is horizontal). After that with the readout is done. Gravitational force increment is calculated with the following formula:

Dg = c (n₂-n₁),

where c (gravimeter digit) – this is gravity force value which corresponds one rotation of micrometer screw (100 digits). One digit corresponds to the accuracy of the gravitational force measurement, for instance 0.03 mGal; n_1, n₂ – readouts of the instrument in the two subsequent measurement points.