SPWLA Glossary

An instrument for measuring variations in gravltational attraction; a gravity meter. Most present gravimeters are of the unstable or astatic type. The gravitational force on a mass in the meter is balanced by a spring arrangement, and a third force is provided which acts when the system is not in equilibrium. This third force intensifies the effect of changes of gravity and increases the sensitivity of the system. In the LaCoste-Romberg gravimeter, the main spring that balances out the gravitational pull on the weight is a “zero-length spring” inclined at an angle. A zero length spring has a stress-strain curve that passes through zero length when projected back to zero strain. (For example, a spring that requires an initial stress before the coils begin to separate.) Zero-length springs have very long periods and high sensitivity.