SEISMOGRAPH

During earthquakes Seismograph is an instrument for measuring oscillation of earth. It has 3 major components-the recorder, the sensor, and the timer. Given figure shows a typical seismograph. The pendulum mass, magnet, string, and support together constitute the sensor. The pen, drum and chart paper constitute the recorder. Motor that rotates the drum at constant speed forms the timer. The pen associate to the tip of an oscillating simple pendulum marks on the chart paper. Magnet around the string provides the needed damping to control the amplitude of the oscillation.

                                        Seismograph

A pair of such type of oscilloscopes is placed at right angles to each other on a horizontal platform. The string pendulum is replaced with a spring pendulum, oscillating around a fulcrum for measuring vertical oscillations. Therefore at each station three oscilloscopes are installed to measure the oscillations in three mutually perpendicular directions.

Today analog instruments are giving way to digital instruments to record the ground motion and process it with microprocessors.