Seismic Recorders

Abstract

Seismometers give out electrical signals, which can be measured with lab instruments. In order to preserve these signals, we need a device for permanently recording them. Since the seismometer output signals generally are small, and maybe noisy, they have to be amplified and filtered before recording. This is the analog signal preparation. In its simplest way, a recorder is any device plotting the signal in a permanent way, like a chart or drum recorder, and we get a seismogram. However, the present most common way of recording is to digitize the signal with an analog to digital converter (ADC) and record it in some computer device.

A recorder and a sensor is called a seismograph and consists in most cases of separate units, while in earlier mechanical seismographs, like the Wiechert seismograph, they were integrated units. The reason for the separation is that the sensitive seismometer has to be placed at the most low noise site possible, with little disturbance from the recorder and people operating it. For field use, the ease of deployment makes it desirable to have one compact unit; in particular strong motion instruments -less sensitive- are sold as complete units with sensor and recorder integrated.