The Mathematical Model of an Electrodynamic Geophone

Electrodynamic geophones are applied in seismic prospecting, seismology and security systems. Devices with a similar design can be used as a generator in devices for energy storage, in active vibration control systems, and for detection of shallow-buried objects, including mines. To control the quality of geophones and verify the constancy of their characteristics during the manufacture, it is necessary to measure their frequency response on a shake table. The mathematical model of the geophone developed by JSC Scientific Research Engineering Institute (Balashikha, Moscow region) installed on a shake table is considered. The geophone schematic design is given, and the sequence of its operation is described. The approach of dividing an electromechanical system into several subsystems with subsequently uniting them into a resulting model is used for developing the geophone overall mathematical model. Detailed descriptions of the electrical, magnetic, and mechanical subsystems are presented. The assumptions used in compiling the overall mathematical model describing the geophone operation on the shake table are listed. A system of equations describing the interaction of the subsystems is compiled. Detailed descriptions of the resulting mathematical model, each of its element, and the interface included in its composition are presented. To estimate the developed mathematical model, the results obtained from the calculations on it are compared with the results from testing two experimental samples in the geophone operating frequency band from 10 to 100 Hz. For better clarity, the obtained results are compared in graphical form. The comparison has shown that the discrepancy between the results does not exceed 5% by the output signal amplitude. From the viewpoint of practical implementation, the developed mathematical model can be used in designing new geophones with other parameters, for example, with another natural frequency, or with a higher value of the output signal. It can also be used to develop more complex mathematical models containing a geophone. The accomplished study became a basis for elaborating a more complex mathematical model of a geophone with two natural frequencies in the operating band.