Coupling Seismometers and Amplifiers for Maximum Signal-to-Noise Ratio

The practical problem of choosing the parameters of the seismometer transducer in order to optimize the ratio of signal-to-instrument noise when working into a given amplifier is analyzed. The manner in which the signal-to-noise ratio varies with transducer coil resistance for constant seismometer damping factor is presented. It is shown that, for amplifiers in which the effective input noise over the desired pass band is smaller than the thermal noise of the amplifier input impedance, it is possible to use transducers spanning a wide range of impedance levels without sacrifice of signal-to-noise ratio. For systems in which amplifier noise predominates, however, the optimum signal-to-noise ratio can be achieved only for a specific choice of transducer parameters. Plots of signal-to-noise ratio are presented for several pairings of seismometers and amplifiers, illustrating the two conditions.