SELF-NOISE SPECTRA FOR 34 COMMON ELECTROMAGNETIC SEISMOMETER PREAMPLIFIER PAIRS

Because of a lack of such information, computed self-noise spectra are presented for a total of 34 frequently used electromagnetic-seismomet er/preamplifier combinations. For convenience, most of these data are given in three sets of units. Peterson's Low Noise Model is included o n each plot for comparison. The self noises of nine frequently employe d electromagnetic seismometers properly matched to their operational a mplifier (op-amp) preamplifiers are plotted. In terms of amplitude den sity spectra in (m/sec*2)/Hz**0.5, the values of the self-noise spect ra at resonance range from a low of 3 x 10(-10) for the GS-13 to a hig h of 1.3 x 10(-8) for the HS-1. Between these two seismometers, in ord er of increasing noise at resonance, are the SV-1, SL-210V, S-13, SS-1 , L-4C, S-6000CD, and the L-22D. To show which seismometers exhibit th e lowest noise with which operational amplifier preamplifiers, the sel f noises of the HS-1, L-22D, L-4C, GS-13, SV-1, and SL-210V are plotte d each paired with four commonly used op-amps: the LT 1 028, OP-227, O P-77, and the LT1012. For the GS-13, the LT1012 was the quietest. For the rest, the OP-227 was the best. For a given seismometer, the differ ences in self noise between op-amps were frequently a factor of 2 or 3 , and as large as 10 in one case. The use of these op-amps in the anal og front ends of five current digital seismic recorders is discussed.