Prior to the tests on the new STS-1 electronics, the Instrumentation Test Facility eight-channel Quanterra Q4120 data logger (serial number 103064) was operated in the BDSN for 8 years. In July 2004, it was repaired, and the calibration was checked by the factory. At the beginning of these tests, the sensitivity, noise floor and crosstalk of the data logger were checked using a reference signal applied first simultaneously and then sequentially to all channels, with the non-driven channels terminated. The relative sensitivities of the data logger channels were checked by applying a high-level ( 19.8 V peak-to-peak) 1 Hz square wave signal simultaneously to all channels. The signal level on each channel was measured and the relative signal levels were compared to the sensitivities on the factory calibration sheet. The results are given in Table 3.15. The sensitivities of four of the channels have not changed by more than 0.01% from the factory calibration values. Of the remaining four channels, three changed by less than 0.3% and the fourth changed by -0.8%.
The Q4120 data logger contains two 4-channel digitizer modules (HH1-HH4 and HH5-HH8). The inter-channel cross-talk was checked by connecting each of the channels in sequence with the high amplitude (20 V P-P) 1 Hz square-wave signal while terminating the other seven channels. The observed cross-talk signal on all channels is below the 2.38 V quantization level of the Q4120 data logger. The cross-talk is thus more than 138.5 dB below the drive signal level. A check of the phase coherence between channels was performed by driving channel HH1 with a 20 V P-P 1 Hz square wave while terminating channels HH2-HH8 with 1k resistors. Spectral phase coherence analysis of the signal between selected channels (HH1-HH2, HH3-HH4, HH5-HH6, and HH7-HH8) shows that there is an inter-channel coherent phase comb present with peaks at 1 Hz and its odd harmonics, on channels within the same digitizer module, when HH1 is driven. At the same time, channels HH5-HH8, which are on a different digitizer module, exhibit no significant inter-channel phase coherence structure.
Berkeley Seismological Laboratory
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