Data Logger Calibration

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 $\pm$0.01% from the factory calibration values. Of the remaining four channels, three changed by less than $\pm$0.3% and the fourth changed by -0.8%.

Table 3.15: Quanterra Q4120 Calibration Check. Deviation is relative to the median inferred drive level of 19.791624 Volts.
Channel Factory DU/V P-P counts Est P-P volts Deviation \(\%\)
1 403640 8012274 19.850050 -0.29
2 435388 8689678 19.958469 -0.83
3 437149 8651000 19.789591 +0.01
4 422829 8365690 19.785043 +0.01
5 420706 8314894 19.764144 +0.14
6 430613 8548404 19.851709 -0.30
7 438570 8680904 19.793657 -0.01
8 434817 8600236 19.778978 +0.01

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 $\mu$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.

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