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Accurate estimation of variometers' frequency response and synchronization errors |
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Marusenkov, A. |
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The Laboratory of Electromagnetic Innovations (LEMI), Lviv, Ukraine |
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INTEMAGNET one-second data specifications include quite strict requirements to time stamping accuracy (50 dB). In order to check that a variometer meets these requirements, the testing methods and facilities have to have even better accuracy. That means, for example, that the target value for time stamp and phase shift accuracy should be of the order 0.001 s for the signals with periods >5 s. The natural geomagnetic variations and artificial magnetic disturbances could degrade the accuracy of such measurements. In order to cancel out the external magnetic signals, one could put the sensor with a calibration coil inside a magnetic shield. However, the magnetic shield itself could deviate proportionality between the AC current passing through the coil and the magnetic test signals measured by the sensor. Another approach for suppressing external signals is to use a reference magnetometer and to analyze difference signals of both instruments. In this study, we tested a number of LEMI-025 variometers and compare the results obtained by applying these approaches.
The two methods were exploited for estimation time stamping accuracy and frequency response: a multiple frequency test (harmonic signals) and a square wave test. In both cases, waveforms were synchronized with UTC second and the variometer output signals were analyzed using the FFT.
In general, the different techniques yield similar results compatible with INTERMAGNET requirements for one-second data. The more details about peculiarities of these measurements will be given in the report. |
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Instrumentation |
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oral |
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