estimation of variometers' frequency response and synchronization


Marusenkov, A.

The Laboratory of Electromagnetic Innovations

(LEMI), Lviv, Ukraine



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