The STAFF (Spatio-Temporal Analysis of Field Fluctuations) experiment is one of the five experiments of the WEC. STAFF uses a three-axis search coil magnetometer to measure magnetic field fluctuations at frequencies up to 4 kHz. The waveform is digitised and telemetered to the ground at low frequencies, while at higher frequencies a digital spectrum analyser calculates the power spectrum and cross-spectrum in near-real time. The spectrum analyser also analyses the two spin-plane components of electric field as measured by the long dipole antennas of the EFW experiment. The three-axis search coil unit is mounted on a rigid boom with its three mutually orthogonal mechanical axes aligned respectively with the spin axis and the axes of the two EFW spin-plane wire antennas. Each sensor consists of a high permeability core embedded inside two solenoids. The main winding has a very large number of turns mounted in separate sections. The frequency response of the sensor is flattened in the frequency range 40--4000 Hz by a secondary winding used to introduce flux feedback. The secondary winding is also used as a calibration loop on which an external signal can be applied through a calibration network included in the preamplifiers. The measured sensitivity is 3 x10^-3 nT Hz^(-1/2) at 1 Hz and 3 x10^-5 nT Hz^(-1/2 )at 100 Hz. The search coils are designed so as to minimise their sensitivity to electric fields. The angles between each magnetic axis and the three mechanical axes have been carefully measured. These angles, at most a few degrees, are known with a precision of 0.1°. The three preamplifiers are mounted inside the spacecraft. The dynamic range of the preamplifiers is about 100 dB, to allow weak signals to be measured in the presence of the large signals induced by the rotation of the spacecraft in the ambient magnetic field. The magnetic preamplifier output is used by:
The Magnetic Waveform Unit
The three signals Bx, By, and Bz from the search coil preamplifier are passed through 7th order ant-aliasing filters (i.e., they have an attenuation of 42 dB per octave) with -3 dB cut-off at either 10 Hz or 180 Hz, depending upon the experiment operating mode. The signals are then applied to three sample and hold devices, and digitised by an ADC, with 16-bit precision to achieve the required dynamic range. The sampling is synchronised by the DWP experiment at either 25 or 450 Hz. This is 2.5 times the filter frequency, so that the rejection of aliased components is at least 40 dB. The output is sent to the DWP experiment. Note that, to facilitate ground data analysis, identical filters are used by the STAFF and the EFW experiments, and the same synchronisation signal is sent to both the STAFF and the EFW experiments. The dynamic range is reduced (by differencing) from 16 to 12 bits inside DWP.
The Spectrum Analyser
The frequency range of 8 to 4000 Hz is divided into three sub-bands, each of covering 3 octaves:
Version:2.4.0
The STAFF (Spatio-Temporal Analysis of Field Fluctuations) experiment is one of the five experiments of the WEC. STAFF uses a three-axis search coil magnetometer to measure magnetic field fluctuations at frequencies up to 4 kHz. The waveform is digitised and telemetered to the ground at low frequencies, while at higher frequencies a digital spectrum analyser calculates the power spectrum and cross-spectrum in near-real time. The spectrum analyser also analyses the two spin-plane components of electric field as measured by the long dipole antennas of the EFW experiment. The three-axis search coil unit is mounted on a rigid boom with its three mutually orthogonal mechanical axes aligned respectively with the spin axis and the axes of the two EFW spin-plane wire antennas. Each sensor consists of a high permeability core embedded inside two solenoids. The main winding has a very large number of turns mounted in separate sections. The frequency response of the sensor is flattened in the frequency range 40--4000 Hz by a secondary winding used to introduce flux feedback. The secondary winding is also used as a calibration loop on which an external signal can be applied through a calibration network included in the preamplifiers. The measured sensitivity is 3 x10^-3 nT Hz^(-1/2) at 1 Hz and 3 x10^-5 nT Hz^(-1/2 )at 100 Hz. The search coils are designed so as to minimise their sensitivity to electric fields. The angles between each magnetic axis and the three mechanical axes have been carefully measured. These angles, at most a few degrees, are known with a precision of 0.1°. The three preamplifiers are mounted inside the spacecraft. The dynamic range of the preamplifiers is about 100 dB, to allow weak signals to be measured in the presence of the large signals induced by the rotation of the spacecraft in the ambient magnetic field. The magnetic preamplifier output is used by:
The Magnetic Waveform Unit
The three signals Bx, By, and Bz from the search coil preamplifier are passed through 7th order ant-aliasing filters (i.e., they have an attenuation of 42 dB per octave) with -3 dB cut-off at either 10 Hz or 180 Hz, depending upon the experiment operating mode. The signals are then applied to three sample and hold devices, and digitised by an ADC, with 16-bit precision to achieve the required dynamic range. The sampling is synchronised by the DWP experiment at either 25 or 450 Hz. This is 2.5 times the filter frequency, so that the rejection of aliased components is at least 40 dB. The output is sent to the DWP experiment. Note that, to facilitate ground data analysis, identical filters are used by the STAFF and the EFW experiments, and the same synchronisation signal is sent to both the STAFF and the EFW experiments. The dynamic range is reduced (by differencing) from 16 to 12 bits inside DWP.
The Spectrum Analyser
The frequency range of 8 to 4000 Hz is divided into three sub-bands, each of covering 3 octaves:
Role | Person | StartDate | StopDate | Note | |
---|---|---|---|---|---|
1. | PrincipalInvestigator | spase://CNES/Person/CDPP-Archive/Patrick.Canu |