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Instrument: FGM : CLUSTER-II Fluxgate Monitor
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The fluxgate magnetometers on Cluster-II are similar to many previous
instruments flown in Earth-orbit and on other, planetary and interplanetary
missions. In order to minimise the magnetic background of the spacecraft, one
of the magnetometer sensors (the outboard, or OB sensor) is located at the end
of one of the two 5.1 m radial booms of the spacecraft, the other (the
inboard, or IB sensor) at 1.5 m inboard from the end of the boom. In flight,
either sensor can be designated as the Primary Sensor, for acquiring the main
data stream of magnetic-field vectors. Selection of the sensors as Primary or
Secondary is made by ground command; in the default configuration, the OB
sensor is used as the Primary Sensor. Data can also be acquired simultaneously
from the other, Secondary Sensor, albeit at a lower rate.

The magnetometers have eight possible operating ranges; of these, five are
used on the Cluster magnetometers. These ranges were selected to provide good
resolution in the solar wind (with
expected field magnitudes between 3 and 30 nT), and up to the highest field
values expected in the magnetosphere along the Cluster orbit (up to about
1,000 nT). The highest range (* 65,500 nT) is used only to facilitate
background testing. Range selection can be automatic (controlled by the
instrument DPU) or commanded from the ground. When in the automatic mode, a
range selection algorithm running in the DPU continuously monitors each
component of the measured field vector. If any component exceeds a fraction
(set at 90 %) of the range, an up-range command is generated and transmitted
to the magnetometer. If all three components are smaller than 10 % of the
range for more than a complete spin period (in fact for more than the
telemetry frame period of 5.15222 s), an automatic down-range command is
generated to the magnetometer.

The instrument uses two 16-bit Analogue-to-Digital Converters (ADC), normally
in cold redundancy. The most significant 14 bits of the converted
field-component values are used for generating the output of the instrument.
The digital resolution, corresponding to the five ranges of the magnetometers.


Online Resources

Instrument Logistics
Instrument Start Date: 2007-07-16
Instrument Owner: NASA/GSFC
Space & Atmospheric Physics Group Imperial College, London
Institut fur Weltraumforschung, Austrian Academy of Sciences, Austria
Institute for Geophysics and Extraterrestrial Physics, Technical University, Germany