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.

See:
http://www.sp.ph.ic.ac.uk/Cluster/