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- The magnetic field experiment on the IMP-8 spacecraft utilizes a tri-axial
fluxgate (saturable inductor) magnetometer. The instrument originally had
three, automatically determined, ranges, +/-12 nT, +/-36 nT, and +/-108 nT, full
scale. Because of a range-change circuit failure occurring in early July 1975,
the experiment was commanded into a fixed +/-36 nT range on July 11, 1975 at
12:55:09 UT and has been in that range ever since. The measurements are A-to-D
converted onboard, to an 8-bit resolution, yielding +/-0.14 nT quantization
sensitivity, which is larger than the intrinsic sensor noise level of 0.025 nT
RMS.
The data from the two-bit (per component) adaptive delta modulator,
incorporated into the instrument, and applied to the intrinsic sample rate of
25 vectors/sec., was never utilized, and hence the rate of the full (8-bit)
vector words, which occur every 320 ms, represents the effective sample period
of the instrument. The sampling rate is synchronized to the spacecraft clock;
the basic spacecraft clock frequency is 6.4 kHz. The sensor unit is mounted on
the end of a boom approximately 4 m from the center of the spacecraft.
For further details, see: http://www-lep.gsfc.nasa.gov/imp8/expr.html
Additional information on the IMP-8 magnetometer can found at:
http://lep694.gsfc.nasa.gov/imp8/imp8_hm.html
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