The Molspin Minispin
spinner magnetometer is a basic, portable field unit interfaced with a computer
(currently a laptop) for control and data acquisition. The software (PMagic)
driving the Minispin executes spin sequences and calculates declination,
inclination, and intensity corrected for the volume of the sample. PMagic also
contains procedures for statistical analysis and plotting. A series of
measurements is made on each sample as it is run through a demagnetization
sequence. Ordinarily, six separate spin orientations are required to produce an
accurate measurement. In general, the processing rate will vary with the NRM
intensity and in response to demagnetization of the samples from a particular
The Minispin can measure both rock and sediment samples up to 2.54 cm (1 in)
cubed in size. According to the manual, the noise level varies from 0.2 mA/m
(short spin) to 0.1 mA/m (long spin) for a 12.87-cm3 sized sample. The minimum
measurable intensity is on the order of 0.1 mA/m and the maximum is on the order
of 2500 mA/m. Parameters that can be specified in the PMagic software include
short (6 s for 24 spins) vs. long (25 s for 120 spins) integration time and
sensitivity range and four or six spin positions per sample. In general four
spins are sufficient. Six spins are used when the operator is trying to get the
maximum accuracy for a weak rock.
Specimen size: Up to 1 " x
1" (2.54cm) cylindrical specimen.
Integration time: Either 6 seconds (24 spins), or 24 seconds (1 20 spins).
Sensitivity/Noise level: 2.5 x 10-8 EMU.CM-3 (2.5 x I 0-5 A/m) for 4 spins at
the 24 secs time constant.