Molspin Minispin Magnetometer

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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 lithologic unit.

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.

Minispin Specification:

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.

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