The principle of spinner instruments is the generation of an alternating voltage by the continuous rotation of a magnetized sample within or near a coil or fluxgate system. For a given sensor configuration, the amplitude of the output voltage is proportional to the component of magnetic moment perpendicular to the rotation axis, and the phase of the voltage is utilized to relate the direction of the measured component to a reference direction in the sample. The total vector is determined by spinning the sample about a second orthogonal axis, although in practice the sample is rotated successively about three axes to obtain average values of the NRM components and reduce the effect of in-homogeneity.
Spinner Magnetometer JR-6A
Model/Make:JR-6A/AGICO, Czech
Specifications
Cylinder Specimen Size
25.4 mm / 22 mm
Cubical Specimen Size
20 mm on edge
Sensitivity
2 x 10 -6 A/m (high speed)
Rotation Speed
High: 87.7 rps Low: 16.7 rps
Measuring Ranges
up to 12,500 A/m
Power
110 V / 60 Hz or 220 V / 50 Hz
Power Supply Dim & Wt.
200 x 160 x 120 mm; 2.5 kg
Pick-up Unit Dim. & Wt.
290 x 130 x 310 mm; 24kg
Principle
The instruments operate by rotating a rock specimen at a constant angular speed in the pick-up unit inside a pair of Helmholtz coils. Inside the coils an AC voltage is induced whose amplitude and phase depend on the magnitude and direction of the remanent magnetization vector.
Description
The instruments consist of a spinner/pickup unit and a measurement control unit. All functions are microprocessor controlled, including digital filtration of the signal, control and test of the speed of specimen rotation, and execution of automatic tests for erroneous conditions. The measurement process is fully controlled from a computer.
Application
The world’s most sensitive and accurate instruments for measurement of remanent magnetization of rocks based on classical (non-cryogenic) design. The new JR-6A has two rotation speeds – the higher one enabling the maximum sensitivity to be reached, and the lower one enabling the measurement of soft sediment specimens. These instruments enable measurement of even very weakly magnetic sedimentary rocks including limestone.
