Low-field variation of magnetic susceptibility measured by the KLY-4S Kappabridge and KLF-4A magnetic susceptibility meter: Accuracy and interpretational programme

Abstract

The KLY-4S Kappabridge and KLF-4A Magnetic Susceptibility Meter enable automated measurement of susceptibility variation with field in the ranges of 2–450 A/m and 5–300 A/m (in effective values), respectively. Unfortunately, the measurement accuracy decreases with decreasing field and it is not easy to decide whether the susceptibility variation at the lowest fields is natural phenomenon or results from measuring errors. To overcome this problem, the accuracies of both the above instruments were investigated experimentally using artificial specimens (mixture of pure magnetite and plaster of Paris) with variable susceptibilities ranging from 1 × 10⁻⁵ to 5 × 10⁻². The complete curve of the field variation of susceptibility of each specimen was measured 10 times and the relative error was calculated for each field.

In the KLY-4S Kappabridge, in specimens with susceptibilities higher than 100 × 10⁻⁶, the relative errors are lower than 3% in all fields and lower than 1% in the fields stronger than 10 A/m. In the KLF-4A Magnetic Susceptibility Meter, in relatively strongly magnetic specimens with susceptibilities 5 × 10⁻⁴ to 5 × 10⁻², the relative error is less than 1.5% in the entire field range. While the former instrument is convenient for investigating almost all rock types, the latter instrument is convenient for measuring moderately and strongly magnetic specimens.

To facilitate work with field variation of susceptibility curves, showing variable accuracies with field, the programme FieldVar was written. One of its options is plotting the measured data with corresponding field-variable error bars. In this way, a tool is offered for interpreting such susceptibility changes that are sound and reasonable from the point of view of measuring accuracy.