Material Response
The degree to which a substance becomes magnetized when placed in an external magnetic field represents a critical material property in precision mass metrology. This property, known as magnetic susceptibility, dictates how strongly a calibration weight will interact with magnetic fields generated by the balance or the environment. High-precision weights are made from alloys with extremely low values to minimize force errors.
The measurement of this property is a pre-requisite for high-accuracy mass calibration.
Mass Accuracy
Magnetic forces between the weight and the balance can be mistaken for gravitational force. If the magnetic susceptibility of the weight is too high, the balance displays an incorrect mass. This bias can exceed the tolerance limits for high-class weights.
Interference Mitigation
Environmental magnetic fields from power lines and steel structures can perturb mass measurements. A low magnetic susceptibility ensures that the weight remains unaffected by these external factors. When working with sub-milligram tolerances, even tiny magnetic fields can cause measurable drift in the balance readings.
Standard mass sets are kept in non-magnetic storage cases to prevent contamination.
Metrological Limit
International standards, such as OIML R111, specify the maximum allowable limits for the susceptibility of weights used in calibration laboratories. The magnetic susceptibility of stainless steel alloys used in high-precision masses is verified during the manufacturing process using a gaussmeter and a reference magnet. If the alloy fails to meet the limit, it must be rejected for use in high-class calibrations.
This parameter must be re-evaluated if the weights are subjected to strong magnetic fields or mechanical shock.
