Material Property
Electrical current carrying capacity of a substance determines how effectively it supports the flow of charge under an applied electric field. The value of target conductivity dictates the strength of the eddy currents induced in a metal object during electromagnetic sensing. This parameter is typically measured in Siemens per meter or as a percentage of the International Annealed Copper Standard.
Induced Current
Alternating magnetic fields from the sensor coil generate circular currents on the surface of the metal object. The magnitude of these currents is proportional to the electrical conductivity of the metal. These currents create a secondary magnetic field that opposes the sensor field and reduces the coil inductance.
Measurement Sensitivity
Impedance changes in the sensing circuit are highly dependent on the electrical properties of the metal object being measured. When the object has high conductivity, the resistive losses are low and the reactive changes are large, which produces a distinct signal path. Low-conductivity alloys generate larger resistive losses and smaller reactive shifts, which alters the calibration curve of the sensor.
The instrument must be calibrated for the specific metal alloy to ensure accurate displacement or thickness measurements.
Thermal Influence
Temperature changes modify the electrical resistance of the metal object, which shifts the measured impedance vector over time. This thermal shift can be mistaken for a change in position or thickness if not properly compensated. Standard designs use temperature sensors to apply real-time corrections to the measurement data.
