Distance Correction
Signal processing methods that account for the air gap between a sensor and the target surface ensure the accuracy of eddy current and ultrasonic measurements. The liftoff compensation adjusts the raw data to remove the signal attenuation caused by varying distances during a scan. Without this correction, a small increase in the gap could be misinterpreted as a change in material thickness or conductivity.
Phase Analysis
Electronic circuits monitor the phase and amplitude of the reflected signal to determine the instantaneous proximity of the probe. By applying a mathematical correction factor, liftoff compensation allows for hand-held inspections where the operator cannot maintain a perfectly constant pressure. Modern digital instruments implement this through look-up tables or real-time algorithm execution.
Precision Baseline
Verification of this feature involves moving a probe over a wedge-shaped reference standard to simulate a gradual increase in the air gap. The tolerance for the compensated signal is defined by the maximum permissible error in the final thickness reading. If the correction fails, the resulting drift makes it impossible to distinguish between a surface coating and a structural flaw.
Edge Effect
Shielded probes reduce the sensitivity to external magnetic fields that might distort the distance calculation.
