Differential probe

The differential probe has two coils that you guide parallel to the weld. One coil generates the magnetic field, the other measures the reaction of the material. If the material structure changes or there is a crack, the coils react differently – you evaluate this difference. This way you can also find fine cracks or structural changes that other testing methods can't resolve. It's important that the probe runs cleanly and evenly over the weld. If you tilt it or don't keep the distance constant, you'll get interference signals and miss real defects.