Sensor position with respect to the magnets can also affect the measured signal. The effects of axial sensor position with respect to the magnet poles were calculated using finite-element analyses.(7)

Effects of Sensor Axial Position

The curves shown above correspond to a 2.0-inch long, 50 percent deep, circumferential notch. Five axial positions of the sensor with respect to the pole pieces are shown. For a static or slow moving system, a sensor located midway between the poles measures a symmetric signal for a symmetric metal-loss region. Away from the midpoint, the measured static signal is asymmetric. For moving systems, though, the effects of axial sensor position are different. Asymmetry is introduced even for measurements at the midpoint.