When vehicles passing ring coil detector, the interaction of vehicle body's substance and ring coil changes resonant frequency of the ring coil and forms a curve of frequency variation.

Then use the coil ring machine rolled into a circle, with the electrode to weld the interface firmly, welding mouth to carry out X spectroscopy.

The Jumping ring Trick Now, with the coil current turned on, grasp the aluminum ring in your fingers and hold it down against the coil end.