声音最小：
Smallest sound
磁棒线圈：
Magnetic coil
电磁接收头：
Electromagnetic Accept end
电缆：
Cable
磁力线：
Magnetic field lines
Input audio current signal between the cable conductor and the ground. Put the
inductance coil magnet perpendicular to the ground, and place it just above the cable
under test to find out the position where you hear the smallest sound in the headphone
(the valley). Write down its corresponding ground position A, then move the magnetic
antenna close to the ground and make it tilt to the ground with 45 °
angle(perpendicular to the direction of the cable) and move left or right along the
cable to find out the valley points B and C. In both positions, the magnetic field lines
is perpendicular to the axis of the coil, so the magnetic field lines passing through the
coil is the least, so that you can hear the smallest sound in the headphones. Line BO
and CO connecting two valley point B or C and the cable location O are 45 degrees to
the straight line AO, which makes triangles AOB and AOC right angle isosceles
triangle, i.e. AB = AC = AO. Therefore, distance between the valley point A just
above the cable and the other two valley points B or C, is equal to the depth of buried
cables.
3. tips when measuring the path
The general cable has shielding layer. If the path signal is applied between the
core wire and cable sheath, due to the shielding effect of the sheath of the cable, the
electromagnetic signal on the ground is weak, which will greatly affect the path
detection range. To detect long-distance path, you have to increase the output power
of the signal generator, while the effect is not necessarily good. In circumstances
when the output power of the signal source if in certain, you should disconnect the
grounding wire on both ends of the cable from the system. The output of the cable
