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electromagnetic wave in the transmission process and the principle of electromagnetic
induction, combined with digital filtering, wireless reception and software control.
Electromagnetic induction: its basic working principle is: electric and magnetic wave
generated by the transmitter and the transmission connection by different ways to
send signals to the underground cable, being detected underground cable after
induction to the electromagnetic wave, the underground cable surface induced current,
induced current will spread along the cable into the distance, in the process of current
transmission, and underground cables to the ground by the radiation of
electromagnetic wave, so that the local cable detector receiver detection on the ground,
in the underground cables are above ground receives electromagnetic wave signal,
through changes in the received signal strength can distinguish the position of the
underground cables and direction.
This principle to achieve conditions: first of all, let there be enough electricity source,
have formed in the power transmission line current, current in the process of flow and
a magnetic field around the line; Second, it is necessary to have a circuit capable of
receiving this particular magnetic field, showing the change of the magnetic field in
the form of electrical signals.
2.3.2 Signal output mode - transmitter working mode
The transmitter can output different communication signals and can be applied to the
target cable in three kinds (direct connection, coupling and induction). To ensure
reliable transmission of signals on the target cable, reliable circuits must be provided.
Indirect circuit, it can be made up of the earth can be formed by long enough cable
between the earth and the distributed capacitance of capacitive loop, also can be
composed of line fault point between direct circuits. Different circuits meet different
tests.
(1) Direct method
The transmitter's signal is directly connected directly to the target cable (power cut
cable). Straight line bonus, black line, the red line is connected to a certain line of