the sea hunter underwater metal detector
The less-common technology used by metal detectors nowadays is pulse induction (PI), which commonly uses a single coil that serves as a transmitter and a receiver. Pulses of current are sent to the coil that creates magnetic fields. The number of pulses ranges from 22 to 1,000 pulses per second, 100 pulses per second being generally used. After which the polarity of the magnetic field reverses and collapses, resulting in an electrical spike that lasts for a few microseconds. Another current, called the reflected pulse lasting for about 30 microseconds, runs through the coil. This process repeats. When a metal is detected, the reflected pulse takes longer than 30 microseconds, and this is being tracked by the sampling circuit, which sends this signal to an integrator, transforming these signals to a direct current (DC) voltage. The DC voltage, which increases when there is a metal, is connected to the audio output that reacts in proportion to the voltage it receives. Since a reflected pulse varies in each type of metal and cannot be separated easily. VLFs prove to be more reliable in discrimination than PIs. Nonetheless, PIs are more useful in salt-water exploration, since they are able to detect metals located in deeper locations.
