METAL DETECTORS: pulse induction (PI). Typical PI systems use a coil of cable on one side of the belt region as the transmitter and receiver. This technology sends a strong current, data over a wire coil. Each datum produces a short magnetic field. When the current ends, the magnetic field pole reverses and changes very suddenly, resulting in a sharp electric current. This current lasts for a few microseconds and causes another current to run through the coil. This is the data reflected in the next stream and takes only 30 microseconds. Another data is sent then the process is repeated. A typical PI-based metal detector sends about 100 data per second, but the number increases by about 25 data per second to 1000 data per second, which can vary widely by manufacturer and model. If a metal object passes through the metal detector, it creates a reverse magnetic field with the data object. The data reflects the magnetic field, the reflected data is in time relation, the more a large metal object is in the magnetic field, the longer the data is sent. This process works like an echo: when shouted in a room with only a few hard surfaces, only a very short echo is likely to be heard, or not at all. The echo lasts longer if you shout into the room with a lot of hard surfaces.