Among the detectors of metal objects, using a pulse signal with the subsequent evaluation of its changes in time and belonging to a relatively a new category of TD (Time Domain), you can also select several basic groups.
The first group includes the so-called radar detectors. In such devices estimated parameters of the microwave signal reflected from metal object. The amplitude of the reflected signal depends not only on object's size, but also on the conductivity of the material. In addition to the amplitude analyzed and delay of the reflected signal, carrying information about the depth the occurrence of a metal object.
The second group of detectors category TD are devices in which as the emitted signal is also used as a pulse signal. However the duration of these pulses is much greater than in the radar the metal detectors. This provides excitation in the metallic object eddy currents which information is analyzed in the respective cascades. Such devices are sometimes referred to by the acronym TR-PI (Transmitter Receiver - Puls Induction) or simply PI.
It should be noted that the basis for the functioning of all the above devices in this category are based on the principle of "transmit - receive". However, the main constructive contrast to, for example, metal detectors TR-PI devices type TR-IB is that in pulsed devices as a reception area and transmission can use the same coil.
Author: M. V. Adamenko