Like radar detectors, pulse detectors are to devices category TD (Time Domain) using the pulse signal (Fig. 1.6). In this case, the repetition frequency of pulses generated in these devices, ranging from a few dozen to a few hundred Hertz.
Fig. 1.6. A simplified block diagram of the pulse detector
In the pulse type detectors PI (Pulse Induction) to assess the presence metal objects in the search area used is the phenomenon of occurrence of eddy surface currents in the metal object under the influence of external of the electromagnetic field. However, unlike the earlier device type TR-IB in the pulse detector analyzes the signal generated in the metal after exposure is not continuous, but pulsed signal.
The pulse signal generated by pulse generator is amplified and fed to transmitting coil, in which, respectively, AC is initiated an electromagnetic field. With the appearance of a metal object within range this field on its surface periodically, under the influence of pulse signal eddy currents. These currents are the source of secondary signal, which is received by receiver coil, amplified and fed to analyzer. It should be noted that due to the phenomenon of self-induction duration the secondary signal will be greater than the duration of the emitted transmission coil pulse. The parameters of the trailing edge of the secondary pulse signal and used for analysis, followed by the formation of data for the block display.
It is easy to assume that if there is a special isolation device or switch in the pulse detectors instead of transmitting and receiving coils could be used only one coil, which in turn would apply to transmission and reception of signals (Fig. 1.7).
Fig. 1.7. A simplified block diagram of a pulse detector with a single coil
The main advantages of pulse detectors are relatively high sensitivity and simplicity of design of the coils. However circuit solutions of individual units (for example, a pulse generator, switch, analyzer) still have considerable complexity. In addition to all other things in such devices microprocessors with appropriate software. Programming microprocessors also requires appropriate equipment and skills. Therefore, to collect a similar design can only be prepared by Amateurs.
Author: M. V. Adamenko