Recently very popular metal detectors TR-IB (Transmitter Receiver - Induction Balance), or just TR, based on the principle "the handover" (Fig. 1.4). In such devices, called balanced metal detectors, coils are balanced to zero mutual induction.
The main feature of devices TR-IB is that on the spool receives no reflected signal transmitter and the signal source which are eddy currents excited on the surface of a metal object.
Fig. 1.4. A simplified block diagram of the detector working on the principle transfer - receiving
The transmit signal generated by reference oscillator, is fed to the transmitter and further to the transmitting coil. With the appearance of a metal object in the zone radiation of the transmitting coil on its surface under the influence of VLF signal initiated by vortex or surface currents. These currents are the source the secondary signal, which is received by receiver coil of the metal detector. With the receiver output signal is fed to the analyzer, where the assessment of its parameters. On the basis of the analysis corresponding signal is generated to the display unit.
It should be noted that the main advantages of such detectors are high sensitivity, the possibility of exclusion from not only the background of the soil, but from various debris. And, of course, these devices allow you to determine the type metal. The main disadvantage of balanced detectors should be considered the difficulties inherent in the manufacture and balancing of the system of coils.
Author: M. V. Adamenko