A STUDY OF ZERO-CROSSING TIME RESPONSE OF COIL CURRENT GENERATED FROM METAL BY USING PULSE INDUCTION

Abstract

This paper proposes a study of zero-crossing time response of coil current generated from each kind of metal by using pulse induction (PI). The goals of this research are as follows: 1) build an electronic circuit to on/off PWM (pulse width modulation) signal which passes a round coil and propagates toward a metal which are placed far away within 15 cm, 2) write an AVR ATmega168 microcontroller program to control the operation and generate PWM signals whose widths are varied so as to test and find out the characteristic of each kind of metal, 3) find out a technique for reading, storing, and analyzes the experimented results in order to construct many graphs which identify the falling edge time response of coil current generated from each metal, and 4) be a first guideline to build a metal detector in the future. The experimental results have been shown that both the coil driver and the microcontroller programming, proposed in this research, can be operated completely as desired and each metal has owned its zero-crossing time response of current on coil which is differentiated each other absolutely. A lot of response values of each metal at each distance are read successfully by microcontroller and are plotted many graphs. The tendencies of these graphs have the same direction. However, if the tested metal is far away until the Eddy current in that metal hardly can be received, the zero-crossing time differences of the current in the coil is nearly to be zero, i.e., the tested metal cannot be detected. Moreover, the testing distances are still relied on the size of each metal and the detectable distance is increased because the metal’s size is bigger or the coil’s diameter is larger.