SIMULATION OF THE RESONANT EDDY-CURRENT CONVERTER OF THE TRANSFORMER TYPE FOR THE GAP CONTROL BETWEEN MAGNETIC CORE AND FERROMAGNETIC SAMPLES

Abstract

The results of theoretical researches of the interaction between resonant eddy-current converter of the transformer type with a coupled measuring oscillatory circuit and ferromagnetic samples for improve the accuracy of the eddy-current control are presented. The main operation procedure of the eddy-current converter is the resonant method of adjustment from the effect of the gap. The interaction of the electromagnetic field of the winding of the eddy-current converter and the ferromagnetic sample is investigated.
On the basis of the presented mathematical model, the eddy-current defectoscope was improved. Its measuring subsystem contains two identical oscillatory circuits with a transformer coupling, namely the coupled measuring and standard circuits. The measuring oscillatory circuit consists of an overhead eddy-current current converter, which is installed on a controlled surface of a ferromagnetic product with some appear gap due to surface dirtying. The output of the sinusoidal self-oscillator is connected in parallel to the inputs of the connected measuring and associated reference oscillatory circuits. The output of the connected measuring oscillatory circuit is connected through the high pass filter to the indicator. The outputs of the connected measuring and associated reference oscillatory circuits are connected to the inputs of the adder, the output signal of which is stimulated to the control input of the sinusoidal self-oscillator through a low pass filter.
The appearance of the crack results in a sharp change in the output signal from the coupled measuring oscillatory circuit with a transformer coupling. Such fast impulse changes are smoothed by the low pass filter and do not affect the self-oscillator, but the signal from them is received to the indicator. The signal due to the gap change is slow and take places in the bandwidth of the low pass filter and is received to the controller input of the self-oscillator. It thus maintains a constant value of the frequency in a coupled measuring oscillatory circuit of the transformer type.
Such an appliance is used in the eddy-current (electromagnetic) defectoscopy for automatic and manual control of metal products in cases where it is important to fix the gap between the overhead eddy-current converter (inductor) with the measuring oscillatory circuit and the controlled surface of the ferromagnetic product. The problem of increase the accuracy of the eddy-current control by the specified calculation of the characteristics of the measuring system of the resonance eddy-current defectoscope is solved.

Keywords: eddy-current defectoscopy, oscillatory circuit, eddy-current converter