SIMULATION AND ANALYSIS OF THE ELECTROMAGNETIC NOISE DISTURBING PROBLEM IN ULTRASONIC NONDESTRUCTIVE TESTING SYSTEM

摘要

The problem of electromagnetic noise disturbing in ultrasonic Nondestructive Testing (NDT) system has been addressed in this paper. Low signal-noise ratio directly causes some important objective defect information being overwhelmed. Normal methods are adopted, but effect is not obvious. Through many a time experiments, we find out that Direct Current (DC) motor-drivers are the major source that noises come from. Since dual-polarities Pulse Width Modulation (PWM) technique is applied to provide power conversion in DC motor-drivers, high frequency current fluctuation is inherent. Therefore, what we could do is limiting current fluctuation to an acceptable extent. By theoretical analysis, we conclude that there are three factors in affecting current fluctuation. Among them, only parameter of armature inductance L_a could be changed easily in practice. In order to verify this method's feasibility and determine the optimal adjusting range of added inductance value, simulation experiments, based on a reasonable simplified control system's model, are supposed to be conducted. The results of simulating prove that the method is highly effective, and the requirements of both restraining noises and guaranteeing specified servo performance could be fulfilled. With the assistance of simulating, setting optimal controlling parameters of actual system becomes much convenient.