A PC-based instrument for measurement and analysis of the starting current of a motor

A novel instrument has been designed and implemented to measure and analyze the real-time current and voltage of sudden change, which often occurs at the startup of motors. This paper gives the algorithm for eliminating errors in RMS value estimations and the algorithm for compensating voltage variation. The digitized signals are sent to a PC directly through an EPP (enhanced parallel port), so neither the special communication interface nor additional buffers are needed. That makes the instrument simple in realization and convenient for use. With Hall effect probes, this instrument can measure currents as high as 6000 amps fast and accurately. The measured values can be displayed either in real-time waveforms or in RMS value curves according to the user´s choice