Time Domain Analysis of Machinery Vibration Signals Using Digital Techniques

The design and implementation of a general purpose processing system to analyze machinery vibration signals in the time domain are presented. The system comprises a data acquisition stage, where analog signals having a maximum frequency content up to 4 kHz and a dynamic range up to 72 dB, are converted into digital form and a processing stage, where modular software algorithms are employed to perform specific operations in an interactive environment. Processing capabilities encompass scaling, integration and the computation of statistical parameters such as means, RMS, standard deviation, maximum and minimum values. The input signal dynamic range and maximum frequency content are shown to be the governing criteria in the design and performance of the analysis system. The influence of hardware precision level and sampling rate on the overall accuracy of the obtained results is illustrated by digitizing standard waveforms under different processing parameters. Extraneous components introduced at the digitization and integration stages are identified and eliminated by employing a versatile digital filter algorithm. The performance of the system in processing acceleration signals from a 3 HP, 14000 RPM internal combustion engine is demonstrated and the different application aspects of such a facility in the machinery maintenance field are outlined.