2S10: Time Waveform Analysis

Scott Dow, Senior Instructor, Mobius Institute


All vibration data begins as a digitized time sample – the “raw data”. Despite that, many analysts limit themselves by failing to develop a thorough understanding of the various aspects of the TW plot, aspects that range from proper setup (the technical details and how they relate to spectrum) to analysis (understanding what you are seeing) and diagnosis (relating it back to the machine). While the FFT is a powerful tool and the resulting spectrum remains our “go to” plot for analysis, the fact of the matter is that the FFT has weaknesses that make certain types of faults more difficult – even virtually impossible – to assess. Many of these are the very same faults that are easiest to analyze using the TW – once you understand it!

This presentation will begin by using case study examples comparing TW and spectral data for known faults that show you the necessity of utilizing the TW plot (or missing a severe fault) before a brief primer on understanding the TW setup, including the “2.56” relationship between the TW and spectrum settings and some practical tips to being successful.


A mechanical engineer by trade, Scott Dow has been working in the vibration world for over 25 years. During that time, he has worked extensively as a field analyst and as a trainer, teaching formal classes and also mentoring clients individually and in small groups. During the mid-90s, Scott developed an innovative training technique based on recreating interesting and educational case studies he had encountered. Students would receive the actual data to analyze and were free to request any field tests they thought would help them diagnose the problem, which eventually they would have to do in the form of a submitted report that was assessed in light of the actual (known) case fault(s). In practice, this method has proven to be highly successful, allowing students to bridge the divide between theory and successful application of that theory in identifying machinery faults. You can find this case study technique being used as an important part of Mobius’ new class on Time Waveform Analysis (TWA).

Scott currently owns his own business, CBM Consultants, with one of his primary duties being  the Principle Instructor for Mobius Institute North America. When he is not conducting Mobius classes, he continues to mentor both individuals and small groups with either on-site or remote support for database setup, building analysis skills, field testing and more.