1S9: VFDs: The vibration analysts’s worst nightmare

Scott Dow, Senior Instructor, Mobius Institute


For the average vibration analyst, VFDs are shrouded in mystery, components that, we are told, provide great benefit to the company and the process. What we do know is that they can create great confusion when it comes to analyzing vibration data, throwing the rules we know and rely on into what seems like a state of chaos and doubt. But have those rules really changed, or do we simply need to better understand what, exactly, the VFD is doing and adjust how we approach the analysis process?

This presentation starts with a short primer on what VFDs do and how they do it. After that, we will step through some of the unique frequencies that VFDs generate followed by a series of analysis exercises that clearly illustrate some of the potential vibration-related pitfalls VFDs create along with some simple techniques that will prevent them from making potentially-serious misdiagnoses.


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 method 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. Originally called InterActive Training when it was introduced, the cases have recently been updated and the classes are now being offered by Mobius as Analyst Flight School. Scott currently owns his own business, CBM Consultants, with one of his primary duties being a Senior Instructor for the Mobius Institute N.A. 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.