Introduction to Modal Testing

ERI is offering a better approach to modal test training. We go beyond training test engineers to use one software package. We see modal testing as one part of your investment in an overall dynamics program. The investment impacts your bottom line not only in the direct cost of analysis and test, but also in the cash flow impact of successfully getting your new product to market on time.

We train your people to see this larger picture. Engineering management needs to allocate its overall dynamics budget for maximal benefit at least cost. Your analysts need to understand not only how to set up a finite element analysis but how to do this within financial limits. They can't progress professionally without having their analyses experimentally checked in the test laboratory. To keep a program on track, the test conductor not only needs to know how to push the right button at the right time, but to fully understand test objectives.

We start at the beginning with the questions, "What is a mode?" and "Why do I need to either calculate or measure our modes?" Do your engineers think they know the answers to these questions? Misconceptions abound. Calculating or measuring modes cost time and money; the course presents trade offs that assist leader decision on amount of modal testing required.

The focus of the class is modal testing, and we'll present the principles in detail, so your people can use any modal software, can get needed data and can extract modes confidently and correctly. In addition to the "big picture" described above, specific modal test topics to be covered include:

Test Planning

Test Instrumentation - Specification, installation, and checkout

Test conduct - Excitation types, operator display options, accepting the data

Signal Processing Basics

FRF -the Frequency Response Function - understanding and measuring it.

• Modern modal testing is FRF based - what exactly is an FRF?
• Using poles and zeroes to "see" the modes as soon as data is taken

The Coherence Function - understanding and using it.

Extracting modes

• The Modal Indicator Function
• The Polyreference Method
• Correlation Matrix
• Stability Diagram
• Setting up the solution
• Modal animation
• Orthogonality

Our instructor, Leland H. "Lee" Smith has a wealth of experience to share with you. Please read about Lee. In 40 years of shock and vibration engineering, Lee has been on numerous design, analysis and test teams. Lee was test conductor of the first aerospace modal test using digital FFT-based technology. He has since conducted many modal tests, most recently including rocket engine and satellite tests at Boeing's Huntington Beach, California laboratory. Lee brought home every test in spec and on budget. Your people will learn Lee's methods.