Optical Vibration Measurement with VIC-3D FFT & Phantom T3610 High-Speed Cameras

The VIC-3D HS FFT system – the flagship digital image correlation software from Correlated Solutions - is a powerful measurement tool which combines state-of-the-art DIC software with the latest high-speed cameras from around the world. As we prepare for the release of VIC-3D 10 - which includes significant advances in vibration measurements and visualization capability - we are eager to put the best high-speed cameras through their paces to see how they perform. Recently, our engineers had the chance to spend some time with two T3610 Monochrome cameras from Phantom. These cameras are capable of just over 38,000 fps at full 1 Megapixel resolution of 1280 x 800 and up to approximately 875,000 fps at reduced resolutions. (Note: these reduced resolutions might not be sufficient resolution for DIC) Featuring a compact and easy to use platform, the T3610 uses back-side illumination (BSI) sensor technology to maximize sensitivity for sub-microsecond exposure time for optical vibration analysis.

To put the T3610’s impressive frame rates to the test in conjunction with the updated FFT vibration measurement module in VIC-3D 10, we designed a simple test to measure the vibrations during the excitation of two objects designed specifically with vibration in mind - a call bell and a tuning fork. After the objects were prepared for DIC using matte white paint and the Correlated Solutions Speckling Kit, the cameras were mounted using our custom stereo mounting system, which is extremely rigid, but highly adjustable. The cameras were positioned and focused on the measurement area, and they were calibrated using Correlated Solutions calibration targets which are laser marked right here in our SC headquarters. The cameras were synchronized via a hardware connection and armed in endless loop recording to the onboard memory. After the objects were excited, the cameras were hardware triggered to capture images of the vibration event. Approximately 10,000 stereo image pairs were downloaded using VIC-Snap Image Acquisition software and analyzed using VIC-3D 10 which computes full-field displacements over the entire surface for each image. The full-field x, y, and z displacements (referred to as u, v, and w in VIC-3D) were computed and displayed as contour plots, and data points and areas were extracted to show the displacement graphically. Next, VIC-3D’s powerful built-in FFT software module was activated to compute the frequencies and amplitudes of the operational deflection shapes or ODSs. In these two examples, VIC-3D found multiple ODSs from each of these objects.

What is especially impressive about combining DIC with a robust FFT algorithm, is that only one impact is necessary to excite the specimen and identify multiple frequencies and shapes displayed in the frequency domain. In addition, DIC data acquisition of a vibration event takes only a few seconds and results in thousands of images and millions of data points which means richer data and a measurement noise floor reduced to a nanometer resolution. This is in stark contrast with typical laser doppler vibrometer measurements, which require meticulous laser scanning to generate only a few hundred data points. This can be time-consuming and costly. What is more, these laser systems generally cannot be used to measure ODSs from transient events like a door slam or the response of a structure during an earthquake. In the upcoming version of VIC-3D, these ODSs can easily be statically displayed, animated, and exported for further analysis directly in the FFT module or edited alongside text, graphics, and other image sequences in VIC-3D’s powerful iris visualization engine. Segments were produced entirely within VIC-3D 10 and demonstrate the capabilities of the software to export striking 4K visualizations of your FFT testing quickly and conveniently to the necessary platform.

Overall, the T3610, like other Phantom high-speed cameras, is a solid counterpart to the VIC-3D High Speed FFT system. This combination of technologies provides a powerful tool for engineers working with ODSs to gain a greater understanding of the nuances of vibration mechanics.