Stay On Point with SRTD
Sine Resonance Track & Dwell (SRTD) seems like a straightforward test. Run a Sine sweep, find a resonance frequency, then dwell on that frequency for a pre-determined time or until the DUT fails.
Sadly, things are not that simple in the real world. Resonances shift as material fatigues and, for the test to be valid, the test frequency also needs to shift. An engineer needs insight into these shifts; ideally, the engineer should also be able to learn the details of multiple resonances, select a resonance for a Dwell, and then run that test with confidence that the frequency will stay on the resonance.
This level of confidence is critical to the testing process but difficult without the right tools. Fortunately, there is a an easy, budget friendly way to get that capability, especially for labs already using VibrationVIEW for Sine. With SRTD, users can run a sweep and display a resonance table with the details of multiple resonances; the software automatically selects resonances, using transmissibility between input and response as the determining characteristic of a resonance. For each identified frequency the software displays the transmissibility, phase relationship, and Q factor.
To use SRTD, go to the resonance table and select the resonance where the test will dwell, define how long the dwell test will run, and set the amplitude of desired control channel. Finally, before running the test, check the ‘phase tracking’ box and set the desired phase relationship. In theory, a resonance occurs at -90˚, but the real world doesn’t always follow the theory.
As the test runs, SRTD establishes the phase relationship between the control channel and a response channel. As the material fatigues and the response’s resonant frequency shifts, the software tracks it by adjusting the drive output to maintain a constant phase relationship between the two channels. Engineers can watch these shifts in real-time, while capturing the information for graphing and reporting. Most importantly, they can be confident their Dwell is performing a valid test.
Peak tracking – new in VibrationVIEW ‘18
Peak Tracking in VibrationVIEW 2018 deals with shifting resonances by finding and maintaining the peak transmissibility between two channels.
Peak tracking works by constantly oscillating the phase between the two channels and observing if the peak transmissibility increases or decreases. As more data is collected, the amount of phase change becomes narrower in frequency and slower in time, limiting the amount of oscillation while still accurately tracking the peak.
This powerful feature minimizes the need for precise detection during the sine sweep, so users can sweep faster. Most importantly, it ensures that peak transmissibility is maintained throughout the tracked dwell portion of the test.
To implement, click the peak detect box in the SRTD Controls panel.
A quick, cost-effective upgrade
VibrationVIEW with Sine customers can add the SRTD module with an electronic key. The pricing is low, simplifying the approval process and making it a realistic, productive use for funds remaining in a 2018 budget.