Peak Tracking in VibrationVIEW
First, a quick summary of Peak Tracking and Phase Tracking.
Peak Tracking is a better way to track a shifting resonance during the Dwell portion of a Sine Resonance Track and Dwell (SRTD) test, delivering superior results to the traditional Phase Tracking method. VibrationVIEW offers you both options.
As material fatigues and the resonance shifts, Phase Tracking adjusts the drive frequency to maintain the originally measured phase difference between the control and response sensors. Phase Tracking isn’t bad, offering a clear advantage over tests that do not adjust at all to resonance shifts. However, there are three limitations to the Phase Tracking methodology.
- Phase relationships measured during an initial sweep are imprecise.
- If the product has a non-linear amplitude response, a change in amplitude between the detection portion of the test and the dwell portion of the test may result in both a different resonant frequency and a different phase relationship.
- Fatigue may behave in a non-linear fashion, causing the phase difference at peak transmissibility to change as fatigue effects progress.
Peak Tracking allows the controller to adjust both the output frequency and the phase difference between the two channels to maintain peak transmissibility. It works by constantly oscillating the phase difference between the control and the response channels and observing if the transmissibility increases or decreases.
There is, of course, a 1-to-1 relationship at any point in time between frequency and phase difference during a test. Saying that ‘the software is oscillating the phase’ really means that it is using an algorithm that changes the frequency in a way that achieves the desired phase change. For frequencies close to the resonant frequency, a very small change creates a significant change in the phase difference.
At the same time, the software tracks the transmissibility to see if it increase or decreases, learning if it is approaching the peak or moving away from the peak.
Peak Tracking Parameters in VibrationVIEW
VibrationVIEW has 6 parameters to control Peak Tracking:
- Delta Starting Frequency determines where the phase oscillations begin
- Initial Range sets the initial oscillation range in degrees
- Min Range sets a lower limit on the phase oscillation range
- Max Range sets an upper limit on the phase oscillation range
- Initial Period sets the initial time in seconds for a phase oscillation
- Max Period sets the upper limit on the time for an oscillation
Within the limits set by these parameters, the controlling algorithm will try to reduce the sweep range from the Initial Range, as it oscillates around the peak in transmissibility. It will also slow down when it begins to oscillate around the peak in transmissibility until it reaches the Max Period value.
You can just accept the default values, which are reasonable for most tests or adjust the parameter values to fit your specific test situation.