When preparing to run a vibration test, a test engineer is faced with the question of what kind of test should be run with any particular set-up. One option is a SINE vibration test.
What is SINE Testing?
A SINE vibration test is a test that exposes a DUT (Device Under Test) to a single frequency sine tone at a specific amplitude at a single time. There are different ways to conduct a sine test. Sometimes an engineer will run a sine sweep – exposing the DUT to a single sine tone; one with a frequency that is varied across a specified frequency range. After a sine sweep, a test engineer will often choose one or more specific frequencies – the resonance frequencies of the DUT – and expose the DUT to those specific frequencies until a failure occurs in the DUT, or sufficient time is spent at each resonance frequency to ensure that the failure will not occur when the DUT is used in the “real world.”
In Figure 1, a drive waveform plot shows the single sine tone that is being applied to the DUT during a sine sweep test. In Figure 2, an acceleration profile is plotted, showing peak amplitudes at two points on the DUT vs the sine frequency. The control point is the mounting point of the DUT. The response point is the second point on the DUT. The resonances at the response point are easily identified. Identifying resonances is a primary use of a sine test. The amplification factor of a resonance is typically what causes the DUT to fail. A test engineer could further design a sine test to dwell at the first large resonance (192.6 Hz) until a failure occurs in the DUT, or sufficient time is spent at the resonance frequency to ensure the DUT will survive.
The signal driving the shaker is always a nice clean sine tone as shown in Figure 1. The measured signal at the DUT often is not so nice and clean. The measured signal includes harmonics and other mechanical and electrical noise sources. Sine testing requires measuring and controlling the energy at a single frequency. A filter (tracking filter) is required to remove from the measurement the energy that is not at the single frequency.
Figure 1: A sine tone that is applied to the DUT
Figure 2: Results of a sine sweep test.
Why Should I Use SINE?
Sine vibration testing is beneficial for several reasons:
- A sine test is among the simplest tests to set-up and perform.
- Sine testing is among the best ways to accurately identify resonances in a DUT.
- If a DUT has a specific resonance and a test engineer needs to know the time it takes to bring the DUT to failure (assuming the failure arises from excitation of the known resonance), a sine test at that specific frequency is an effective means to bring the DUT to failure.
- A sine test focuses all the power of the shaker on the resonance frequency where the failure will occur.
When Should I Use SINE?
Vibration test engineers should use sine vibration testing to:
- Identify resonances in a DUT. Use a sine sweep test across a wide range of frequencies to identify the frequencies with the largest response signals.
- Validate Shakers. Sine tests work well to identify any trouble with shaker system (cracked armature, loose bolts). Periodically run a sine-sweep for the shaker system to evaluate that the response is the same. Variations in response, especially resonances that shift significantly, indicate issues in the shaker system.
- Validate Fixtures. Sine tests identify resonances in fixtures. If the fixture has resonances in the frequency range that is being tested, the results of the test are questionable.
- Qualify a product. Controllers that utilize a sine-track-and-dwell algorithm which adjusts the sine test frequency to keep the shaker exactly on the resonance as the DUT begins to weaken and fail, can effectively fatigue a DUT to failure or demonstrate the DUT can survive such a vibration.
