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The focus of Sine vibration testing is to see how the object performs under constant vibration in a safe environment of a testing laboratory. A Sine vibration test exposes the object or structure to a Sine tone at a defined amplitude and frequency.
The reason behind the prevalence of Sine vibration testing is the fundamental nature of the Sine wave. This is the wave type of AC current, RF or radio frequency, audio test signals, and many naturally occurring vibrations. A pure Sine wave is free of harmonics, with its energy confined to a single frequency.
Sine vibration testing is used in a large variety of fields: robotics, calibration and certification, battery testing, logistics, automotive, and many others.
A Sine vibration test operates with the following parameters:
Figure 1: Sine vibration profile window in RULA software
Normally, Sine signal sweeps at a set rate (interval per bandwidth) in octaves per minute or other values such as Hertz.
Figure 2: Sweep rate settings of Sine vibration profile in RULA software
Engineers can get necessary Sine Vibration parameters from field measurements or national standards such as MIL-STD-810, DO-160, ISO-16063, IEC-60068, and others.
Sine Vibration tests can be separated into three main types:
All three types of SV can be run in a sequence depending on the task. First, engineers run a Sine sweep test to expose the test object to sine tone on a set frequency range. This helps determine the resonant frequencies of the object. Next, Sine dwell is used to establish, how long the object survives under constant exposure to vibration on its natural resonance frequencies to ensure its safety in the real-life conditions.
Now let’s talk about each type in more detail.
Sine Dwell is the purest form of Sine vibration testing, with a Sine wave applied to the test object at a constant rate.
The only parameters required for Sine dwell test are vibration amplitude, frequency and duration. In RULA software, you can define amplitude in values of acceleration (g), velocity or displacement.
Figure 3: Sine dwell in the Pre-test diagnostics mode of RULA software
With Sine sweep, the values of amplitude and frequency of a Sine wave gradually change at a set sweep rate following the points of the profile. This change forms a tracking curve that will be displayed in the vibration control software. The addition of a curve makes it easier to compare the actual vibration amplitude with that of the set target.
Figure 3: Multiple Sine sweeps displayed on the graphs
One of the subtypes of Sine Sweep is stepped Sine where the frequency is increasing in a step-like fashion with user-set interval between each step.
Figure 4: Stepped Sine profile in RULA software
To ensure that the test is safely within the shaker limits, the software also displays the maximum peak values of acceleration, velocity and maximum peak-peak values of displacement alongside shaker capabilities. The deviation from the curve is limited by two thresholds: normally, ±3 dB and ±6 dB. If the amplitude exceeds the second level, the test is automatically aborted to prevent equipment damage.
Contrary to the clean Sine tone we use to drive the shaker, a signal measured at the test object will contain harmonics and noise. To get rid of them, we apply a number of low-pass and high-pass dynamic filters to the signal.
A simple Sine sweep test allows an engineer to quickly identify resonance frequencies of the test object or structure. High resonance peaks on certain frequencies help to find weak points of the test object. With this knowledge in mind, an engineer could design a Sine test to dwell on a resonance until the object is destroyed or until a certain test duration is reached to ensure the object survives the same exposure in a real-life scenario.
Figure 6: Resonance dwell and tracking in RULA software
Even though Sine vibration testing is considered to be a staple method, it has its share of limitations:
The way to account for these weak points is to use Random vibration testing, which we will cover in our next article.
Need to perform Sine vibration testing in your factory or lab? Choose a vibration controller from our catalog and contact us for further information.