Test Types: System Check & Sine
March 29, 2018
Back to: VibrationVIEW Syllabus
System Check
System Check confirms that the shaker and accelerometers are functioning properly. It also makes sure the system allows the controller to control the vibration of the shaker.
Sine Test
Sine testing has limited use in the vibration industry because a sine test cannot generate real-world vibration. Its usefulness comes from its simplicity; therefore, sine tests are a good point of entry into the study of vibration.
Sine testing requires a basic understanding of resonant frequencies. A resonant frequency is equivalent to a product’s natural frequency and results in magnified vibration.
Sine testing is primarily used to determine the amount of damage inflicted on equipment or a product. According to Tustin, “The best pro-sine reasons are to search for product resonances to 1. study modal responses; 2. determine fatigue life in each mode” (pg. 205).
Applications of a Sine Test
A vibration controller is used to send sinusoidal vibration to a shaker. The controller can sweep up or down a frequency band to determine which frequencies resulted in product resonance. After locating the resonant frequencies, a test can be set up to dwell at those locations for a set amount of time. The dwell will determine how long a product can resonate before failing.
Think of bending a paper clip back and forth until it breaks. As time passes, the paper clip becomes easier to bend until it snaps. Dwelling at resonance has much of the same effect. As the product deteriorates, the resonant frequency will begin to shift. Controllers can track the resonance shift and automatically adjust to maintain the peak resonance (see Module 1.2).
Other than testing for resonant frequencies, sine testing can also be used to determine the amount of damage to equipment. A baseline can be generated by running a sine sweep before any random or shock test. After the random/shock test is conducted, another sweep is employed. One can determine the amount of damage by comparing the differences in the data files. An example would be a shift in the natural resonant frequencies, which possibly suggests there are loose bolts that need to be better secured or tightened.
Sine tests are simple and do not have real-world applicability, but they are still widely used in testing labs for baseline readings, resonance studies, and damage estimation.