Introduction to Analyzer Package Graphs
January 2, 2019
Data collected by the VibrationVIEW Analyzer package are displayed in four primary graphing functions and two less common functions.
VibrationVIEW Analyzer Graphing Functions
The transfer function compares the ratio of PSD values for two signals across a specific frequency range as well as the phase relationships between the two signals. It is used for random and shock testing.
Total Harmonic Distortion (THD)
THD determines the amount of harmonic content in a signal by comparing the accelerations at a specific frequency with the accelerations at the next ten harmonics of that frequency. THD can also be used to measure how well a shaker recreates the signal from a controller. It is used for sine testing.
Coherence plots a correlation calculation value across the frequency domain. It is a statistic that examines the relationship between two values or signals. Two signals are coherent if they have a constant phase difference and the same frequency and waveform. Coherence graphs are used for random and shock testing.
Cross spectrum graphs display the amplitude and phase of multiple signals across a range of frequencies. They are used for random testing.
A spectrum graph plots the FFT for a signal. The scatter plot compares one selected input to a second selected input.
Additional Options in Test Settings
When the Analyzer key is enabled, two additional tabs appear in test settings: Pre-Test and Analyzer (Figure 1.1).
Under the Pre-Test tab, select the Enable Pre-Test option for an open-loop pre-test analysis and a prediction of test results. The pre-test applies a low-level, open-loop output to a shaker with just enough amplitude to overcome the noise floor of the shaker. Using the output and the measured response, the pre-test option can predict the amplitude levels of the full-level test and provide insight into test responses, such as the location of resonances. Early visibility is especially useful when there is a concern about potential over-testing.
To use the Pre-Test option, click New Test, and select the appropriate test type. Then, click Advanced > Pre-Test. Select Enable Pre-Test to configure the pre-test (Figure 1.2). The configuration includes the target frequency range, outputs, and channel limits.
Click the Analyzer tab to set analysis parameters. The parameter choices will depend on the type of test selected (Figure 1.3).
Note: For sine tests, it is very important to select the Swept THD option before starting the test so the THD data is collected. Additionally, it may be beneficial to increase FFT Analysis Lines beyond the default value of 2,048.
Programming the Analyzer Key
VibrationVIEW Analyzer is an optional feature and the software key must be programmed to enable the feature. Please contact sales to purchase or renew an Analyzer key.