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After viewing and interpreting real-time results, what happens to the
archived data?
If the original streams were stored on an instrumentation tape recorder,
data can be played back as originally recorded through a bit synchronizer
and decommutator. Data can once again be viewed, processed, archived to
disk, distributed, or sent to strip chart recorders for reports. You can
continually repeat this process if you are interested in analysis by inspection.
The tape can be replayed multiple times in real time if the ground system
components (bit sync, decom, processor, and disk) all support these higher
rates.
Another visual analysis technique extracts all instances of measurands
for the entire test (hours, even days totaling millions of points) for
display in a single window. While this places many instances on a single
vertical line, out of tolerance data, whether trends or spikes, is highly
visible. You can repeatedly focus in on significant data using a zoom
technique until multiple pixels show a single instance. This technique
greatly reduces the time required to seek aberrations and review areas
of interest (from hours to milliseconds).
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In addition to visual analysis, a host of third-party general-purpose
analysis and visualization programs can be utilized to evaluate archived
data, extract results, and produce reports. Each has its benefits and
followers and is available for both UNIX and PC platforms. Some are essentially
high-level analysis languages (MATLAB and PV-Wave), while others are GUI-based
(Excel, DADiSP). All include a rich set of signal analysis and statistical
tools from Fast-Fourier Transforms (FFTs) to t-tests. They may have links
to process piped data for near real-time processing as shown in the example
below, where MATLAB is used to feed a power spectral density (PSD) graphic
from FFT algorithms. Often, scripts are used to create a batch process
of reports from an entire test. |
