CIFER®-MATLAB Interfaces: Development and ... - Cal Poly

functionality of these programs and utilities will be discussed in the following sections along with
a brief description of the linear screen interface that drives them. In addition to these tools there
are a large number of other utilities for viewing results and organizing the CIFER ® database. The
primary CIFER ® programs this project dealt with were the first three main programs, all three
analysis utilities, and a small selection of other programs.
2.1 Creating a Frequency Response – FRESPID
FRESPID (Frequency Response Identification) is the first step in any CIFER ® analysis. This
program takes time history data and generates frequency responses based on the input and output
channel measurements. A very important aspect of CIFER ® occurs in FRESPID, which is the
“windowing” of the data. The data comprises a number of discrete frequency points over a time
duration. FRESPID uses the CZT to average the data points of a smaller time window of data. It
breaks the full time history into segments based on this window and performs computations based
on averages for each given window size.
There is a distinct tradeoff in the selection of window lengths relative to the total time history
length. Windows that are a smaller fraction of the total length provide a large number of averages
that can more easily identify high-frequency responses by countering noise effects.
Unfortunately, low-frequency identification degrades because low-frequency responses tend to
occur in larger intervals than the small windows encompass. When the window size is enlarged,
low-frequency identification becomes more accurate at a cost to the high-frequency end due to a
decrease in the number of averages.
CIFER ® solves this trade-off issue by allowing the user to specific up to five different windows in
FRESPID. A frequency response is generated based on each window. This ensures that both low
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