7-4
Chadwick-Helmuth Company, Inc.
Chapter 7
- Spectrum Analysis
7.3.1 Using the Spectrum Setup Screen
Once the Spectrum Setup screen parameters have been modified, you may alternately press
SPECTRUM
to save the changes and return to the Spectrum mode, or
START
to save the changes and
begin spectral data acquisition. In effect, both of these keys execute an implicit
ENTER
before
performing their respective functions.
The rest of this section explains in greater detail the various Spectrum Setup screen fields.
7.3.1.1 Maximum Frequency
The maximum frequency is the highest frequency for which spectral data can be acquired. Use the
numeric keypad to enter an appropriate value, which may range from 200 RPM (3.3 Hz) to
600, 000RPM (10KHz). The default i s 10,000R PM (166.7Hz).
Note that, as the maximum frequency increases, amplitude values at the low end of the spectrum suffer
a loss of resolution. Low-frequency resolution can fall off dramatically when there is a large amount of
activity at low frequencies and the maximum range has been set high (above 1 0 0,000RPM). In
general, the upper three-fourths of the range contain the most valid data. You must therefore select
maximum frequency that is as close as possible to the area of spectral activity you wish to examine.
7.3.1.2 Frequency Units
The acquisition frequency may be displayed in either RPM or cycles per second (Hertz). Use the
<CHANGE>
soft key to convert the frequency from one form to the other. Once this parameter is set,
all other displays of frequency data are made in the selected units. The default is RPM.
7.3.1.3 Seek Amplitude
If the seek peak function is enabled, the seek amplitude becomes the minimum vibration signal
amplitude that can be recognized by the spectral plot cursor. The allowable range is from 0.010IPS to
10.0 0IPS. The default is 0. 010IPS.
7.3.1.4 Vibration Units
Vibrations may be displayed in units of velocity (IPS, 0-pk) acceleration (g’s or in./sec
2
), or
displacement (mils, DA). Use the
<CHANGE>
soft key to convert the units from one form to the other.
Once this parameter is set, all other displays of vibration data are made in these units. A mil equals
0.001in.
7.3.1.5 Repetition Mode
The repetition mode parameter indicates whether single or multiple spectral data frames are to be
acquired. In single mode only one set of data is collected and displayed. The data are retained and can
be scaled and manipulated, as described below. In multiple mode, data sets are continuously collected
and displayed, purging the current set during each pass. This process continues indefinitely until the
STOP
key is used to abort data acquisition. The multiple mode displays are always labeled with th
word
MULTIPLE
at the top of the screen. The default repetition mode parameter is
SINGLE
.
7.3.1.6 Seek Peak Function
Enabling the seek peak function confines the spectral plot cursor to those points that exceed th
specified vibration amplitude level. Otherwise, the cursor has free movement across the range of the
plot. Use the
<CHANGE>
soft key to turn the seek peak function on or off. The default is seek on.
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