Rockwell Automation 1440-VSE02-01RA XM-122 gSE Vibration Module - Manual (Page 177)

Publication GMSI10-UM013D-EN-P - May 2010
DeviceNet Objects 167
Format attribute. In all cases, the spectrum data array values are normalized
and must be converted to floating point to obtain the true values.
The total size of the Spectrum Data structure in DWORD is:
• For Real or Power Data Format: 3 + (Number of Spectrum Lines / 2)
• For Complex Data Format: 3 + (Number of Spectrum Lines)
If the data format is Real Data or Power Data then the Normalized Value
Array is an array of UINT (16-bit unsigned integers ranging from 0 to 65535).
The number of UINTs in the spectrum data array is equal to the Number of
Spectrum Lines. To convert the normalized spectrum data into floating point
values, use the following equation:
Where Float Data
n
is the value for the nth spectrum bin, and 0 ≤ n ≤
Number of Spectrum Line.
The Float Data value represents an amplitude value if Data Format is real
data. The Float Data represents a power value if Data Format is power data.
If the data format is Complex Data then the Normalized Value Array is an
array of INT (16-bit signed integers ranging from -32768 to 32767). There are
two INTs (real and imaginary values) in the array for each spectrum bin (the
array size is twice the Number of Spectrum Lines). To convert the
Table C.54 Spectrum Data Structure
Byte (DWORD)
offset within
structure
Structure Member Data Type Description
0 (0) Number of Spectrum
Lines UDINT Number of lines or bins in the spectrum data. This should
be equal to the Number of Spectrum Lines attribute
setting. It is provided within this structure to assist in
determining the size of the structure.
4 (1) FMAX REAL The maximum frequency or order of the spectrum data.
This is the actual FMAX of the spectrum data and may
vary from the FMAX attribute setting.
8 (2) Amplitude
Reference REAL Normalization factor
This factor is used to convert the normalized array data
into floating point values.
12 (3) Normalized Value
Array Array of INT or UINT The normalized spectrum data points
These must be converted to floating point values using
the Amplitude Reference value. The Data Format
attribute determines whether these are INT or UINT and
exactly what conversion should be applied.
Float Data
n
Amplitude Reference
Normalized Data
n
65536
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