Rockwell Automation 1440-VST02-01RA XM-120 Eccentricity Module - Manual (Page 109)

Publication GMSI10-UM010C-EN-P - May 2010
DeviceNet Objects 101
Get_Waveform_Chunk
This service returns a portion of the respective data structure. It is likely that
the waveform data structure will be too large to transfer over the network in
one message. This service allows the data structures to be transferred over the
network in smaller portions so that the explicit message buffer does not need
to be so large.
The Waveform Data structure contains an array of values that, taken together,
are the output of the sampling performed by the Spectrum/Waveform
Measurement Object on the input signal. The Waveform Data array values are
normalized and must be converted to floating point to obtain the true values.
The total size of the Waveform Data structure in DWORD is: 3 + (Number
of Waveform Points / 2)
The Waveform Data is an array of INT (16-bit signed integers ranging from
-32768 to 32767). The number of INTs in the Waveform Data array is equal to
the Number of Waveform Points. To convert the normalized Waveform
Data into floating point values, use the following equations:
Where Float Data
n
is the value for the nth waveform point, and 0 ≤ n ≤
Number of Waveform Points.
Table C.39 Waveform Data Structure
Byte (DWORD)
offset within
structure
Structure Member Data Type Description
0 (0) Number of
Waveform Points UDINT Number of points in the waveform data. This should be
equal to the Number of Waveform Points attribute
setting. It is provided within this structure to assist in
determining the size of the structure.
4 (1) Period REAL The period of the waveform.
This is the actual period of the waveform and may vary
from the Period 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 The normalized waveform data points
These must be converted to floating point values using
the Amplitude Reference value.
Float Data
n
Amplitude Reference
Normalized Data
n
32768
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