Rockwell Automation 1440-DYN02-01RJ XM Dynamic Measurement Module - Manuel (Page 140)

140 Publication ICM-UM002F-EN-E - March 2013
Appendix B CIP Objects
Get_Spectrum_Chunk/Get_Waveform_Chunk
These services return a portion of the respective data structure. It is likely that
the spectrum and waveform data structures will be too large to transfer over
the network in one message. These services allow 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 Spectrum Data structure contains an array of values that, taken together,
are the output of the spectrum measurement performed by the
Spectrum/Waveform Measurement Object on the input signal. The size of the
Spectrum Data structure and format of the data array depends on the Data
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
Table B.40 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.