420 Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Appendix A CIP Objects
Attribute Semantics
Enabled Instances
The following bit-coding scheme is used to identify which channel setup
instances are enabled.
Disabled instances return error 0x08 (Service Not supported) when disabled
instances are addressed with common services.
Sampling Control
The following are different aspects of Sampling Control.
Bit Description
0…3 Measurement channels 0…3
0: disabled
1: enabled
4…7 Reserved for full multiplexing
8…12 Reserved for full multiplexing
13…15 Reserved - set to 0
Table 151 - Sampling Control
Category Description
Fundamentals SRD represents sample rate divide and must be set equal across a channel pair (0/1
and 2/3) unless multiplexing individual channels.
Actual sample rate is the base sample rate that is divided by the SRD
With the A/D in single mode (most applications), the base sample rate is 93,750 Hz.
With the A/D in double mode (frequencies up to 40 kHz), the base sample rate is
187,500 Hz.
Limits (Asynchronous and Synchronous Processing) Based on Nyquist, the setting of SRD/sample rate determines the maximum frequency
that can be assessed.
For synchronous sampling, the maximum frequency and the configured number of
samples per revolution dictates the maximum machine speed that can be successfully
processed.
The module confirms a maximum machine rpm for a given configuration by way of
instance attribute 2.
Further guidelines are as follows:
• Filter -3 dB points must always be set at less than
[Sample rate] / 2.048
• Bandwidth of an FFT in the same configuration, is less and calculated by
[Sample rate] / 2.56
• The center frequency of the highest line of an N line FFT is given by
[Sample rate] * [N-1] / [2.56 * N]
Example for SRD 32 (single mode)
• Filter -3 dB must be less than 1431 Hz
• FFT bandwidth (decimation = 1) is 1144.41 Hz
• Corresponding center frequency of highest line of an 800 line FFT is 1142.98 Hz, 1600
line FFT is 1143.69 Hz.
Note: The preceding information applies to all FFT of whatever line resolution and
whether used for Condition Monitoring or FFT Band Data.
The calculation of sample rate must include any decimation that is applied to the samples
before the (FFT or filter) processing, see also, in the following information, decimation.
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