Campbell Scientific CDM-VW300 Series Dynamic Vibrating-Wire Analyzer System - Manual (Page 17)

CDM-VW300 Series Dynamic Vibrating-Wire Analyzers
4.6.4 Rainflow Histograms
Rainflow histograms are 3-D representations of the rainflow counting
algorithm of Matsuiski and Endo (1968). Rainflow histograms can be used to
monitor fatigue levels of structures under stress, such as components of a large-
scale transportation bridge. The histograms are calculated by the CDM-
VW300 analyzer to ease the processing burden required of the controlling
datalogger.
CRBasic Help topic for the Rainflow() instruction has more information about
rainflow histograms.
4.6.5 System Diagnostics
Several diagnostic values will help you scrutinize basic CDM-VW300
measurements. Excitation level and low / high frequency or amplitude
warnings are provided for each dynamic measurement. A standard deviation is
provided once each second.
Excitation level is bounded by setting the amplitude at which the wire in the
sensor is to be maintained. That figure is reported so that excitation levels can
be monitored. If the analyzer-sensor system experiences a low amplitude, high
amplitude, low-frequency, or high frequency condition, that information is also
provided.
Once each second, a standard deviation of a dynamic measurement is provided.
Unexplained changes in the standard deviation from baseline levels may
indicate noise or other interference.
5. Specifications
5.1 Features
• Measurement of standard, single-coil circuit, vibrating-wire sensors
• Dynamic-sampling rates of 20 to 333.3 Hz
• On-board frequency-output conversion
• Two (CDM-VW300) or eight (CDM-VW305), simultaneously-sampled
channels per module
• Time synchronization of multiple modules using one datalogger
• Thermistor input for each vibrating-wire channel measured at 1 Hz
• On-board temperature conversion
• Rainflow-histogram compilation
• Superior noise immunity and effective measurement resolution (precision)
• Continuous resonant vibration in the sensor
• Spectral analysis method protected under U.S. patent no. 7,779,690. An
additional U.S. patent that relates to the dynamic vibrating-wire
measurement technique is pending.
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