User Manual
5
Figure 4-5. Laboratory-mode measurement system diagram
4.5
Field Mode
Field mode is used for long-term measurement and data acquisition. As shown in
Figure 4-6, a connection is made from the CDM-VW300 to a Campbell Scientific
datalogger through the SC-CPI interface. A Campbell Scientific datalogger with a
customized CRBasic program configures, controls, and collects data from the
CDM-VW300. Specific installation procedures are found in Section 6.2.2,
Field-
Mode Installation Procedure
.
Figure 4-6. Field-mode data-acquisition system diagram
4.6
Data Uses
Users should consult authoritative sources concerning the use of vibrating-wire
data in structural analysis applications. Following is a short introduction to the
use of data made available by CDM-VW300 series analyzers.
4.6.1
Static Measurements
Each sensor is measured for a static frequency once per second. The static
frequency is used to obtain a result with finer spectral bin resolution than that
which can be achieved at the dynamic measurement rates. This measurement can
be helpful in detecting the rare case, for example, in which a noise frequency very
near the resonant frequency affects dynamic sampling measurements.
4.6.2
Dynamic Measurements
Each analyzer can be configured in a 20, 50, 100, 200, or 333.3 Hz sampling
mode. By capturing multiple readings each second from a vibrating-wire sensor,
rapid changes or events can be captured and evaluated. Due to the Nyquist
sampling theorem, only responses equal to or less than half of the sampling
Summary of Contents for CDM-VW300 Series
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Page 59: ...User Manual 47 Figure 7 16 LoggerNet connect screens showing frequencies from CDM VW300 ...
Page 70: ...CDM VW300 Series Dynamic Vibrating Wire Analyzers 58 ...
Page 76: ...Appendix B SC CPI Datalogger to CPI Interface B 4 ...
Page 80: ...Appendix C CDM Devices and CPI Bus C 4 Figure C 2 Long cable lengths of a distributed CPI bus ...
Page 86: ...Appendix E Calculating Measurement Error E 4 ...
Page 116: ...Appendix G CRBasic Program Library G 26 ...