Campbell Scientific CR6 CR6 Measurement and Control System - Page 357
Vspect Connections, 1.5.1.4 Vspect Programming
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Section 8. Operation Prevent Spectral Leakage Matching the swept excitation to the expected resonant-frequency range prevents spectral leakag (p. 508)e from complicating the spectral analysis. Vibrating-wire sensors are usually optimized for a single resonant frequency that to overwhelm harmonic and sub-harmonic responses, so spectral leakage usually has little impact. Nevertheless, the figure Wide Sweep, High Noise (p. 354), with its wider excitation sweep, shows a harmonic peak that the narrower sweep does not show. In this case, the wide separation between the harmonic and resonant responses, and the small harmonic response, minimize the effect of harmonic leakage. Measurements of poorly constructed vibrating-wire gages that may have large harmonic and sub-harmonic responses are more susceptible to spectral leakage. Calculating Measurement Error See Appendix E in the manual CDM-VW300 Series Dynamic Vibrating-Wire Analyzers available at www.campbellsci.com http://www.campbellsci.com. 8.1.5.1.3 Vspect Connections Refer to the table CR6 Terminal Assignments (p. 73) to determine the number of vibrating-wire sensors that can be connected directly to the CR6. Sensor cabling is sold as part of the sensor, so refer to documentation from the sensor manufacturer for wire-color codes. 8.1.5.1.4 Vspect Programming The table VibratingWire() Instruction: Controls (p. 357) lists BeginFreq and EndFreq as the parameters in the VibratingWire() instruction that control sweptfrequency range. The table VibratingWire() Instruction: Outputs (p. 358) lists outputs from the measurement. Frequency data are output in hertz (Hz), but can be converted to units of measure, such as pressure, by subsequent CRBasic code. RTD data are output in temperature, when manufacturer provided coefficients are applied, or ohms (Ω), when coefficient arguments are set to 0. The CRBasic example Vspect Vibrating-Wire Measurement (p. 364) lists code to make the measurements and convert the outputs to standard units. Table 83. VibratingWire() Instruction: Controls Parameter Units Description BeginFreq hertz (Hz) Minimum excitation and analysis frequency (≥ 100 Hz) EndFreq hertz (Hz) Maximum excitation and analysis frequency (≤ 6500 Hz) ExOpt Excitation voltage 1 5 V peak to peak 2 12 V peak to peak 357