Campbell Scientific CDM-VW300 Series Dynamic Vibrating-Wire Analyzer System - Manual (Page 65)

CDM-VW300 Series Dynamic Vibrating-Wire Analyzers
one diagnostic code for each measurement. In total, 800 diagnostic codes are
received each second.
8.5.1.1 Description of Diagnostic Parameters
Excitation strength — reports the voltage applied by the CDM-VW300
analyzer to keep the vibrating-wire of a sensor in motion. Excitation strength
is reported as bit values between 0 and 255, which represent excitation voltages
between 0 and 6 V.
Excitation voltage is set indirectly by the user when the user
enters the Resonant Amplitude of the vibrating wire in
DVWTool or the ResonAmp parameter of the
CDM_VW300Config() CRBasic instruction. The excitation
level is calculated by the analyzer and applied each time a
measurement is made. NOTE
To translate the bit value to volts, divide the bit value by 42.5. For example, an
excitation bit value of 180 is equivalent to an excitation voltage of 4.235 V.
To reduce the computational load on the datalogger processor, multiply the bit
value by the reciprocal of 42.5, which is 0.02353. A multiplication operation
consumes less datalogger processor time than a division operation, which is a
consideration in fast throughput applications. Results will be substantially the
same as those obtained by a division operation.
Low-amplitude warning flag — flag is set true when the resonant amplitude
of the vibrating wire falls to or below 50% of the value entered in DVWTool or
CDM_VW300Config(). Resonant amplitude must be maintained higher than
50% to ensure an accurate measurement.
High-amplitude warning flag — flag is set true when the resonant amplitude
of the vibrating wire reaches or exceeds 200% of the value entered in
DVWTool or CDM_VW300Config(). Resonant amplitude must be maintained
less than 200% to ensure an accurate measurement.
Low-frequency warning flag — flag is set true when the frequency of the
vibrating wire falls between the Actual Min Freq (Hz) shown in DVWTool
and the Minimum Frequency (Hz) entered in DVWTool. The
CDM_VW300Config() instruction equivalent to Minimum Frequency (Hz)
is the LowFreq parameter. When a low-frequency limit is entered into
DVWTool or the CRBasic program, an error window is created that spans the
bandwidth between the frequency cut-off requested (Minimum Frequency or
LowFreq) and the frequency cut-off the analyzer can actually establish (Actual
Min Freq). If a measured frequency falls within the error band, the low-
frequency warning flag is set true. For example, if a low-frequency limit of
500 Hz is entered, and the closest the analyzer can come to complying is to set
the limit at 476.85 Hz, any frequency below 476.85 Hz is discarded, and any
frequency above 476.85 Hz is used. However, any frequency between 476.85
Hz and 500 Hz will activate the low-frequency warning flag, indicating that the
data includes at least one measurement below the user set limit. See Section
8.5.1.2, Calculating Low- and High-Frequency Boundaries, for more
information.
High-frequency warning flag — flag is set true when the frequency of the
vibrating wire falls between the Actual Max Freq (Hz) shown in DVWTool
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