Campbell Scientific AVW200 AVW200-series Vibrating Wire Interfaces - Page 17

TABLE 2-2., AVW200 Measurement Outputs, Output, Units, Description, Contact Campbell Scientific

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AVW200-series 2-Channel Vibrating Wire Spectrum Analyzer Modules TABLE 2-2. AVW200 Measurement Outputs Output Resonant Frequency Response Amplitude Signal-to-Noise Ratio Noise Frequency Decay Ratio Thermistor Resistance (see Section 2.2) Units Hz mV rms unitless Hz unitless Ohms Description Frequency of the peak response Amplitude of the peak response1 Response amplitude divided by amplitude of largest noise candidate1 Frequency of largest noise candidate1 Ending time-series amplitude divided by the beginning time-series amplitude1 On-gage thermistor resistance2 Notes: 1. Use for measurement diagnostics. 2. Optional output, not measured if Therm50_60Hz is set to 0. When using firmware version Std.04 (or higher) and the Response Amplitude diagnostic is measured as less than 0.01 mV rms (10 microvolts), the Resonant Frequency reading will be modified to warn the user about the occurrence of low signal strength amplitudes. If SDI-12 is used to communicate with the AVW200-series device, the frequency will be given as -9,999,999 under those conditions. For all other communication methods, the frequency will be given as NAN (not-a-number) when experiencing this low signal strength condition. If the user desires the frequency to be returned as NAN for a higher (i.e., more pessimistic) threshold than 0.01 mV, this can be done by using an optional parameter in the AVW200 CRBasic Instruction. See Section 6.1, AVW200 Instruction, for details about how this can be done. The Resonant Frequency reading is also used to warn the user when there is an invalid voltage supply in the hardware of the device (firmware Std.04 and higher). If an internal calibration factor is outside of the expected range, then the value of -555,555 is returned for the frequency measurement. This indicates to the user that there is a hardware issue on the device which requires a factory examination and/or repair. Contact Campbell Scientific for instructions when this value is given as the Resonant Frequency reading. FIGURE 2-2 (a representative output from the Device Configurator's Troubleshooter) illustrates the AVW200 measurements. The bottom graph shows the raw time series data recorded from a vibrating sensor after the sensor has been excited with the frequency-swept voltage signal, and the top graph shows the spectrum after the AVW200 has applied the fast Fourier transform (FFT). In addition to the wire's resonant frequency, the spectrum shows the response amplitude, noise amplitude, and noise frequency. The AVW200 computes the signal-to-noise ratio diagnostic by dividing the response amplitude by the noise amplitude. The AVW200 computes the decay ratio diagnostic from the time series ending amplitude divided by the beginning amplitude shown on the bottom graph in FIGURE 2-2. 9

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AVW200-series 2-Channel Vibrating Wire Spectrum Analyzer Modules
TABLE 2-2.
AVW200 Measurement Outputs
Output
Units
Description
Resonant Frequency
Hz
Frequency of the peak response
Response Amplitude
mV rms
Amplitude of the peak response
1
Signal-to-Noise Ratio
unitless
Response amplitude divided by
amplitude of largest noise candidate
1
Noise Frequency
Hz
Frequency of largest noise candidate
1
Decay Ratio
unitless
Ending time-series amplitude divided
by the beginning time-series
amplitude
1
Thermistor Resistance
(see Section 2.2)
Ohms
On-gage thermistor resistance
2
Notes:
1.
Use for measurement diagnostics.
2.
Optional output, not measured if Therm50_60Hz is set to 0.
When using firmware version Std.04 (or higher) and the Response Amplitude
diagnostic is measured as less than 0.01 mV rms (10 microvolts), the Resonant
Frequency reading will be modified to warn the user about the occurrence of
low signal strength amplitudes.
If SDI-12 is used to communicate with the
AVW200-series device, the frequency will be given as -9,999,999 under those
conditions.
For all other communication methods, the frequency will be given
as NAN (not-a-number) when experiencing this low signal strength condition.
If the user desires the frequency to be returned as NAN for a higher (i.e., more
pessimistic) threshold than 0.01 mV, this can be done by using an optional
parameter in the AVW200 CRBasic Instruction.
See Section 6.1,
AVW200
Instruction
, for details about how this can be done.
The Resonant Frequency reading is also used to warn the user when there is an
invalid voltage supply in the hardware of the device (firmware Std.04 and
higher).
If an internal calibration factor is outside of the expected range, then
the value of -555,555 is returned for the frequency measurement.
This
indicates to the user that there is a hardware issue on the device which requires
a factory examination and/or repair.
Contact Campbell Scientific for
instructions when this value is given as the Resonant Frequency reading.
FIGURE 2-2 (a representative output from the Device Configurator’s
Troubleshooter) illustrates the AVW200 measurements.
The bottom graph
shows the raw time series data recorded from a vibrating sensor after the sensor
has been excited with the frequency-swept voltage signal, and the top graph
shows the spectrum after the AVW200 has applied the fast Fourier transform
(FFT).
In addition to the wire’s resonant frequency, the spectrum shows the
response amplitude, noise amplitude, and noise frequency.
The AVW200
computes the signal-to-noise ratio diagnostic by dividing the response
amplitude by the noise amplitude.
The AVW200 computes the decay ratio
diagnostic from the time series ending amplitude divided by the beginning
amplitude shown on the bottom graph in FIGURE 2-2.
9