Campbell CR9000, Инструкция по эксплуатации

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Section 7. Measurement Instructions
7-34
Parameter
Enter
FFTFILT PARAMETERS
Dest
Variable or
Array
The Variable in which to store the results of the instruction.
Because FFTFilt returns all or part of
an entire spectrum (see ILow and IHigh) for each Rep , Dest usually must be an array.
Reps
Constant
The number of times to repeat the measurements and subsequent FFTs on consecutive
CR9052DC channels. Spectra from multiple
Reps are placed head-to-tail in the Dest array.
Range
Constant
The voltage range for the measurement.
The CR9052 normally replaces out-of-range
measurements with not-a-number (NaN) which is displayed in PC9000 as Range? . Users may
choose to have out-of-range measurements to be replaced by the analog-to-digital converter
saturation value with a special code in FiltOption
.
Alpha Code Numeric Code Voltage
Range Module Excitation
Board Supported
mV1000 0 ± 5000 mV CR9052DC, CR9052IEPE
mV1000 1 ± 1000 mV CR9052DC, CR9052IEPE
mV200 4 ± 200 mV CR9052DC
mV50 5 ± 50 mV CR9052DC
mV20 6 ± 20 mV CR9052DC
Fslot Const The number of the slot that holds the CR9052 Module to be used for the measurement.
Chan
Constant The CR9052 channel number on which to make the first measurement. When Reps are used, subsequent
measurements will be automatically made on the following differential channels.
FiltOption
Constant
The sample ratio for the measurement (how many measurements are made within one cycle of
the highest frequency in the pass band). The sample ratio determines the top of the pass-band
(
F
PASS
) and the beginning of the stop-band ( F
STOP
) of the anti-aliasing low-pass filter relative
the sample rate ( F
SAMPLE
). The sample rate is the inverse the scan interval in the CRBASIC
program. FiltOption must be the same for all channels of a single CR9052DC Filter Module.
The CR9052 normally replaces out-of-range measurements with not-a-number (NaN) which is
displayed in PC9000 as
Range? . Out-of-range measurements may be replaced by the analog-
to-digital converter saturation value by adding 1000 to the FiltOption codes shown below.
Numeric Code Sampling Ratio
F
PASS
F
STOP
2 2.5 F
SAMPLE
/2.5 F
SAMPLE
/2.01
5 5
F
SAMPLE
/5 F
SAMPLE
/3.37
10 10 F
SAMPLE
/10 F
SAMPLE
/5.08
20 20
F
SAMPLE
/20 F
SAMPLE
/6.81
1* 2.155
23.2 Khz 26.8 kHz
FiltOption 1 is available only when FsampRate is 50 kHz. At this sample rate, no additional
filtering beyond that provided by the CR9052DC hardware is required to anti-alias the data.
Because the CR9052DC processor is not performing additional anti-alias filtering, this
FiltOption increases the CR9052DC’s FFT throughput. To achieve spectra from seamless
snapshots with FsampRate equal to 50 kHz on six channels, FiltOption must be 1.