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The Data Acquisition module of MIDA is designed to acquire data
from very large binary files stored on hard drives or
CD's by digital tape recorders. Only limitation to the size of
binary files is the size of storage medium. Typical file sizes
could be several hundred megabytes or gigabytes large.
The data acquisition module supports file
browsing, snapshot time data acquisition, acquisition with tachometer
and/or trigger signals in time domain with options for, on the fly,
spectral conversion. In addition, shaft speed (rpm) proportional
windowing with optional conversion to angle base is supported. RPM
proportional data acquisition especially with angle base conversion
while averaging through slightly changing shaft speeds is the most
powerful method of obtaining leakage free data.
Features of the user interface are
Acquisition Channel
Selection:
Allows selection of any combination of channels
present in the binary file. Binary files up to 64 channels are
supported.
Tachometer settings:
The tachometer channel, signal level and the number of
tach. pulses per revolution can be interactively selected. The
tachometer level is displayed in the upper data window and can be
controlled by the slider bar in the tachometer control group.
Trigger Settings:
The trigger channel, level, slope and delay
can be selected. The trigger level is display in the lower data window
and can be controlled by the slider bar in the trigger control group.
Rising and falling edge triggering is control by a push button in the
same group of controls.
Data Browsing and
Snapshot Acquisition:
Simple to use data browsing controls allow
play back, fast forward, fast rewind, rewind and user specified rpm
search. Three RPM search algorithms are provided for searching
ascending, descending and arbitrarily changing RPM using the tachometer
signal.
The Snapshot Acquisition feature allows taking time data
with user specified number of samples. This feature is especially
useful for transient data signals.
Tachometered and
Triggered Acquisition:
This capability allows data acquisition at specified
shaft speeds with ascending or descending RPM tracking. RPM
tracking may be performed with or without triggering. Acquisition
without tracking RPM but only triggering or
continuously taking data at specified block sizes is also
available.
Time or frequency domain acquisition modes may be
selected with the following options.
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Time domain data acquisition
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Constant block size
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Variable block size inversely
proportional to tach. signal
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Angle base conversion with
variable block size
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Averaging (including during angle
base conversion*)
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Frequency domain acquisition
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Rectangular, Hanning, Hamming and
Flattop windows with amplitude and energy correction factors
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Peak or RMS amplitude scaling
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Spectrum and Auto-spectrum
averaging**
* Averaging during conversion to
angle base use re-sampling of the data to achieve acquisition at constant
angular rotation intervals. Even if the shaft speed may change
during averaging re-sampling at constant angular intervals ensures
leakage free acquisition. **
Spectrum and auto-spectrum averaging offer different forms of
averaging. Auto-spectrum averaging is obtained by averaging
auto-spectra but not by taking auto-spectrum of the averaged
spectra.
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