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Technical Information
Display Range
This section provides information on the numeric range of the digital display
used in the VM-83.
For simplification, the range is assumed to be "100" and "30", and the display
characteristics setting EQ PEAK. Because the overload point of this unit is
approximately three times the range full-scale point, the display range at the
range "100" setting is about 300, and at the "30" setting (actually 31.6) is about
90, assuming that there is no overload in the intermediate circuits. The display
resolution is 0.1 and 0.01. Therefore the possible display range is as follows:
Range 100 0.1 to 300.0
30 0.01 to 90.00
The VM-83 directly feeds the raw waveform of the vibration signal to an A/D
converter and then performs filter processing, rms conversion, and other func-
tions using a DSP. When the number of effective digits for display decreases,
display accuracy cannot be maintained. Therefore the indication UNDER ap-
pears on the display when the displayed value falls below 0.5% of the full-scale
point. This warns the user that the current range setting is not appropriate. To
assure accurate readings, the range setting should be made so that the UNDER
indication does not appear. At a level of 0.2% of the full-scale point and lower,
the lowest bit level of the A/D converter is reached, so that readings will be
indeterminate. At a range "30" setting, this corresponds to 0.06% of the full-
scale point. This means that readings below this limit will be highly imprecise,
and that the display reading may not be 0 even if the actual vibration signal is
very low.
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