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2)9
The stand-off distance is measured from the front panel of the sensor head
OFV-303/-353. The optimal stand-off distances are:
, n = 0; 1; 2; ...
i.e. at 232mm; 437mm; 642mm; etc.
2)9
The stand-off distance is measured from the shoulder of the connector for the
mini sensor or the fiber head. The optimal stand-off distances are:
, n = 0; 1; 2; ...
i.e. at 135mm; 340mm; 545mm; etc.
2)9
When making two point measurements the stand-off distance is the difference
between the stand-off distances of both arms. The optimal stand-off distances
are:
, n = 0; 1; 2; ...
i.e. at 0mm; 205mm; 410mm; etc.
When making single point measurements with the reference head OFV-151
the stand-off distance is measured from the shoulder of the connector for the
mini sensor or the fiber head. The optimal stand-off distances are:
, n = 0; 1; 2; ...
i.e. at 63mm; 268mm; 473mm; etc.
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The light source of the vibrometer is a helium neon laser. This is a multimode
laser in which a maximum of two modes can exist. The interference of the two
modes leads to the intensity of the resulting optical signal varying periodically
with the stand-off distance. The intensity increases to a maximum i.e. a maxi-
mum of visibility is present if the optical path difference is an even numbered
multiple of the length of the laser cavity (205mm). As the optical path differ-
ence is equal to twice the stand-off distance (the beam goes there and back),
a maximum of visibility is present once per laser cavity length.
In practice, it is not usually necessary to search for the maximum of visibility
as the vibrometer is sensitive enough to make a measurement even close to
the minimum. A minimum is indicated during the warm-up phase by periodic
fluctuation on the signal level display.
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