4-2
4 Measuring
4.2
Selecting Suitable Settings
4.2.1
Frequency Range
With the PSV-3D, the accuracy of the in-plane vibration measurement
depends on the following parameters:
•
Accuracy of the laser beam overlap
•
Local wavelength of the vibration
The accuracy of the laser beam overlap should be at least one order of
magnitude better than the local wavelength of the vibration. In general, for 3D
measurements it is recommended to use video triangulation to optimize the
overlap accuracy of the laser beams.
With vibration frequencies in the MHz range, the local wavelength of the
vibration and the diameter of the focused laser beam may have the same
order of magnitude. In this case you have to be aware of considerable
measurement uncertainties with the in-plane components of the measurement
signal, even if you use video triangulation.
For bandwidths in the MHz range, it is generally recommended to estimate
the measurement uncertainty for the concrete measurement task. As the
measurement uncertainties depend on the local wavelength of the vibration, it
is not possible to specify a general frequency limit.
4.2.2
Measurement Range
The available measurement ranges depend on the bandwidth set. For this
reason, first select the bandwidth. Thus, the list of the available measurement
ranges is updated. Select your measurement range depending on the
expected maximum velocity. The available measurement ranges are given in
the specifications (refer to S
Many applications are covered by the 50 mm/s measurement range.
Therefore select this measurement range for the first measurements with the
system. Use the smallest possible measurement range to minimize the noise
and to maximize the optical sensitivity.
If either the positive or the negative limit of a measurement range is reached,
the Overrange of the measurement range is displayed in the software. Then
select the next highest measurement range. However, note that this
Overrange display can also be activated by very brief overloading which is
caused by noise spikes. In such cases, you can maintain the velocity
measurement range as long as it is suitable for the amplitude of the wanted
signal. Observe the signal in the time domain to obtain information about this.
When there is an extremely weak optical signal, a permanently Overrange
display can be caused by noise due to the system. If switching on the tracking
filter (refer to S
4.2.3) does not resolve this problem, check the
following:
•
Have you focused the laser optimally?
•
Can you treat the surface of the object under investigation for optimizing
the reflectivity?
•
Can you change the stand-off distance?
Содержание PSV-500-3D
Страница 19: ...2 4 2 Introduction ...
Страница 55: ...4 10 4 Measuring ...
Страница 63: ...6 6 6 Troubleshooting ...
Страница 97: ...A 12 A Optional Accessories ...
Страница 101: ...C 2 C Declaration of Conformity ...