Dear .
I have a Laser vibrometry unit with a scanning head PSV 500 and a sensor head OFV-505/503.
The optimal stand of for OFV-505/-503 is "234mm +(n.l)"
The optimal stand of for PSV-500 is 234mm +(n.l) is "141+(n.l)"
I would like to know 234-141 mm where tha come from?
Second using this information how to know if I have the correct distance between object and vibrometry?
This is a result of the Helium-Neon-Laser potentially having two longitudinal modes. The slight frequency difference leads to the effect, that for certain optical path differences (between the internal reference path and the external measurement path) the signals on the photodiode can cancel out. The resonator length of the laser (204mm) determines this frequency difference and is exactly the distance the unfavorable distances are spaced apart. It is called the coherence repeat length.
For the PSV 500 the optimum object distances are for instance 141mm, 345mm, 549mm and so on. The adverse distances to avoid are exactly half way between these. In fact only very close to the adverse distances the signal power can become very weak. Measurement results will still be exact as long as there is some signal power.
Optimum working distances for OFV505 are 234mm, 438mm, 642mm and so on. Also here, its more important to avoid working distances exactly half way between these numbers.
Alexander Dräbenstedt I am new to this technology, for my unit it contain both PSV 500 and OFV505 ....What I am willing to do is to position the unit at 4 meters from the object (ofcourse I will calculate the exact distance).
the question is how to calculate it? based on PSV 500 or OFV505?
--- Also I had another technical question, how to know signal power? is it from software window or the Back light in the unit?
--- My second question, in several documentation, it is mentionned that displacement is measured directly through the unit? while now I am integrating the velocity using signal processing by adding a filter to eliminate integration error. am I correct??
Thanks a lot for the answer
For PSV500 the optimum distances close to 4m are 3813mm and 4017mm and for the OFV505 these are 3906mm and 4110mm.
Signal power can be read from the LED bar graphs on the measurement heads themselves, from a bargraph in the controller display and from an BNC jack on the back of the controller called "signal" or "RSSI". If vibsoft or PSV software is connected via RS232 or Ethernet, then it is also shown in software window.
Depending on the used decoder, primary demodulation can be displacement or velocity. Edit: If there are both outputs available on the controller you should prefer to use these outputs over creating the other output through integration/differentiation to avoid influences of offset voltages.
Alexander Dräbenstedt Thank you sir a lot for your guidelines, I come to resolve a big issue thanks to you, just one and last question regarding the controller.
I notice that displacement is available but it doesn 't allow anything. (showed in the attached picture).
in the manual they just mention that this need be installed, so can I fix the issue alone and how to read displacement?
Thanks again and again for the effort you are making answering my annoying questions
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering