Vibromet Multi Beam Laser Doppler Vibrometer FAQ

MetroLaser Special Order Product

VibroMet™ Multi Beam Laser Doppler Vibrometer
Frequently Asked Questions

1.	What does the system measure?
2.	How does it compare to a scanning LDV?
3.	How many points can one measure with the MB-LDV?
4.	What is the beam configuration at the target?
5.	How do I measure an entire surface?
6.	Can it also measure displacement and acceleration?
7.	How would I know if the specs of the MB-LDV VibroMet meet my measurement requirements?
8.	Do I need to focus the laser beam to each target distance?
9.	Can I test an MB-LDV VibroMet to make sure that it meets my measurement needs?
10.	Can the MB-LDV VibroMet tolerate changes in signal amplitude, which may occur when particles or other obscurants block the laser beam?
11.	Is the laser visible?
12	What is the laser class?
13.	Do I need to mount the system on a stable table?
14.	How much training is required to operate the MB-VibroMet?
15	How does the user view the MB-LDV VibroMet output signals?

1.	What does the system measure? It measures the velocity and frequency of vibration at multiple points simultaneously of a vibrating target. The output signal is the velocity vs. time of all the measured points of the target. Return to Top
2.	How does it compare to a scanning LDV? The scanning LDV measures one point at the time while the MB-LDV measures multiple points at the time. Return to Top
3.	How many points can one measure with the MB-LDV? Typically between 9 and 30. Return to Top
4.	What is the beam configuration at the target? We have produced two configurations: 1) a line of sixteen beams and 2) a matrix of 4 x 4 beams. Other configurations are possible. Return to Top
5.	How do I measure an entire surface? The system offers scanning capability where an entire line of sixteen (or more) beams is swept over the target surface by scanning one mirror. Return to Top
6.	Can it also measure displacement and acceleration? Yes. Both of these parameters can be obtained in software by direct integration and derivation of the velocity. Return to Top
7.	How would I know if the specs of the MB-LDV VibroMet meet my measurement requirements? There are three parameters that define the measurement requirements: 1) distance to target, 2) frequency of vibration, and 3) velocity of vibration. 1) Distance to target. The typical range of standoff distances of the MB-LDV is about 0.5m to 1.5 m or 2m to 6 m. The optical configuration should be optimized for each standoff distance. 2) Frequency of vibration. The MB-LDV VibroMet can measure frequencies from 5 Hz to greater than 20 kHz. 3) Velocity of vibration. This parameter has a maximum value of 500 mm/s and may be calculated as follows: V = 2 PI * displacement * frequency. Return to Top
8.	Do I need to focus the laser beam to each target distance? Yes. The MB-LDV VibroMet uses focused beams that need to be optimized for each standoff distance. Return to Top
9.	Can I test an MB-LDV VibroMet to make sure that it meets my measurement needs? We can usually arrange for a demonstration at MetroLaser. Return to Top
10.	Can the MB-LDV VibroMet tolerate changes in signal amplitude, which may occur when particles or other obscurants block the laser beam? Yes. The MB-LDV VibroMet measures optical phase changes due to target vibration. This optical phase change is manifested as a frequency modulated signal upon mixing the target signal with the reference beam local oscillator. Thus signal amplitude fluctuations would have very little effect on the signal frequency provided that the amplitude of the signal stays above a reasonable threshold. If the signal amplitude falls below the threshold then the instrument would experience a "dropout." Our software would look at regions between dropouts and report the valid data. Return to Top
11.	Is the laser visible? Yes. The laser is green (532 nm) and can readily be seen on most targets. Return to Top
12.	What is the laser class? It is III-b. While each beam is only a few mW the fact that the system puts out multiple beams yields a total laser power of about 50 mW to 100 mW. Return to Top
13.	Do I need to mount the system on a stable table? No. One of our customers uses a forklift to haul the system around. Return to Top
14.	How much training is required to operate the MB-VibroMet? We recommend a couple of days of training. Return to Top
15.	How does the user view the MB-LDV VibroMet output signals? Due to the large number of simultaneous output signals we provide, as part of the system, a multi-channel data acquisition system and custom software to display and analyze all of the signals. Individual channels can also be viewed on an oscilloscope or spectrum analyzer. Return to Top