Frequently Asked Questions about Laser Doppler Vibrometer
Question number FAQ-1345
Advantages of Using a Laser Doppler Vibrometer
- Non-contact measurement does not apply any load to the object.
- The laser beam can be focused down to a few micrometers, resulting in high spatial resolution and enabling multi-point measurement of small objects.
- Since the standard output is 'speed', it can be easily converted to acceleration and displacement through first-order calculus processing.
| ■ | Like an accelerometer, when the detector comes into contact with the target, the issue of 'contact resonance' arises due to the influence of the contact surface. This occurs because the stiffness of the mounting point, which includes the contact surface, and the mass of the accelerometer form a vibrating system. This phenomenon creates a 'spring' between the target and the detector, leading to resonance. The frequency at which contact resonance occurs varies depending on the method of fixation. As a guideline for mounting accelerometers, the best fixation using screws is around 20kHz, while fixation using adhesive or thin double-sided tape is around 10kHz. This is the main reason why accelerometers cannot be used for vibration measurements exceeding 20kHz. |
| ■ | Non-contact vibration measurement using a Laser Doppler Vibrometer allows for vibration measurement without any impact on the vibrations themselves. Since the beam spot can be narrowed down to a few micrometers, it is possible to measure vibrations in small and narrow areas. The measurement frequency is normally 3 MHz (LV-1710), with an option for up to 20 MHz, and a system configuration that can simultaneously detect vibrations in three axes is also possible. |
| ■ | When measuring the motion (vibration) of an object using a Laser Doppler Vibrometer, "velocity" (m/s) is very advantageous. When measuring the object's minute vibrations using "displacement" in an environment affected by background noise, the displacement of the background noise is large, and the object's displacement becomes buried, making waveform observation difficult. To eliminate this effect, a high-performance vibration isolation table is required. On the other hand, when observed with velocity output, the velocity values of low-frequency background noise are smaller than the vibration velocity of the object, making it easier to observe the vibration waveform of the object. For objects that vibrate at high speeds, such as ultrasonic transducers, observing with velocity output becomes less susceptible to the effects of background noise. |
Last updated: 2004-04-19