Frequently Asked Questions about Laser Doppler Vibrometer

To detect the vibration force, a force detector (force head) is attached between the oscillator and the object of vibration. The impedance head is an integrated structure combining a force detector and an acceleration detector. Usually, the two detectors built into this impedance head can measure acceleration (acceleration/force). When measuring mobility with a Laser Doppler Vibrometer, a simple combination of force heads is sufficient.

The reason for using an impedance head is that many objects measured with Laser Doppler Vibrometer have low masses and require mass cancellation, making impedance heads with built-in accelerometers more convenient.

In the frequency domain, excluding near resonance and anti-resonance points, if the magnitude of the self-mobility at the excitation point of the target object is greater than "0.01/(fm)" (m: added mass kgf: frequency Hz), it is considered that this influence cannot be ignored, and mass cancellation (mass removal) should be performed.

Mass cancellation is adopted as "Detected excitation force" − "Acceleration at the excitation point" × (mass) = "True excitation force." By using the mass cancellation amplifier (MA-5500^＊) in combination with the impedance head, it is possible to easily remove the force signals caused by mounting fixtures, etc., attached to the top of the impedance head, using the acceleration signals output from the accelerometer built into the impedance head.

^＊MA-5500 has been discontinued and is displayed.