Impedance head and mass-cancellation

To obtain the excitation force, mount the force detector (force head) between the vibration exciter and the excitation object. The impedance head has the integrated structure of the force detector and the accelerometer. Generally, two detectors which are built-in the impedance head measures the accelerence (acceleration/ force). To measure the mobility with the laser doppler vibrometer, the simple combination of the power heads is available. The impedance head with built- in accelerometer is reasonable for the laser doppler vibrometer measurement because most of the target measurement object is small in mass and the mass-cancellation (remove the mass) is necessary.

 

When the size of direct mobility of the excitation point of the target measurement object which is in the frequency area except for the resonance and anti-resonance point area measurement is larger than [0.01/ fm)] (m: mass load kg, f: frequency Hz), the mass cancellation is necessary because the affection cannot be ignored. The mass-cancellation is to obtain the excitation force with the following formula: [Detecting excitation force] – [Acceleration of the excitation point] × (Mass) = [True excitation force]

 

The force signal which is occurred at the fixing jig of the top of the impedance head can be easily removed by the acceleration signal which is outputted by the built-in accelerometer of the impedance when the mass-cancellation amplifier (MA-5500) and the impedance head are used in combination.

 

 

 

Revised:2004.04.19



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