Vibration measurement for object in the liquid with Laser Doppler Vibrometer
Laser Doppler vibrometer can measure vibrating objects in the liquid by adjusting the conditions. There are a variety of devices used in liquid. Typical devices are ultrasonic cleaning tanks that clean semiconductors and machine parts and fish detectors. They are products that radiate and vibrate ultrasonic waves in liquids and usage their characteristics in various ways. Since these devices use ultrasonic vibrators that vibrate at a few tens of kHz to a few MHz, they cannot be measured with contact-type vibration detectors. Also when they are used in the air, it is difficult to operate correctly and demonstrate the characteristics as these devices are premised on usage in the liquid and the great load differences between liquid and air cause impedance mismatch. Therefore, in order to design and verify these devices, it is necessary to use them in actual operation in the liquid. By using laser Doppler vibrometer under appropriate conditions, it enables to obtain highly accurate vibration measurement to solve these problems.
|LV-1800||Laser Doppler vibrometer|
|LV-0160||20 MHz Wideband unit||Measurement speed range: min. 2 mm/s, frequency range: up to 20 MHz|
|LV-0030||Large size Magnet stand||Attach LV-0015 fine positioning XY stage if necessary|
|4||DS-3000||Data station||Up to 40kHz or 100kHz|
|5||Digital Oscilloscope||Select if necessary|
Example of analysis data
Display screen of High speed Digital Oscilloscope
Vibration waveform of ultrasonic vibrator in water (upper ch1), drive signal (lower), each after averaging.
Even in the case of normal water (underwater), water itself has a characteristic that it is difficult to transmit light having a wavelength longer than about 450 nm. Blue light is easily transmitted, but red and infrared light are attenuated. The He-Ne (helium neon) laser used in the laser Doppler vibrometer with its wavelength of about 633 nm and red light has the characteristic of being greatly attenuated in water. Although the spectral transmission characteristics differs depending on the nature of the liquid, entering the light to excess into the liquid for a long time will make, S / N ratio worse.
The laser Doppler vibrometer enables to measure the vibration frequency of the liquid surface of ultrasonic cleaning tank, etc. The following two points are important when measuring vibration of liquid surface.