Laser Doppler Vibrometer Working Principle

Our laser Doppler Vibrometer system measures vibrational displacement according to the heterodyne interferometer principle, which generates a high-frequency carrier signal at the photo detector with the aid of a acousto-optic frequency modulator (AOM). The beam of a helium neon laser is pointed at the vibrating object and scattered back from it. The velocity or displacement of a vibrating object generates a frequency or phase modulation due to the Doppler effect. The object beam is thereby subjected to a small frequency shift which is described as the Doppler frequency fD. The Doppler frequency is a function of the velocity component v in the direction of the object beam according to

fD = 2 * v/λ,

where λ is the laser wavelength. The AOM also generates an optical frequency shift fB in the reference beam (40MHz). After superimposed the measurement and the reference beam, an electrical signal is generated at the photo-detector with the instantaneous frequency

fc(t) =  fn+fD(t) = fn + 2  * v/λ

This is a carrier frequency signal with the central frequency fB, which is frequency modulated with the signed Doppler frequency. Through frequency demodulation the velocity can be decoded. In PNV-RD-AVD1 demodulation of the Doppler signal is purely based on a digital process. In contrast to the conventional vibrometers which use analogy, this means that the measurement accuracy is virtually independent of aging and environmental influences. State of-art FPGA technology makes it possible to realize excellent measurement system characteristics, despite the compact design and minimal energy consumption.

	Single-Point Laser Doppler Vibrometer ● Mesurement distance 0.2m - 5m ● 1 LDV head, direct connection to computer, no control box  ● Frequence measurement range 0.1hz to 5Mhz ● Resolution Velocity displacement 1pm
	Multi-Point Laser Doppler Vibrometer ● Mesurement distance 0.2m - 5m ● 2/4/8 LDV head, With multi point control box  ● Frequence measurement range 0.1hz to 5Mhz ● Resolution Velocity displacement 5pm
	Long Distance Laser Doppler Vibrometer ● Mesurement distance 20m - 200m ● 1 LDV head, with control box ● Frequence measurement range 0.1hz to 250Khz ● Resolution Velocity displacement 10pm

Single and Multi-Point Laser Doppler Vibrometer 

Product Brochure: Single-point Laser Doppler | Multi-point Laser Doppler 

Long Distance Laser Doppler Vibrometer 

Product Brochure: Long-distance Laser Doppler

Laser Head Layout

1, Digital output interface (USB3.0, connect to computer for digital data output)
2, Analog output interface (SMA interface, +/-10V, connect to oscilloscope or data acquisition devices)
3, Trigger interface（SMA interface，5V TTL signal）
4, Power interface （15V/5A DC）
5, Signal strength indicator

Software Interface

(1) Start/stop switch button:
(2) Time-domain waveform display window:
(3) Waveform display window color mode switch:
(4) Time axis display setting: Rotate this knob will adjust the time axis display range from 200ns/DIV to 100ms/DIV (2ms to 1s for the whole time-domain waveform)
(5) Frequency range selector:
(6) Frequency-domain X-axis(Frequency) display setting: 
(7) FFT window and resolution setting:
FFT window: This software has 5 windows (Rectangular, Hamming, Hann, Flattop and Blackman) to select, 
FFT resolution: The frequency resolution of frequency-domain spectrum can be select in this drop-down list, 
(8) Measurement range setting:
(9) Frequency-domain waveform display window:

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