The LV-0121A Digital Laser Displacement Meter (Fringe counter) can be used in combination with the laser doppler vibrometer. It is an option for the displacement measurement applies the interference meter, which is incorporated in the sensor head. It counts the lightness and darkness of the light (Interference fringe) created by the phase deviation between the reference light and reflection light from the target measurement object, and outputs the displacement by digital and analog signals.

 

Digital signal: Maximum sampling 1 MHz, maximum resolution 0.55 nm (It is necessary to use the LV-0930 Displacement Analysis Software.)

 

Analog (displacement) signal: Capable of measuring the minute displacement measurement including DC offset in the frequency range of DC 100 kHz (-3 dB) maximum

 

The LV-0121A Digital Laser Displacement Meter measures the transient displacement (rectangular) from the still state (DC) of the object, or the displacement amplitude including the DC offset. The displacement output of the digital laser displacement meter is used for the measurement of low frequency amplitude, or the displacement including the offset, and the velocity output of the laser doppler vibrometer is used for the high frequency amplitude measurement. It makes the wideband amplitude measurement possible.

 

Principle

 

The operating principal for the LV-0121A Digital Laser Displacement Meter is utilized the phenomenon of the overlap light phases (hill and dale of the wave) of the reflection laser light, which irradiates an object and the incident laser light. If the light phases are matched, the light becomes maximum strength. If the light phases are directly opposite, the light is cancelled with each other and becomes dark. In the following figure of L₁ = L₂, when the overlap light phases of the return light of the reference mirror and the measurement mirror are matched, the light becomes bright. When the measurement mirror is moved, and the light pass distance is λ/2 (λ = wavelength oscillator of laser), the light becomes the anti-phase (180° out of phase) and becomes dark. Therefore, when the measurement mirror (target measurement object) is moved, the light and dark interference fringe is occurred in every λ/2 of the light way difference between L₁ and L₂. The displacement amount can be measured by counting these interference fringes.

 

 

(Caution)
The He-Ne laser wavelength oscillation (λ) for the LV series is around 632.8 nm. The LV-0121A Digital Laser Displacement Meter measures the displacement based on this wavelength.

Measurement example

 

 

The rectangular displacement value of the cantilever when the use of LV-0121A Digital Laser Displacement Meter