CLV-3D Compact 3D Laser Vibrometer

CLV-3D Compact 3D Laser Vibrometer

Polytec’s CLV-3D non-contact vibration sensor simultaneously measures all three linear velocity components at a single point on a vibrating structure. The individual vibration components are available as analog outputs. The CLV-3D’s wide dynamic range, excellent bandwidth and low noise enable its use in many advanced applications.

The system comprises a three-channel CLV Compact Laser Vibrometer Controller unit coupled to the CLV-3D Optical Sensor Head containing three independent CLV optical systems, all focused to the same measurement point approximately 140 mm (or 300 mm) from the front lens.

Optical Sensor

The CLV-3D Optical Sensor Head contains the optical components of three independent CLV-700 sensors. Each output beam is inclined at a 12° angle with the f-160 mm lens version with respect to the surface, but from three slightlydifferent directions separated by 120° in the output plane. A 12° angle is small enough to allow the sensors to collect enough back-scattered light to make a high-quality measurement, but still large enough for good sensitivity to the in-plane vibration components. Furthermore, the narrow angle allows the beams to pass through small holes or windows in wind tunnels or environmental test chambers. For even narrower angle applications, a 310 mm focal length front lens may be fitted in combination with a f310 mm version of the geometry module.

Signal Outputs

The CLV-3D provides separate analog outputs for the vibration velocity along the three laser beams vL, vR and vT. These outputs can be used to calculate the Cartesian velocity components vx, vy and vz. For external software calculations, these raw outputs are connected to a three-channel data acquisition board and processed by a computer. A better choice is Polytec’s internal geometry calculation module where the Cartesian velocity components vx, vy and vz are provided as three separate, real-time, analog outputs. With a “perfect” surface such as 3M™ Scotchlite™ retroreflective tape, vx and vy have a noise floor of better than 1 µm/s measured in a 10 Hz resolution bandwidth. Vz is better than 0.5 µm/sec.

Hardware

The controller unit is divided into upper and lower sections.  The lower section contains three CLV laser modules (CLV-810) plus the master power supply module.  The upper section comprises a three-channel vibrometer signal processor, which generates the three analog velocity outputs vx, vy and vz in addition to the "raw" outputs vL, vR and vT.

Doppler signal demodulation is performed by a combination of three input modules (type CLV-M200) and three velocity decoding modules (type CLV-M020.B for the 50 kHz version or CLV-M030.B for the 250 kHz version) chosen according to the bandwidth demanded by the application. A range selector knob controls the velocity rangesetting for all three channels. Each input module generates an LED bar proportional to gathered light. 

A single output module conditions the raw Doppler signals from the three laser beams and outputs vL, vR and vT. The single geometry module performs an analog coordinate transform and outputs the true vx, vy and vz components. A switchable 10 Hz high-pass filter is provided for removing low-frequency vibrations.

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