What is Laser Doppler Velocimeter?

Laser Doppler Velocimetry (LDV) measures the Doppler signal of tracer particles passing through a laser probe and then obtains the velocity based on the relationship between velocity and Doppler frequency. Because it is a laser measurement, it does not interfere with the flow field and has a wide speed measurement range. Moreover, because the Doppler frequency has a linear relationship with the speed and has nothing to do with the temperature and pressure of the point, it is currently the most accurate speed measurement instrument in the world.

Due to its “non-contact” measurement characteristics, there is no wear and tear, which can not only minimize the maintenance cost of the production line, but also significantly improve the reliability of the assembly line, improve production efficiency and product quality, ensure accurate product specifications, and greatly reduce production costs.


speed and length measurement, what is laser doppler velocimetry


How does a laser velocimeter work?


The working principle of the laser velocimeter is based on the emission and reception of laser beams. A laser velocimeter emits a narrow, steady laser beam through a laser. This laser beam is directed and shined onto the object. When a laser beam strikes an object, part of the laser light is reflected by the object.

Next, the laser velocimeter receives the reflected laser beam through a receiver. The receiver converts the received laser beam into an electrical signal and sends it to a computer for processing.

The computer calculates the object’s speed based on the received laser signal. This calculation is done by measuring the time it takes for a laser beam to elapse from emission to reception. Since the speed of light is known, the speed of an object can be calculated based on time and distance.


Advantages of Laser doppler velocimeter

1) It is a non-contact measurement. The laser convergence point serves as a measurement probe and does not interfere with the flow field. It can accurately measure on almost any surface (such as flames, corrosive fluids and other harsh environments).

2) No flow correction is required

3) Does not depend on other physical parameters such as temperature, density and fluid composition, but is only velocity sensitive. Anti-electromagnetic interference, stable and reliable

4) The amount taken out is linearly related to the speed

5) The sensitivity of measuring speed direction is good, and “0” speed can be measured

6) Fast dynamic response, wide speed measurement range, etc.


Laser Doppler Velocimeter application

Laser Doppler velocity and length measurement is widely used and can be used to measure the flow velocity in combustion mixtures, flames, rotating machinery, narrow channels, chemical reaction flows, wind tunnels or circulating water tunnels, etc. Especially in the industrial field, it is widely used in length measurement of metallurgy, textile, film, papermaking, cables, wires, wood, building materials and other products. It can also be used in the field of rail transportation to measure train speed and train positioning.

Application of LDV in metallurgical field

This system is suitable for the manufacturing of various metal products such as bars, pipes, wires, plates, strips, hot rolling, cold rolling, etc. It can accurately measure speed and length online in real-time and can measure steel billets with a temperature of 1000°C.


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