Dear Kabilan,

Last year I did some measurements using 2D LDA, to measure water flowing velocity in a flume. I don't know what you are measuring, however I hope my answers will help you. 

1-Regarding the angle between two beams? I think it is one of the Laser head specifications.

2- Sampling frequency depends on the seeding and the velocity of the flow.

3- Sampling time is the time for your measurement.

4-  Shifting frequency is that the scattered light from particle is shifted when detected by a stationary detector due to the movement of the particle from one position to another.

Thanks

Manar

thanks

Kabilan,

What system are you using, Dantec, or TSI? You can measure the angle between the laserr beams using the Cosine rule. You will need to use a tape measure. Let the both beams pointed to a wall, then measure the distances from the focal point to the wall ans the distance between the locations where the beams hit. You can then use these distances to determine the angle between the laser beams.

Sampling frequency will depend on the availability of the particles in the flow. You can not control the sampling frequency.

You can figure out the frequency range you need to use by estimating the probe volume dimensions and the expected velocity values. f=V/d

The shift frequency is usually a set number for a system, and it is usually 40 MHz. This is needed to determine the direction of the flow correctly, in the ccase you have a flow reversal.

Ask specific questions when you have time,