Remote velocity detection

[alansimpson]

I would like to measure the velocity of a surface 0-150mm/s with a non contact sensor and a high refresh rate, 10kHz. I would like to output signal to oscilloscope or PC, pulse or analogue signal would do.
Sensor can be close to surface and I can can mark the surface with lines like an encoder track. Lines would have to be <0.2mm.
I have tried a high speed contrast laser sensor but it was too slow even at 0.05ms switching time.
I thought of high speed opto-switch with microscope and even optical mouse sensor technology.
I cant find reflective encoder technology that doesn't require really high accuracy between surface and sensor.

Know of any suppliers in the industry that may have a solution?

 

[MintJulep]

Your specs imply that you need a speed resolution of 1.5E-9 m/sec.

Really?

 

[alansimpson]

How do you work that out?

 

[sreid]

To get velocity with a high update rate, you will need a much finer encoder resolution. In general, you need two position transitions per update cycle to calculate delta position/ delta time. Any chance that you could attach a high resolution encoder to some drive shaft?

 

[MintJulep]

Well, possibly incorrectly. Ran out of coffee this morning.

 

[IRstuff]

I think what MJ was trying to calculate was the encoder resolution; assuming a minimum speed of 1 mm/s and a 10 kHz sample rate, the platform will have only moved 0.1 micrometers. Assuming a 10:1 test accuracy ratio, you'd need 10 encoder lines, or 20 lines/spaces in that interval. This means the lines and spaces on the encoder would need to be 5 nm wide, which is pretty darn small.

Perhaps you need to consider something like a linear velocity transducer:

http://www.transtekinc.com/linear_vel.htm

TTFN

FAQ731-376

 

[MintJulep]

Yeah, yeah, that's what I was trying to do

 

[IceStationZebra]

Or if you can connect to a shaft that drives the belt, you could possibly run an encoder on a jackshaft at 10x speed (or some other multiple) to gain the resolution. The negative would be possible backlash issues.
ISZ

 

[YoungTurk]

If you have the ability to take your measurement parallel to the surface rather than normal (get ahead of / behind your object) a displacment laser could work. They can output analog signals with resolutions down to single digit nanometers.