Integrated measurement of pressure and velocity

[Chata]

hehe, I have time 🙂

Let's say I have equipment set up (someone will do that for my team) and I receive signals, what is, in short, the best practice (timers or ?) in this case if I want to represent that data in Labview (velocity of body, regarding time the body travelled between two optical barriers and known distance).

thank you in advance 🙂

[Ray.R]

You need to place at least 3 sensors spaced far enough apart to so that the time resolution of the Timer / Counter is at least 2 ticks (more preferred).  You can figure this out by knowing the estimated velocity m/s and knowing the frequency (tick resolution in ms / us) of the TImer/Counter. 

I would use the sensors to trigger a sample for the channel where the sensor detected the bullet and write how many ticks have elapsed since the main trigger (start of counter and shot fired).  Store the tick count in the DAQ buffer for each channel.

Your first sensor would be a baseline (t=0).  The second & third sensors would give you time deltas between sensor 1&2 , sensor 2 & 3, and sensor 1&3. 

Acquire the tick counts (waveforms) using Labview.  The rest is all simple math.

The above is a simplified explanation, but I'm sure you can fill in the blanks to make the system more accurate. 😉

RayR

[sophr2]

Any luck with this? I wrote something to calculate velocity from screens a known distance apart, but the sample rate I used gives poor resolution.

[Chata]

I have started something, but its far from over.

[Henrik_Volkers]

Its done here

http://www.ptb.de/en/org/1/13/133/index.htm

Your charge amplifier f_max (-3dB) might be to slow to get the peak (depending on your gunpowder combustion). I would try to read at least the resonance frequency of your sensor.  

Serious speed measurement are done with at least 3 curtains to get 3 speed reading for validation

Message Edited by Henrik Volkers on 09-08-2008 03:52 PM

[Chata]

thx