Integrated measurement of pressure and velocity

[Chata]

Hello dear friends, I would like to measure pressures in bullet (5,56mm up to 12.7mm) combustion chamber (using pressure piezo transducer + charge amplifier + NI DAQ card) and also velocity of the bullet (using optical barriers - measuirng time trevelled by bullet between two barriers with infra red curtain). Can someone give me guiding points on what things I should pay attention, what kind of problems might arise? Also if someone has samo similar basic programs (VI's) on this topic any contribution would be very appreciable. Alan

[Ray.R]

For the pressure transducer side, I would make sure that you apply proper signal conditionning in the acquisition hardware to make sure you have a clean signal of level suitable for your DAQ card.  For instance if your DAQ card supports input levels of 10V, then provide sufficient gain so that the max output of the transducer matches the input level of the DAQ. Also make sure that proper shielding is provided to avoid adding any noise to your signal.  I would place the amplifier as close to the transducer as possible. 

For the bullet travel time, you are probably using IR curtains, which typically give you a digital signal (signal received / not received).  You will still need some sort of DAQ that has a time resolution smaller than the time it takes for the bullet to cross the curtain.  As a matter of fact, the higher the sampling rate, the better accuracy (so at least 1/2 the time & better).  I would also match with the input level of whatever card you are using.  I wonder if a high speed frame grabber card would be fast enough to capture a series of images and you could extrapolate the distance from that (or use marker in the photo).

I am only aware of two companies that do similar projects.  One in the USA and the other in Montreal (Canada).  I doubt that they would share any code.  I do know the one in the USA uses Labview.  I think they use C/C++ in Mtrl.

RayR 

[Chata]

Thanks Joe for sharing your toughts. I'll keep some of those things in mind.
I didn't mention that I already have all the equipment (except calibration sensor which I will buy soon) needed for this tests. Equipment needs to be rearanged, and some components assembled, but it is functional.
So... main point of my interest now is how to make application in Labview. Further plans include making GUI in Visual C# and Internal Ballistic module (maybe in Fortran) according by NATO standards.
But as far am I concerned, my main wories for now include making the right application in Labview for precise measuring aquisition.

Message Edited by Chata on 05-12-2008 02:43 PM

[Aashish_M]

Hey Chata,

I am not sure as to how experienced you are in LabVIEW, but here are some links that will help you get started with the data acquisition in LabVIEW;

Getting Started with NI-DAQmx: Main Page

Learn 10 Functions in NI-DAQmx and Handle 80 Percent of Your Data Acquisition Applications

For further help, I believe you will need to be a bit more specific as to what problems you have to make full use of the experts that monitor this forum.

Hopefully this helps!!

[Chata]

Thanks Aashish, this is quite helpful. I'll get back to this when I finish my application and share it here. Cheers.

[Chata]

One more question... If I have this info for my piezo-electric transducer (picture bellow) how can I scale the voltage to the measured phenomena. Note: sensor gives electrostatic charge signal in pC, then I lead it to charge amplifier (data shown in picture 2). How can I accuratelly represent obtained pressure data in Labview, using this sensor and this charge amplifier (and M series NI DAQ card)? I tried to find topics related to this but I didn't menage to find anything useful. Alan

[Aashish_M]

Hey Alan,

It seems you just need to scale the voltage. This can be done in a few ways, but the easiest way is to create a task and configure custom scaling using Measurement Automation Explorer. You can then use these tasks or custom scales in your programming.

Also you could have a look at Programmatically Create a Custom Scale in DAQmx. This shows the use of the Create Scale.vi under the DAQmx - Data Acquisition>>DAQmx Advanced>>DAQmx Scale Setup in the functions palette.

Hopefully this helps!!

[Chata]

thanks for help.

Alan

[Chata]

if I want to measure average velocity of the bullet using optical barriers (conected to DAQ card) how can I programmatically do that in labview.

[Ray.R]

The programming part in Labview will be the easier part..  Setting up the hardware correctly to make sure the bullet is detected by the sensors, correct placement (distance) of each sensor, and having DAQs with precise timing (maybe Counter / Timer over RTSI bus)...

Describing everything would take a bit of time.. 😮

RayR