seeking simple sonic pitch-catch meas. vi.

[abd4]

 New to LabView.  Looking for simple code to sample ultrasound pitch-catch waveform, and calculate time-of-flight. (Typical ap., I imagine?)
  Voltage waveform consists of a burst of about 20 cycles of sine wave, followed by some dead time, followed by the smaller (20 cycles) burst of the received echo.  I can digitize it, but don't know how to trigger on the transmit, then the receive pulse, and calculate the time difference.  The whole thing needs to be in real time, so that the pitch-catch time difference is output to a data file each time the trasmit burst is repeated, thus creating a time history of the proximity of the ultrasonic pulser and the surface it's echoing off of.

Thanks!
-Andy

[AlanArmstead]

Hi Andy,

Could you please post a little more info?  Like:

1) What hardware are you using?

2) What driver are you using, and what version?

3) What version of LabVIEW are you using?

-Alan A.

[abd4]

I couldn't get into the computer to see the card, nor get access to the system to find the driver. 
I found something labeled NI-488.2, so perhaps that's the card.  It's definitely multi-challen I/O.  The interface is an NI  BNC-2090.
The version of LabView is 7.1.
The pulser hardware is a simple Airmar introductory PC board, with ultrasonic air transducers.

Thanks,
Andy

[LV_Pro]

The board marked 488.2, isn't a multichannel DAQ, rather it is a GPIB controller card for controlling external instruments (Signal Generators, O'scopes, etc.). Do you see an application called Measurement and Automation Explorer (MAX) on the desk top? If the answer to that is yes, then you can find out what is installed on your machine, if they are National Instruments cards (MAX only works with NI products).

P.M.

Message Edited by LV_Pro on 11-09-2005 11:37 AM

[abd4]

Yes, I found it.  We have a PCI MIO 16E-4.
Also, the computers in question have varying OS's - XP or Win2000
Thanks
Andy

[AlanArmstead]

Looks like you might need an analog start triggered application.  See the example finder in LabVIEW by going to Help>>Find Examples.  Then navigate to Hardware Input and Output>>DAQmx>>Analog Measurements>>Voltage.  Then take a look at "Cont Acq&Graph Voltage-Int Clk-Analog Start.vi".  That might give you a good starting point.  You might have to do some post-processing to determine the distance between the two sets of sine waves.  For example, if you are sampling at 100KHz, and your second sine wave starts at the 200th sample after the first sine wave started, then your time difference is 2msec.  Hope this helps.

-Alan A.

[LV_Pro]

Some aspects to keep in mind. Your board has a max sample rate of 500KS/s (only one channel sampling) limiting your maximum frequency to less than 250KHz. To achieve the best distance resolution over shorter distances you will need the highest frequency you can deal with. As the previous post mentions you can measure the distance by sampling over a given period, and doing the math on the returned data, which will be in the form of an array of numeric values. You determine which  set of data in the array has an average magnitude considerably greater than a following one, with both being larger than some set of data between. Now you will also want to remember to measure from the start of the "Ping" set to the start of the "Echo". On possible problem is that the Ping may be orders of magnitude larger than the Echo, and there may be ambient noise that approaches the level of the Echo, so it will be an interesting exercise (a lot goes into sonar systems!)

P.M.