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EVM430-FR6043: Selection Criteria for the pipe

Akshat Lalit
Prodigy 70 points
Part Number: EVM430-FR6043

Hello, can someone tell the criteria for the selection of the air blow pipe which will contain the ultrasonic sensors for the time of flight method? I mean what factors should one consider for the air blow like diameter, length,etc

My pipe looks like this. It is 17 cm in length. I am using 200Khz sensors.

  • 0
    TI__Guru 66291 points

    Hello Akshat,

    Refer to section 2.2 in our Gas Meter Design Guide.  Depending on the range of airflow you are designing for, the smaller the internal diameter, or in your case the width, can impact the flow.  The smaller the cross sectional area, the higher the flow will be, like a venturi. For the spacing of the transducers, its a bit of a trade-off between distance and signal amplitude.  You need to take into account the distance the pulses will need to travel as well as the speed of sound in air, and  the number of pulses you will need.  But if spaced too far apart, it may not be possible to receive the transmitted signal, even with the PGA on the FR6043.

    So there is the time to generate the pulses and may take a little trial and error. At 200kHz (that is one pulse every 5us) if you determine you need 10 pulses, that is 50us or the transmit time.  Then there is the travel time for the pulses to make it to the other transducer.  If assuming the speed of sound is 330m/sec or 0.33mm / usec at 20C, you should be able to get something up and running to start with, then modify to tune for the time and amplitude.

    What is the distance from one transducer to the other in your design?

  • 0 in reply to Dennis Lehman
    Prodigy 70 points

    The distance between two transducers is 8cm

  • 0 in reply to Akshat Lalit
    TI__Guru 66291 points

    Hi Akshat,

    Checking to see if made any progress.  With an 8cm length between the two transducers, you have about 233us from when the first pulse reaches the second transducer.  Is this close to your calculations? You will need to set the "Gap between pulse start and ADC capture" on the Parameters tab of the GUI to something a little less this. Start with 230us.

    You can find information about how to setup the GUI in the TI resource explorer.

  • 0 in reply to Dennis Lehman
    TI__Guru 66291 points

    Hi Akshat,

    It's been a while since we have heard from you, so I'm going to assume you were able to move forward with your project.
    I will mark this posting as RESOLVED, but if this isn’t the case, please click the "This did NOT resolve my issue" button and reply to this thread with more information. If this thread is locked, please click the "Ask a related question" button, and in the new thread describe the current status of your issue and any additional details you may have to assist us in helping to solve your issues.

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