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EVM430-FR6047: Calculating V transducer spacing

Anthony Davidson
Prodigy 170 points
Part Number: EVM430-FR6047


Tool/software:

We are using the EVM430-FR6047 to evaluate a water flow measurement system using transducers clamped on to the outside of a water pipe. We are getting good results but have an issue we don't understand. That issue is the calculation of the spacing (or separation) between 2 transducers on a given pipe. We are using Snell's law, the dimnesions for a given pipe, and geometry to calculate the transducer spacing for V configured transducers. We have discovered that the calculated spacing is a starting point followed by increasing the separation a little bit at a time to maximize the amplitude of the received signal in the ADC Capture tab of the USS software spplication. Once the spacing has been optimized, then we adjust other settings to optimize the performance for making TOF measurements.

From our experince so far, it seems we always have to increase the transducer spacing from the calculated spacing using the process mentioned above. Increaseing the trasnducer separation is needed regardless of the transducer configuration we are using in a particular instance: Z, N, or V. Incidentally, we've never been able to make the W configuration work - there just isn't enough signal.

Can you provide some insight or comments regarding having to increase the transducer separation from the claculated spacing?

  • 0
    TI__Mastermind 46765 points

    Hi,

    Actually, I have nothing to share about. Since the distance between transducer is not used for calculation the time of flights result. And the distance is only used in estimate water temperature function. We do not pay much attention to this character. Why do you need to calculate the distance here?

    And for W type of pipe, I think it is hard to control the signal direction after multiply reflections. 

    Best regards,

    Cash Hao 

  • 0 in reply to Cash Hao11
    Prodigy 170 points

    Reason's for wanting the transducer separation:

    1. We'd like to be able to attach the clamped on transducers on the pipe. If grease is used as the ultrasonic couplant between transducer and pipe, the grease gets scraped off as one slides the transducers back and forth while looking for the maximized receive signal. If a rubber strip is used as the couplant, sliding the transducers to optimize signal strength is almost impossible due to the high friction of the rubber material.
    2. We'd like to be able to also calculate the time of flight.
    3. We'd like to understand why the calculated separation is different from the actual separation. Is the Snell's law calculation not accurate? What else is needed in the model?
  • 0 in reply to Anthony Davidson
    TI__Mastermind 46765 points

    Hi,

    Well, I do not have more things to share since we do not usually care about the distance on a residential meter. 

    But I did a little search on this 'Snell's law'. It turns out that it is used in optical computing not acoustic calculations. We are dealing with ultrasound here, so I think the 'Snell's law' does not apply to it. 

    Best regards,

    Cash Hao

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