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MSP430FR5043: Relationship Between "Meter Constant" and Pipe Geometry in Ultrasonic Sensing Design Center

?? ??
Prodigy 230 points
Part Number: MSP430FR5043


Tool/software:

Dear TI Engineers,

I have a question regarding the "Meter Constant" parameter in the Ultrasonic Sensing Design Center.

According to the Application Report: Waveform Capture Based Ultrasonic Sensing Water Flow Metering Technology (SLAA889A), the flow velocity and flow rate are calculated as follows:

Flow velocity:
v = L/2 x (1/T12 - 1/T21)
Flow rate:
Q = S x v = S x L/2 x (1/T12 - 1/T21)
Where:
L is the distance between transducers,
S is the cross-sectional area of the pipe,
T12 and T21 are the ultrasonic propagation times.

Given this, is it correct to assume that the Meter Constant used in the Design Center corresponds to:

Meter Constant = S × L / 2

If not, could you please clarify how the Meter Constant is derived and what physical parameters it represents?

Thank you for your support.

  • 0
    TI__Mastermind 46765 points

    Hi,

    You can consider the Meter Constant = S × L / 2. However, this conclusion is derived using a simplified pipeline model. The S and L is not easy to get from an actual pipe. 

    Best regards,

    Cash Hao

  • 0 in reply to Cash Hao11
    Prodigy 230 points

    Dear Hao,

    Thank you for your response. As you pointed out, we understand the limitations. Our intention is to check whether the meter constant calculated from our pipe model roughly matches the meter constant that should be set. We are not aiming for high accuracy.

    Could you please let us know the units used for S (cross-sectional area) and L (length)?

    Best regards,

  • 0 in reply to ?? ??
    TI__Mastermind 46765 points

    Hi,

    The unit depends on the VFR unit. 

    If the VFFR unit is L/h, it is kind of dm^3/h, You may need to change it to m^3/s then you can use meter as the unit of the L and m^2 as the S and use second for the unit of TOF results. 

    Best regards,

    Cash Hao

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