SLAA889A March   2019  – July 2021 MSP430FR6041 , MSP430FR6043 , MSP430FR60431 , MSP430FR6045 , MSP430FR6047 , MSP430FR60471

 

  1.   Trademarks
  2. 1Flow Metering Background
    1. 1.1 Water Flow Velocity Estimation
      1. 1.1.1 Velocity of Ultrasound in Water is Known
      2. 1.1.2 Velocity of Ultrasound in Water is Unknown
  3. 2Algorithms for Ultrasonic Water Flow Metering
    1. 2.1 Correlation Based Technique for Differential TOF Estimation
    2. 2.2 Absolute Time-of-Flight (AbsTOF) Measurement (Tup and Tdn)
      1. 2.2.1 AbsTOF Calculation
        1. 2.2.1.1 Acquisition Algorithm for AbsTOF
        2. 2.2.1.2 Tracking Algorithm for AbsTOF
  4. 3References
  5. 4Revision History

1 Flow Metering Background

This document describes the ultrasonic time-of-flight (TOF) based algorithms for water flow measurement. Figure 1-1 shows different configurations that are used in practice for the ultrasonic TOF technique.

GUID-2F7A826C-4D2D-48A9-ACA0-27FE133B51D6-low.gifFigure 1-1 Configurations for Ultrasonic TOF Based Measurement

This document uses the structure in Figure 1-2 for analysis of ultrasonic TOF techniques.

GUID-97D94EE0-33D4-4E1F-B1A8-C217309AB54E-low.gifFigure 1-2 Transmit and Receive Transducers for Ultrasonic Measurements

In Figure 1-2, the two transducers are numbered 1 and 2, T12 is the propagation time for the ultrasonic signal from transducer 1 to 2, and T21 is the propagation time for the signal from transducer 2 to 1. Equation 1 and Equation 2 calculate the propagation times in the two directions as a function of the velocity of ultrasound in water and the velocity of water flow. The parameters in the equation are c = velocity of ultrasound in water, v = velocity of water flow, and L = the propagation length of the pipe along the flow of water. Because this length is much larger than the radius r of the pipe, the propagation length of the wave perpendicular to the flow is neglected in this analysis.

Equation 1. T12=Lc+v
Equation 2. T21=Lc–v

The objective is to solve for the velocity v of the water flow so that can be used to indicate the water flow volume which would be given by volume = A × v, with the assumption that the cross sectional area A of the pipe is known.

Equation 3 calculates the differential TOF of the upstream and downstream signals.

Equation 3. ΔT=T21–T12