SLAAES9 March   2025 MSP430FR5043 , MSP430FR6005 , MSP430FR6007 , MSP430FR6043 , MSP430FR6045 , MSP430FR6047

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Flow Meter Measurement Theory
    1. 2.1 TOF Measurement Algorithm Implementation
      1. 2.1.1 AbsTOF Calculation Method – Lobe
      2. 2.1.2 AbsTOF Calculation Method – Hilbert Wide
      3. 2.1.3 dTOF Calculation Method - Cross-Correlation
        1. 2.1.3.1 Get a High-Precision dTOF Result
        2. 2.1.3.2 Optimization in Cross-Correlation Method
    2. 2.2 Differences between ADC Approach and TDC Approach
  6. 3MSP430 MCUs for USS Application
    1. 3.1 USS Module
    2. 3.2 Differences Between USS and USS_A Module
    3. 3.3 Software Implementation on MSP430 MCUs
  7. 4Hardware Design Flow
    1. 4.1 Schematics
      1. 4.1.1 Water Meter Schematic – MSP430FR6047 and MSP430FR6007
      2. 4.1.2 Water Meter Schematic – MSP430FR6043 and MSP430FR5043
      3. 4.1.3 Gas Meter Schematic – MSP430FR6043 and MSP430FR5043
    2. 4.2 PCB Layout Guide
  8. 5Software Design Guide
    1. 5.1 USS Demo Projects and Related Resources
    2. 5.2 Demo Project Instruction
      1. 5.2.1 Files in Demo Project
      2. 5.2.2 Properties Setting in Demo Project
  9. 6Summary
  10. 7References

2.1.1 AbsTOF Calculation Method – Lobe

Estimating an accurate absToF in water means that a temperature sensor is not needed to compute the velocity of sound in water. In the USS SW Library used in this reference design, the absToF is determined by computing the envelope of the received signal.

A peak value for each lobe is first computed. Then, the maximum lobe peak is chosen. The envelope crossing threshold as a given ratio of this maximum is then determined. The algorithm picks the nearest lobe peak to the threshold as the absTOF measurement end point. The absToF is then calculated by a constant offset from this threshold crossing of the envelope, as shown in below figure.

Lobe Algorithm Figure 2-2 Lobe Algorithm

The UPS and DNS absToF are therefore given by Equation 5.

Equation 5. absTOF = Tprop+TabsTOF_offset

where:

  • Tprop is the propagation time which is preprogrammed from USS Design Center GUI (gap between pulse start and ADC capture) or application configuration and corresponds to approximate propagation time for the ultrasound signal in the given meter.

Typically, this value can range from 35 to 70µs. The absTOF offset corresponds to the time from the ADC trigger to the envelope crossing a certain ratio of the signal maximum. TI recommends to choose the second visible lobe according to the ADC capture data, since the first lobe is usually weak and sometimes hard to distinguish from the noise.