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 Flow Meter Measurement Theory

The ultrasonic flow meter design is based on the principle of ToF measurement. This measurement refers to the time a signal takes to travel from a transmitting transducer to a receiving transducer. Figure 2-1 shows a typical flow pipe.

Typical Flow Pipe Figure 2-1 Typical Flow Pipe

The propagation time of a signal traveling from the first transducer to the second transducer is given by T12. T21 represents the propagation time in the opposite direction. Calculate these timings according to the following equations as a function of the velocity of the ultrasound in gas and the velocity of gas flow. Because this length is much larger than the radius of the pipe, r, the propagation length of the wave that is perpendicular to the flow is considered to be negligible in the following analysis.

Equation 1. T 12 = L c   +   v
Equation 2. T 21 = L c - v
Equation 3. ∆ t = T 21 - T 12

where:

  • c is the velocity of the ultrasound in the medium.
  • v is the velocity of gas flow.
  • L is the propagation length of the pipe along the flow of gas.

Use Equation 1 through Equation 3 to derive the velocity of gas flow (v), which is possible even without knowing the velocity of the ultrasound in the medium (c). This reference design calculates gas flow assuming that the velocity of the ultrasound is unknown. In this case, derive Equation 4 from Equation 1 and Equation 2 by eliminating c.

Equation 4. v = L 2 × 1 T 12 - 1 T 21 = L 2 × T 21 - T 12 T 21 × T 12 = L 2 × ∆ t T 21 × T 12