TIDUEJ6A January   2019  – July 2022

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Flow Measurement
      2. 2.2.2 ToF Measurement
        1. 2.2.2.1 ADC-Based Acquisition Process
        2. 2.2.2.2 Ultrasonic Sensing Flow-Metering Library
      3. 2.2.3 Low-Power Design
        1. 2.2.3.1 Energy-Efficient Software
        2. 2.2.3.2 Optimized Hardware Design
        3. 2.2.3.3 Efficient Use of FRAM
        4. 2.2.3.4 The LEA Advantage
    3. 2.3 Highlighted Products
      1. 2.3.1 MSP430FR6043
      2. 2.3.2 OPA836 and OPA838
      3. 2.3.3 TS5A9411
    4. 2.4 System Design Theory
      1. 2.4.1 Signal Processing for ToF
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
        1. 3.1.1.1 EVM430-FR6043
      2. 3.1.2 Software
        1. 3.1.2.1 MSP Driver Library (MSP DriverLib)
        2. 3.1.2.2 Ultrasonic Sensing Flow Metering Library
        3. 3.1.2.3 Application
          1. 3.1.2.3.1 Application Customization
          2. 3.1.2.3.2 LCD Stand-Alone Mode
        4. 3.1.2.4 USS Design Center (PC GUI)
      3. 3.1.3 Transducer and Meter
        1. 3.1.3.1 Frequency Characterization of Transducer and Meter
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
        1. 3.2.1.1 Connecting Hardware
        2. 3.2.1.2 Building and Loading Software
          1. 3.2.1.2.1 Using Code Composer Studio IDE
          2. 3.2.1.2.2 Using IAR Embedded Workbench IDE
        3. 3.2.1.3 Executing Application
        4. 3.2.1.4 Configure Device and Observe Results Using GUI
        5. 3.2.1.5 Customization and Optimization
      2. 3.2.2 Test Results
        1. 3.2.2.1 Single-Shot Standard Deviation
        2. 3.2.2.2 Zero-Flow Drift
        3. 3.2.2.3 Absolute Time of Flight Measurements
        4. 3.2.2.4 Variability in Zero Flow Drift Across Transducers
        5. 3.2.2.5 Flow Measurements
        6. 3.2.2.6 Average Current Consumption
        7. 3.2.2.7 Memory Footprint
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 Bill of Materials
      3. 4.1.3 PCB Layout Recommendations
        1. 4.1.3.1 Layout Prints
      4. 4.1.4 Altium Project
      5. 4.1.5 Gerber Files
      6. 4.1.6 Assembly Drawings
    2. 4.2 Software Files
    3. 4.3 Related Documentation
    4. 4.4 Terminology
    5. 4.5 Trademarks
    6. 4.6 Support Resources
  10. 5About the Authors
  11. 6Revision History

2.2.1 Flow Measurement

The ultrasonic gas-flow meter design is based on the principle of ToF measurement. This measurement refers to the time it takes a signal to travel from a transmitting transducer to a receiving transducer.

Figure 3-2 shows a flow pipe.

GUID-5C11CE12-5FAB-4C7B-BA4E-01F3B370D168-low.gifFigure 3-2 ToF in Flow Meter

The propagation time of a signal traveling from the first transducer (XDR1) to the second transducer (XDR2) 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. T12=Lc+v
Equation 2. T21=Lc–v
Equation 3. ∆t=T21–T12

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 = L2×1T12–1T21=L2×T21-T12T21T12=L2×∆TT21T12

Using Equation 4, calculate the actual propagation times, T12 and T21, in the two directions along the cross section of the pipe.