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

2.2.2 ToF Measurement

In the implementation discussed in this reference design, the MSP430FR6043 MCU performs the complete acquisition process using the USS module in the device for signal conditioning. Figure 3-3 shows this acquisition process.

At the beginning of the sequence, the MSP430FR6043 MCU sends a train of pulses to the first transducer, XDCR1. The signal is then received by the second transceiver, XDCR2 , after propagation time T12. The difference in time between transmission and reception determines the upstream (UPS) ToF, or ToFUPS .

The MSP430FR6043 MCU repeats the same process in the opposite direction during the downstream stage, resulting in the propagation time, T21, which represents the downstream (DNS) ToF, or ToFDNS.

The DToF, Δt, can then be calculated as the difference between T12 and T21, as described in Equation 3.

The DToF is typically measured using two techniques: Zero-crossing using a time-to-digital converter (TDC) or through Correlation using the ADC captured signal

The TIDM-02003 design uses the ADC-based technique instead of the TDC technique due to the following advantages.

  • Improved performance: the correlation acts as a digital filter to suppress noise, which results in a benefit of approximately three to four times lower noise standard deviation. Similarly, the correlation approach also acts as a low-pass filter that suppresses other interference like line noise.
  • Improved robustness for signal amplitude variations: because the algorithm is insensitive to the received signal amplitude, transducer-to-transducer variation, and temperature variation.
  • The envelope of the signal is obtained naturally. This signal enables tuning to the transducer frequencies, as well as slow variations in the envelope across time, which can be used to maintain performance even with aging transducers or meters.