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

3.2.1.5 Customization and Optimization

The TIDM-02003 design was tested using third party meters and other proprietary meters described in Section 3.1.3. However, the system allows for easy customization and optimization using other transducers and meter designs.

Developers are encouraged to use the MSP430 Ultrasonic Design Center Tool GUI to adjust the different configuration parameters, to achieve the required balance between performance and power consumption.

For example, developers can select a signal sampling frequency (SIG_SAMPLING_FREQ) of 8 MHz to achieve higher resolution at the expense of higher current consumption; however, this would be unnecessary for transducers in the range of 200 kHz to 500 kHz. In such case, developers can select a sampling frequency of 1 or 2 MHz, which results in lower power consumption.

The following GUI parameters should be adjusted based on the characteristics of the meter and transducers:

  • Transmit Frequency (kHz): depends on the excitation frequency of the transducer. For example, selecting f1 = 200 kHz generates an excitation signal at 200 kHz for a 200-kHz transducer.
  • Gap between pulse start and ADC capture (µs): depends on the dimensions of the meter and should be characterized to allow for an appropriate signal capture at different flow rates and temperature variations.
  • Number of Pulses: affects the peak amplitude and, in turn, the energy received by the receiving transducer. This affects the SNR and the single-shot STD achieved by the meter; however, this parameter is also directly proportional to current consumption. Developers must adjust this value to generate an appropriate signal amplitude and standard deviation while meeting current consumption targets.
  • UPS and DNS gap (µs): developers must select an appropriate delay, ensuring a idle channel, before the start of the next excitation.
  • UPS0 to UPS1 gap (ms): the gap between the end of a measurement and the start of the next measurement and it controls the measurement rate. A setting of 1000 ms gives an approximately 1-Hz measurement rate.
  • GUI based gain control: selects the gain setting of the PGA in the USS module on the MSP430FR6043 MCU.
  • Meter constant: constant used to calculate volume flow rate as a function of the ToF and the area of a given meter, as described in Equation 4. A typical procedure to calculate this constant is to provide a constant flow (for example, 200 lph or 1 gpm) and adjust the meter constant to provide the corresponding volume flow rate using the GUI.
  • USSXT (kHz): selectable between 4 MHz and 8 MHz, depending on the frequency of the USSXT on the EVM430-FR6043 EVM. The EVM is usually shipped with an 8-MHz resonator and should use with this parameter set to 8 MHz. Users must set this value appropriately if using a different USSXT on the EVM.
  • SIG_SAMPLING_FREQ (kHz): selectable between 6800, 7200, 7600, or 8000 kHz and must be high enough to meet the Nyquist criterion for reduced error during interpolation. The recommended sampling rate is > 3.4 times of the transducer frequency. Developers can modify it for a tradeoff between resolution and power consumption.
  • ADC Over Sampling Rate: selectable between 40 or 80. Here, 80 is used for an ADC sampling frequency of ≤ 1 MHz and 40 is used for an ADC sampling frequency of 2 MHz. The MSP430FR6043 MCU only supports ADC sampling frequencies between [3.4 MHz to 4 MHz] or between [6.8 MHz to 8 MHz]. Sampling frequencies between 4 MHz to 6.8 MHz are not supported by the device.
  • Delta ToF offset (ps): adjustment is made to the differential ToF during the calculation of volume flow rate inside the ultrasonic flow meter library. Developers can optionally make their custom calculation of the volume flow rate based on the ToF values provided by the library.
  • Absolute ToF additional delay (ns): adjustment is made to the absolute ToF to account for any additional delays. The value depends on the shape of the signal and the envelope threshold discussed following. Developers can optionally set this value to zero and make their own adjustments of the absolute ToF in the application layer.
  • Capture duration (µs): depends on the shape of the signal received from the transducer. Must be characterized to allow for an appropriate signal capture at different flow rates and temperature variations.
  • Param 2 (ULPBiasDelay): selects the delay in applying the bias after the initialization of the USS module. TI recommends setting this to 3 (representing 300 µs) and should not be modified.
  • Start PPG Count (ns): sets the delay between the start of the internal timer in the USS module in FR6043 and the start of the excitation pulses (PPG pulse trigger). TI recommends setting this to 10000 (for 10 µs).
  • Turn on ADC Count (ns): sets the delay between the start of the internal timer in the USS module in FR6043 and enables the sigma-delta high-speed ADC. TI recommends setting this to 5000 (for 5 µs).
  • Start PGA and IN Bias Count (ns): sets the delay between the start of the internal timer in the USS module in FR6043 and the start of the bias application. TI recommends setting this to 0 (for 0 µs).
  • USS XTAL Settling Count (µs): sets the settling time for USSXT. TI recommends setting this to 120 µs for the resonator (USSXT) on the EVM.