TIDUF25A June   2023  – March 2025 ADS131M08 , MSPM0G1507

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 End Equipment
    2. 1.2 Electricity Meter
    3. 1.3 Power Quality Meter, Power Quality Analyzer
    4. 1.4 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 External Supply Voltage Supervisor (SVS) With TPS3840
      2. 2.2.2 Magnetic Tamper Detection With TMAG5273 Linear 3D Hall-Effect Sensor
      3. 2.2.3 Analog Inputs
        1. 2.2.3.1 Voltage Measurement Analog Front End
        2. 2.2.3.2 Current Measurement Analog Front End
    3. 2.3 Highlighted Products
      1. 2.3.1  ADS131M08
      2. 2.3.2  MSPM0G3507
      3. 2.3.3  MSP430FR4131 for Driving Segmented LCD Displays
      4. 2.3.4  TPS3840
      5. 2.3.5  THVD1400
      6. 2.3.6  ISO6731
      7. 2.3.7  ISO6720
      8. 2.3.8  TRS3232E
      9. 2.3.9  TPS709
      10. 2.3.10 TMAG5273
  9. 3System Design Theory
    1. 3.1  How to Implement Software for Metrology Testing
    2. 3.2  Clocking System
    3. 3.3  UART Setup for GUI Communication
    4. 3.4  Real-Time Clock (RTC)
    5. 3.5  LCD Controller in MSP430FR4131
    6. 3.6  Direct Memory Access (DMA)
    7. 3.7  ADC Setup
    8. 3.8  Foreground Process
      1. 3.8.1 Formulas
    9. 3.9  Background Process
    10. 3.10 Software Function per_sample_dsp()
      1. 3.10.1 Voltage and Current Signals
      2. 3.10.2 Frequency Measurement and Cycle Tracking
    11. 3.11 LED Pulse Generation
    12. 3.12 Phase Compensation
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Required Hardware and Software
      1. 4.1.1 Hardware
      2. 4.1.2 Cautions and Warnings
    2. 4.2 Test Setup
      1. 4.2.1  Connecting the TIDA-010243 to the Metering Test Equipment
      2. 4.2.2  Power Supply Options and Jumper Settings
      3. 4.2.3  Electricity Meter Metrology Accuracy Testing
      4. 4.2.4  Viewing Metrology Readings and Calibration
        1. 4.2.4.1 Viewing Results From LCD
        2. 4.2.4.2 Calibrating and Viewing Results From PC
      5. 4.2.5  Calibration and FLASH Settings for MSPM0+ MCU
      6. 4.2.6  Gain Calibration
      7. 4.2.7  Voltage and Current Gain Calibration
      8. 4.2.8  Active Power Gain Calibration
      9. 4.2.9  Offset Calibration
      10. 4.2.10 Phase Calibration
      11. 4.2.11 Software Code Example
    3. 4.3 Test Results
      1. 4.3.1 SVS Functionality Testing
      2. 4.3.2 Electricity Meter Metrology Accuracy Results
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
      3. 5.1.3 PCB Layout Recommendations
      4. 5.1.4 Layout Prints
      5. 5.1.5 Gerber Files
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Author
  13. 7Revision History

1.2 Electricity Meter

Utility providers and utility customers are driving the need for more features from electricity meters. Advanced features, such as harmonic analysis, are increasingly being required from meters which mandates higher processing and accuracy requirements for the MCUs. As an example, adding harmonic analysis capabilities to an electricity meter can require an increase in the sample rate of the meter to capture the desired frequency range. Often such increases in sample frequency must be done without compromising on accuracy, while the higher sample rate, in turn, also requires more processing.

As both the accuracy requirements and amount of processing expected from electricity meters rapidly increase, it becomes more and more difficult to solve this with a single metrology system on chip (SoC). A common answer to this problem is to utilize a dual-chip approach with a standalone ADC and a standard host microcontroller (MCU). Using an accurate state-of-the-art standalone ADC typically has the following advantages:

  • Enables meeting the most stringent of accuracy requirements
  • Enables meeting minimum sample rate requirements (without compromising on accuracy) that cannot be obtainable with application-specific products or metrology SoCs
  • Enables flexibility in selecting the host microcontroller, because the MCU only needs to meet the application requirements, such as processing capability, minimum RAM and Flash storage for logging energy usage, and microcontroller security features for providing meter data security

To properly sense energy consumption, voltage and current sensors translate mains voltage and current to a voltage range that an ADC can sense. To sense the energy consumption when a multiphase distribution system is used, it is necessary for the current sensors to be isolated so the sensors can properly determine the current drawn from the two different lines without damaging the ADC. As a result, current transformers, which inherently have isolation, have historically been used for the current sensors for split-phase, two-phase, and three-phase electricity meters.

In this reference design, Class 0.1 three-phase CT-based energy measurement is implemented by using a standalone ADC device, which senses the mains voltage and current. When there are new ADC samples available, the host MCU communicates to the standalone ADC through SPI bus to read out the new samples and calculate multiple metrology parameters. In addition, the host also communicates to a PC GUI through either the isolated RS-232 circuitry or isolated RS-485 circuitry on the board. As an additional safeguard, an external SVS device is added to the design to reset the host MCU when the supplied voltage to power the host MCU is not sufficient. In general, using an (optional) external supply voltage supervisor (SVS) provides more security than the internal SVS on a host microcontroller.

In this design, the test software specifically supports calculation of various metrology parameters for 3-phase energy measurement. These parameters can be viewed either from the calibration GUI or on an optional LCD display. The key parameters calculated during energy measurements are:

  • Active, reactive, apparent power, and energy
  • RMS current and voltage
  • Power factor
  • Line frequency