TIDUF98 October   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 End Equipment
      1. 1.1.1 Electricity Meter
    2. 1.2 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1 ADS131M03
      2. 2.2.2 MSPM0L2228
      3. 2.2.3 THVD1400
      4. 2.2.4 ISO6731
      5. 2.2.5 DRV5032
    3. 2.3 Design Considerations
      1. 2.3.1 Design Hardware Implementation
        1. 2.3.1.1 Analog Inputs
          1. 2.3.1.1.1 Voltage Measurement Analog Front End
          2. 2.3.1.1.2 Current Measurement Analog Front End
      2. 2.3.2 Energy Metrology Software
        1. 2.3.2.1 Software Architecture
        2. 2.3.2.2 Setup
          1. 2.3.2.2.1 Clocking Scheme
          2. 2.3.2.2.2 SPI
          3. 2.3.2.2.3 UART Setup for GUI Communication
          4. 2.3.2.2.4 Real-Time Clock
          5. 2.3.2.2.5 LCD Controller
          6. 2.3.2.2.6 Direct Memory Access
    4. 2.4 Hardware, Software, Testing Requirements, and Test Results
      1. 2.4.1 Required Hardware and Software
        1. 2.4.1.1 Cautions and Warnings
        2. 2.4.1.2 Hardware
          1. 2.4.1.2.1 Connections to the Test Setup
          2. 2.4.1.2.2 Power Supply Options and Jumper Settings
        3. 2.4.1.3 Calibration
      2. 2.4.2 Testing and Results
        1. 2.4.2.1 Test Setup
          1. 2.4.2.1.1 Viewing Metrology Readings and Calibration
            1. 2.4.2.1.1.1 Viewing Results From LCD
            2. 2.4.2.1.1.2 Viewing Results From PC GUI
        2. 2.4.2.2 Electricity Meter Metrology Accuracy Testing
        3. 2.4.2.3 Electricity Meter Metrology Accuracy Results
  9. 3Design Files
    1. 3.1 Schematics
    2. 3.2 Bill of Materials
    3. 3.3 PCB Layout Recommendations
      1. 3.3.1 Layout Prints
    4. 3.4 Altium Project
    5. 3.5 Gerber Files
    6. 3.6 Assembly Drawings
  10. 4Related Documentation
    1. 4.1 Trademarks
  11. 5About the Authors

2.1 Block Diagram

Figure 2-1 depicts a high-level block diagram of this one-phase electricity meter application.

TIDA-010940 TIDA-010940 Block Diagram Figure 2-1 TIDA-010940 Block Diagram

The resistance of the shunt current sensor is selected based on the maximum current value required for energy measurements and needs to also minimize the power dissipation of the shunt.

The choice of voltage divider resistors for the voltage channel is selected to make sure the Mains voltage is divided down to adhere to the normal input ranges of the ADS131M03 device. Since the ADS131M03 ADC have a large dynamic range and a large dynamic range is not needed to measure voltage, the voltage front-end circuitry is purposely selected so that the maximum voltage seen at the inputs of the voltage channel ADC is only a fraction of the full-scale voltage. By reducing the input voltage range, voltage-to-current crosstalk, which actually affects metrology accuracy more than voltage ADC accuracy, is reduced at the cost of voltage accuracy. In Figure 2-1, a simple voltage divider is used for translating the Mains voltage to a voltage that can be sensed by the ADC, while current sensor is used for sensing the line current, whereas the neutral current is not monitored.

In this design, only two ADC channels are used, hence using the pin-compatible ADS131M02 can reduce the system design cost even further. The ADS131M03 device interacts with the MCU in the following manner:

  1. The CLKIN clock used by the ADS131M03 device is provided from the M0_CLKOUT signal output of the MSPM0+ MCU.
  2. The ADS131M03 device divides the clock at the CLKIN pin by two and uses this divided clock as the delta-sigma modulation clock.
  3. When new ADC samples are ready the ADS131M03 device asserts the DRDY pin.
  4. After being alerted of new samples, the MSPM0+ MCU uses one SPI interface in combination with the DMA controller to read the voltage and current samples from the ADS131M03 device.

Other signals of interest in Figure 2-1 are the active and reactive energy pulses used for accuracy measurement and calibration, named ACT and REACT. The design supports an isolated RS-485 interface through the use of the ISO6731 and THVD1400 devices on the board.