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
2.3.1.1.1 Voltage Measurement Analog Front End

The nominal voltage from the mains is from 100V–240V and has to be scaled down to be sensed by the ADC. Figure 2-4 shows the analog front end used for this voltage scaling after J2, where the Line voltage and Neutral are applied.

Equation 1. VADC_Swing,Voltage=±VRMS×2R32R21+R22+R23+R28+ R29+R30+R32
TIDA-010940 Analog Front End for Voltage InputsFigure 2-4 Analog Front End for Voltage Inputs

In the analog front end for voltage, there consists a spike protection varistor (R3), a protection resistor R24, footprints for electromagnetic interference filter beads (resistors R6 and R7), a voltage divider network (R21, R22, R23, R28, R29, R30 and R32), and an RC low-pass filter (R33, C29, C54 and C53).

At lower currents, voltage-to-current crosstalk affects active energy accuracy much more than voltage accuracy. Since the ADCs of the ADS131M03 device are high-accuracy ADCs, using the reduced ADC range for the voltage channels in this design still provides more than enough accuracy for measuring voltage.

Equation 1 shows how to calculate the range of differential voltages fed to the voltage ADC channel for a given Mains voltage and selected voltage divider resistor values. Based on this equation for a mains voltage of 230V, the input signal to the voltage ADC has a voltage swing of ±164 mV (116 mVRMS). The ±164-mV voltage range is well within the ±1.2V input voltage that can be sensed by the ADS131M03 device with selected PGA gain value of 1 for the voltage channel.