TIDUF72 August   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
    2. 1.2 End Equipment
    3. 1.3 Electricity Meter
    4. 1.4 Power Quality Meter, Power Quality Analyzer
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Magnetic Tamper Detection With TMAG5273 Linear 3D Hall-Effect Sensor
      2. 2.2.2 Analog Inputs of Standalone ADCs
      3. 2.2.3 Voltage Measurement Analog Front End
      4. 2.2.4 Analog Front End for Current Measurement
    3. 2.3 Highlighted Products
      1. 2.3.1 AMC131M03
      2. 2.3.2 ADS131M02
      3. 2.3.3 MSPM0G1106
      4. 2.3.4 TMAG5273
      5. 2.3.5 ISO6731
      6. 2.3.6 TRS3232E
      7. 2.3.7 TPS709
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
      1. 3.1.1  Software Requirements
      2. 3.1.2  UART for PC GUI Communication
      3. 3.1.3  Direct Memory Access (DMA)
      4. 3.1.4  ADC Setup
      5. 3.1.5  Foreground Process
      6. 3.1.6  Formulas
        1. 3.1.6.1 Standard Metrology Parameters
        2. 3.1.6.2 Power Quality Formulas
      7. 3.1.7  Background Process
      8. 3.1.8  Software Function per_sample_dsp()
      9. 3.1.9  Voltage and Current Signals
      10. 3.1.10 Pure Waveform Samples
      11. 3.1.11 Frequency Measurement and Cycle Tracking
      12. 3.1.12 LED Pulse Generation
      13. 3.1.13 Phase Compensation
    2. 3.2 Test Setup
      1. 3.2.1 Power Supply Options and Jumper Setting
      2. 3.2.2 Electricity Meter Metrology Accuracy Testing
      3. 3.2.3 Viewing Metrology Readings and Calibration
        1. 3.2.3.1 Calibrating and Viewing Results From PC
      4. 3.2.4 Calibration and FLASH Settings for MSPM0+ MCU
      5. 3.2.5 Gain Calibration
      6. 3.2.6 Voltage and Current Gain Calibration
      7. 3.2.7 Active Power Gain Calibration
      8. 3.2.8 Offset Calibration
      9. 3.2.9 Phase Calibration
    3. 3.3 Test Results
      1. 3.3.1 Energy Metrology Accuracy Results
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 PCB Layout Recommendations
      4. 4.1.4 Layout Prints
      5. 4.1.5 Altium Project
      6. 4.1.6 Gerber Files
      7. 4.1.7 Assembly Drawings
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Authors

2.2.3 Voltage Measurement Analog Front End

The nominal voltage from the mains in many regions of the world varies from 100V–240V so the voltage needs to be scaled down to be sensed by an ADC. Figure 2-4 shows the analog front end used for this voltage scaling J2 is where the voltage is applied for Phase A to Neutral (one-phase, two-wire or 1P2W) or Phase A to Phase B (split-phase, two-wire or 2P2W).

TIDA-010944 Analog Front End for Voltage Input Figure 2-4 Analog Front End for Voltage Input

The analog front end for voltage inputs has a voltage divider network (R28, R29, R30, and R31), and an RC low-pass filter (R32, R33, C54, C29) and the C53.

At lower currents, voltage-to-current crosstalk affects active energy accuracy much more than voltage accuracy, if power offset calibration is not performed. To maximize the accuracy at these lower currents, in this design the entire ADC range is not used for the voltage channels. 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.

Equation 1. V A D C _ S w i n g ,   V o l t a g e = ± V R M S × 2 R 32 R 28 +   R 29 +   R 30 +   R 31

Based on this formula and the selected resistor values in Equation 1, for a mains voltage of 120V (as measured between the line and neutral), the input signal to the voltage ADC has a voltage swing of ±128.56mV (90.90mVRMS).

For a mains voltage of 230V (as measured between the line and neutral), the 230V input to the front-end circuit produces a voltage swing of ±246.42mV (174.24mVRMS)). The ±128.56mV and the ±246.42mV voltage ranges are both well within the –1.3V to + 2.7V range, that can be sensed by the ADS131M02.