TIDUF25 june   2023 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

2.2.3.1 Voltage Measurement Analog Front End

The nominal voltage from the Mains is from 100 V – 240 V so the voltage needs to be scaled down to be sensed by an ADC. Figure 2-3 shows the analog front end used for this voltage scaling. J1 is where the voltage is applied for Phase A, similar circuitry is used for each of the Phases B and C.

GUID-20230605-SS0I-DNQL-HGJD-4ZNHTXVC88LZ-low.svg Figure 2-3 Analog Front End for Voltage Inputs

In the analog front end for voltage, there consists a spike protection varistor (R6), footprints for electromagnetic interference filter beads (resistor footprints R1 and R9), a voltage divider network (R2, R3, R4, and R7), and an RC low-pass filter (R5, R8, C1, C3, and C2).

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 only a small part of the full ADC range is used for voltage channels. Since the ADCs of the ADS131M08 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.

Equation 1. VADC_Swing,Voltage=±VRMS×2R7R2+R3+ R4+ R7

Based on this formula and the selected resistor values in Figure 2-3, for a mains voltage of 120 V (as measured between the line and neutral), the input signal to the voltage ADC has a voltage swing of ±128 mV (91 mVRMS). For a mains voltage of 230 V (as measured between the line and neutral, the 230-V input to the front-end circuit produces a voltage swing of ±245.33 mV (173.48 mVRMS). The ±128-mV and the ±245.33-mV voltage ranges are both well within the ±1.2-V input voltage that can be sensed by the ADS131M08 device for the selected PGA gain value of 1 that is used for the voltage channels.