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

3.2.4 Calibration and FLASH Settings for MSPM0+ MCU

Calibration is key to any meter performance, and calibration is absolutely necessary for every meter to go through this process. Initially, every meter exhibits different accuracies due to silicon-to-silicon differences, sensor accuracies, and other passive tolerances. To nullify the effects, every meter must be calibrated. To perform calibration accurately, there must be an accurate AC test source and a reference meter available. The source must be able to generate any desired voltage, current, and phase shifts (between V and I). To calculate errors in measurement, the reference meter acts as an interface between the source and the meter being calibrated. This section discusses a simple and effective method of calibration of this split-phase electricity meter design.

The GUI used for viewing measurement results can also easily be used to calibrate the design. During calibration, parameters called calibration factors are modified in the test software to give the least error in measurement. For this meter, there are six main calibration factors for each phase: voltage scaling factor, active power offset (erroneously called voltage AC offset in the GUI), current scaling factor, reactive power offset (erroneously called current AC offset in the GUI), power scaling factor, and the phase compensation factor. The voltage, current, and power scaling factors translate measured quantities in metrology software to real-world values represented in volts, amps, and Watts, respectively. The power offset is used to subtract voltage to current crosstalk, which appears as a constant power offset and causes greater inaccuracies at lower currents. Offset calibration was not used for testing this specific design. The last calibration factor is the phase compensation factor, which is used to compensate any phase shifts introduced by the current sensors and other passives. The voltage, current, and power calibration factors are independent of each other. Therefore, calibrating voltage does not affect the readings for RMS current or power.

When the meter software is flashed on the MSPM0G1106 device for the first time, default calibration factors are loaded into these calibration factors. Calibration factors or values are modified through the GUI during calibration. The calibration factors are also stored in the last MSPM0+ MCU FLASH sector and therefore, remain the same if the meter is restarted.

Calibrating any of the scaling factors is referred to as gain correction. Calibrating the phase compensation factors is referred to as phase correction. For the entire calibration process, the AC test source must be ON, meter connections consistent with Figure 3-9, and the energy pulses connected to the reference meter.