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

2.4.2.2 Electricity Meter Metrology Accuracy Testing

For cumulative active energy error, cumulative reactive energy error testing, and individual phase active energy testing, current is varied from 50mA to 100A. For cumulative active energy and individual phase error testing, a phase shift of 0° (PF = 1), PF = 0.5i (inductive) and PF = 0.8c (capacitive) is applied between the voltage and current waveforms fed to the reference design. Based on the error from the active energy output pulse, a plot of active energy % error versus current is created for the three PF values.

For cumulative reactive energy error testing, a similar process is followed except that a phase shift of 90° (sin ϕ = 1i), sin ϕ = 0.5i (inductive) and sin ϕ = 0.8c (capacitive) are used, and cumulative reactive energy error is plotted instead of cumulative active energy error.

All these tests were run using the 8000 samples per second rate setting of the ADS131M03 device.

For the VRMS accuracy test on Phase A, the voltage was varied from 10V to 270V while current was held steady at 10A. Testing beyond 270V can also be done; however, this requires the 275V varistors to be removed from the design and replaced with varistors that are rated for a higher voltage.

For the IRMS accuracy test on Phase A, the voltage was kept steady at 120V, while current was varied from 0.1A to 100A.

The following two plots for Active and Reactive Power are per IEC 62053-22 limits for class 0.5S accuracy, assuming Inominal = 15A, hence the 5% point of Inominal is at 750mA.

The average error for each measurement is calculated from five test series, taken sequentially for each current value, and the maximum deviation from these five measurements is calculated (not shown in the following plots) to confirm the stability of this metrology subsystem being below 10% of the maximum error allowed.