TIDUEM7A April   2019  – February 2021

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 End Equipment
      1. 1.1.1 Electricity Meter
    2. 1.2 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1 ADS131M04
      2. 2.2.2 TPS7A78
      3. 2.2.3 MSP432P4111
      4. 2.2.4 TPS3840
      5. 2.2.5 THVD1500
      6. 2.2.6 ISO7731B
      7. 2.2.7 TRS3232E
      8. 2.2.8 TPS709
      9. 2.2.9 ISO7720
    3. 2.3 Design Considerations
      1. 2.3.1 Design Hardware Implementation
        1. 2.3.1.1 TPS7A78 Cap-Drop Supply
        2. 2.3.1.2 TPS3840 SVS
        3. 2.3.1.3 Analog Inputs
          1. 2.3.1.3.1 Voltage Measurement Analog Front End
          2. 2.3.1.3.2 Current Measurement Analog Front End
      2. 2.3.2 Current-Detection Mode
        1. 2.3.2.1 ADS131M04 Current-Detection Procedure
        2. 2.3.2.2 Using an MCU to Trigger Current-Detection Mode
          1. 2.3.2.2.1 Using a Timer to Trigger Current-Detection Mode Regularly
          2. 2.3.2.2.2 MCU Procedure for Entering and Exiting Current-Detection Mode
        3. 2.3.2.3 How to Implement Software for Metrology Testing
          1. 2.3.2.3.1 Setup
            1. 2.3.2.3.1.1 Clock
            2. 2.3.2.3.1.2 Port Map
            3. 2.3.2.3.1.3 UART Setup for GUI Communication
            4. 2.3.2.3.1.4 Real-Time Clock (RTC)
            5. 2.3.2.3.1.5 LCD Controller
            6. 2.3.2.3.1.6 Direct Memory Access (DMA)
            7. 2.3.2.3.1.7 ADC Setup
          2. 2.3.2.3.2 Foreground Process
            1. 2.3.2.3.2.1 Formulas
          3. 2.3.2.3.3 Background Process
            1. 2.3.2.3.3.1 per_sample_dsp()
              1. 2.3.2.3.3.1.1 Voltage and Current Signals
              2. 2.3.2.3.3.1.2 Frequency Measurement and Cycle Tracking
            2. 2.3.2.3.3.2 LED Pulse Generation
            3. 2.3.2.3.3.3 Phase Compensation
    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 Software
      2. 2.4.2 Testing and Results
        1. 2.4.2.1 Test Setup
          1. 2.4.2.1.1 SVS and Cap-Drop Functionality Testing
          2. 2.4.2.1.2 Electricity Meter Metrology Accuracy Testing
          3. 2.4.2.1.3 Current-Detection Mode Testing
          4. 2.4.2.1.4 Viewing Metrology Readings and Calibration
            1. 2.4.2.1.4.1 Viewing Results From LCD
            2. 2.4.2.1.4.2 Calibrating and Viewing Results From PC
              1. 2.4.2.1.4.2.1 Viewing Results
              2. 2.4.2.1.4.2.2 Calibration
                1. 2.4.2.1.4.2.2.1 Gain Calibration
                  1. 4.2.1.4.2.2.1.1 Voltage and Current Gain Calibration
                  2. 4.2.1.4.2.2.1.2 Active Power Gain Calibration
                2. 2.4.2.1.4.2.2.2 Offset Calibration
                3. 2.4.2.1.4.2.2.3 Phase Calibration
        2. 2.4.2.2 Test Results
          1. 2.4.2.2.1 SVS and TPS7A78 Functionality Testing Results
          2. 2.4.2.2.2 Electricity Meter Metrology Accuracy Results
          3. 2.4.2.2.3 Current-Detection Mode Results
  8. 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
  9. 4Related Documentation
    1. 4.1 Trademarks
  10. 5About the Author
  11. 6Revision History
2.4.2.1.4.2.2.3 Phase Calibration

After performing power gain correction, do the phase calibration. To perform phase correction calibration, complete the following steps:

  1. If the AC test source has been turned OFF or reconfigured, perform Step 1 through Step 3 from Section 4.2.1.4.2.2.1.1 using the identical voltages and currents used in that section.
  2. Modify only the phase-shift to a non-zero value; typically, +60° is chosen. The reference meter now displays a different % error for active power measurement. Note that this value may be negative.
  3. If the error from Step 3 is not close to zero, or is unacceptable, perform phase correction by following these steps:
    1. Enter a value as an update for the Phase Correction field for the phase that is being calibrated. Usually, a small ± integer must be entered to bring the error closer to zero. Additionally, for a phase shift greater than 0 (for example: +60°), a positive (negative) error requires a positive (negative) number as correction.
    2. Click on the Update meter button and monitor the error values on the reference meter.
    3. If this measurement error (%) is not accurate enough, fine-tune by incrementing or decrementing by a value of 1 based on Step 4a and Step 4b. Note that after a certain point, the fine-tuning only results in the error oscillating on either side of zero. The value that has the smallest absolute error must be selected.
    4. Change the phase now to −60° and check if this error is still acceptable. Ideally, errors must be symmetric for same phase shift on lag and lead conditions.

After performing phase calibration, calibration is complete. The new calibration factors (see Figure 2-35) can be viewed if desired by clicking the Meter calibration factors button of the GUI metering results window in Figure 2-32. For these displayed calibration factors, note that the "Voltage AC off" parameter actually represents the active power offset (in units of mW) subtracted from each measurement and the "Current AC offset" parameter actually represents the reactive power offset subtracted (in units of mvar) from reactive power readings.

GUID-759458C7-F1D2-4006-88AE-C2D50A1BF394-low.pngFigure 2-35 Calibration Factors Window

View the configuration of the system by clicking on the Meter features button in Figure 2-32 to get to the window that Figure 2-36 shows.

GUID-FA16AADD-AA0F-4A3C-87CF-BA115AF8359B-low.pngFigure 2-36 Meter Features Window