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
2.4.2.2.2 Electricity Meter Metrology Accuracy Results

For the following test results, gain, phase, and offset calibration are applied to the meter. At higher currents, the % error shown is dominated by shunt resistance drift caused by the increased heat generated at high currents.

Table 2-8 Active Energy % Error Versus Current,
200-µΩ Shunts
CURRENT (A)0°60°–60°
0.050.06250.1370.034
0.100.0360.0480.072
0.25–0.00270.0410.058
0.50–0.0220.0040.022
1.00–0.01230.004–0.014
2.00–0.0293–0.024–0.019
5.00–0.0123–0.0240.001
10.00–0.0127–0.0230.0003
20.00–0.0233–0.032–0.032
30.00–0.019–0.019–0.028
40.00–0.025–0.026–0.032
50.00–0.03–0.05–0.03
60.00–0.058–0.075–0.062
70.00–0.088–0.117–0.092
80.00–0.1243–0.164–0.151
90.00–0.181–0.224–0.219
GUID-3104D0A7-49DB-4DA1-A213-E132035A131B-low.gifFigure 2-37 Active Energy % Error Versus Current, 200-µΩ Shunts
Table 2-9 Active Energy % Error Versus Current,
100-µΩ Shunts
CURRENT (A)0°60°–60°
0.050.1470.2160.209
0.10–0.042–0.052–0.058
0.250.0350.0930.0175
0.500.04530.037–0.009
1.000.0130.0377–0.017
2.00–0.01670.0303–0.011
5.000.0060.032–0.014
10.000.0090.034–0.014
20.00–0.0070.032–0.045
30.00–0.0020.04–0.036
40.00–0.0070.032–0.007
50.00–0.0040.017–0.035
60.00–0.019–0.002–0.058
70.00–0.053–0.032–0.092
80.00––0.083–0.07–0.143
90.00–0.122–0.113–0.19
GUID-751CD09C-B9BF-4C21-BC1B-E861C890AFB9-low.gifFigure 2-38 Active Energy % Error Versus Current, 100-µΩ Shunts
Table 2-10 CT Channel Active Energy % Error Versus Current
CURRENT (A)0°60°–60°
0.050.01–0.004–0.011
0.100.0070.0190.005
0.25–0.0040.017–0.021
0.500.0060.024–0.017
1.000.0090.027–0.009
2.00–0.0110.019–0.041
5.000.0060.0060.001
10.000.0015–0.0040.004
20.00–0.015–0.0190.006
30.00–0.011–0.0450.023
40.00–0.013–0.070.038
50.00–0.004–0.0810.083
60.00–0.005–0.0920.087
70.00–0.001–0.09970.109
80.000.013–0.1060.115
90.000–0.1020.134
100.000.018–0.1110.147
GUID-14A62E64-FB3C-4632-B2E8-B37E5574D068-low.gifFigure 2-39 CT Channel Active Energy % Error Versus Current
Table 2-11 Reactive Energy % Error Versus Current,
200-µΩ Shunts
CURRENT (A)30°60°–30°–60°
0.10–0.0350.0010.1180.056
0.250.0320.008–0.0220.008
1.000.0090.0140.006–0.0013
5.000.0170.0060.0110.006
10.000.01950.0140.0060.006
30.000.0060.00170.0060.006
50.000.017–0.004–0.009–0.0115
70.00–0.019–0.0415–0.063–0.085
90.00–0.1–0.133–0.151–0.194
GUID-50C6D805-15BF-4594-B837-7E4A4C442D4A-low.gifFigure 2-40 Reactive Energy % Error Versus Current, 200-µΩ Shunts
Table 2-12 Active Energy Measurement Error Versus Voltage, 75 to 270 V, 200-µΩ Shunts
VOLTAGE (V)%ERROR
75–0.119
100–0.101
110–0.093
120–0.091
150–0.068
180–0.0435
210–0.0233
220–0.014
2300.003
2400.0053
2500.006
2600.017
2700.02
GUID-D2B320FA-6899-4955-BA9B-8240AE63C06A-low.gifFigure 2-41 Active Energy Measurement Error Versus Voltage, 75 to 270 V, 200-µΩ Shunts
Table 2-13 Cumulative Active Energy Measurement Error Versus Voltage, ±10% Nominal Voltage
VOLTAGE (V)0°, 10 A60°, 10 A300°, 10 A0°, 0.5 A60°, 0.5 A300°, 0.5 A
207–0.028–0.045–0.012–0.00730.0170.027
230–0.01–0.0220.004–0.004–0.007–0.012
2530.006–0.0040.0110.011–0.0090.011
Table 2-14 Cumulative Active Energy Measurement Error Versus Frequency,
±2 Hz From Nominal Frequency, 200-µΩ Shunts
CONDITIONS48 Hz50 Hz52 Hz
0.5 A, 00.0090.0010.006
0.5 A, 600.001–0.012–0.017
0.5 A, 3000.0340.0450.014
10 A, 0–0.007–0.011–0.009
10 A, 60–0.022–0.0245–0.027
10 A, 3000.0060.004–0.001