SBAU487 August   2025

 

  1.   1
  2.   Description
  3.   Getting Started and Next Steps
  4.   Features
  5.   Applications
  6.   6
  7. 1Evaluation Module Overview
    1. 1.1 Introduction
    2. 1.2 Kit Contents
    3. 1.3 Block Diagram
    4. 1.4 Device Information
  8. 2Hardware
    1. 2.1 Power Requirements
    2. 2.2 Header Information
    3. 2.3 Jumper Information
    4. 2.4 Slide Switches and Push Buttons
    5. 2.5 Test Points
    6. 2.6 Cautions and Warnings
    7. 2.7 Analog Inputs
      1. 2.7.1 Voltage Inputs
        1. 2.7.1.1 Voltage Measurement Analog Front End
      2. 2.7.2 Current Sensor Inputs
        1. 2.7.2.1 Current Measurement Analog Front End
          1. 2.7.2.1.1 Rogowski Coil Inputs
      3. 2.7.3 Analog Gain Setting
  9. 3Software Installation
    1. 3.1 GUI Operation
    2. 3.2 Launch the Metrology Software
  10. 4Energy Metrology Software Overview
    1. 4.1 Using the ADS131M08MET-EVM
      1. 4.1.1 Measuring Voltage and Current
        1. 4.1.1.1 Calibration Procedure
          1. 4.1.1.1.1 Gain Calibration
          2. 4.1.1.1.2 Voltage and Current Gain Calibration
          3. 4.1.1.1.3 Active Power Gain Calibration
          4. 4.1.1.1.4 Offset Calibration
          5. 4.1.1.1.5 Phase Calibration
    2. 4.2 Test Accuracy Results
      1. 4.2.1 Current Transformer Results
      2. 4.2.2 Rogowski Coil Results
    3. 4.3 Developing an Application
  11. 5Hardware Design Files
    1. 5.1 Schematics
    2. 5.2 Bill of Materials (BOM)
    3. 5.3 PCB Layouts
  12. 6Design and Documentation Support
    1. 6.1 Design Files
      1. 6.1.1 PCB Layout Recommendations
    2. 6.2 Tools and Software
    3. 6.3 Documentation Support
    4. 6.4 Support Resources
    5. 6.5 Trademarks

2.7.1.1 Voltage Measurement Analog Front End

The nominal voltage from the Mains is from 100V–240V so the voltage needs to be scaled down to be sensed by an ADC. Figure 2-1 shows the analog front end used for this voltage scaling. J1 is where the voltage is applied for Phase C, similar circuitry is used for each of the Phases A and C.

In the analog front end for voltage, there is a spike protection varistor (R1), a voltage divider network (R5, R10, R13, R18 and R22), and an RC low-pass filter (R27, R28, C6, C11, and C9).

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×2R22R22+R5+R10+ R13+ R18

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