To test for metrology accuracy in the electricity meter configuration, a source generator is used to provide the voltages and currents to the system at the proper locations mentioned in Test Setup. In this design, a nominal voltage of 230 V between the line and neutral, calibration current of 10 A, and nominal frequency of 50 Hz are used for each of the three phases.

When the voltages and currents are applied to the system, the system outputs the cumulative active energy pulses and cumulative reactive energy pulses at a rate of 6400 pulses/kWh. This pulse output is fed into a reference meter (in the test equipment for this reference design, this pulse output is integrated in the same equipment used for the source generator) that determines the energy % error based on the actual energy provided to the system and the measured energy as determined by the active and reactive energy output pulse of the system. For the 3-phases configuration, cumulative active energy error testing, cumulative reactive energy error testing, individual phase active energy testing, and frequency variation testing are performed after performing the energy gain calibration and phase compensation as described in Section 4.2.5. In addition to the energy error tests, the RMS voltage % error and RMS current % error are measured as well for the two-voltage configuration. For the one-voltage configuration, cumulative active energy error testing and voltage variation tests are also performed.

For cumulative active energy error, cumulative reactive energy error testing, and individual phase active energy testing, current is varied from 50 mA to 100 A. For cumulative active energy and individual phase error testing, a phase shift of 0°, 60°, and −60° 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 0°, 60°, and –60° phase shifts. For cumulative reactive energy error testing, a similar process is followed except that 30°, 60°, –30°, and –60° phase shifts are used, and cumulative reactive energy error is plotted instead of cumulative active energy error. In the cumulative active and reactive energy testing, the sum of the energy reading of each phase is tested for accuracy. In contrast, the individual phase energy readings (Phase A, Phase B, and Phase C) are tested for the individual phase active energy testing. When testing the individual energy accuracy of a phase, the other phase is disabled by providing 0-A input for the current of this other phase so that the cumulative active energy reading is ideally equal to the individual phase voltage, which allows the cumulative energy pulse output to be used for testing individual phase accuracy.

In addition to testing active energy by varying current, active energy was also tested by varying the RMS voltage from 240 V – 15 V and measuring the active energy % error. Another set of energy tests performed were frequency variation tests. For this test, the frequency is varied by ±2 Hz from the 60-Hz nominal frequency. This test is conducted at 0.5 A and 10 A at phase shifts of 0°, 60°, and −60°. The resulting active energy error under these conditions are logged.

To test RMS accuracy, the RMS readings were used from the GUI since the pulse output that was used for the energy accuracy tests cannot be used for RMS voltage and current. For the voltage testing, 10-A current is applied for each phase and the voltage is varied from 9 V – 270 V on each phase simultaneously. The voltage was not varied beyond 270 V because of the 275-V varistor present on the board, which can be removed for testing at voltages beyond 275 V. After applying each voltage, the resulting RMS voltage reading from the GUI is logged for each phase after the readings stabilize. Once the measured RMS voltage readings are obtained from the GUI, the actual RMS voltage readings are obtained from the reference meter, which is necessary because the source generator may not generate the requested values for voltage, especially at small voltages. With the reference meter measured RMS voltage and the RMS voltage value of the GUI, the RMS voltage % error is calculated. A similar process is used to calculate the RMS current % error by using 120 V for each phase and varying current from 50 mA to 100 A.

All these tests have been run using the 8 kSPS sample rate setting of the ADS131M08.