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 the cumulative active and reactive energy testing, the sum of the energy reading of each phase is tested for accuracy. For cumulative active energy error and cumulative reactive energy error testing, current is varied from 100mA to 100A. For cumulative active energy, 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.

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.

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 0A input for the current of this other phase so that the cumulative active energy reading is equal to the individual phase voltage (in the best case), which allows the cumulative energy pulse output to be used for testing individual phase accuracy.

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, 10A current is applied for each phase and the voltage is varied from 9V–270V on each phase simultaneously. The voltage was not varied beyond 270V because of the 275V varistor present on the board, which can be removed for testing at voltages beyond 275V.

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 does not necessarily 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 120V for each phase and varying current from 50mA to 100A.

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

For the V_RMS accuracy test on Phase A, the voltage was varied from 9V to 270V while current was held steady at 10A. For the I_RMS accuracy test on Phase A, the voltage was kept steady at 120V, while current was varied from 0.025A to 100A.

The following two plots for Active and Reactive Power are per IEC 62053-22 limits for class 0.2S and 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.

For the following test results, gain, phase, and offset calibration are applied to the meter.

The test data are recorded with calibrated value data of: • V_in =120V • I_in = 10A • Phase calibrated at 60° • Phases = 3 • Energy Pulses for ACT and REACT = 6400 • Room temperature