71M6521 Demo Board User’s Manual
Page: 54 of 111
© 2005-2009 TERIDIAN Semiconductor Corporation
Revision 2.18
Figure 2-2: Phase Angle Definitions
The calibration procedures described below should be followed after interfacing the voltage and current
sensors to the 71M6521 chip. When properly interfaced, the V3P3 power supply is connected to the meter
neutral and is the DC reference for each input. Each voltage and current waveform, as seen by the 6521, is
scaled to be less than 250mV (peak).
2.2.2 CALIBRATION PROCEDURE WITH THREE MEASUREMENTS
The calibration procedure is as follows:
1. All calibration factors are reset to their default values, i.e. CAL_IA = CAL_VA = 16384, and PHADJ_A =
0.
2. An RMS voltage V
ideal
consistent with the meter’s nominal voltage is applied, and the RMS reading
V
actual
of the meter is recorded. The voltage reading error Axv is determined as
Axv = (V
actual -
V
ideal
) / V
ideal
3. Apply the nominal load current at phase angles 0° and 60°, measure the Wh energy and record the
errors E
0
AND E
60
.
4. Calculate the new calibration factors CAL_IA, CAL_VA, and PHADJ_A, using the formulae presented in
section 2.1.1 or using the spreadsheet presented in section 2.2.4.
5. Apply the new calibration factors CAL_IA, CAL_VA, and PHADJ_A to the meter. The memory locations
for these factors are given in section 1.9.1.
6. Test the meter at nominal current and, if desired, at lower and higher currents and various phase angles
to confirm the desired accuracy.
7. Store the new calibration factors CAL_IA, CAL_VA, and PHADJ_A in the EEPROM of the meter. If a
Demo Board is calibrated, the methods shown in section 1.9.2 can be used.
2.2.3 CALIBRATION PROCEDURE WITH FIVE MEASUREMENTS
The calibration procedure is as follows:
1) All calibration factors are reset to their default values, i.e. CAL_IA = CAL_VA = 16384, and PHADJ_A =
0.
2) An RMS voltage V
ideal
consistent with the meter’s nominal voltage is applied, and the RMS reading
V
actual
of the meter is recorded. The voltage reading error Axv is determined as
Axv = (V
actual -
V
ideal
) / V
ideal
3) Apply the nominal load current at phase angles 0°, 60°, 180° and –60° (-300°). Measure the Wh energy
each time and record the errors E
0
, E
60
, E
180
, and E
300
.
Voltage
Current
+60°
Using Energy
Generating Energy
Current lags
voltage
(inductive
)
Current leads
voltage
(capacitive
)
-60°
Voltage
Positive
direction
