Manual

71M6541 Demo Board REV 3.0 User’s Manual
40 Rev 4.0
2.3 CALIBRATION PROCEDURES
2.3.1 CALIBRATION EQUIPMENT
Calibration requires that a calibration system is used, i.e., equipment that applies accurate voltage, load current
and load angle to the unit being calibrated, while measuring the response from the unit being calibrated in a re-
peatable way. By repeatable we mean that the calibration system is synchronized to the meter being calibrated.
Best results are achieved when the first pulse from the meter opens the measurement window of the calibration
system. This mode of operation is opposed to a calibrator that opens the measurement window at random time
and that therefore may or may not catch certain pulses emitted by the meter.
It is essential for a valid meter calibration to have the voltage stabilized a few seconds be-
fore the current is applied. This enables the Demo Code to initialize the 71M6541F and to
stabilize the PLLs and filters in the CE. This method of operation is consistent with meter
applications in the field as well as with metering standards.
During calibration of any phase, a stable mains voltage has to be present on phase A. This
enables the CE processing mechanism of the 71M6541F necessary to obtain a stable cali-
bration.
2.3.2 PHASE-BY-PHASE CALIBRATION
Each meter phase must be calibrated individually. Some calibration systems do not allow selective control of
currents in each phase. Each phase can still be individually calibrated using the following sequence:
• When calibrating phase A, the calibration coefficient for the current in phase B is set to zero. This way,
the pulses are generated solely based on phase A. The kH factor of the calibration system must be ad-
justed by -50% to account for the suppression of 50% of the energy.
• When calibrating phase B, the calibration coefficient for the current in phase A is set to zero. This way,
the pulses are generated solely based on phase B. The kH factor of the calibration system must be ad-
justed by -50% to account for the suppression of 50% of the energy.
• For the final step, both current calibration coefficients are set to their calibration values and the meter
can be tested at the original kH setting.
2.3.3 DETAILED CALIBRATION PROCEDURES
The procedures below show how to calibrate a meter phase with either three or five measurements. The
PHADJ equations apply only when a current transformer is used for the phase in question. Note that positive
load angles correspond to lagging current (see Figure 2-6).
Figure 2-6: Phase Angle Definitions
Voltage
Current
+60°
Using EnergyGenerating Energy
Current lags
voltage
(inductive
)
Current leads
voltage
(capacitive
)
-60°
Voltage
Positive
direction