Maxim Integrated 78M6631 - Manual (Page 15)

UG_6631_078 78M6631 Firmware Description Document
Rev 2 15
2.3.5 Calibration
As with any measurement system, there are also multiple sets of coefficients that are used to
compensate for system inaccuracies. Input registers for all coefficients can be manually modified and
saved to flash. Alternatively, high level calibration routines can be invoked. These routines automatically
determine the coefficients for common parameters and save them to flash memory. The different types of
compensation parameters include:
• Voltage: gain and offset for voltage sense circuit
• Current: gain and offset for current sense circuit
• Phase: voltage-to-current phase offset introduced by transformer or filters in sense circuits
• Temperature: offset for junction temperature at room temp
• Temperature: coefficients for temperature curve
• RMS and Power offset: fixed offsets for voltage and current and power at light loads
The calibration routines compensate for sensors and system inaccuracy. The new coefficients computed
during calibration can be stored in the on-chip flash.
In order to perform a calibration, an external stable AC source (Voltage/Current) and AC load are
required. The calibration routines have a target voltage and current (Register Itarget) used for all phases
to match. The target calibration voltage and current values are specified in the registers Vtarget and
Itarget.
A
Neutral
B
C
VC VB VA IAP IAN IBP IBN ICP ICN V3
P3
A
A
Neutral
B
C
78M6631
AC SOURCE
AC
LOAD
AC
LOAD
AC
LOAD
NOTE: ONE OR MORE
PHASES CAN BE
CALIBRATED
SIMULTANEOUSLY
D
/Y
Figure 8. 3-Phase System Calibration Test Setup Example