71M6521 Demo Board User’s Manual
Revision 2.18
© 2005-2009 TERIDIAN Semiconductor Corporation
Page: 59 of 111
Figure 2-7: 71M6521 with Shunt and CT
Calibrating for Shunt Resistor (Channel A):
1. Calculate
IMAX
for the shunt resistor (
IMAX_SHUNT
). This can be done by using the following
formula:
IMAX_SHUNT
= Vi
MAX
/R
SH
The Vi
MAX
value is the maximum analog input voltage for the channel, typically 177mV (RMS), and
R
SH
is the resistance value of the shunt resistor.
The value obtained for
IMAX_SHUNT
is stored at the MPU address 0x0A, using the command
)A=
IMAX_SHUNT
of the Demo Code supplied by TERIDIAN.
2. Compute
WRATE_SHUNT
based on
IMAX_SHUNT
and
VMAX
and the formula given in 1.8.2:
WRATE_SHUNT
= (
IMAX_SHUNT
*
VMAX
* 47.1132) / (Kh * In_8 *
N
ACC
* X)
Use
VMAX
= 600V (RMS) for the 6521 Demo Board if the resistor divider for VA has not been
changed.
3. Update the
WRATE
register (at CE address 0x11) with
WRATE_SHUNT
, using the command
]11=
WRATE_SHUNT.
4. Test for accuracy at 15A, 240V at phase angle 0, phase angle 60° and at phase angle –60°.
5. Apply the error values to the calibration spreadsheet (revision 2.0 or later) and determine the
calibration factors for channel A, i.e.
CAL_IA
,
CAL_VA
, and
PHADJ_A
.
6. Update the CE registers 0x08, 0x09 and 0x0E of the compute engine with the calibration factors
obtained from the spreadsheet, using the commands
]8=
CAL_IA,
]9=
CAL_VA
, and
]E=
PHADJ_A
.
7. Retest for accuracy at several currents and phase angles.
At this point, channel A is calibrated.
WSUM
will be based on the voltage applied to the meter and the current
flowing through the shunt resistor. The pulses generated will be based on the parameters entered for
channel A.
IA
VA
IB
LOAD
LIVE
NEUT
CT
SHUNT
V3P3
71M6511
71M6521