71M6515H
A Maxim Integrated Products Brand
Energy Meter IC
DATA SHEET
JULY 2011
Subtract 8 from 7:
9.
E60 − E300 = 2AXV AXI tan(60)sin(φS )
use equation 5:
E0 + E180 + 2
cos(φS )
10.
E60 − E300
=
tan(60)sin(φS )
11.
E60 − E300 = (E0 + E180 + 2) tan(60) tan(φS )
(E60 − E300
tan(60)(E0 + E180 + 2)
)
φS = tan−1
12.
Now that we know the AXV, AXI, and φS errors, we calculate the new calibration voltage gain coefficient from the previous ones:
CAL _V
CAL _VNEW
=
AXV
We calculate PHADJ from φS, the desired phase lag:
tan(φS )
[
1+ (1− 2−9 )2 − 2(1− 2−9 )cos(2πf0T)
]
PHADJ = 220
(1− 2−9 )sin(2πf0T) − tan(φS )
1− (1− 2−9 )cos(2πf0T)
Finally, we calculate the new calibration current gain coefficient, including compensation for a slight gain increase in the phase
calibration circuit.
CAL _ I
1
CAL _ INEW
=
2−20 PHADJ(2 + 2−20 PHADJ − 2(1− 2−9 )cos(2πf0T))
AXI
1+
1− 2(1− 2−9 )cos(2πf0T) + (1− 2−9 )2
Alternative Calibration Procedures
It is possible to implement a fast calibration based on only one measurement with a zero-degree load angle. Details can be
found in the TERIDIAN Application Note AN_651X_022 (Calibration Procedures).
Calibration Procedure for Rogowski Sensor
Rogowski coils generate an output signal that is the derivative of the input current. The 6515H Rogowski module implemented
in the Rogowski CE image digitally compensates for this effect and has the usual gain and phase calibration adjustments.
Additionally, calibration adjustments are provided to eliminate voltage coupling from the sensor input.
Current sensors built from Rogowski coils have relatively high output impedances that are susceptible to capacitive coupling
from the large voltages present in the meter. The most dominant coupling is usually capacitance between the primary of the
coil and the coil’s output. This coupling adds a component proportional to the derivative of voltage to the sensor output. This
effect is compensated by the voltage coupling calibration coefficients.
As with the CT procedure, the calibration procedure for Rogowski sensors uses the meter’s display to calibrate the voltage
path and the pulse outputs to perform the remaining energy calibrations. The calibration procedure must be performed to each
phase separately, making sure that the pulse generator is driven by the accumulated real energy for just that phase. In other
words, the pulse generator input should be set to WhA, WhB, or WhC, depending on the phase being calibrated. The IC has to
be configured for Rogowski mode (IMAGE=01). In preparation of the calibration, all calibration parameters are set to their
default values. VMAX and IMAX are set to reflect the system design parameters. WRATE and PULSE_SLOW, PULSE_FAST are
adjusted to obtain the desired Kh.
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