71M6515H Datasheet, PDF (41/57 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6515H
Energy Meter IC
DATA SHEET
MARCH 2008
IASQFRACT (0x4A), IBSQFRACT (0x4B), ICSQFRACT (0x4C)
These read-only registers hold the difference between the 10-bit residual squared current sum of the current accumulation
interval and the 10-bit residual squared current sum of the previous interval. If IASQSUM, IBSQSUM, or ICSQSUM are
used to calculate current, the value obtained over several accumulation intervals will be accurate due to averaging, but the
individual values will have a higher uncertainty than when using IASQFRACT, IBSQFRACT, and ICSQFRACT.
The most accurate calculation of the squared current for a phase X (IXSQ) uses the formula:
IXSQ = IXSQSUM + 2^-10 IXSQFRACT
INSQFRACT (0x4D)
This register holds the difference between the 10-bit residual squared neutral currents of the current accumulation interval
and the 10-bit residual squared neutral currents of the previous interval. The value can be used to improve the accuracy of
the squared neutral current reading by applying the formula:
INSQ = INSQSUM + 2^-10 INSQFRACT
INSQSUM (0x3C)
This register holds the sum of the square of the calculated neutral current collected during the previous accumulation
interval. The calculation is implementing the following equation:
INSQSUM = _∑ (I 0 + I1+ I 2)²
The magnitude of the accumulated samples is determined by:
LSB = ^{IMAX 2} 9.4045 ⋅10^−13 A² h
In _ 8²
IPHASE_ABC (0x0F)
This register holds voltage-to-current phase information for all three phases. Positive phase means lagging current
(inductive load). One LSB is equivalent to 1 degree. The range is from (2⁸ – 1) to –(2⁸ – 1). Since the phase calculation
involves the post-processor, these registers will not be functional when the CE_ONLY bit in the CONFIG register is set.
Bits 8-0: These bits (IPHASE_C) represent the voltage-to-current phase angle in phase C.
Bits 17-9: These bits (IPHASE_B) represent the voltage-to-current phase angle in phase B.
Bits 26-18: These bits (IPHASE_A) represent the voltage-to-current phase angle in phase A.
IRMS_A (0x0C), IRMS_B (0x0D), IRMS_C (0x0E)
These registers hold the post-processed RMS current for each phase. Only the 16 most significant bits are used. The
magnitude of the values is determined by:
LSB = ^{6.8781⋅10−9 IMAX}
A rms
In _ 8 SUM _ CYCLES
Since the RMS calculation involves the post-processor, these registers will not be functional when the CE_ONLY bit in the
CONFIG register is set. If higher precision is required, the host must calculate the RMS currents from the values in the
IASQSUM, IBSQSUM, and ICSQSUM registers. For even higher precision, the IASQFRACT, IBSQFRACT, ICSQFRACT
registers should be used.
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