71M6515H
Energy Meter IC
DATA SHEET
MARCH 2008
WH_A (0x00), WH_B (0x01), WH_C (0x02)
These registers hold the real energy collected during the previous accumulation interval. The magnitude of the values is
determined by:
VMAX IMAX
LSB = 9.4045⋅10−13
Wh
In _8
Example: The register WH_A reads the value 236,675 for one accumulation interval of one second. Assuming
600V for VMAX, 208A for IMAX, and unity gain, we determine the real energy to be:
E = 236,675*600*208*9.4045*10-13 Wh = 0.0277781Wh.
By multiplying with 3,600, we get 100Wh/h, which means the applied power is 100W.
FREQ_DELTA_T (0x11)
This register holds frequency and temperature information in two bytes each.
Bits 31-16: These bits (FREQUENCY) represent the frequency of the input signal selected with the F_SELECT bit of the
CONFIG register. One LSB is equivalent to 0.1Hz.
MAIN_EDGE_CNT (0x35)
This register holds the number of zero crossings of the input phase selected by the F_SELECT bits in the CONFIG register
detected in the previous accumulation interval. The value in MAIN_EDGE_CNT can be used by the host to correct its own
RTC or to synchronize events to the line voltage.
Registers Controlling Alarms and Thresholds
CREEP_THRSLD (0x1D)
The four bytes written to this register determine the creep threshold. Setting a creep threshold helps suppressing I2H, Wh
and VARh readings when the values of WSUM and VARSUM are determined to be below the creep threshold.
Example: The creep threshold of a meter operating with an accumulation interval of 1000ms is to be configured
to be 15mA at 240V. The meter is using a VMAX of 600V, an IMAX of 208A, and is not using the additional gain
of 8. The numerical value for the CREEP_THRSLD register is to be determined.
With 15mA, the power per phase will be 3.6W, or 0.001Wh per second. With the LSB of WSUM readings given
as 9.4045*10-13*VMAX*IMAX [Wh], we determine the value to:
n = 0.001Wh / (9.4045*10-13*VMAX*IMAX /In_8 Wh) = 8520.2
The rounded down value of 8520 is written to the CREEP_THRSLD register.
SAG (0x2E)
This register holds the voltage and timing threshold for sag detection.
Bits 15-0: These bits (SAG_CNT) hold the sag count. A sag condition must persist for at least SAG_CNT samples before a
sag alarm is generated. The allowed range is 1 to (215-1), and the default is 80 (31.7ms). The time period defined by
SAG_CNT is:
T = SAG_CNT*397μs
Bits 31-16: These bits (SAGTHR) hold the voltage threshold that is to be applied for sag detection. The peak voltage must
exceed SAGTHR once each SAG_CNT samples in order to prevent a SAG warning. One LSB is defined as:
LSB = 7.8798 ⋅216 ⋅10−9 VMAX
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