71M6515H
Energy Meter IC
DATA SHEET
MARCH 2008
Example: A meter operating at 50Hz and 240V (RMS) is supposed to apply a sag threshold of 180V (RMS) for
at least four periods before a sag warning is issued. VMAX is 600V. Which values are to be selected for SAG?
Four periods translate to T = 4 * 20ms = 80ms. This means that
SAG_CNT = T/397μs = 202.
180V (RMS) translate to 255V (peak), so SAGTHR is determined by
255
255
SAGTHR =
=
= 823
7.8798 ⋅216 ⋅10−9 600
LSB
START_THRESHLD (0x40)
This register holds the voltage and current thresholds that apply to the calculation of frequency, zero crossings, voltage
phase and energy values. If the current is below the value stored in I_START, calculation of RMS current, and energy (Wh,
VARh and VAh) is suppressed.
Bits 15-0: These bits (I_START) hold the threshold to be applied for under-current. If ISQSUM< I_START, all post-
processed values are set to zero for that phase. This includes reported values for Wh, VARh, VAh, IRMS, VPHASE,
IPHASE, PULSER, PULSEW, PULSE3 and PULSE4. This applies only if CREEP_THRSLD is not set to zero. One LSB is
defined as:
IMAX 2
LSB =
⋅9.4045 ⋅10−13 A2h
In _8
Elements with ISQSUM< I_START will set the creep bits in the STATUS register.
Bits 31-16: These bits (V_START). hold the threshold to be applied for under-voltage. If VRMS<V_START, the values for
frequency (register FREQ_DELTA_T), zero crossings (register MAIN_EDGE_CNT), and voltage phase (register
V_PHASE_ABC) are set to zero. Additionally, if VRMS< V_START, the reported value of VRMS is set to zero. One LSB is
defined as:
LSB = VMAX 2 ⋅216 ⋅9.4045 ⋅10−13 V 2 h
Elements with VRMS< V_START will not set the creep bits in the STATUS register.
VI_PTHRESHOLD (0x17)
This register holds the threshold for over-voltage and over-current alarms.
Bits 15-0: These bits (I_PTHRESHOLD) hold the threshold to applied for over-current alarm. The threshold comparison is
applied to the upper 16 bits of the values in IRMS: One LSB is defined as:
450.76 ⋅10−6 IMAX
LSB =
Arms
In _8 SUM _ CYCLES
Bits 31-16: These bits (V_PTHRESHOLD). hold the threshold to applied for over-voltage alarm. The threshold comparison
is applied to the upper 16 bits of the values in VRMS One LSB is defined as:
450.76⋅10−6VMAX
LSB =
V rms
SUM _ CYCLES
Example: A meter designed with VMAX=600V and IMAX=208A is supposed to apply an overvoltage threshold
of 520V (RMS) and an over-current threshold of 400A (RMS). Which values are to be selected for
V_PTHRESHOLD and I_PTHRESHOLD?
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