78M6610+LMU Data Sheet
Power Calculations
This section describes the detailed flow of power calculations in the 78M6610+LMU. Generic equations
for AC power measurement are listed in the table below.
Register
Description
Time Scale
PA
PB
Instantaneous Active Power
1 sample
PQA
PQB
Instantaneous Reactive Power
Average Active Power (P)
WATT_A
WATT_B
WATT_C
VAR_A
VAR_B
VAR_C
Average Reactive Power (Q)
Apparent Power (S)
Power Factor
1 interval
VA_A
VA_B
VA_C
PFA
PFB
PFC
NOTE: WATT_C, VAR_C and VA_C outputs are always scaled by a factor of 0.5.
Active Power (P)
The instantaneous power results (PA, PB) are obtained by multiplying aligned instantaneous voltage and
current samples. The sum of these results are then averaged over N samples (accumulation time) to
compute the average active power (WATT_A, WATT_B), and the aggregate average power (WATT_C).
N-1
PA_SUM
If |x|< |y|
z = 0
VA
IA
x
z
N
N
X
PA
PB
∑
n=0
WATT_A
WATT_C
y
+
PA_OFFS
N-1
∑
PB_SUM
VB
IB
If |x|< |y|
z = 0
X
x
z
WATT_B
n=0
y
PB_OFFS
Figure 21. Active Power Computation
The value in the Px_OFFS register is the “Power Offset” for the power calculations. Full scale values in
the Px_OFFS register are subtracted from the magnitude of the averaged active power. If the resulting
active power value results in a sign change, zero watts are reported.
31
Rev 0
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
