78M6610+LMU Data Sheet
Energy Calculations
Energy calculations are included in the 78M6610+LMU to minimize the traffic on the host interface and
simplify system design. Low-rate power measurement results are multiplied by the number of samples
(DIVISOR) to calculate the energy in the last accumulation interval. Energy results are summed together
until a user defined “bucket size” is reached. When every bucket of energy is reached, the value in the
energy counter register is incremented by one.
All energy counter registers are low-rate 24-bit output registers that contain values calculated over
multiple accumulation intervals. Both import (positive) and export (negative) results are provided for active
and reactive energy.
Register
Description
PA_POS_CNT
PB_POS_CNT
Positive Active Energy Counter
PA_NEG_CNT
PB_NEG_CNT
Negative Active Energy Counter
Positive Reactive Energy Counter
Negative Reactive Energy Counter
Apparent Energy Counter
PQA_POS_CNT
PQB_POS_CNT
PQA_NEG_CNT
PQB_NEG_CNT
SA_CNT
SB_CNT
Energy results are cleared upon any power down or reset and can be manually cleared by the user using
the CONTROL register. The CYCLES register can be used to detect device resets (loss of energy data)
or to track time between energy reads. A bit in the STATUS register also indicates when a reset has
occurred.
Bucket Size for Energy Counters
The BUCKET register allows the user to define the unit of measure for the energy counter registers. It is
an unsigned 48-bit fixed-point number with 24 bits for the integer part and 24 bits for the fractional part.
High Word
Low Word
Bit Position 23
22
…
…
2
22
1
21
0
20
.
23 22
2-1 2-2
21
2-3
20
2-4
…
1
0
Value
223 222
…
2-23 2-24
The units should be set large enough to keep the accumulators and counters from overflowing too
quickly. To increment the energy counters in watt-hours for example, the value in BUCKET should be
equal to the number of seconds in an hour (3600) multiplied by the Sample Rate (4000) and divided by
Full Scale Watts (VFSCALE x IFSCALE).
3600푠 ∗ 4000푆/푠
푊푎푡푡ℎ표푢푟푠 (푊ℎ) =
푉퐹푆퐶퐴퐿퐸 ∗ 퐼퐹푆퐶퐴퐿퐸
Full Scale Watts is defined by the sensors being used (see the Scaling Registers section). As an
example, if the voltage sources are 400 volts-peak at full scale (VFSCALE) and the currents are 30 amps-
peak at full scale (IFSCALE), then full scale watts would be 12000 watts (VFSCALE x IFSCALE). The
bucket value can be saved to flash memory as the register default.
34
Rev 0
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
