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Operating Instructions
These values are reset to zero when “1” is written to the
register. You may also reset
them to zero or load preset values by writing to these registers.
Negative Energy
The negative energy registers are exactly like the positive energy registers except they accumulate
negative energy. The reported energy values will be positive. In other words, if the WattNode
measures 1000 kWh of negative energy,
EnergyNegSum
will report 1000 (not -1000).
The negative energy registers are reset to zero (except for
EnergySumNegNR
) when “1” is writ-
ten to the
register. You may also reset them to zero or load preset values (except for
EnergySumNegNR
) by writing to these registers.
EnergyNegSum
Every second, the measured real energies for each active phase are added together. If the
result is negative, it is added to
EnergyNegSum
. If it is positive, then
EnergyNegSum
is left
unchanged.
EnergyNegSumNR
The
EnergySumNegNR
is identical to
EnergyNegPos
except that it cannot be reset to zero.
EnergyNegA, EnergyNegB, EnergyNegC
These are the per-phase negative real energy registers.
Reactive Energy
EnergyReacSum, EnergyReacA, EnergyReacB, EnergyReacC
Reactive energy is also known as kVAR-hours. Inductive loads, like motors, generate positive
reactive power and energy, while capacitive loads generate negative reactive energy. These are all
bidirectional registers that can count up or down depending on the sign of the reactive power.
The WattNode meter only measures the fundamental reactive energy, not including harmonics.
These values are reset to zero when “1” is written to the
register. You may also reset
them to zero or load preset values by writing to these registers.
Apparent Energy
EnergyAppSum, EnergyAppA, EnergyAppB, EnergyAppC
Apparent energy (kVA-hours) is the accumulation of apparent power over time. The apparent
power is essentially the RMS voltage multiplied by the RMS current for each phase. For example,
if you have 120 VAC RMS, 10 amps RMS, one phase, the apparent power will be 1200 VA. At the
end of an hour, the apparent energy will be 1.2 kVA-hour. Apparent energy is always positive.
The WattNode meter’s apparent energy includes real harmonics, but not reactive harmonics.
These values are reset to zero when “1” is written to the
register. You may also reset
them to zero or load preset values by writing to these registers.
Power Factor
The power factor is the ratio of the real power to the apparent power. Resistive loads, like incan-
descent lighting and electric heaters, should have a power factor near 1.0. Power-factor corrected
loads, like computers, should be near 1.0. Motors can have power factors from 0.2 to 0.9, but are
commonly in the 0.5 to 0.7 range.
If the power for a phase is negative, the power factor will also be negative. The reported power
factor will be 1.0 for any phases measuring zero power, and will be 0.0 for any inactive phases
(line voltage below 20% of nominal VAC).
