Operating Instructions 49
PhaseAdjustA, PhaseAdjustB, PhaseAdjustC
(1615, 1616, 1617)
For maximum accuracy, there may be cases where you wish to compensate for the phase angle
error of the current transformers you are using. The
PhaseAdjust
registers allow the phase angle
to be adjusted on each phase by up to ±8 degrees in increments of one millidegree. For example,
if your CT causes a phase lead of 0.6 degrees (or 36 minutes), you could correct for this by
setting
PhaseAdjustA
,
B
, and
C
to -600, which subtracts 600 millidegree or 0.6 degree from the
phase lead. Use negative values to compensate for a phase lead in the CT (most common). The
default adjustment is 0.
CreepLimit
(1618)
Creep refers to the situation where the wheel on an traditional electro-mechanical energy meter
moves even though there is no power being consumed. The WattNode meter has no wheel, but
all electrical systems have some noise, which can cause small readings in the absence of any
power consumption. To prevent readings due to noise, if the readings fall below the creep limit,
the meter forces the real and reactive power values to zero, and stops accumulating energy. This
is performed independently for each measurement phase using the following equation.
MinimumPower = FullScalePower / CreepLimit
Any measured power or reactive power below
MinimumPower
is forced to zero.
FullScalePower
is
defined as the nominal line-to-neutral VAC (see
-
) multiplied by
the full-scale or rated CT current.
Generally, the default value of 1500 (which sets the creep limit to 1/1500th of full-scale power)
works well. Sometime, in electrically noisy environments, you may see non-zero power readings
when the power should be zero. You can adjust the creep limit to eliminate this problem. For
example, to adjust the creep limit to 1/500th of full-scale (0.2%), set
CreepLimit
to 500.
PhaseOffset
(1619)
The WattNode meter cannot directly measure line-to-line voltages (
,
). To estimate these voltages, the meter must know the phase offset of the electrical
service being measured. This setting has no effect on any other measurements or registers and is
only needed if you plan to monitor the line-to-line voltages.
PhaseOffset
(degrees)
Electrical Service Type
0
Single-phase (all line-to-line voltages will read zero). Use this set-
ting when monitoring multiple independent branch circuits.
60
Three-phase grounded delta (grounded leg), where one phase is
connected to earth (rare)
90
Four-wire delta (wild leg): 120/208/240
120 (default)
Three-phase: 120/208, 230/400, 277/480, 347/600
180
Single-phase three-wire (mid-point neutral): 120/240
VoltAB
will report the line-to-line voltage.
VoltBC
and
VoltAC
will
report zero regardless of the actual phase C voltage.
Table 11: PhaseOffset Values
Zeroing Registers
ZeroEnergy
(1620)
Writing 1 to
ZeroEnergy
will simultaneously set all of the energy registers to zero, except those
ending in “NR” (for non-resettable). They can also be set to zero or a preset value by writing the
desired value directly to each energy register. If a
ConfigPasscode
has been set, then you must
unlock the meter before you can zero or preset the energy.
