METREL MD 9235 Bedienungsanleitung Seite 10

MD 9235 Clamp Meter Series
In ACA function, activating the Hz function during significant measurements can get the
most appropriate trigger level to avoid electrical noises in most cases. Activating the Hz
function at AC 40.00A range (before making significant measurements) can get the
lowest trigger level (highest sensitivity).
HOLD mode
When any function is auto-selected or manual-selected, press HOLD
momentarily toggles to Hold mode. The annunciator "
the display for later viewing.
Notes on Displacement Power Factor & Total Power Factor
Introduction: Power is the rate of change of energy with respect to time (in terms of
voltage V and current A). Instantaneous (real) power w = vi where v is the
instantaneous voltage and i the instantaneous current. The average (real) power is the
mean of vi and is given by:
W = /2 vi dt , over the interval from 0 to 2 /
Displacement Power Factor (more traditional): Assuming V and A are pure sinusoidal
waveforms without harmonics (as in most traditional cases), that is, v = V sin t and i = I
sin ( t - ), the expression can be simplified to:
W = 1/2 x V x I x Cos where V and I are the peak values,
power factor angle, and Cos is the displacement power factor. Using RMS values, it is
written as:
W = V x A
rms
Practically, in such cases without harmonics,
current A to the voltage V. An inductive circuit is said to have a lagging power factor
since current A lags voltage V (phase-shift angle
capacitive circuit is said to have a leading power factor since current A leads voltage V
(phase-shift angle
Total Power Factor (encountering harmonics): When encountering distorted waveforms
with the presence of harmonics, however, the simplified power expression should not be
used since substituting the above mentioned pure sinusoidal V and A functions cannot
fulfill the actual conditions. Cosine of phase-shift angle (Cos ), or the displacement
power factor, is no longer the only component constituting the overall power factor.
Harmonics do increase apparent power and thus decrease the overall power factor.
That is, the Total Power Factor is actually affected by both phase-shift angle and
harmonics, and is given by the expression:
Total Power Factor (PF) = Real Power (W) / Apparent Power (VA)
In order to improve overall system power factor, nowadays power-system engineer
needs to address both phase-shift and harmonics problems. Practically, harmonics
should be dealt with (e.g. filtering out) before phase-shift to be corrected (e.g. installing
capacitors in parallel with inductive loads).
x Cos
rms
and thus Sin are both "-").
" turns on. Hold mode freezes
is also called the phase-shift angle of the
and thus Sin are both "+"), and a
10
Operation
button
is the displacement