1745
Users Manual
38
Measurement Theory
The following are the equations used by the Logger and PQ Log to produce the
results you see in PQ Log. Measurement Function A logs current and voltage
harmonics, while Measurement Function P does not:
TRMS value of voltage
and current. Basic values
on 200 ms per phase
∑
=
=
N
i
i
bas
V
N
V
1
2
.
1
∑
=
⋅
=
N
i
i
bas
I
N
I
1
2
1
N: Number of samples in 200 ms intervals (2048)
RMS value of voltage and
current per logging
interval per phase
∑
=
=
M
j
basj
RMS
V
M
V
1
2
.
1
∑
=
⋅
=
M
j
j
bas
RMS
I
M
I
1
2
1
M: Number of samples in 200 ms intervals per
logging interval
Active power calculated
from FFT from samples of
voltage and current. Basic
value on 200 ms per phase
n
n
n
n
I
V
P
ϕ
cos
.
.
=
V
n
: RMS value of voltage harmonics of order n
I
n
: RMS value of current harmonics of order n
n Order of the harmonics
φ
n
: Phase angle between current and voltage
harmonics of order n
P
n
: Harmonics of the active power of order n
Fundamental
∑
=
=
50
1
n
n
bas
P
P
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