Description:
The following describes how the PowerMaster
®
specifically calculates power according to the
user’s selections above:
TIME DOMAIN
1
In Time Domain, data is processed on a point by point basis and the results integrated over
precisely one cycle of the incoming signal. The quantities calculated are:
Calculations
V(TDRMS) - The processing properly accounts for
the exact number of samples in a cycle including
fractional data points
Active Power (Pa) – Calculation includes any DC
component as well as all frequencies in the signal
up to the cutoff frequency of 32 kHz.
∑∑
−=
=
−=
=
•===
1
0
2
1
1
0
2
1
Ni
i
i
N
Ni
i
i
N
rmsrms
IVIVVASa
Apparent Power (Sa) - Calculation includes any
DC component as well as all frequencies in the
signal up to the cutoff frequency of 32 kHz.
Reactive Power (Qa) – There is not a good
formulation in the time domain for directly
computing Q. We have adopted the approach of
computing it from the “Power Triangle”
assumption.
FREQUENCY DOMAIN
2
In Frequency Domain (FFT), every 2048 data points a complete Fourier analysis is performed.
The user has control over the maximum number of harmonics to be included in the analysis as
well as the ability to set a threshold which can exclude harmonics whose amplitude is below the
user set threshold (see Section 13.9.1
). While time domain calculations of power quantities yield
energy directly because they are integrals, Fourier calculations deliver average rates over the
time interval of the analysis.
According to Fourier’s Theorem any periodic signal can be represented in the following manner:
( )
∑
∞
=
++=
1
)()(
2
)( 00
0
n
tnSinbtnCosa
a
tV
nn
ωω
The PowerMaster
®
calculates
,
and
for n = 0 to 100. Given these parameters we can
calculate any of the quantities of interest as follows:
Rev 1.5 132
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