5.5 Manipulating the Data
The 2105 directly measures the voltage, current and power used by a single-phase system.
Volt-Amperes (VA), Reactive Volt-Amperes (VAR), power factor (PF), and phase angle (
φ
) are
not displayed but can easily be calculated from the voltage, current and power measurements.
The following paragraphs describe the methods for calculating VA, VAR, PF, and
φ
.
5.5.1 VA, VAR, PF and
ϕ
The relationships between VA, Watts, VAR, PF and
φ
can best be described in a graphical
manner. Figure 5-6 illustrates these relationships. VA is calculated by multiplying the true RMS
voltage and true RMS current measurements of the digital power analyzer. PF is the cosine of
the angle between VA and Watts and can be calculated using basic trigonometry. VAR is
calculated from VA and Watts using Pythagorean's theorem. Phase angle (
φ
) may be calculated
after the power factor has been determined. The relative phase (in degrees) between the
voltage and current waveforms is the anti-cosine (cos
-1
) of the power factor.
Figure 5-6
𝑉𝐴
=
𝑇𝑅𝑀𝑆
𝑉𝑂𝐿𝑇𝑆
∙ 𝑇𝑅𝑀𝑆
𝐴𝑀𝑃𝑆
𝑉𝐴𝑅
=
�𝑉𝐴
2
− 𝑊
2
𝑉𝐴
=
�𝑉𝐴𝑅
2
− 𝑊
2
𝑊
=
�𝑉𝐴
2
− 𝑉𝐴𝑅
2
21
