7 Technical specifications
69
Δ
ph
= 100 (1-
sin(φ-Δφ)
sinφ
) [%]
,
sin φ ≠ 0
In both formulas,
means the actual phase shift angle between the current and voltage com-
ponents, and
means the total phase error for a given frequency. The conclusion which can be
drawn from these relationships is that power measurement uncertainty for the same phase error
very clearly depends on the displacement power factor between current and voltage. It is shown in
Fig. 24.
Fig. 24. Additional uncertainty from phase error depending on phase shift angle.
Example
Calculation of measurement uncertainty of active power fundamental
component.
Conditions:
= 60
, U
RMS
U
nom
, I
RMS
= 5% I
nom
.
Fundamental uncertainty equals
±√1.0
2
+ Δ
ph
2
%
.
For the 0..200Hz frequency range, the PQM-700 phase error is < 1
. After
substituting to the equation:
𝛥
𝑝ℎ
= 100 (1 −
𝑐𝑜𝑠(𝜑+𝛥𝜑)
𝑐𝑜𝑠𝜑
) = 100 (1 −
𝑐𝑜𝑠(61°)
𝑐𝑜𝑠(60°)
) = 3,04%
then, the measurement uncertainty is:
𝛿 = ±√1,0
2
+ 3,04
2
= ±3,20%
Under the same conditions, but with the phase shift
= 10
, we will ob-
tain:
𝛥
𝑝ℎ
= 100 (1 −
𝑐𝑜𝑠(11°)
𝑐𝑜𝑠(10°)
) = 0,32%
and the measurement uncertainty is:
𝛿 = ±√1,0
2
+ 0,32
2
= ±1,05%
The above calculations do not take into account additional errors caused
by used clamps and transducers.
Summary of Contents for PQM-700
Page 85: ...85 Notes...
