Metrix CX 1651

170
DC POWER uncertainty
Uncertainty of DC power can be calculated from the following formula:
d P = √ ( dU
2
+ dI
2
+ 0.01
2
) [%]
where dP is uncertainty of output power [%]
dU is uncertainty of set voltage [%]
dI is uncertainty of set current [%]
DC ENERGY uncertainty
Depends on voltage, current, time values. The best uncertainty is 0.016 %.
ACV uncertainty
See table of ACV uncertainty.
ACI uncertainty
range % value + % range max. voltage [V]
2 mA – 20 mA
0.05 + 0.010
3
20 mA – 200 mA
0.05 + 0.005
3
200 mA - 2 A
0.05 + 0.005
3
2 A – 10 A
0.05 + 0.010
1.5
PHASE uncertainty
frequency range [Hz]
phase uncertainty d
ϕ
[
°
]
40 – 200
0.15
200 – 400
0.25
AC POWER uncertainty
Uncertainty of AC power can be calculated from the following formula:
for active power d P = √ ( dU
2
+ dI
2
+ dPF
2
+ 0.03
2
) [%]
for reactive power d P = √ ( dU
2
+ dI
2
+ dPF*
2
+ 0.03
2
) [%]
for apparent power d P = √ ( dU
2
+ dI
2
+ 0.03
2
) [%]
where dP is uncertainty of power [%]
dU is uncertainty of set voltage [%]
dI is uncertainty of set current [%]
dPF is uncertainty of power factor (cosϕ) [%]
For calculation of dPF is valid following formula:
dPF = (1 – cos (ϕ+dϕ)/cos ϕ) * 100 [%]
where ϕ is set phase shift between voltage and current outputs
dϕ is uncertainty of set phase shift in table above
dPF* is uncertainty of of sinϕ [%]
For dPF* is valid following formula:
dPF* = (1 – sin (ϕ+dϕ)/sin ϕ) * 100 [%]
Example:
Set parameters: U = 100 V, I = 10 A, cos ϕ = 0.5, f = 50 Hz, displayed value of active power in W
Output voltage uncertainty: dU = 0.025 % value + 0.010 % range = 0.045 %
Output current uncertainty: dI = 0.10 % value + 0.03 % range = 0.7 %
Uncertainty due the set phase shift: PF 0.5 corresponds phase shift 60 °
dPF = (1 – cos (60+0.15)/cos 60) * 100 = (1 – 0.4977/0.5) * 100 = 0.45 %
Output power uncertainty: dP = √ ( 0.045
2
+ 0.7
2
+ 0.45
2
+ 0.03
2
) = 0.95 %