MI 2892 Power Master
Theory and internal operation
160
Instrument has 3 different counters sets:
1.
Total counters
TOT
are used for measuring energy over a complete recording. When recorder
starts it sums the energy to existent state of the counters.
2.
Last integration period
LAST
counter measures energy during recording over last completed
interval. It is calculated at end of each interval.
3.
Current integration period
CUR
counter measures energy during recording over current time
interval.
Start of
Recording
Recording Intervals
1
2
3
m
m -1
Last interval
Current interval
Current
Time
LAST
CUR
Total Energy
TOT
Figure 5.7: Instrument energy counters
5.1.8
Harmonics and interharmonics
Standard compliance: IEC 61000-4-30 Class A (Section 5.7)
IEC 61000-4-7 Class I
Calculation called fast Fourier transformation (FFT) is used to translate AD converted input signal to
sinusoidal components. The following equation describes relation between input signal and its
frequency presentation.
FFT
Voltage harmonics and THD
10 periods
t
n
1 2 3 4 5 6
50
U
FFT
10 periods
t
n
1 2 3 4 5 6
50
I
Uhn
Ihn
Current harmonics and THD
Figure 5.8: Current and voltage harmonics
