Ametek TR-2100, Руководство по эксплуатации, Страница: 81 / 105

TR-2100 User Manual 75
RMS Measurement
The true RMS value for every channel is generated twice per cycle. The data for one cycle
are squared and summed. The square root is taken of this value divided by the number of
samples per cycle. The number of samples per cycle will vary with the sample rate.
96
96
1
2
∑
= =
n
n
rms
V
V
Frequency Correction
Because the system frequency varies by small but finite amounts during normal operation,
uncorrected RMS and vector measurements will have an error that is a function of frequency
deviation. Since the TR-2100 measures the system frequency, it corrects for these errors.
For a frequency of 49.9 Hz the uncorrected errors are:
Amplitude error = 0.01%
Phase error = 0.7
°
Calculation of Derived Parameters
A range of fundamental quantities may be computed from the fundamental voltage and
current vectors.
Sequence components
Positive
+
− − −
= + +
1
2
3 V V a V a V
a b
−
c
−
c
−
3 Zero
0
− − −
= + +
V V V V
a b
Negative
−
− − −
= + +
1
2
3 V V a V a V
a b c
V
a
−
represents the vector form of the a phase voltage
(operator
a rotates the vector by 120
°
)