User Manual

CHAPTER 7. HARMONIC MEASUREMENT FUNCTION 34
Measurement function %r %f (7.1)
Harmonic distortion factor of voltage
U(k)
U(total)
U(k)
U(1)
(7.2)
Harmonic distortion factor of current
I(k)
I(total)
I(k)
I(1)
(7.3)
Harmonic distortion factor of active power
P (k)
P (total)
P (k)
P (1)
(7.4)
Total harmonic distortion rate of voltage
√
max
∑
k=2
U(k)
2
U(total)
√
max
∑
k=2
U(k)
2
U(1)
(7.5)
Total harmonic distortion rate of current
√
max
∑
k=2
I(k)
2
I(total)
√
max
∑
k=2
I(k)
2
I(1)
(7.6)
Total harmonic distortion rate of active power







√
max
∑
k=2
P (k)
2
P (total)

















√
max
∑
k=2
P (k)
2
P (1)










(7.7)
NOTE Total harmonics are calculated as follows: U (total) =
√
max
∑
k=0
U(k)
2
, I(total) =
√
max
∑
k=0
I(k)
2
,
P (total) =
max
∑
k=0
P (k) . “k” indicates the harmonic order, and max indicates the upper limit of analysis orders,
and the max is determined by the frequency of the PLL source automatically, at most 50.
7.3.3 PLL source
In the harmonic mode, 5335B uses a PLL to multiply the input signal fundamental. The frequency
multiplication is used as the A/D sampling clock in the instrument in order to achieve ideally synchronous
sampling. The range of the PLL source is from 10Hz to 1.2kHz. To maximize accuracy, select the cleanest
signal source available, either the voltage or the current. This improves measurement consistency and stability,
especially in relation to harmonic analysis.
If the amplitude level of the signal input into the unit as the PLL source is small relative to the range, PLL
synchronization might fail. If the crest factor is set as 3, the amplitude level of the PLL source should be greater
than 50% of the range. If the crest factor is set as 6, the amplitude level of the PLL source should be greater
than 100% of the range.
When the fundamental wave frequency is less than 200Hz, the frequency lter should be turned on. When lower
than 440Hz and containing high-frequency components, it is also best to turn on the frequency lter. This lter
only applies to the frequency measurement circuit.
If the frequency of the PLL source changes, the correct measured value will be displayed after data are updated
several times. The frequency of the PLL source needs to be tested again via the PLL circuit in the instrument in
case of changes of the PLL source or its frequency, the correct measured value will be determined afterward.
NOTE If the analysis window determined by the fundamental frequency of the PLL source is longer than the
data updating cycle, no harmonic data will be detected. In this case, the data update cycle should be lengthened.
For example, when the fundamental wave frequency of the PLL source is 10Hz (cycle: 100ms), the analysis
window is one-wave long, and the data measurement interval is 100ms. In this case, the harmonic measurement