Harmonic Measurement Function
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6.3.2 Distortion factor
Distortion is either calculated relative to the fundamental (%f) or to the total signal (%r). Internally, the 5335B calculates
according to the following equations:
Measurement function
%r
%f
Harmonic distortion factor of voltage
𝑈(𝑘)
𝑈(𝑡𝑜𝑡𝑎𝑙)
𝑈(𝑘)
𝑈(1)
Harmonic distortion factor of current
𝐼(𝑘)
𝐼(𝑡𝑜𝑡𝑎𝑙)
𝐼(𝑘)
𝐼(1)
Harmonic distortion factor of active power
𝑃 (𝑘)
𝑃 (𝑡𝑜𝑡𝑎𝑙)
𝑃 (𝑘)
𝑃 (1)
Total harmonic distortion rate of voltage
√
𝑚𝑎𝑥
∑
𝑘=2
𝑈(𝑘)
2
𝑈(𝑡𝑜𝑡𝑎𝑙)
√
𝑚𝑎𝑥
∑
𝑘=2
𝑈(𝑘)
2
𝑈(1)
Total harmonic distortion rate of current
√
𝑚𝑎𝑥
∑
𝑘=2
𝐼(𝑘)
2
𝐼(𝑡𝑜𝑡𝑎𝑙)
√
𝑚𝑎𝑥
∑
𝑘=2
𝐼(𝑘)
2
𝐼(1)
Total harmonic distortion rate of active power
∣
√
𝑚𝑎𝑥
∑
𝑘=2
𝑃 (𝑘)
2
𝑃 (𝑡𝑜𝑡𝑎𝑙)
∣ ∣
√
𝑚𝑎𝑥
∑
𝑘=2
𝑃 (𝑘)
2
𝑃 (1)
∣
Table 6.3
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.
6.3.3 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 filter should be turned on. When lower than
440Hz and containing high-frequency components, it is also best to turn on the frequency filter. This filter 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 time is
approximately more than or equal to 150ms (data measurement interval and data processing time). Therefore, select
the data update rate of 250ms or more for measurement and display of harmonic data.
