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IM WT1801-01EN
• Select a signal that has the same period as the signal that you want to measure the harmonics of. For
stable harmonic measurement, choose an input signal for the PLL source that has as little distortion and
fluctuation as possible. If the fundamental frequency of the PLL source fluctuates or if the fundamental
frequency cannot be measured due to waveform distortion, correct measurements will not be obtained.
When the measured item is a switching power supply and in other cases where the distortion of the voltage
signal is smaller than that of the current signal, we recommend that the PLL source be set to the voltage.
• If all of the input signals are distorted or the amplitude is small compared to the measurement range, the
specifications may not be met. To achieve stable, accurate measurements on high harmonics, set the
PLL source to an external clock signal and apply a signal with the same period as the input signal to the
external clock input connector.
• If the fundamental frequency is less than or equal to 440 Hz and the signal contains high frequency
components, we recommend that you turn the frequency filter on. This filter is only effective on the
frequency measurement circuit.
• If the amplitude level of the signal applied to the element that is specified as the PLL source is small
compared to the range, PLL synchronization may not be achieved. If the
measurement range so that the amplitude level of the PLL source is at least 50%. If the crest factor is set
to CF6, set the measurement range so that the amplitude level of the PLL source is at least 100%.
• If the frequency of the PLL source changes, correct measured values are displayed four data updates
after the change. Correct measured values may not be obtained immediately after the PLL source or its
frequency changes, because the PLL circuit inside the WT1800 redetects the frequency.
Measured Harmonic Orders (Min Order/Max Order)
The harmonic measurement range can be specified. The harmonic orders specified here are used to determine
the numeric data of the distortion factor.
Minimum Harmonic Order to Be Measured (Min Order)
Select from the following.
• 0: The 0th order (DC) component is included when numeric harmonic waveform data is determined.
• 1: The 0th order (DC) component is not included when numeric harmonic waveform data is determined. The
harmonic measurement data (the harmonic waveform data) is determined from the 1st order (the fundamental
wave).
Maximum Harmonic Order to Be Measured (Max Order)
You can select a value between 1 and 500.
However, the maximum measurable harmonic order is the smallest of the three orders listed below.
• The specified maximum harmonic order to be measured
• The value determined automatically according to the PLL source frequency (see section 6.6 in the getting
started guide, IM WT1801-03EN)
• When the data update interval is 50 ms, the maximum measurable harmonic order is 100.
The numeric data corresponding to harmonic orders above the maximum measurable harmonic order is
displayed as “-------” (no data).
• If the minimum harmonic order to be measured is set to 1, the data of the DC component is not included
when the distortion factor is determined.
• There is no overload value indication (“-OL-”) or zero indication (suppression to zero) for the numeric data
of harmonic orders 0 (DC) to 500. For information about the overload value indication (“-OL-”) and zero
indication (suppression to zero) in normal measurement, see section 6.4 in the getting started guide, IM
WT1801-03EN.
3 Harmonic Measurement Conditions (Option)
