7-2
IM WT5000-01EN
• 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 terminal.
• If the fundamental frequency of the input signal is less than the following frequencies and the input signal
contains high frequency components, we recommend that you turn on the frequency filter and set the cutoff
frequency as follows.
Fundamental Frequency of the Input Signal
Cutoff Frequency of the Frequency Filter
100 Hz or less
0.1 kHz
1 kHz or less
1 kHz
10 kHz or less
10 kHz
100 kHz or less
100 kHz
• If the amplitude level of the signal applied to the element that is specified as the PLL source is small compared
to the measurement range, PLL synchronization may not be achieved. If the
is set to CF3, set the
measurement range so that the amplitude level of the PLL source is at least 50%. If the crest factor is set to
CF6 or CF6A, 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 this instrument redetects the frequency.
Measured Harmonic Orders (Min Order/Max Order)
The harmonic measurement range can be specified for groups Hrm1 and Hrm2. 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 6.7 in the Getting
Started Guide, IM WT5000-03EN)
• When the data update interval is 50 ms or Auto, 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 (rounding to zero) for the numeric data
of harmonic orders 0 (DC) to 500. For information about the overload value indication (“-OL-”) and zero
indication (rounding to zero) in normal measurement, see sections 6.15 and 6.16 in the Getting Started
Guide, IM WT5000-03EN.
7 Harmonic Measurement Conditions
