App-24
IM 760201-01E
As another example, if an inverter is being measured and the distortion of current
waveforms is smaller than voltage waveforms, set the synchronization source to the
current signal.
Voltage waveform
Current waveform
Synchronization
source setting
: Current signal
Zero crossing
• The rising (or falling) zero crossing is the time when the synchronization source
passes through level zero (the center of the amplitude) on a rising (or falling) slope.
The measurement period on the WT500 is between the first rising (or falling) zero
crossing and the last rising (or falling) zero crossing in the data update interval.
•
The WT500 determines whether to define the measurement period using the rising
or falling zero crossing automatically by choosing the method that will result in the
longest measurement period.
Data update interval
Measurement period
Synchronization
source
Rising zero crossing
Falling zero crossing
When the Period of the Synchronization Source Cannot Be Detected
If there is not more than one rising or falling zero crossing on the input signal set as the
synchronization source within the data update interval, the period cannot be detected.
Also, the period cannot be detected if the AC amplitude is small. (See “Accuracy”
under “Frequency Measurement” in Section 14.6, “Functions” for information about the
detection levels of the frequency measurement circuit.) If this happens, the entire data
update interval becomes the measurement period, and the sampled data of the entire
period is averaged.
Data update interval
Measurement period
Because of the reasons described above, the measured voltage and current values may
be unstable. If this happens, lower the data update rate so that more periods of the input
signal fit within the data update interval.
Appendix 5 Setting the Measurement Period
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