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App-26
IM 760301-01E
Appendix 6 Setting the Measurement Period
The measurement period must be set properly to make correct measurements on this
instrument. There are two cases for setting of the measurement period depending on the
data update rate.
• When the data update rate is set to 50 ms, 100 ms, 5 s, 10 s, or 20 s
The measurement period must be set.
• When the data update rate is set to 250 ms, 500 ms, 1 s, or 2 s
The measurement period does not have to be set.
Details of each case are given below.
When the Data Update Rate Is Set to 50 ms, 100 ms, 5 s, 10 s, or 20 s
The WT3000 detects the period of the selected input signal using the frequency
measurement circuit (see section 2.1). The measurement period is the integer multiple of
this period. The WT3000 determines the measured values by taking the average of the
sampled data in the measurement period. The selected input signal for defining the
measurement period is called synchronization source.
Thus, the measurement period is automatically set inside the WT3000 by specifying the
synchronization source. This computation method is referred to as Average for the
Synchronous Source Period (ASSP). This method is effective for short data update rates
and for efficient measurement of low-frequency signals.
Select the signal to be the synchronization source from the choices below.
U1, I1, U2, I2, U3, I3, U4, I4, Ext Clk (external clock), or None
*
The selectable items vary depending on the installed elements. For the specifications of the
Ext Clk (external clock), see section 12.7.
For example, if the synchronization source for input element 1 is set to I1, an integer
multiple of the period of I1 becomes the measurement period. By averaging the sampled
data in this measurement period, the WT3000 computes the measured values for input
element 1 such as U1, I1, and P1.
• Deciding on Which Input, Voltage or Current, to Use for the Synchronization Source
Select an input signal with stable input level and frequency (with little distortion) for the
synchronization source. Correct measured values can be obtained only if the period of
the synchronization source signal is detected accurately. To see whether the
frequency of the synchronization source signal is being measured correctly, display
the frequency of the selected input signal on the WT3000 according to section 5.3,
“Selecting the Frequency Measurement Source.” The input signal whose
measurement result is accurate and more stable is suitable for the synchronization
source.
For example, if a switching power supply is being measured and the distortion of
voltage waveforms is smaller than current waveforms, set the synchronization source
to the voltage signal.
Voltage
waveform
Current
waveform
Synchronization source
setting: Voltage signal
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