YOKOGAWA WT500 User Manual page 343

Appendix 5
Voltage waveform
Current waveform
IM 760201-01E
Setting the Measurement Period
To make correct measurements on the WT500, you must set its measurement period
properly.
The WT500 uses its frequency measurement circuit (see section 2.1 for details) to detect
the period of the input signal that is selected using the measurement period setting (see
section 4.7 for details). The measurement period is an integer multiple of this detected
period. The WT500 determines the measured values by averaging the data sampled
in the measurement period. The input signal used to define the measurement period is
called the synchronization source.
The measurement period is automatically set inside the WT500 when you specify the
synchronization source.
You can select the synchronization source signal from the choices listed below.
U1, I1, U2, I2, U3, I3, Ext Clk (external clock), and None
* The selectable items vary depending on the installed elements. For the Ext Clk (external
clock) specifications, see section 14.6.
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 WT500 computes the measured values for input
element 1, such as U1, I1, and P1.
Deciding Whether to Use Voltage or Current Input as the Synchronization
Source
Select an input signal with a stable input level and frequency (with little distortion) for the
synchronization source. Correct measured values can only be obtained 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, follow the procedure
in section 5.14, "Selecting What Frequency to Measure," to display the frequency of the
selected input signal on the WT500. The most suitable synchronization source is the
input signal whose measurement results are the most accurate and stable.
For example, if a switching power supply is being measured and the voltage waveform
distortion is smaller than the current waveform distortion, set the synchronization source
to the voltage signal.
1
2
3
4
5
6
7
8
9
10
11
12
Synchronization
source setting
: voltage signal
13
14
App
Index
App-23