Appendix 7 Supplemental Technical Information
A20
If the signal to be measured changes too fast relative
to the sampling period, beginning at a certain fre-
quency, non-existent slow signal fluctuations are re-
corded. This phenomena is aliasing.
With the Memory function, the sampling period can be
significantly affected by the timebase setting, so care
is necessary to avoid aliasing when selecting the
timebase.
Because the timebase determines the measurement
frequency limit, the fastest possible timebase setting
should be used.
When the signal can be recorded repeatedly, the
auto-ranging function
(p. 76) may be used to select
the optimum timebase.
Displaying waveforms by their sampled values with
adequate resolution of characteristics such as sine
wave peaks requires a minimum of about 25 samples
per waveform period.
The measurement frequency limit is determined by
the timebase.
Aliasing
Measurement Frequency Limit
Sampling Period
Actual Input
Signal
Sampling Points
Measured Waveform
Aliasing occurs when the sampling
period is longer than half of the input
signal period.
One Signal Period
2
3
23
24
25
1
Timebase
[/div]
Sampling
period
Measure-
ment limit
frequency
Timebase
[/div]
Sampling
period
Measure-
ment limit
frequency
Timebase
[/div]
Sampling
period
Measure-
ment limit
frequency
100 μs
200 μs
500 μs
1 ms
2 ms
5 ms
1 μs
2 μs
5 μs
10 μs
20 μs
50 μs
40 kHz
20 kHz
8 kHz
4 kHz
2 kHz
800 Hz
10 ms
20 ms
50 ms
100 ms
200 ms
500 ms
100 μs
200 μs
500 μs
1 ms
2 ms
5 ms
400 Hz
200 Hz
80 Hz
40 Hz
20 Hz
8 Hz
1 s
2 s
5 s
10 s
30 s
1 min
2 min
5 min
10 ms
20 ms
50 ms
100 ms
300 ms
600 ms
1.2 s
3 s
4 Hz
2 Hz
0.8 Hz
0.4 Hz
0.13 Hz
0.067 Hz
0.033 Hz
0.013 Hz
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