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This means that CHI is used as the triggering signal when
investigating the length of time by which the signal of CH2
is delayed from the signal of CHI. CH2 is used in the
reversed case. In other words, the signal leading in phase is
selected as the triggering signal source.
If this process is reversed, the portion to be measured may
sometimes not appear on the screen. Thereafter, equalize
the amplitudes of the two signals appearing on the screen or
superimpose one on another.
Read the time difference by the interval between 50% am
plitude points of the two signals.
Sometimes the superimposing method is more convenient
from the point of view of procedure.
Time
difference
J
Equalize
amplitudes
' by VAR
Time
difference
J
(a) Equal amplitude
measuring method
< CAUTIONS >
(b) Suerposition
measuring method
Since the pulsed wave contains many high-frequency wave
components (higher harmonics) depending on its width or
period, pay the same attention as given to high frequency
signals when handling it. Accordingly, use a probe or coax
ial cable and shorten the earth lead wire as much as possible.
(5) Measurement of rise (fall) time
To measure the rise time pay attention not only to the
abovementioned items but also to measurement error.
The following relationship exists between the rise time Trx
of the waveform to be measured, the rise time Trs of oscil
loscope, and the rise time Tro displayed on the screen.
Tro = V Trx^ + Trs^
When the rise time of the pulse going to be measured is
sufficiently longer than the rise time of the oscilloscope
(7ns in our case), the effect of the rise time of the oscil
loscope on the measurement can be neglected. However, if
both are close to each other, measurement error may be
caused.
The true rise time is given by
Trx^
Tro^ - T rs^
Moreover, in general, in a circuit free from waveform dis
tortion such as overshoot and sag, the following relation
ship is established between frequency band and rise time.
22
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