Tektronix 47E5A

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RISETIME MEASUREMENTS
Risetime measurements use the same methods as time-
duration measurements, except the measurements are
made between the 10% and 90% points of the waveform.
Falltime is measured between the 90% and 10% points on
the trailing edge of the waveform.
Obtain a Normal Sweep Display. Set A SLOPE to +. Use
a
sweep speed setting that displays several cycles or
events (if possible) and be sure the VAR TIME/DIV control
is in the calibrated detent. Set the VOL TS/DIV switch and
VAR
control (or signal amplitude) for exactly a five/divi-
sion display. Set vertical positioning so the display bottom
touches the 0% graticule line and the display top touches
the 100% graticule line.
Set
the TIME/DIV switch for a single-event display with
the risetime spread horizontally as much as possible.
Horizontally position the display so the 10% pOint on the
waveform intersects the second vertical graticule line (see
Fig. 19).
Measure the horizontal distance between the 10% and
90% points and multiply the distance measured by the
setting of the TIME/DIV switch.
EXAMPLE: The horizontal distance between the 10%
and 90% points is 5 divisions (see Fig. 19) and the
TIME/DIV switch is set to 1 J1.s.
SIGNAL
AMPLITUD
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HORIZONTAL
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DISTANCE
Fig. 19. Risetime.
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Using the time duration formula to find risetime:
Time
Duration
(risetime)
horizontal
distance X
(divisions)
Substituting the given values:
TIME/DIV
setting
Risetime = 5 X 1 J1.S = 5 microseconds.
@
475A/OM44 Operators 39