Risetime Measurements - Tektronix 7B51 Instruction Manual

Use the following procedure:
1. Measure the time duration of one complete cycle of
the waveform as described in the previous application.
2. Take the reciprocal of the time duration to determine
the frequency.
Example. The frequency of the signal shown in Fig.
2·10 which has a time duration of 0.5 milliseconds is:
Frequency
=
time duration 0.5 ms
2 kilohertz
Risetime Measurements
R isetime measurements employ basically the same
techniques as time-duration measurements. The main differ-
ence is the points between which the measurement is made.
The following procedure gives the basic method of meas-
uring risetime between the 10% and 90% points of the
waveform. Falltime can be measured in the same manner on
the trailing edge of the waveform.
1. Connect the signal to either Vertical plug-in.
2. Set the MODE switch to display the plug-in used.
3. Set the VOL TS/DIV switch and the VARIABLE
control to produce a signal an exact number of divisions in
amplitude.
4. Center the display about the center horizontal line
with the vertical POSITION control.
5. Set the A Triggering controls to obtain a stable
display.
6. Set the TIME/DIV switch to the fastest sweep rate
that displays less than eight divisions between the 10% and
90% points on the waveform.
7. Determine the '10% and 90% points on the rising
portion of the waveform. The figures given in Table 2-1 are
for the points 10% up from the start of the rising portion
and 10% from the top of the rising portion (90% point).
®
Operating Instructions-Type 7B51
TABLE 2-1
Vertical
Divisions vertically
display 10% and 90% between 10% and
(divisions) points 90% points
4 0.4 and 3.6 divisions 3.2
5 0.5 and 4.5 divisions 4.0
6
0.6 and 5.4 divisions 4.8
8. Adjust the horizontal POSITION control to move the
10% point of the waveform to the first vertical line of the
graticule. For example, with a five-division display as shown
in Fig. 2-11, the 10% point is 0.5 division up from the start
of the rising portion.
1--
I-~
~
1,.--
~
VI'
~
'-90%
V
/
V
~10%
--
, ,
,
r
Oint
,
,
'
I '
H
. ,
k
orlzontal
~
, distance ,
Point
Fig. 2-11. Measuring risetime.
H+
9. Measure the horizontal distance between the 10% and
90% points. Be sure the A VAR IABLE control is set to
CAL.
10. Multiply the distance measured in step 9 by the set-
ting of the TlME/DIV switch. If sweep magnification is
used, divide this answer by 10.
Example. Assume that the horizontal distance between
the 10% and 90% points is four divisions (see Fig. 2-11) and
the TIME/DIV switch is set to 1 lls with the MAG switch
set to X10. Applying the time duration formula to risetime:
2-15