Determining Frequency; Risetime Measurements - Tektronix 7B70 Time Base Instruction Manual

Operating Instructions-7B70 (SN B205000 and Up)
Substituting the given values:
6. Set the TIMEIDIV switch to the fastest sweep rate
that displays less than eight divisions between the 10% and
5 X 0.1 ms
90% points on the waveform.
Time Duration =
1
The time duration is 0.5 milliseconds.
Determining Frequency
The time measurement technique can also be used to
determine the frequency of a signal. The frequency of a
periodically recurrent signal is the reciprocal of the time
duration (period) of one complete cycle.
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:
7. Determine the 10% and 90% points on the rising por-
tion 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).
TABLE 2-1
Risetime Measurements
Vertical vertically
display
(divisions)
4
)
0.4 and 3.6 divisions
1
3.2
5
1
0.5 and 4.5 divisions
1
4.0
6 0.6 and 5.4 divisions
1
4.8
-
8. Adjust the horizontal POSITION control to move the
10% point of the waveform to the center measurement
area. For example, with a five-division display as shown in
Fig. 2-1 1, the 10% point is 0.5 division up from the start of
the rising portion.
1
Frequency
=
-
-
- -
I -
2 kilohertz
time duration 0.5 ms
9. Measure the horizontal distance between the 10% and
90% points. Be sure the A VARIABLE control i s set to
Risetime Measurements
CAL.
R isetime measurements employ basically the same
techniques a s time-duration measurements. The main differ-
ence is the points between which the measurement i s made.
The following procedure gives the basic method of
measuring 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, Corlnect the signal to either Vertical plug-in.
10. Multiply the distance measured in step 9 by the
setting of the TIMEIDIV switch. If sweep magnification is
used, divide this answer by 10.
Example. Assume that the horizontal distance between
the 10% and 90% points i s three divisions (see Fig. 2-1 1)
and the TIMEIDIV switch is set to 1 ps with the MAG
switch set to X10. Applying the time duration formula to
risetime:
2, Set the MODE switch to display the plug-in used.
horizontal
distance
x
TIMEIDIV
Time Duration = (divisions) setting
3. Set the VOLTSIDIV switch and the VARIABLE con-
( Risetime)
trol to produce a signal an exact number of divisions in
magnification
amplitude.
Substituting the given values:
4, Center the display about the center horizontal line
with the vertical POSITION control.
Risetime
=
3 x 1 ~ s
10
5. Set the Triggering controls to obtain a stable display.
The risetime is 0.3 microsecond.
Scans by ArtekMedia O 2006