Frequency Measurement; Risetime Measurement - Tektronix 1S1 Instruction Manual

Operating Instructions – Type 1S1
6. Measure the horizontal distance between the point of
interest on the second waveform and the vertical reference
line obtained with the first waveform.
7. Determine the time interval between the two points in
the manner described previously.
Fig. 2-20 is a double-exposure photograph illustrating
the measurement of time comparison between points on two
waveforms. In the example, the horizontal deflection of
6.28 cm multiplied by the sweep rate of 5 nsec/cm gives a
time difference of 31.4nsec. Since the time window starts
at the left edge of the crt screen, the 50% level of the
waveform to the left in the display occurs 31.4nsec earlier
in time than the 50% level of the waveform to the right.
Fig. 2-20. Double-exposure of crt display for making time-
comparison measurement between points on two different
signals. Example: 6.28 cm X 5µsec/cm = 31.4µsec.

Risetime Measurement

The risetime of a pulse or signal is measured with the
time-interval method. Unless otherwise specified, the rise-
time is measured between the 10% and 90% levels of the
signal rise. Use the following procedure:
1. Set the TIME/CM switch so the rise will cover several
cm horizontally. Leave the Time/Cm VARIABLE control at
CAL position.
2. With the TIME POSITION control, position the pulse
rise near the center of the crt screen.
3. Set the mVOLTS/CM switch and mVolts/Cm VARI-
ABLE control to produce some even number of centimeters
of vertical deflection.
4. Measure the horizontal distance between the 10% and
90% levels on the pulse rise. Table 2-5 gives the vertical
deflection measurement between the 10% and 90% levels.
TABLE 2-5
Risetime Deflection Guide
Total Cm of
Deflection
4 cm
5 cm
6cm
2-26
Deflection Between
10% and 90% Points
3.2 cm
4.0 cm
4.8 cm
For example, if the horizontal distance between the 10%
and 90% points is 4.8 cm (see Fig. 2-21), and the sweep rate
is 0.1 nsec/cm, the risetime of the pulse is equal to 4.8 cm
multiplied by 0.1 nsec/cm, or 0.48 nsec (480 psec).
Fig. 2-21. Risetime measurement.
Example: 4.8 cm X 0.1 nsec/cm = 0.48 nsec, or 480 psec.

Frequency Measurement

Since the frequency of any repetitive signal is equal to the
reciprocal of its period (time interval of 1 cycle), the fre-
quency can be calculated directly from the time interval of
one cycle. If, for example, the period of a repetitive wave-
form is measured to be 105 nsec (see Fig. 2-22), the fre-
quency of the signal is 1/105 nsec, or 9.5 Mc.
Fig. 2-22. Frequency measurent using relation f = 1 /period.
Example: 5.25 cm X 20 nsec/cm = 105 nsec.
1
= ×
9 5 . 10
105 n sec
Another method of determining frequency that is some-
times easier and faster to use is obtained by dividing the
average number of cycles displayed per cm by the sweep
rate of the display (see Fig. 2-23). To use this method, de-
termine the frequency as follows:
6 =
9 5 . Mc