Time Duration Measurements; Determining Frequency - Tektronix 7B51 Instruction Manual

Operating Instructions-Type 7851
Horizontal
Conversion
Factor
2.19 milliseconds
. 2 X 8
1.37
Then, with a TIME/DIV switch setting of 50 ]..Is, the
repetition rate of an unknown signal which completes one
cycle in seven horizontal divisions can be determined by
using the repetition rate formula (step
6):
Repetition
Rate
50 ]..Is X 1.37 X 7
=
480 ]Js
This answer can be converted to frequency by taking the
reciprocal of the repetition rate (see application on Deter-
mining Frequency Measurements).
Time-Duration Measurements
To measure time between two points on a waveform, use
the following procedure:
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 to display about four
divisions of the waveform.
4. Set the A Triggering controls to obtain a stable
display.
5. Set the TIME/DIV switch to the fastest sweep rate
that displays less than eight divisions between the time
measurement points (see Fig. 2-8). (See the topic entitled
Horizontal Sweep Rate in this section concerning non-
linearity of first and last divisions of a display.)
6. Adjust the vertical POSITION control to move the
points between which the time measurement is made to the
center horizontal reference line.
7. Adjust the horizontal POSITION control to position
the time-measurement points within the center eight
divisions of the graticule.
8. Measure the horizontal distance between the time
measurement points. Be sure the A VARIABLE control is
set to CAL.
2-14
9. Multiply the distance measured in step 8 by the set-
ting of the TIME/DIV switch. If sweep magnification is
used, divide this answer by 10 .
Example. Assume that the distance between the time
measurement points is five divisions (see Fig. 2-10), and the
TIME/DIV switch is set to .1 ms with the magnifier at XL
Using the formula:
Time Duration
=
horizontal
distance
(divisions)
X
TIME/DIV
setting
magnification
Substituting the given values:
Time Duration
=
5XO.1 ms
The time duration is 0.5 milliseconds.
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Fig. 2-10. Measuring the time duration between points on a
waveform.
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.
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