Tektronix 442, Instruction Manual

Page: 29 / 170

Operating Instructions—442 Service
measurement points (see Figure 2-14). The MAGNIFIER
may be set to X10 (button in) to expand the display when
measuring portions of more complex waveforms. If this
technique is employed, the final time duration figure in
step 9 must be divided by ten.
Frequency Measurements
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 cycle.
6. Adjust the vertical POSITION control to move the
display measurement points to the center horizontal
graticule line.
7. Adjust the horizontal POSITION control to center
the display within the center 8 graticule divisions.
8. Measure the horizontal distance between the time
measurement points. Verify thattheSEC/DIVVARcontrol
is set in the calibrated detent (fully cw).
9. Multiply the distance measured in step 8 by the
setting of the SEC/DIV switch.
EXAMPLE: Assume the distance between time
measurement points is 5 divisions (see Figure 2-14) and
the SEC/DIV switch is set at .1 m.
Use the following procedure:
1. Measure the time duration of one cycle of waveform
as described in the previous application.
2. Calculate the reciprocal of the time duration to
determine the frequency.
EXAMPLE: The frequency of the signal shown in
Figure 2-14, which has a time duration of 0.5 millisecond,
is calculated as follows:
Frequency =
time duration 0.5 ms 0 . 5 X 1 0 4
Using the formula:
horizontal SEC/DIV
Time Duration = distance X settjng
(divisions)
Substitute given values:
Time Duration = 5 X 0.1 m
The time duration is 0.5 millisecond.
(2 3 7 3 - 1 4 ) 2 3 7 4 - 7 1
Figure 2-14. Measuring the time duration between points on a
waveform.
Risetime Measurements
Risetime measurements are made in the same manner
as time duration measurements, except the
measurements are made between the 10% and 90% points
of the waveform amplitude (see percentage markings on
the left edge of the graticule).
Use the following procedure to measure risetime:
1. Adjust the VOLTS/DIV switch and VAR control for a
display amplitude of exactly 5 divisions.
2. Adjust the vertical POSITION control so that the
display bottom just touches the 0% graticule line and the
display top j ust touches the 100% graticule li ne (see Figure
2-15).
3. Measure the horizontal distance (divisons) between
the 10% and 90% points on the waveform (point Ato point
B, Figure 2-15).
Use the following formula to find risetime:
Risetime =
horizontal
distance
(divisions)
SEC/DIV
setting
2 -1 4
REV A MAY 1980