Applications— Type 1A1
6. Apply the reference signal to Channel 1 and the sig
nal to be compared to Channel 2. Use coaxial cables or
probes having equal delay.
7. Set the oscilloscope Trigger Slope switch to externally
trigger on the signal.
8. Set the oscilloscope time-base controls for a calibrated
sweep rate which will allow accurate measurement of the
distance between the two waveforms.
9. Measure the horizontal distance between the reference
waveform and the Channel 2 waveform (see Fig. 3-3).
Fig. 3 -3 . Measuring time delay between pulse waveforms.
10. Multiply the distance measured for each channel by
the setting of the oscilloscope Time/Cm switch to obtain the
apparent time interval.
11. To obtain the actual time interval, divide the apparent
time interval by the amount of sweep magnification, if
sweep magnification is used, and by 1 if no sweep mag
nification is used. The formula is as follows:
Time Delay
(Time/Cm switch setting) (Distance in cm)
Sweep Magnification
For example, assume that the Time/Cm switch setting
is 2
[is,
the Magnifier is set for 5 X magnification, and there
is a horizontal distance of 3 cm (as shown in Fig. 3-3)
between the leading edge of the reference waveform and
the leading edge of the waveform displayed by Channel
2. Then, substitute these values in the preceding formula:
_.
_ ,
(2 us) (3 cm)
Time Delay = —
---------- = 1.2 //s
o
Phase Measurements
Phase comparison of two signals of the same frequency
can be made using the dual-trace feature of the Type 1A1.
To make the comparison, proceed as follows:
1. Follow the procedure outlined in the first seven steps
under Time-Difference Measurements.
2. Set the oscilloscope sweep rate to obtain a display
of less than 1 cycle of the waveform.
Fig. 3 -4 . Measuring phase shift between electrical waveforms.
3. Adjust the VARIABLE VOLTS/CM controls for each
channel so the waveform amplitudes are equal and fill
the graticule area vertically. Reset the VOLTS/CM switches,
if necessary, to obtain equal-amplitude waveform displays.
(Equal amplitudes are used to make comparisons easier.)
4. Use the POSITION controls to center the waveforms
vertically; that is, an equal distance each side of the grati
cule centerline.
5. Turn the oscilloscope Variable Time/Cm control coun
terclockwise until 1 cycle of the reference signal occupies
9 cm horizontally. Use the Trigger Slope and Triggering
Level controls to trigger on the reference waveform at any
3-4
Fig. 3-5. Computing the phase shift when the oscilloscope sweep
range is increased 5X.
