Tektronix 2235A Instruction Manual page 41

Operatlng lnstructlons
-
2235A
lnstructlon
frequency limit of the vertical deflection system. To make
a phase comparison, use the following procedure:
1. Preset instrument controls and obtain a baseline
trace, then set the A & B SOURCE switch to CH 1.
2. Set both Input Coupling switches to the same
position, depending on the type of input coupling
desired.
3. Using either probes or cables with equal time
delays, connect a known reference signal to the
Channel 1 input and the unknown signal to the
Channel 2 input.
4. Select BOTH Vertical MODE; then select either ALT
or CHOP, depending on the frequency of input
signals. The reference signal should precede the
comparison signal in time.
5. If the two signals are of opposite polarity, press
INVERT button to invert the Channel 2 display.
6. Set both VOLTSIDIV switches and both Variable con-
trols so the displays are equal in amplitude.
7. Adjust the A TRIGGER LEVEL control for a stable
display.
8. Set the A SECIDIV switch to a sweep speed which
displays about one full cycle of the reference
waveform.
'.
9. Position the displays and adjust the SECIDIV
Variable control so that one reference-signal cycle
occupies exactly 8 horizontal divisions at the 50%
rise-time points (see Figure 2-1 8). Each division of
the graticule now represents 45" of the cycle (360"
s
8 divisions), and the horizontal calibration can be
stated as 45" per division.
CHANNEL 1
CHANNEL 2
MEASURE
TlME FROM
@
TO
@
HORIZONTAL
DIFFERENCE
I
I
8
DIVISIONS
, I
I
(360°)
I
4207-19
Figure 2-17. Phase difference.
Substituting the given values into the phase
difference formula:
Phase difference = 0.6 div x 45"Idiv
=
27"
More accurate phase measurements can be made by
using the XI 0 Magnifier function to increase the sweep
speed without changing the SECIDIV Variable control
setting.
EXAMPLE: If the sweep speed were increased 10
times with the magnifier (XI0 Magnifier knob out),
the magnified horizontal calibration would be
45°/division divided by 10 (or 4.5OIdivision). Figure
2-18 shows the same signals illustrated in Figure
2-17, but magnifying the displays results in a
horizontal difference of 6 divisions between the two
signals.
10. Measure the horizontal difference between corre-
sponding points on the waveforms at a convenient
horizontal graticule line and calculate the phase dif-
ference using the following formula:
horizontal horizontal
Phase
=
difference
x
calibration
Difference (divisions)
(degldiv)
Example: The horizontal difference is 0.6 division
with a graticule calibration of 45" per division, as
shown in Figure 2-1 7.
Figure 2-18. High-resolution phase difference.
Scans by ARTEK MEDLQ =>
CHANNEL
1
(REFERENCE)
CHANNEL 2
MEASURE
TlME FROM
@
TO
@
- t
0,
.
j ,
HORIZONTAL
, j
DIFFERENCE
4207-20
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