Tektronix SC 502, Инструкция по эксплуатации

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Multl�trace Phase Difference Measurement
Phase
comparison between
two
or more si g nals of the
same frequency can be made u
s
i n g both vertical i n put
channels.
This
method of phase difference
measurement
can be
used up to
the freq uency limit
of
the vertical
system .
To
make
the comparison.
use the
followi ng
procedure:
1 . Set
the
AC-G ND-DC
switches
of
the am plifier
channels
to
either
AC
or
DC.
2.
Set
the
MODE
switch to either CHOP or ALT.
I n
general ,
CHOP is
more
suitable
for l ow-frequency signals
and t he AL T position is more suitable f or high-freq uency
signals.
More
i nformation
on determ i n i ng the mode
is
given under Vertical Displays i n thi s section.
3.
Se
t
th e triggering
switches
to tri gger the
d
i spla y on
channel 1
or channel 2, whichever
channel provides the
most stable and correct
triggeri ng for
both channels.
4.
Connect
the reference si g nal to the channel 1 input
con nector and co
m
p
a
riso n signal to the c
h
a n ne l 2 input
connector.
The
reference sig nal
should precede
the
comparison signal
in
time.
Use
coaxi al cables or
probes
that
have similar
time-del ay
characteri stics
to con nect
the
signals
to the input connectors.
5. If
the si gnals are of opposite polarity due
to 1 80°
p
h a s e
difference. take
this i nto account i n t he fi nal
cali bration.
6 . Set the
channel
VOL TS/DI V
switches
and
the
variable
VOL TS/ D I V controls
so the
displays are
equal
and about five divisions i n am plitude.
7.
Set the
triggeri ng control s to obtai n a stable
di splay.
Set
the
SECONDS/DIV switch
to a sweep rate that
displays about one cycle of
the
waveform.
8.
Move the waveforms to the center of the graticule
w i t
h the channel
POSITION
controls.
9.
Turn
the variable
SECONDSIDIV
control
until
one
cycle of
the reference
signal (chan nel l ) occupies exactly
eight divisions
between
the second and tenth vertical li nes
of
the graticule (see Fig. 2-8) .
Each
division of the
grati cule
represents 45°
of
the
cycle (360°
-:-
8
divisi ons
=
45°
Idivisio n ) .
The
s w e e p rate
can be
stated i n
terms of
de g re e s as 45° Idivision.
@
MAY 1 980
Operating Instructlons-SC 502
Ch.nnel 1
(reference)
Ch.nnel 2
("gging)
HorlZOngl
dlat.nce
•
•
•
I
I
8 Dlvislona
•
(360° )
---4'�
1
Fig. 2-8.
urlng ph
..
e dlHerence.
1 878-4
10.
Measure the hori zontal
difference between cor­
respondi ng poi nts
on the waveforms.
11.
M ulti ply the measured distance ( i n divisi ons) by
45°/division
(sweep
rate)
to obtai n the exact amount of
phase difference.
EXAM PLE:
Assume
a
hori zontal difference
of 0.6
d
i
v
i
sio n with a sweep rate of 45° Idl visi on as show n i n Fig.
2-8. Use the formula:
Phase horizontal
sweep
rate
D
i
ffer
- =
difference
X
(degreesl
=
(0.6) (45° )
=
27°
ence
(divisions) di visions)
The
phase
difference is 27° .
High Resolution Phase Measurement
More accurate
dual-trace
phase
measurements can be
made by increasing the sweep rate
(without
changi ng the
variable SECONDS/DIV
control
setting).
One of the
easiest
ways to
increase
the sweep
rate i s with the X l 0
sweep m agnifier.
EXAMPLE:
If
the
sweep
rate
were
increased 1 0 times
with
the
mag nifier,
the
m
a g n i
fi
e
r
sweep rate shoul d be
45° Idivision ";-
1 0
=
4.5° Idivision. Fig.
2-9
shows
the
sam e
signals
as used
in Fig.
2-8,
but
with
t
h e
Xl0 SWP MAG
control pulled
out. With a horizontal difference
of
si x
divisi ons,
the phase
difference
is:
magnified
Phase horizontal sweep
Differ-
=
difference
X
rate
= (6) (4.5° )
=
27°
ence (divisions) (degreesl
division)
The phase difference Is 27°
.
2·1 3