Eliminating Common-Mode Signals - Tektronix 2247A Operator's Manual

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Basic Applications
d. Select CH 1 and CH 2 VERTICAL MODE.
e. Set TRIGGER SOURCE switch to VERT.
f. Set both VOL TS/DIV switches to produce displays of about two or
three divisions In amplitude.
g. Adjust the CH 2 VOL TS/DIV switch and VAR control so that the
CH 2 display Is about the same amplitude as the cor\-fponent to be
canceled In the CH 1 waveform (see Figure 5-9A).
5-24
CH 1 SIGNAL
WITH UNWANTED
LINE FREQUENCY
COMPONENT
CH 2 SIGNAL
FROM LINE
FREQUENCY
SOURCE
SIGNAL WITH
LINE FREQUENCY
COMPONENT
CANCELLED
- - ~ - - ... lriiri,
100
1 . .--:,... . . . . , " ,.._
,...
.
.
,: -,;,· . .
. ...
,,,_.
90 -~ - -
r--. ----
,--
.....
_..
,_
~,
'
10
/I?' ""~
_....v
"
-----
~
... ...... . .
(A) CH 1 AND CH 2 SIGNALS.
I
1°'!
90-+--+---+-+--+---+-+--+--.L-----I
~--- -----
~- ~--·--
-- --~-
-
--
--
--
1~
-+---+--+-+---+--+-+---1--'----1
r ·.
(B) RESULTANT SIGNAL.
6556-35
Figure 5-9. Eliminating common-mode signals.
2247 A Operators
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Basic Applications
h. Select ADD, and then turn on CH
2
INVERT (unless cancellation
signal Is already 180° out of phase). Turn off the CH 1 and CH 2
displays and slightly readjust the CH 2 VOL TS/DIV VAR control for
maximum cancellation of the line-frequency component ( see Figure
5-9B).
I. The SEC/DIV setting may be set to a faster sweep speed to expand
the waveform, and the display amplitude may be Increased by
advancing both VOL TS/DIV switches and readjusting the VOL TS/
DIV VAR controls as necessary to maintain cancellation of the
undesired signal component .
..J
J
224 7 A Operators
5-25