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t
NEGATIVE
REFERENCE
LINE
-----------
-- --
J
VERTICAL
DEFLECTION
.....
..........
.
-----
,----
POSITIVE
REFERENCE LINE
MEASURE POSITIVE
AMPLITUDE
TO
OR NEGATIVE AMPLITUDE
TO
4732·08
Figure
4-2.
Instantaneous
voltage measurement.
10.
Calculate the instantaneous
voltage,
using the fol-
lowing formula:
lnstanta-
neous
Voltage
vertical
deflection x polarity x
(divisions)
(
+
or
-
)
VOLTS/DIV
switch setting
indicated by 1 X
(or 1
OX
when 1
OX
probe is used)
EXAMPLE: The measured
vertical
deflection from the
reference line is 4.6 divisions (see Figure 4-2), the wave-
form point is above the reference
line,
a 1
OX
attenuator
probe is being used, and the VOLTS/DIV switch is set to
2 V (at 1
OX
PROBE setting).
Substituting the given values:
Instantaneous Voltage
=
4.6 div x (
+
1) x 2 V/div
=
9.2 V.
Algebraic Addition
With the VERTICAL MODE switches set
to
BOTH and
ADD, the waveform displayed is the algebraic sum of
the
signals applied to the Channel
1
and Channel 2 inputs (CH 1
+
CH 2). If
the
Channel
2 INVERT button is pressed
in,
the
waveform displayed is
the
difference between the signals
applied to the Channel 1 and Channel 2 inputs (CH 1
-
CH
2). When both VOLTS/DIV switches are set to the same
deflection
factor,
the
deflection factor in the ADD mode is
equal to the deflection factor indicated by either VOLTS/DIV
switch.
The following general precautions should be observed
when using the ADD
mode.
Operating
Procedures-2215A
Operators
a. Do not exceed the input voltage rating of the
oscilloscope.
b. Do not apply signals that exceed the equivalent
of
about eight times the VOLTS/DIV switch
settings,
since large voltages may distort the display. For
ex-
ample,
with a VOLTS/DIV switch setting of 0.5
V,
the
voltage applied to that
channel
should
not
exceed ap-
proximately 4
volts.
c. Use
Channel
1 and Channel 2 POSITION
control
settings which most nearly position the signal on each
channel to midscreen, when viewed in either CH 1 or
CH 2 VERTICAL
MODE.
This ensures the greatest
dynamic range for ADD mode operation.
d. To attain similar response from each
channel,
set
both the Channel
1
and Channel 2 Input Coupling
switches to the same position.
Common-Mode
Rejection
The following procedure shows
how
to eliminate
un-
wanted ac input-power frequency components. Similar
methods could be used either to eliminate other unwanted
frequency components or
to
provide a de offset.
1
.
Preset instrument controls and obtain a baseline
trace.
2.
Apply the signal containing the unwanted
line-
frequency components
to
the CH 1 input connector.
3.
Apply
a line-frequency signal to the CH 2 input con-
nector. To
maximize
cancellation,
the
signal
applied to
Channel 2 must be
in
phase with the unwanted
line-
frequency component on the Channel 1 input.
4.
Select
BOTH and ALT VERTICAL MODE and set
both
VOLTS/DIV
switches to produce displays of approxi-
mately 4- or 5-divisions in amplitude.
5.
Adjust either VOLTS/DIV switch and VOLTS/DIV
Variable control so that both display signals are the same
amplitude.
6.
Adjust
the CH 2 VOLTS/DIV switch and CH 2
VOLTS/DIV Variable
control
so that the Channel 2 display is
approximately the same amplitude as the undesired portion
of
the
Channel 1
display
(see Figure 4-3A).
4-3
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