Tektronix 1A2 Instruction Manual page 8

Operating Instructions—Type 1A2
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Fig. 2-1. Chopped-mode waveforms: (A) trace broken up into
segments, (B) chopped-mode switching action from channel to
channel, and (C) switching transients blanked out.
set the trigger controls for + external triggering. Both Chan-
nel 1 and 2 should display the calibrator waveform. Each
waveform should be 2 cm in amplitude.
NOTE
If the waveforms are not exactly 2 cm in amplitude,
overlook the inaccuracy until completing this oper-
ating procedure. Subsequent paragraphs describe
how to properly set the gain of the unit.
14. Set the MODE switch to ADD. There should be one
waveform display 4¢cm in amplitude. This is the addition
of the Channel 1 and 2 signals (2cm each), Notice that
only the Channel 1 POSITION control will move the display
vertically.
15. Pull out the Channel 1 PULL TO INVERT switch and
free run the time base. The display should be a straight
2-2
line, indicating the algebraic difference between the two
signals. Since both signals have equal amplitudes and wave-
shape, the difference is zero.
NOTE
If the display is not a straight line, this indicates
that the gains of the channels are not matched.
This may be overlooked until this operating pro-
cedure is completed. Subsequent paragraphs
describe how to properly set the gain of each
channel.
Before the Type 1A2 is used for accurate measurements,
the GAIN and VAR ATTEN BAL for each channel should be
adjusted. These adjustments are described in the following
paragraphs.
Gain Adjustments
The gain adjustments should be checked periodically to
assure correct vertical deflection factors, particularly when
the Type 1A2 is used for the first time or is moved from one
oscilloscope to another. Use the following procedure to
check the gain of each channel:
1. Set the applicable Type 1A2 front-panel controls for
both channels as follows:
AC-DC-GND DC
VOLTS/CM .05
PULL TO INVERT Pushed in
POSITION Centered
VARIABLE CALIBRATED
MODE CH 1
TRIGGER SELECTOR CH 1
2. Set the oscilloscope sweep rate and triggering controls
for a 0.1 msec/cm free-running sweep.
3. Apply a 0.2-volt peak-to-peak signal from the oscillo-
scope calibrator through a coaxial cable to the Channel 1
Input connector.
NOTE
For maximum accuracy use a calibrator signal
source which has an amplitude accuracy of better
than 3%.
4. The resulting display should be exactly 4m in ampli-
tude. If not, set the Channel 1 GAIN for the correct wave-
form amplitude. (Use the Channel 1 POSITION control to
align the display with the graticule markings.}
5. Set the MODE switch to CH 2 and apply the calibrator
signal to the Channel 2 input connector.
6. The display should be exactly 4cm in amplitude. If
not, adjust the Channel 2 GAIN contro! for the proper display
amplitude. Use the Channel 2 POSITION control to align the
display with the graticule markings.
7. Disconnect the calibrator signal.