Tektronix 502A, Instruction Manual

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Operating Instructions —Type 502A
Magnifier
To expand a particular part of the display horizontally,
first use the Horizontal POSITION Control to position
the desired part of the display to the center of the
graticule. Then turn the HORIZONTAL DISPLAY switch to the
magnification desired. The portion of the display at the
center of the graticule will then be expanded 2, 5, 10, or
20 times depending on the setting of the HORIZONTAL
DISPLAY switch. At the same time, the SWEEP MAGNIFIER
ON indicator lamp will light, indicating that the display has
been expanded. Any portion of the original unmagnified
display can then be shown by rotating the Horizontal POSI­
TION Control.
HORIZONTAL
DISPLAY
HORIZONTAL
Fig. 2-9. Magnified sweep. The portion of the waveform at the
vertical centerline remains stationary as the sweep is magnified.
The displayed waveform is expanded left and right from the center-
line. The lower waveform is a two times magnification of the upper
waveform.
In magnified sweep operation, the sweep rate is multiplied
by the magnification. This means that the time per centi­
meter indicated by the TIME/CM switch must actually be
divided by the magnification to obtain the correct time re­
quired for the sweep to move one centimeter. For example,
if the TIME/CM switch is set at 5 mSEC, and the magnifier is
set at X5, the true time per centimeter is 5 milliseconds
divided by 5, or 1 millisecond per centimeter.
Magnified sweep rates are all calibrated within 3% ac­
curacy so long as their true time per centimeter is 1 mico-
second or more. Sweep rates faster than this are uncali­
brated and may be nonlinear. The SWEEP MAGNIFIER UN­
CALIBRATED indicator lamp lights whenever the maximum
calibrated sweep rate is exceeded, to indicate that the sweep
is uncalibrated.
X-Y Operation
On the Type 502A, it is possible to horizontally deflect
one or both of the spots across the screen by means of some
externally derived waveform, rather than by means of the
internal sweep circuits. This permits the oscilloscope to
be used for either single or dual-beam X-Y curve tracing.
For single-beam applications where equal horizontal
and vertical-deflection factors are desirable, the UPPER
BEAM amplifier can be switched to the crt horizontal deflec­
tion plates by placing the HORIZ DEF PLATE SELECTOR
switch at the UPPER BEAM AMP position. This type of opera­
tion provides .1 mVOLTS PER CM to 20 VOLTS PER CM sen­
sitivity and differential input for both horizontal and vertical
deflection. The LOWER BEAM is used for vertical deflection
while the UPPER BEAM is automatically positioned off the
screen while waiting for an input signal. A panel light
indicates when the UPPER BEAM amplifier is connected to
the horizontal deflection plates.
For dual-beam X-Y applications, an external waveform can
be applied to the horizontal amplifier by connecting the
waveform to the EXTERNAL Horizontal Input Connector. The
horizontal deflection sensitivity is controlled by the setting of
the HORIZONTAL DISPLAY switch, which has a maximum
sensitivity of .1 v/cm. The HORIZ DEF PLATE SELECTOR
switch must be in TIME BASE AMP position for dual-beam
X-Y applications.
Voltage Measurements
Accurate voltage measurements
of inputs to the vertical
amplifiers can
be made using the calibrated deflection fac­
tor feature of the Type 502A. The following instructions
tell you how to use the oscilloscope for this purpose and
how to obtain the greatest possible accuracy in your mea­
surements. It is important that proper techniques be used
in order that errors are not introduced in the results.
During voltage measurements, you should always display
the waveform across as much of the crt face as is possible
since, as a general rule, the accuracy of your measurements
will increase as the vertical size of the displayed wave­
form is increased. In measuring voltages, it is important
to remember that the width of the trace may be an appreci­
able part of the overall measurement and care should be
used that the trace width is not included in the vertical de­
flection readings
you obtain. You should consistently make
all readings from one side of the trace. If the bottom side
of the trace is used for one reading, it should be used for
all succeeding readings.
NOTE
Make sure the VARIABLE SENSITIVITY Control is
in the CALIBRATED position prior to any vertical
measurements, unless you have calibrated the
instrument with the VARIABLE SENSITIVITY control.
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