Tektronix 2A63 Instrument Reference Book page 25

Type 2A63
position from l mVOLTS through .2 VOLTS and to about
+50 volts when the VOLTS/DIV. switch is set at .5, 1, or
2 VOLTS. In the 5, 10, and 20 VOLTS positions of the
VOLTS/DIV. switch, the common-mode signal at the INPUT
connectors may be as high as +500 volts.
For best results, the signal or signals to be displayed
should always be applied through a shielded cable, with
the shield connected to the chassis of both the oscilloscope
and the signal source. All leads and cables should be kept
as short as practicable.
High impedance attenuator probes are available for use
with the Type 2A63 module. These probes reduce the re-
sistive and capacitive loading effects of the module and, at
the same time, attenoate the signal to allow the display of
larger signals than would otherwise be possible. These
probes and other accessories are described in the Acces-
sories section of the oscilloscope manual.
Displaying a Signal
To display a signal with the Type 2A63 module, pro-
ceed as follows:
1. Connect the signal to one or both INPUT connectors as
described in the foregoing paragraphs.
2. Establish a common ground between the oscilloscope
and the signal source. This can be done by connecting the
ground clip on a Tektronix attenuator probe to signal
ground.
3. Adjust the time-base controls to obtain a stable dis-
play.
4. Set the VOL TS/DIV. switch and the POSITION control
so that the signal is placed as desired on the graticule. In
general, if you are interested only in the ac component of
the signal, you should set the appropriate AC-DC-GND
switch to AC; if you are interested in the de level of the
signal, you should set the appropriate AC-DC-GND switch
to DC. An exception to this is in observing low-frequency
signals. When the AC-DC-GND switch is in the AC posi-
tion, and the AC STABILIZED switch is in the OFF position,
the lower bandpass limit (3-db point) of the module is about
r
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~-
-
-
r
-
~--
......
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-
-
----
1.5 cps. Therefore, when displaying signals with frequency
components of less than about 2 cps (0.2 cps when using a
1 OX attenuator probe), the best response will be obtained
with the AC-DC-GND switch in the DC position.
When looking at ac signals of very small amplitude (less
than about l O millivolts), you may wish to use the AC
STABILIZED switch to eliminate de drift in the oscilloscope
trace. Placing this switch in the ON position introduces ac
coupling into the amplifier whenever the VOLTS/DIV. switch
is in one of its five most sensitive positions (1 mVOL TS
through 20 mVOLTS). This prevents small de drift conditions
in the Input Amplifier of the module from causing trace
shift on the screen. When the VOLTS/DIV. switch is at
1 mVOLTS and the AC STABILIZED switch is ON, the lower
bandpass limit (3-db point) of the module is about 10 cps.
Note that the small neon lamp to the left of the AC
STABILIZED switch lights when either AC-DC-GND switch
is in the DC position while the AC STABILIZED switch is ON.
This is to warn the operator that the amplifier is ac coupled
when the VOL TS/DIV. switch is in one of its five most
sensitive positions, even though the AC-DC-GND switch is
in the DC position. (The light can be ignored if the
VOLTS/DIV. switch is not in one of these positions.) If you
wish to measure de levels in one of the five most sensitive
positions of the VOL TS/DIV. switch, you must set the
AC
STABILIZED switch to OFF.
Probe Compensation
If an attenuator probe is used, its input time constant must
be compensated to that of the module for best signal
response. It is advisable to check the compensation of the
probe each time it is used. To compensate a Tektronix
attenuator probe, proceed as follows:
1. Connect the probe to the INPUT connector with which
it will be used, and touch the probe tip to the CAL. OUT
connector.
2. Set the oscilloscope controls to display several cycles
of the Calibrator waveform, as shown in Fig. 4.
3. Adjust the variable capacitor in the body of the probe
to obtain a square leading corner on the positive half-cycle
--
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Under-compensated Properly compensated
Over-compensated
Fig. 4. Probe compensation waveforms.
2