Basic Applications - Tektronix 3A6 Instruction Manual

Operating Instructions—Type 3A6
NOTE
The TRIGGER switch should be pushed in to obtain
the triggering signal from the algebraically added
signal only. If pulled out, the time base will be
triggered by the undesired signal and may result
in an unstable display.
In addition to common-mode rejection applications as
described above, the ADDED mode can be used for differen-
tial applications (signal addition and subtraction}, de offset
or other applications. An example of the use of de offset
would be a low-frequency signal on a large de level that
could not be positioned on the display area. Ac coupling
cannot be used because the input time-constant would distort
the signal. However, the ac signal could be displayed using
de coupling if the de level were not present. The de level
can be effectively removed by applying a de offset voltage
to one channel and the signal to the opposite channel. With
the MODE switch in the ADDED position, increase the offset
voltage until the ac signal can be viewed on the screen.
When signals are being displayed in the ADDED mode,
these precautions should be observed:
Do not exceed the input voltage rating of the amplifier.
Do not apply signals that will exceed an equivalent of 20
major divisions of deflection. As an example, with a VOLTS/
DIV switch setting of 1, the voltage applied to that channel's
input connector should not exceed 20 volts. If this limit is
exceeded, signal distortion will result.
Before displaying signals in the ADDED mode, set the
MODE switch to ALTER or CHOP and position both channel
signals to the center of the dipslay area. This is also a pre-
caution against display distortion.
BASIC APPLICATIONS
The following information describes the procedures and
techniques for making basic measurements with a Type 3A6
and an associated Tektronix indicator unit and time base. No
attempt has been made to describe these applications in
detail as each one must be adapted to the individual re-
quirements. Familiarity with the Type 3A6 will enable these
basic techniques to be applied to a wide variety of uses.
In the following procedures it is assumed that the Type 3A6
is placed in the left-hand or vertical compar'ment of the
indicator unit and an appropriate time-base unit is placed in
the right-hand compartment (except in a Type 565).
Voltage Measurements—AC
To measure the voltage level of an ac signal, set the AC
DC GND switch to AC. In this position the de component of
the signal will be blocked. However, if the ac signal is very
low frequency, the DC position should be used to avoid dis-
tortion of the signal.
To make a peak-to-peak measurement, use the following
procedure:
1. Set the VOLTS/DIV switch to a setting at least /% of
the expected voltage. For example, if the voltage will be
about 10 volts in amplitude, set the VOLTS/DIV — switch
to 2 (.2 if 10 probe is used).
2-4
2. Apply the signal to either input connector.
3. Set the MODE switch to the channel used.
4, Set the AC DC GND switch to AC.
5. Set the time-base triggering controls to obtain a stable
display. Set the time/division switch to a position that will
display several cycles of the waveform.
6. Turn the POSITION control so that the lower portion of
the waveform coincides with one of the graticule lines below
the centerline. With the time-base Position control, move the
display so one of the upper peaks lies near the vertical
centerline (see Fig. 2-1).
Vertical
Deflection
Fig. 2-1. Measuring the peak-to-peak voltage of a waveform.
7. Measure the divisions of vertical peak-to-peak deflection.
Make sure the VARIABLE control is in the CALIB position.
8. Multiply the peak-to-peak distance measured in step
6 by the VOLTS/DIV setting. Also include the attenuation
factor of the probe, if any.
As an example of this method of measurement, assume
that the peak-to-peak vertical deflection is 4.6 divisions (see
Fig. 2-1) using a 10 probe and a VOLTS/DIV setting
of 5, Using the formula:
vertical probe
volt to. eak
deflection
X von"
X attenuation
p
P
(divisions)
ing
factor
Substituting the values given above:
Volts peak-to-peak = 4.6 X 5 X 10
The peak-to-peak voltage would be 23 volts.
Voltage Measurements—Instantaneous DC
To measure the de level at a given point on a waveform,
use the following procedure:
1. Set the VOLTS/DIV switch to a setting at least % of
the expected voltage. For example, if the voltage will be
about 10 volts in amplitude, set the VOLTS/DIV switch to 2
(.2 if 10X probe is used).
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