Signal Connections - Tektronix 3A6 Instruction Manual

Operating Instructions—Type 3A6
12. Set the time/division switch to 2 microseconds and
readjust the triggering controls for a stable display. Turn
the intensity up slightly and notice the overshoot on the
display. This is the switching transient between the channels.
Set the ert cathode selector switch on the indicator unit rear-
panel to chopped blanking. The switching transient should
be removed from the display. Return the time/division
switch to 5 milliseconds and the ert cathode selector switch
to the normal position.
13. Set the MODE switch to ADDED. The display should
be 4 divisions in amplitude. The Channel 1 and 2 signals
(2 divisions each) are added for this display. Note that
either POSITION control will move the trace.
14, Set the INV (CH 1} NORM switch to INV. The display
should be a straight line. Since both displays are two
divisions in amplitude but of opposite polarity, the algebraic
sum is zero.
15. Set either VOLTS/DIV switch to 1. A square wave is
again displayed indicating that the algebraic sum of Chan-
nel 1 and 2 is no longer zero.
CALIB Adjustment
Whenever the Type 3A6 is inserted into a plug-in com-
partment, check and adjust the gain to compensate for the
differences between indicator units. Allow about 10 minutes
warmup before performing this adjustment.
1. Set both AC DC GND switches to DC.
2. Set the MODE switch to CH 1.
3. Set both VOLTS/DIV switches to .02.
4, Turn the VARIABLE controls fully clockwise so the
UNCAL lights are off.
5. Set the time-base controls for automatic triggering.
6. Connect the calibrator output to Channel 1 input.
7. Set the indicator unit calibrator to 100 millivolts.
8. Set the CALIB control for exactly 5 major divisions of
deflection.
9. Set the MODE switch to CH 2.
10, Connect the calibrator output to Channel 2 input.
11. The deflection should be exactly 5 divisions, If in-
correct, refer to the Channel 2 gain adjust procedure in
Section 5.
DC BAL Adjustment
Check. To check the de balance of either channel, set the
AC DC GND switch to GND and the VOLTS/DIV switch
to .01. Set the time-base controls for automatic triggering.
Rotate the VARIABLE contro! throughout its range. If the
trace moves vertically, adjust the DC BAL contro! according
to the procedure which follows.
Adjustment. The following procedure can be used to adjust
the de balance of either channel. Set the MODE switch
to display the desired channel. Allow about 10 minutes
warmup before performing this adjustment.
2-2
1. Set the AC DC GND switch to GND.
2. Set the VOLTS/DIV switch to .01.
3. Set the time-base controls for automatic triggering.
4. Turn the POSITION control to mid-range.
5. With the VARIABLE control in the CALIB position
adjust the DC BAL control to bring the trace near graticule
center.
6. Turn the VARIABLE control fully counterclockwise and
position the trace to the graticule centerline with the POSI-
TION control.
7. Return the VARIABLE control to the CALIB position.
Measure the exact distance the trace is displaced above or
below the centerline.
8. Adjust the DC BAL control to move the trace exactly
half this distance (measured in step 7) past the graticule
centerline.
NOTE
Both DC BAL controls are the dual-range or
coarse-fine type. To use this type of control, turn
the control slightly past the desired point of ad-
justment (coarse adjust). Then, reverse the direc-
tion of rotation and use the fine adjustment
(about 30° range) to establish balance.
9. Check the balance by rotating the VARIABLE control
throughout its range. If the amplifier is not properly bal-
anced, repeat steps 6, 7 and 8.
Signal Connections
In general, 10 attenuator probes offer the best means
of coupling a signal to the input of the Type 3A6. The 10x
attenuator probe offers a higher input impedance and
allows the circuit under test to operate more closely to
actual operating conditions. The signal probes are shielded
to prevent pickup of any electrostatic or electromagnetic
interference.
In some cases, the signal can be connected to the Type
3A6 inputs with short unshielded leads. This is particularly
true with high-level, low-frequency signals. When such leads
are used, be sure to establish a common ground between the
Type 3A6 and the equipment under test. Attempt to posi-
tion the leads away from any stray interference to avoid
errors in the display. If interference is excessive with un-
shielded leads, use a coaxial cable or a probe.
In high frequency applications requiring maximum over-
all bandwidth, use coaxial cables terminated in their
characteristic impedance at the input of the Type 3A6.
Loading Effect of the Type 3A6
As nearly as possible, simulate actual operating conditions
in the equipment under test. Otherwise, the equipment
under test may not produce a normal signal. The 10x
attenuator probes mentioned previously offer the least
circuit loading. Tektronix 10 attenuator probes have an
input resistance of 10 megohms with very low shunt
capacitance.