Tektronix TYPE CA Instruction Manual page 8

Probe Adjustment
An adjustable capacitor compensates for slight
variations in input capacitance from one in ­
strument to another. This capacitor is located
in the probe body in the P510, P410, and in
the termination block at the instrument end
of the cable in the P6017. It takes only a
few seconds to check this adjustment, and it
is a good practice to make this check each
time the probe is to be used.
the probe to the oscilloscope calibrator-output
terminal and observe the calibrator waveform
on the screen. If necessary, adjust the trimmer
for a flat top on the calibrator square wave.
To adjust the Type P6000 probe, touch the
probe tip to the calibrator output connector
and display several cycles of the calibrator
waveform. If the top and bottom of the dis ­
played waveform is not flat, loosen the locking
ring by turning it in a counterclockwise direc ­
tion. Rotate the barrel of the probe as neces ­
sary to compensate the probe. Tighten the lock ­
ing ring carefully after compensating the probe,
being careful not to disturb the probe adjustment.
Input Coupling
It is sometimes undesirable to display the dc
level of the waveform being observed. Placing
the AC-DC switch in the AC position inserts
a capacitor in series with the input so the
dc component of the waveform is blocked
and only the ac component is displayed. The
low-frequency response is about 2 cps when ac
coupling is used.
Output Polarity
It will be desirable to invert the displayed
waveform at times, particularly when using
the dual-trace feature of the Type CA. The
POLARITY switch has two positions. In the
NORMAL position the displayed waveform will
have the same polarity as the input signal.
In the INVERTED position the displayed wave ­
form will be turned upside down; that is, a
positive-going pulse will be displayed as a
negative going pulse.
DC Balance Adjustment
After the plug-in unit has been in use for
a period of time you will notice that the trace
will change position as the VARIABLE control
is rotated. This is caused by tube aging and
2-2
the resultant shift in operating potentials. To
correct this condition see Calibration ection.
Gain Adjustment
Aging of the tubes will also affect the gain
of the plug-in unit.
for this adjustment.
Positioning
imply touch
The Vert Pos Range control balances the dc
output level so the full range of the front ­
panel positioning controls can be utilized.
Calibration ection for this adjustment.
Types of Operation
Generally , three types of operation will be per ­
formed using the Type CA Unit; ALTERNATE,
CHOPPED, and ADDED ALGEBRAICALLY. The
three types of operation are fundamentally
different so we will examine them in the order
stated.
ALTERNATE
Connect the two signals to be compared to
the two signal inputs and turn the MODE switch
to A ONLY.
operation and adjust the VOLT /CM and VER ­
TICAL PO ITION controls as necessary to
display the waveform. Turn the MODE switch to
B ONLY and adjust the corresponding controls
as necessary to display the other waveform.
Now turn the MODE switch to ALTERNATE.
If necessary, touch up the oscilloscope's sweep
triggering controls to obtain a stable image.
Both waveforms will now be displayed on the
crt screen. As the control of each amplifier
is independent you can position, attenuate, or
invert the signals as necessary to compare
their shape, relative amplitudes, etc.
Use the AC LF REJECT triggering mode
and ALTERNATE sweeps for INTernal trig ­
gering on signals having components above
10 kc. For lower-frequency signals, use the
AC triggering mode. In the AC LF REJECT
position, an rc filter is inserted into the cir ­
cuit allowing it to recover quickly from the
dc level changes encountered with the ALTER ­
NATE sweep. To compare the phase difference
between
externally using the reference signals as the
trigger signal.
Operating Instructions - Type CA
ee Calibration
Adjustment
et the sweep up for triggered
two signals, you should trigger
ection
ee
AA