Tektronix 422, Instruction Manual

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Operating Instructions—Type 422 AC-DC
does not indicate the tim e relationship between the signals.
In the CH 1 position, the tw o signals are displayed showing
true time relationship. If the signals are not time related,
the Channel 2 waveform w ill be unstable in the CH 1
Source switch position.
Chopped Mode. The CHOPPED position of the vertical
Mode switch produces a display which is electronically
switched between channels. In general, the CHOPPED
mode provides the best display at sweep rates slower than
about 0.2 millisecond/division or whenever dual-trace, non-
repetitive phenomena is to be displayed. A t faster sweep
rates the chopped switching becomes apparent and may
interfere w ith the display.
Proper internal triggering fo r the CHOPPED mode is pro­
vided w ith the TRIGGERING Source switch s e tto C H 1. If
the CH 1 & 2 position is used, the sweep circuits are trigger­
ed from the between-channel switching signal and both
waveforms w ill be unstable. External triggering from a sig­
nal which is time-related to either signal provides the same
result as CH 1 triggering.
Two signals which are time-related can be displayed in
the chopped mode showing true time relationship. How­
ever, if the signals are not time-related, the Channel 2 dis­
play w ill appear unstable.
Two non-repetitive transient or random signals occurring
w ithin the time interval determined by the T IM E /D IV
switch (10 times sweep rate) can be compared using the
CHOPPED mode. To trigger the sweep correctly, the Chan­
nel 1 signal must precede the Channel 2 signal. Since the
display shows true tim e relationship, time-difference meas­
urements can be made.
Algebraic Addition
General. The ALG AD D position of the vertical Mode
switch can be used to display the sum or difference o f two
signals, fo r common-mode rejection to remove an undesired
signal, or fo r DC offset (applying a DC voltage to one chan­
nel to offset the DC component of a signal on the other
channel). The common-mode rejection ratio of the Type
422 is greater than 100:1 at 50 kilohertz.
Deflection Factor. The overall deflection in the ALG
ADD position of the vertical Mode switch w ith both
VO LTS/D IV switches set to the same position is the same
as the deflection factor indicated by either VO LTS/DIV
switch. The amplitude o f an added mode display can be
determined directly from the resultant CRT deflection
m ultiplied by the deflection factor indicated by either
VO LTS/DIV switch. However, if the Channel 1 and 2
VO LTS/D IV switches are set to different deflection factors,
the resultant voltage is d iffic u lt to determine from the CRT
display. In this case, the voltage amplitude of the resultant
display can be determined accurately only if the amplitude
of the signal applied to either channel is known.
Precautions. The follow ing general precautions should
be observed when using the ALG ADD mode:
1. Do not exceed the input voltage rating o f the Type
422.
2. Do not apply signals that exceed an equivalent of
about eight times the VO LTS/DIV switch setting. For ex­
ample, w ith a VO LTS/D IV switch setting of .5, the voltage
applied to that channel should not exceed about fo ur volts.
Larger voltages may distort the display.
3. Use Channel 1 and 2 POSITION control settings
which most nearly position the signal of each channel to
mid-screen when viewed in either the CH 1 or CH 2 posi­
tions of the vertical Mode switch. This insures the greatest
dynamic range fo r ALG ADD mode operation.
4. For similar response from each channel, set the Chan­
nel 1 and 2 Input Coupling switches to the same position.
Trigger Source
CH 1 & 2. In the CH 1 & 2 position o f the TRIG G ER­
ING Source switch, the trigger signal is obtained from the
displayed signal. This position provides the most convenient
operation when displaying single channel displays. How­
ever, fo r dual-trace displays, special considerations must be
made to provide the correct display. See Dual-Trace Opera­
tion in this section fo r dual-trace triggering information.
CH 1. The CH 1 position of the TRIGGERING Source
switch provides a trigger signal from only the signal appled
to the INPUT 1 connector. This position provides a stable
display o f the Channel 1 signal and is useful fo r certain
dual-trace applications (see Dual-Trace Operation).
EXT. An external signal connected to the TRIG IN con­
nector can be used to trigger the sweep in the EXT position
o f the TRIGGERING Source switch. The external signal
must be time-related to the displayed signal to produce a
stable display. An external trigger signal can be used to
provide a triggered display when the internal signal is too
low in amplitude fo r correct triggering, or contains signal
components on which it is not desired to trigger. It is also
useful when signal tracing in amplifiers, phase-shift net­
works, wave-shaping circuits, etc. The signal from a single
point in the circuit can be connected to the TRIG IN con­
nector through a signal probe or cable. The sweep is then
triggered by the same signal at all times and allows examin­
ation o f amplitude, time relationship or wave-shape changes
o f signals at various points in the circuit w ith o u t resetting
the TRIGGERING controls.
Trigger
Coupling
Three methods of coupling the trigger signal to the trig ­
ger circuits can be selected w ith the TRIGGERING Coup­
ling switch. Each position permits selection or rejection of
the frequency components of the trigger signal which trig ­
ger the sweep.
AC. In the AC position of the TRIGGERING Coupling
switch, the DC component of the trigger signal is blocked.
Signals w ith low-frequency components below about 50
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