Operating Instructions—Type 422 AC-DC
does not indicate the time relationship between the signals.
In the CH 1 position, the two signals are displayed showing
true time relationship. If the signals are not time related,
the Channel 2 waveform will 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. At faster sweep
rates the chopped switching becomes apparent and may
interfere with the display.
Proper internal triggering for the CHOPPED mode is pro
vided with the TRIGGERING Source switch settoCH 1. If
the CH 1 & 2 position is used, the sweep circuits are trigger
ed from the between-channel switching signal and both
waveforms will 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 will appear unstable.
Two non-repetitive transient or random signals occurring
within the time interval determined by the TIME/DIV
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 time relationship, time-difference meas
urements can be made.
Algebraic Addition
General. The ALG ADD position of the vertical Mode
switch can be used to display the sum or difference of two
signals, for common-mode rejection to remove an undesired
signal, or for 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 with both
VOLTS/DIV switches set to the same position is the same
as the deflection factor indicated by either VOLTS/DIV
switch. The amplitude of an added mode display can be
determined directly from the resultant CRT deflection
multiplied by the deflection factor indicated by either
VOLTS/DIV switch. However, if the Channel 1 and 2
VOLTS/DIV switches are set to different deflection factors,
the resultant voltage is difficult 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 following general precautions should
be observed when using the ALG ADD mode:
1. Do not exceed the input voltage rating of the Type
422.
2. Do not apply signals that exceed an equivalent of
about eight times the VOLTS/DIV switch setting. For ex
ample, with a VOLTS/DIV switch setting of .5, the voltage
applied to that channel should not exceed about four 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 for 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 of the TRIGGER
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, for dual-trace displays, special considerations must be
made to provide the correct display. See Dual-Trace Opera
tion in this section for 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 of the Channel 1 signal and is useful for 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
of 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 for 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 of amplitude, time relationship or wave-shape changes
of signals at various points in the circuit without resetting
the TRIGGERING controls.
Trigger Coupling
Three methods of coupling the trigger signal to the trig
ger circuits can be selected with 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 with low-frequency components below about 50
2-17
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