BK Precision 2120C Instruction Manual Download Page 15

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3. To view both waveforms simultaneously, set the

VERTical MODE

switch to

DUAL

and select either

ALT

(alternate) or

CHOP

with the

PULL CHOP

switch.

4. In the

ALT

sweep mode (

PULL CHOP

switch

pushed in), one sweep displays the channel 1 signal
and the next sweep displays the channel 2 signal in an
alternating sequence. Alternate sweep is normally
used for viewing high-frequency or high-speed wave-
forms at sweep times of 1 ms/div and faster, but may
be selected at any sweep time.

5. In the

CHOP

sweep mode (

PULL CHOP

switch

pulled out), the sweep is chopped (switched) between
channel 1 and channel 2. Using

CHOP

, one channel

does not have to “wait” for a complete swept display
of the other channel. Therefore, portions of both chan-
nel’s waveforms are displayed with the phase relation-
ship between the two waveforms unaltered. Chop
sweep is normally used for low-frequency or low-
speed waveforms at sweep times of 1 ms/div and
slower; or where the phase relationship between chan-
nel 1 and channel 2 requires measurement.

If chop sweep is used at sweep times of 0.2 ms/div and
faster, the chop rate becomes a significant portion of
the sweep and may become visible in the displayed
waveform. However, you may select chop sweep at
any sweep time for special applications.

6. Adjust the channel 1 and 2

▲

▼

POS

ition controls to

place the channel 1 trace above the channel 2 trace.

7. Set the

CH 1

and

CH 2 VOLTS/DIV

controls to a

position that gives 2 to 3 divisions of vertical deflec-
tion for each trace. If the display on the screen is
unsynchronized, refer to the “Triggering” paragraphs
in this section of the manual for procedures for setting
triggering and sweep time controls to obtain a stable
display showing the desired number of waveforms.

8. When the

VERTical MODE

switch is set to

ADD

, the

algebraic sum of CH 1 + CH 2 is displayed as a single
trace. When the

PULL INV

switch is pulled out, the

algebraic difference of CH 1 – CH 2 is displayed.

9. If two waveforms have no phase or frequency relation-

ship, there is seldom reason to observe both wave-
forms simultaneously. However, these oscilloscopes
do permit the simultaneous viewing of two such unre-
lated waveforms, using alternate triggering. Refer to
the paragraphs on “Triggering - Trigger SOURCE
Switch”, for details on alternate triggering.

TRIGGERING

The

Oscilloscopes provide

versatility in sync

triggering for ability to obtain a stable,

jitter-free display

in single-trace, or dual-trace operation

. The proper settings

depend upon the type of waveforms

being observed and

the type of measurement desired. An

explanation of the

various controls which affect synchroni

zation is given to

help you select the proper setting over a

wide range of

conditions.

Trigger COUPLING Switch

1. In the

AUTO

position, automatic sweep operation is

selected. In automatic sweep operation, the sweep
generator free-runs to generate a sweep without a
trigger signal. However, it automatically switches to
triggered sweep operation if an acceptable trigger
source signal is present. The

AUTO

position is handy

when first setting up the scope to observe a waveform;
it provides sweep for waveform observation until other
controls can be properly set. Once the controls are set,
operation is often switched back to the normal trigger-
ing mode, since it is more sensitive. Automatic sweep
must be used for dc measurements and signals of such
low amplitude that they will not trigger the sweep.

2. The

NORM

position provides normal triggered

sweep operation. The sweep remains at rest until the
selected trigger source signal crosses the threshold
level set by the

TRIG LEVEL

control. The trigger

causes one sweep to be generated, after which the
sweep again remains at rest until triggered. In the
normal triggering mode, there will be no trace unless
an adequate trigger signal is present. In the

ALT

VERTICAL MODE

of dual trace operation with the

SOURCE

switch also set to

ALT

, there will be no

trace unless both channel 1 and channel 2 signals are
adequate for triggering. Typically, signals that pro-
duce even one division of vertical deflection are ade-
quate for normal triggered sweep operation.

3. The

TV H

and

TV V

positions are primarily for

viewing composite video waveforms. Horizontal sync
pulses are selected as trigger when the trigger

COU-

PLING

switch is set to the

TV H

position, and vertical

sync pulses are selected as trigger when the trigger

COUPLING

switch is set to the

TV V

position. The

TV H

and

TV V

positions may also be used as low

frequency reject and high frequency reject coupling,
respectively. Additional procedures for observing video
waveforms are given later in this section of the manual.

OPERATING INSTRUCTIONS

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