BK PRECISION 2120 oscilloscope INSTRUCTION MANUAL

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— MANUAL MODEL2120
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TEST INSTRUMENT SAFETY
| WARNING |
Normal use of test equipment exposes you to a certain amount of danger from electrical shock because
testing must often be performed where exposed high voltage is present. An electrical shock causing
10 milliamps of current to pass through the heart will stop most human heartbeats. Voltage as low as
35 volts dc or ac rms should be considered dangerous and hazardous since it can produce a lethal current
under certain conditions. Higher voltage poses an even greater threat because such voltage can more easily
produce a lethal current. Your normal work habits should include all accepted practices that will prevent
contact with exposed high voltage, and that will steer current away from your heart in case of accidental
contact with a high voltage. You will significantly reduce the risk factor if you know and observe the
following safety precautions:
Don’t expose high voltage needlessly in the equipment under test. Remove housings and covers only when necessary.
Turn off equipment while making test connections in high-voltage circuits. Discharge high-voltage capacitors after
removing power.
If possible, familiarize yourself with the equipment being tested and the location of its high voltage points. However,
remember that high voltage may appear at unexpected points in defective equipment.
Use an insulated floor material or a large, insulated floor mat to stand on, and an insulated work surface on which to
place equipment; make certain such surfaces are not damp or wet.
Use the time-proven “one hand in the pocket” technique while handling an instrument probe. Be particularly careful to
avoid contacting a nearby metal object that could provide a good ground return path.
When using a probe, touch only the insulated portion. Never touch the exposed tip portion.
When testing ac powered equipment, remember that ac line voltage 1s usually present on some power input circuits such
as the on-off switch, fuses, power transformer, etc. any time the equipment 1s connected to an ac outlet, even 1f the
equipment is turned off.
Some equipment with a two-wire ac power cord, including some with polarized power plugs, is the “hot chassis” type.
This includes most recent television receivers and audio equipment. A plastic or wooden cabinet insulates the chassis
to protect the customer. When the cabinet is removed for servicing, a serious shock hazard exists if the chassis is touched.
Not only does this present a dangerous shock hazard, but damage to test instruments or the equipment under test may
result from connecting the ground lead of most test instruments (including this oscilloscope) to a “hot chassis”. To make
measurements in “hot chassis” equipment, always connect an isolation transformer between the ac outlet and the
equipment under test. The B+K Precision Model TR-110 or 1604 Isolation Transformer, or Model 1653 or 1655 AC
Power Supply is suitable for most applications. To be on the safe side, treat all two-wire ac powered equipment as “hot
chassis” unless you are sure it has an isolated chassis or an earth ground chassis.
Never work alone. Someone should be nearby to render aid if necessary. Training in CPR (cardio-pulmonary
resuscitation) first aid 1s highly recommended.
TABLE OF CONTENTS
Page
TEST INSTRUMENT
SAFETY .. a ae ea eee inside front cover
FEATURES... ea a 4e a a ea ae 3
SPECIFICATIONS ....... aereo вене кее 4
CONTROLS AND INDICATORS .................. 6
Vertical Controls. .......... o.oo ii. 6
Horizontal Controls ......................... 7
Triggering Controls .............. cin... 8
Rear Panel Controls ........................... 8
OPERATING INSTRUCTIONS .................. 10
Safety Precautions ................ LL. 10
Equipment Protection Precautions. .............. 10
Operating Tips ...00000000000 10
Initial Starting Procedure . ..................... И
Single Trace Display ......................... li
Dual Trace Display. ................0 000... 12
Triggering......... .........0rerececere ne 12
DA
Page
OPERATING INSTRUCTIONS Cont.)
Magnified Sweep Operation... ................. 14
X=YOperation ...............iiiiiiiiin.. 14
Video Signal Observation ..................... 14
Applications. . ...... RK 14
MAINTENANCE ..... i. 15
Fuse Replacement ........................... 15
Line Voltage Selection. ....................... 15
Periodic Adjustments. ............. e... 15
Calibration Check .............. e... ... 16
Instrument Repair Service. .................... 16
APPENDIX... 00000000... 17
WARRANTY SERVICE INSTRUCTIONS ......... 18
LIMITED TWO-YEAR WARRANTY ............. 19
“Guidebook to Oscilloscopes”
Ordering Information. ............ Inside back cover
FEATURES
DUAL TRACE FEATURES
Dual Trace
Model 2120 has two vertical input channels for displaying
two waveforms simultaneously. Selectable single trace
(either CH 1 or CH 2) or dual trace. Alternate or chop sweep
selectable at all sweep rates.
Sum and Difference Capability
Permits algebraic addition or subtraction of channel 1 and
channel 2 waveforms, displayed as a single trace. Useful for
differential voltage and distortion measurements.
CRT FEATURES
Rectangular CRT
Rectangular CRT with large 8 x 10 centimeter viewing
area.
Convenience
Trace rotation electrically adjustable from front panel.
0%, 10%, 90%, and 100% markers for rise time measure-
ments.
VERTICAL FEATURES
High Sensitivity
5 mV/div sensitivity for full bandwidth. 1 mV/div sensi-
tivity with PULL X5 at reduced bandwidth.
Calibrated Voltage Measurements
Accurate voltage measurements (3%) on 10 calibrated
ranges from 5 mV/div to 5 V/ div. Vertical gain fully adjust-
able between calibrated ranges.
SWEEP FEATURES
Calibrated Time Measurements
Accurate (3%) time measurements. Model 2120 has 19
calibrated ranges from 0.5 s/div to 0.5 us/div. Sweep time 1s
fully adjustable between calibrated ranges.
X10 Sweep Magnification
Allows closer examination of waveforms, increases
maximum sweep rate to 50 ns/div.
TRIGGERING FEATURES
Two Trigger Modes
Selectable normal (triggered) or automatic sweep modes.
Triggered Sweep
Sweep remains at rest unless adequate trigger signal 1s
applied. Fully adjustable trigger level and (+) or (-) slope.
AUTO Sweep
Selectable AUTO sweep provides sweep without trigger
input, automatically reverts to triggered sweep operation
when adequate trigger is applied.
Five Trigger Sources
Five trigger source selections, including CH 1, CH 2,
ALT, EXT, and LINE. In ALT mode, each waveform be-
comes its own trigger (alternate triggering).
Three Trigger Coupling Choices
Selectable AC, TV H (Line), or TV V (Frame) trigger
coupling.
Video Sync
Frame (TV V) or Line (TV H) triggering selectable for
observing composite video waveforms.
OTHER FEATURES
X-Y Operation
Channel 2 can be applied as horizontal deflection (X-axis)
while channel 1 provides vertical deflection (Y-axis).
Built-In Probe Adjust Square Wave
A 0.2 V p-p, 1 kHz square wave generator permits probe
compensation adjustment.
Channel 1 Output
A buffered 500 output of the channel 1 signal 1s available
at the rear panel for driving a frequency counter or other
instruments. The output 1s 50 mV/div into 500.
Supplied With Two Probes
Low Boy Configuration
Low profile housing saves bench space and allows oscil-
loscope to be carried like a briefcase.
SPECIFICATIONS
CRT:
Type:
Rectangular with internal graticule.
Display Area:
8 x 10 div(i div = | em).
Accelerating Voltage:
2 kV.
Phosphor:
P31.
VERTICAL AMPLIFIERS (CH 1 and CH 2)
Sensitivity:
5 mV/div to 5 V/div. 1 mV/div to 1 V/div (PULL X35).
Attenuator:
10 calibrated steps in 1-2-5 sequence. Vernier control
provides fully adjustable sensitivity between steps,
adjustment range 1/1 to 1/2.5.
Accuracy:
13%, £5% at PULL X35.
Input Resistance:
| МО +2%.
Input Capacitance:
35 pF +5 pE
Frequency Response:
5 mV to 5 V/div:
DC to 20 MHz (+3 dB).
I mV/div to 1 V/div (Pull X5):
DC to 10 MHz (+3 dB).
Rise Time:
Approximately 17.5 ns, 35 ns at PULL X5.
Operating Modes:
CH 1: CH 1, single trace.
CH 2: CH 2, single trace.
ALT: dual trace, alternating.
CHOP: dual trace, chopped.
ADD: algebraic sum of CH 1 + CH 2.
Polarity Reversal:
CH 1 only.
Maximum Input Voltage:
400 V dc + ac peak.
Maximum Undistorted Amplitude:
DC-to-20 MHz: 4 divisions.
DC-to-10 MHz: 8 divisions.
HORIZONTAL AMPLIFIER
(Input through channel 2 input)
X-Y mode: switch selectable using X—Y switch.
CH 1: Y axis.
CH 2: X axis.
Sensitivity:
Same as vertical channel 2.
Accuracy:
Y-Axis: 13%.
X-Axis: +6%.
Input Impedance:
Same as vertical channel 2.
Frequency Response:
DC to 2 MHz typical (-3 dB) (to 6 divisions
horizontal deflection).
X—Y Phase Difference:
Approximately 3° at 50 kHz.
Maximum Input Voltage:
Same as vertical channel 2.
SWEEP SYSTEM
Sweep Speed:
0.5 us/div to 0.5 s/div in 1-2-5 sequence, 19 steps.
Vernier control provides fully adjustable sweep time
between steps.
Accuracy:
+3%.
Sweep Magnification:
10X, £6%.
TRIGGERING
Trigger Modes:
AUTO (free run) or NORM.
Trigger Source:
CH 1, CH 2, ALT, EXT, LINE.
Maximum External Trigger Voltage:
200 Y de + ac peak.
MODEL 2120 SPECIFICATIONS
Trigger Coupling:
AC 30 Hz to 30 MHz.
TVH Used for triggering from
horizontal sync pulses.
ТУ У Used for triggering from
vertical sync pulses.
Trigger Sensitivity:
COUPLING | BANDWIDTH INT EXT
AC 30 Hz-30 MHz | 5div | 500 mV
TVV 10 Hz-1.5 kHz |.5div | 500mV
TVH 3 kHz-30 MHz | .5 div 500 mV
OTHER SPECIFICATIONS
Calibrating Voltage:
| kHz (10%) Positive Square Wave,
0.2 V p-p 2%).
CH 1 Output (on rear panel):
Output Voltage:
50 mV/div (into 50-ohm load).
Output Impedance:
Approximately 50 ohms.
Frequency Response:
20 Hz to 10 MHz, —3 dB, into 50 &.
20 Hz to 20 MHz, —6 dB, into 1 MO.
Trace Rotation:
Electrical, front panel adjustable.
Power Requirements:
115 V/230 Y +10%, 50/60 Hz, approximately 35 W.
Dimensions:
320 x 130 x 361 mm (12.6 x 5.1 x 14.2").
Weight:
Approximately 6.8 kg (15 1bs).
SUPPLIED ACCESSORIES:
Two Probes.
Schematic Diagram and Parts List.
AC Power Cord.
OPTIONAL ACCESSORIES:
Deluxe 10:1/Direct Probe, Model PR-37.
100:1 Probe, Model PR-100.
Carrying Case, Model LC-210.
CONTROLS AND INDICATORS
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Fis. 1. Front Panel Controls and Indicators.
VERTICAL CONTROLS 4. AC-GND-DC Switch. Three-position lever switch
CHANNEL 1 CONTROLS
|.
CH 1 VOLTS/DIV Control. Vertical attenuator for
channel 1. Provides step adjustment of vertical sensi-
tivity. When channel 1 VARiable control is sst to
CAL, vertical sensitivity is calibrated in 10 steps from
5 mV/div to 5 V/div in a 1-2-5 sequence. When the
X—Y mode of operation 1s selected, this control pro-
vides step adjustment of Y-axis sensitivity.
VAR/PULL XS Control.
VARiable: Rotation provides vernier adjustment of
channel 1 vertical gain. In the fully clockwise CAL
position, the vertical attenuator 1s calibrated at the
maximum gain point. Counterclockwise rotation de-
creases gain. In X—Y operation, this control becomes
the vernier Y-ax1s gain control.
PULL XS (Push-Pull Switch): Multiplies the chan-
nel 1 gain five times; for example, 5 mV/div sensitivity
becomes 1 mV/div sensitivity.
$ POSition Control. Rotation adjusts vertical position
of channel | trace. In X—Y operation, rotation adjusts
vertical position of display.
which operates as follows:
AC:
Channel ! input signal is capacitively coupled; de
component 1s blocked.
GND:
Opens signal path and grounds input to vertical
amplifier. This provides a zero-volt base line, the
position of which can be used as a reference when
performing dc measurements.
DC:
Direct coupling of channel 1 input signal; both ac
and dc component of signal produce vertical de-
flection.
5. CH 1 (Y) Input Jack. Vertical input for channel |. Ÿ
axis input for X-Y operation.
CHANNEL 2 CONTROLS
6. CH2 VOLTS/DIV Control. Vertical attenuator for
channel 2. Provides step adjustment of vertical sensi-
tivity. When channel 2 VARiable control 1s set to
CAL, vertical sensitivity is calibrated in 10 steps from
5 mV/div to $ V/div in a 1-2-5 sequence. In X-Y
^_^
CONTROLS AND INDICATORS
operation, this control provides step adjustment of
X-axis sensitivity.
7. VAR/PULL XS Control.
VARiable: Rotation provides vernier adjustment of
channel 2 vertical gain. In the fully clockwise CAL
position, the vertical attenuator is calibrated at the
maximum gain point. Counterclockwise rotation de-
creases gain. In X—Y operation, this control becomes
the vernier X-axis gain control.
PULL XS5 (Push-Pull Switch): Multiplies the chan-
nel 2 gain five times; for example, 5 mV/div sensitivity
becomes 1 mV/div sensitivity.
8. $POSItion Control. Rotation adjusts vertical position
of channel 2 trace.
9. AC-GND-DC Switch. Three-position lever switch
which operates as follows:
AC:
Channel 2 input signal 1s capacitively coupled; de
component 1s blocked.
GND:
Opens signal path and grounds input to vertical
amplifier. This provides a zero-volt base line, the
position of which can be used as areference when
performing dc measurements.
DC:
Direct coupling of channel 2 input signal; both ac
and dc component of signal produce vertical de-
flection.
10. CH 2 (X) Input Jack. Vertical input for channel 2.
X-axis input in X—Y operation.
11. VERTICAL MODE Switch Assembly.
NORM/INV 1 Switch:
When this switch is released, the polarity of the
channel 1 signal is normal. When this switch 1s
engaged, the polarity of the channel | input signal
1s reversed.
CH 1/CH 2 Switch:
When this switch is released, the channel 1 signal
is displayed. When this switch is engaged, the
channel 2 signal is displayed.
MONO/DUAL Switch:
When this switch 1s released, the single-trace
mode 1s selected and the signal selected by the
CH 1/ CH 2 switch will be displayed (or the sum
of channels 1 and 2 if the ALT/ CHOP switch is
engaged). When this switch is engaged, both the
channel | and channel 2 signals will be displayed.
ALT/CHOP/ADD Switch:
When this switch 1s released 1n the dual-trace
mode, the channel 1 and channel 2 inputs are
alternately displayed (normally used at faster
sweep speeds). When this switch 1s engaged in
the dual-trace mode, the channel 1 and channel 2
inputs are chopped and displayed simultaneously
(normally used at slower sweep speeds). When
this switch is released in the single-trace mode,
only the signal selected by the CH 1/CH 2 switch
will be displayed. When this switch is engaged in
the single-trace mode, the input from channel 1
and channel 2 are summed and displayed as a
single signal. When the INV 1 switch is also
engaged, the input from channel 1 1s subtracted
from channel 2 and the difference 1s displayed as
a single signal.
12. TRACE ROTATION Control. Use a screwdriver to
adjust the trace to a horizontal position.
13. INTENSITY Control. Adjusts brightness of trace.
14. FOCUS Control. Adjusts trace focus.
15. POWER Control. Turns oscilloscope on and off.
16. POWER Indicator. Lights when is oscilloscope 1s on.
17. CAL Terminal. This terminal provides a 1 kHz,
0.2-volt peak-to-peak square wave signal. This 1s use-
ful for probe compensation adjustment and a general
check of oscilloscope calibration accuracy.
1 .
18. — Jack. Oscilloscope chassis ground, and earth
ground via three-wire ac power cord.
HORIZONTAL CONTROLS
SWEEP CONTROLS
19. Sweep TIME/DIV Control. Provides step selection
of sweep rate. When the VAR SWEEP control 1s set
to CAL, sweep rate 1s calibrated. This control has
19 steps from 0.5 Ls/div to 0.5 s/div, in a 1-2-5 se-
quence.
20. VAR SWEEP Control. Rotation of control 1s vernier
adjustment for sweep rate. In fully clockwise (CAL)
position, sweep rate 1s calibrated.
21. <p» X POSition, PULL X10 Control.
<> X POSition:
Horizontal position control.
PULL 10X MAG:
Selects ten times sweep magnification when
pulled out, normal when pushed in. Increases
maximum sweep rate to 50 ns/div.
CONTROLS AND INDICATORS
22. X-Y Switch. When this switch is engaged, the X-Y
mode of operation is selected. The channel 1 input
becomes the Y-axis and the channel 2 input becomes
the X-axis. The Trigger SOURCE and Trigger COU-
PLING controls are disabled when the X—Y switch 1s
engaged. The VERTICAL MODE switches should
all be disengaged when the X—Y mode of operation 1s
selected.
TRIGGERING CONTROLS
23. Trigger SOURCE Switch. Selects source of sweep
trigger. Four position lever switch with the following
positions:
CH 1:
The channel 1 input signal becomes the sweep
trigger, regardless of the VERTICAL MODE
switch setting.
CH 2:
Channel 2 signal becomes sweep trigger, regard-
less of VERTICAL MODE switch setting.
ALT:
The trigger source follows the VERTICAL
MODE switch setting for single trace operation
(for dual trace operation, the triggering source
alternates between channel 1 and channel 2). This
mode permits each waveform viewed to become
its own trigger signal. For dual-trace, triggering
is impossible unless input signals (with sufficient
triggering level) are applied to both input jacks.
Triggering is also impossible when the CHOP
dual-trace operation 1s selected.
EXT:
Signal from EXT TRIG jack becomes sweep
trigger.
24. Trigger COUPLING Switch. Selects trigger cou-
pling. Four-position lever switch with the following
positions:
AC:
Trigger is capacitively coupled; de component 1s
blocked.
TV H:
Used for triggering from horizontal sync pulses.
ТУ У:
Used for triggering from vertical sync pulses.
LINE:
Signal derived from input line voltage (50/60 Hz)
becomes trigger.
25. TRIG LEVEL/PUSH AUTO Control.
TRIG LEVEL Control:
Trigger level adjustment, determines the point on
the triggering waveform where the sweep 1s trig-
gered. Rotation in the (-) direction (counter-
clockwise) selects more negative point of
triggering, and rotation in the (+) direction
(clockwise) selects more positive point of trig-
gering.
PUSH AUTO Control:
When pushed in, automatic triggering 1s selected.
In automatic triggering mode, sweep 1s generated
in absence of adequate trigger signal; automat-
ically reverts to triggered sweep operation when
adequate trigger signal is present. When pulled
out, normal triggering is selected. In normal trig-
gering mode, sweep is only generated when ade-
quate trigger signal is present.
26. SLOPE Switch. When switch is disengaged, positive
going (+) slope is selected as trigger. When switch is
engaged, negative (—) going. slope is selected as
trigger.
27. EXT TRIG Jack. External trigger input for single and
dual-trace operation.
REAR PANEL CONTROLS
28. CH 1 OUT Jack. Output terminal where sample of
channel 1 signal is available. Amplitude of output is
50 millivolts per division of vertical deflection seen on
CRT when terminated into 50 ohms. Output imped-
ance is 50 ohms.
29. Power Cord Receptacle.
30. Fuse Holder/Line Voltage Selector. Contains fuse
and selects line voltage.
31. Tilt Stand. (Not Shown).
CONTROLS AND INDICATORS
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Fig. 2. Rear Panel Controls.
OPERATING INSTRUCTIONS
SAFETY PRECAUTIONS
| WARNING |
The following precautions must be ob-
served to help prevent electric shock.
When the oscilloscope is used to make measurements
in equipment that contains high voltage, there is al-
ways a certain amount of danger from electrical shock.
The person using the oscilloscope in such conditions
should be a qualified electronics technician or other-
wise trained and qualified to work in such circum-
stances. Observe the TEST INSTRUMENT SAFETY
recommendations listed on the inside front cover of
this manual.
Do not operate this oscilloscope with the case removed
unless you are a qualified service technician. High
voltage up to 2,000 volts is present when the unit is
operating with the case removed.
The ground wire of the 3-wire ac power plug places
the chassis and housing of the oscilloscope at earth
ground. Use only a 3-wire outlet, and do not attempt
to defeat the ground wire connection or float the oscil-
loscope; to do so may pose a great safety hazard.
Special precautions are required to measure or observe
line voltage waveforms with any oscilloscope. Use the
following procedure:
a. Do not connect the ground clip of the probe to
either side of the line. The clip is already at earth
ground and touching it to the hot side of the line
may “weld” or “disintegrate” the probe tip and
cause possible injury, plus possible damage to the
scope or probe.
b. Insert the probe tip into one side of the line voltage
receptacle, then the other. One side of the recepta-
cle should be “hot” and produce the waveform. The
other side of the receptacle is the ac return and no
waveform should result.
Never allow a small spot of high brilliance to remain
stationary on the screen for more than a few seconds.
The screen may become permanently burned. A spot
will occur when the scope is set up for X—Y operation
and no signal 1s applied. Either reduce the intensity so
the spot is barely visible, apply signal, or switch back
to normal sweep operation. It is also advisable to use
low intensity with AUTO triggering and no signal
applied for long periods. A high intensity trace at the
same position could cause a line to become perma-
nently burned onto the screen.
Do not obstruct the ventilating holes in the case, as this
will increase the internal temperature.
Excessive voltage applied to the input jacks may dam-
age the oscilloscope. The maximum ratings of the
inputs are as follows:
CH 1 and CH 2:
400 V dc + ac peak.
EXT TRIG:
200 V dc + ac peak.
Never apply external voltage to oscillo-
scope output jacks.
Always connect a cable from the ground terminal of
the oscilloscope to the chassis of the equipment under
test. Without this precaution, the entire current for the
equipment under test may be drawn through the probe
clip leads under certain circumstances. Such condi-
tions could also pose a safety hazard, which the ground
cable will prevent.
The probe ground clips are at oscilloscope and earth
ground and should be connected only to the earth
ground or isolated common of the equipment under
test. To measure with respect to any point other than
the common, use CH 2-CH 1 subtract operation (ADD
mode and INV 1), with the channel 2 probe to the point
of measurement and the channel | probe to the point
of reference. Use this method even if the reference
point is a dc voltage with no signal.
EQUIPMENT PROTECTION OPERATING TIPS
The following recommendations will help obtain the best
PRECAUTIONS
performance from the oscilloscope.
CAUTION 1. Always use the probe ground clips for best results,
attached to a circuit ground point near the point of
The following precautions will help avoid
measurement. Do not rely solely on an external ground v
damage to the oscilloscope.
10
em
OPERATING INSTRUCTIONS
wire in lieu of the probe ground clips as undesired
signals may be induced.
Avoid the following operating conditions:
a. Direct sunlight.
b. High temperature and humidity.
¢. Mechanical vibration.
d. Electrical noise and strong magnetic fields, such as
near large motors, power supplies, transformers,
etc.
Occasionally check trace rotation, probe compensa-
tion, and calibration accuracy of the oscilloscope using
the procedures found in the MAINTENANCE section
of this manual.
Terminate the output of a signal generator in its char-
acteristic impedance to minimize ringing, especially if
the signal has fast edges such as square waves or
pulses. For example, the typical 50 Q output of a
square wave generator should be terminated into an
external 50 £2 terminating resistor and connected to
the oscilloscope with 50 (Y coaxial cable.
Probe compensation adjustment matches the probe to
the input of the scope. For best results, compensation
should be adjusted initially, then the same probe al-
ways used with the same channel. Probe compensation
should be readjusted when a probe from a different
oscilloscope 1s used.
INITIAL STARTING PROCEDURE
Until you familiarize yourself with the use of all controls,
the settings shown in Fig. 3 may be used as a reference point
to obtain a trace on the CRT in preparation for waveform
observation.
I. Press the POWER switch; the unit will be turned on
and the pilot light will be illuminated.
2. The CH 1/CH 2 switch should be set to CH 1 (disen-
gaged) and the TRIG LEVEL control should be set
to AUTO (pushed in).
3. А trace should appear on the CRT. Adjust the trace
brightness with the INTENSITY control, and the trace
sharpness with the FOCUS control.
SINGLE TRACE DISPLAY
Either channel 1 or channel 2 may be used for single-trace
operation. The advantage of using channel 1 is that the
wavetorm on the display can be inverted if desired with the
INV 1 switch.
1. Perform the steps of the “Initial Starting Procedure”
with the CH 1/CH 2 switch set to CH 1.
2. Connect the probe to the CH 1 (Y) input jack.
3. Connect the probe ground clip to the chassis or com-
mon of the equipment under test. Connect the probe
tip to the point of measurement.
ALL RELEASED
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Fig. 3. Initial Control Settings.
OPERATING INSTRUCTIONS
4. If no waveforms appear, increase the sensitivity by
turning the CH 1 VOLTS/ DIV control clockwise to
a position that gives 2 to 6 divisions vertical deflection.
5. The display on the CRT may be unsynchronized. Refer
to the “Triggering” paragraphs in this section for pro-
cedures on setting triggering and sweep time controls
to obtain a stable display showing the desired number
of waveforms.
DUAL TRACE DISPLAY
In observing simultaneous waveforms on channel 1 and
2, the waveforms are usually related in frequency, or one of
the waveforms is synchronized to the other, although the
basic frequencies are different. If the two waveforms have
no phase or frequency relationship, there 1s seldom reason
to observe both waveforms simultaneously. However, when
the trigger SOURCE switch is set to the ALT position, two
waveforms not related in frequency or period can be simul-
taneously viewed.
|. Connect probes to both the CH 1 (Y) and CH 2 (X)
input jacks.
2. Connect the ground clips of the probes to the chassis
or common of the equipment under test. Connect the
tips of the probes to the two points in the circuit where
waveforms are to be measured.
3. When the MONO/DUAL switch is set to MONO and
the ALT/CHOP/ADD switch is set to ADD, the alge-
braic sum of CH 1 + CH 2 is displayed as a single trace.
When the INV 1 switch is also engaged, the algebraic
difference of CH 2 — CH 1 is displayed.
4. To view both waveforms simultaneously, set
the MONO/DUAL switch to DUAL and select
either ALT (alternate) or CHOP with the
ALT/CHOP/ADD switch.
5. In the ALT mode, one sweep displays the channel |
signal and the next sweep displays the channel 2 signal
in an alternating sequence. Alternate sweep is nor-
mally used for viewing high-frequency or high-speed
waveforms at sweep times of 1 ms/div and faster, but
may be selected at any sweep time.
6. In the CHOP mode, the sweep 1s chopped and
switched between channel 1 and channel 2. Chop
sweep is normally used for low-frequency or low-
speed waveforms at sweep times of | ms/div and
slower.
a. 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 applica-
tions. For example, the only way to observe simul-
taneous events on a dual-trace scope at any sweep
rate is with chop sweep.
b. Note that this oscilloscope is not intended to be
used with the CHOP display mode and the ALT
triggering source mode selected simultaneously. It
may be impossible to synchronize the display with
this combination. Use the ALT display mode 1n-
stead or select a trigger SOURCE of CH 1 or
CH 2.
7. Adjust the channel 1 and 2 §POSition controls to place
the channel 1 trace above the channel 2 trace.
8. 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.
TRIGGERING
The Model 2120 Oscilloscope provides 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 synchronization is given to help you
se lect the proper setting over a wide range of conditions.
PUSH AUTO Switch
|. The pulled out 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 1/2 division of vertical deflection are ade-
quate for normal triggered sweep operation.
2. In the AUTO position (pushed in), 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 1s
handy when first setting up the scope to observe a
waveform; it provides sweep for waveform observa-
tion until other controls can be properly set. Once the
controls are set, operation is often switched back to the
OPERATING INSTRUCTIONS
normal triggering 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.
Trigger SOURCE Switch
The trigger SOURCE switch (CH 1, CH 2, etc.) selects
the signal to be used as the sync trigger.
1. If the SOURCE switch is set to CH 1 (or CH 2) the
channel 1 (or channel 2) signal becomes the trigger
source regardless of the VERTICAL MODE selec-
tion. CH 1, or CH 2 are often used as the trigger source
for phase or timing comparison measurements.
2. When the ALT position 1s selected, the trigger source
is dependent upon the VERTICAL MODE selection.
In this manner, each waveform being observed be-
comes its own trigger signal.
a. When the vertical mode is changed from CH 1 to
CH 2, the trigger source is also changed from CH
1 to CH 2, and vice versa. This is very convenient
for single trace operation.
b. When the ALT dual-trace VERTICAL MODE is
selected, the trigger source alternates between
CH 1 and CH 2 with each sweep. This is conven-
ient for checking amplitudes, waveshape, or wave-
form period measurements, and even permits
simultaneous observation of two waveforms
which are not related in frequency or period. How-
ever, this setting is not suitable for phase or timing
comparison measurements. For such measure-
ments, both traces must be triggered by the same
sync signal.
c. When the CHOP dual-trace VERTICAL MODE
is selected, synchronization of the display is not
always possible. Use the ALT mode instead, or
change the SOURCE switch setting to CH 1, or
CH 2.
If the SOURCE switch is set to the EXT position, the
signal applied to the EXT TRIG jack becomes the
trigger source. This signal must have a timing relation-
ship to the displayed waveforms for a synchronized
display.
TRIG LEVEL and SLOPE Controls
(Refer to Fig. 4)
A sweep trigger is developed when the trigger source
signal crosses a preset threshold level. Rotation of the TRIG
LEVEL control varies the threshold level. In the + direction,
the triggering threshold shifts to a more positive value, and
in the — direction, the triggering threshold shifts to a more
negative value. When the control is centered, the threshold
level is set at the approximate average of the signal used as
I
un
the triggering source. Proper adjustment of this control
usually synchronizes the display.
The TRIG LEVEL control adjusts the start of the sweep
to almost any destred point on a waveform. On sine wave
signals, the phase at which sweep begins is variable. Note
that if the TRIG LEVEL control is rotated toward its
extreme + or — setting, no sweep will be developed in the
normal trigger mode because the triggering threshold ex-
ceeds the peak amplitude of the sync signal.
When the SLOPE control is set to the + position (re-
leased), the sweep 1s developed from the trigger source
waveform as it crosses a threshold level in a positive-going
direction. When the SLOPE control is set to the — position
(engaged), a sweep trigger is developed from the trigger
source waveform as it crosses the threshold level in a
negative-going direction.
SLOPE “-” RANGE
SLOPE +” RANGE +
DT ee
Fig. 4. Function of Slope and Level Controls.
Trigger COUPLING Switch
|. Use the AC position for viewing most types of wave-
forms, The trigger signal 1s capacitively coupled and
may be used for all signals from 30 Hz to 20 MHz.
2. 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 (with a cut off frequency of about
400 Hz). Additional procedures for observing video
waveforms are given later in this section of the manual.
3. Ifthe COUPLING switch is set to the LINE position,
triggering 1s derived from the input line voltage
(50/60 Hz) and the trigger SOURCE switch is dis-
abled. This 1s useful for measurements that are related
to line frequency.
Sweep TIME/DIV Control
Set the sweep TIME/DIV control to display the desired
number of cycles of the waveform. If there are too many
cycles displayed for good resolution, switch to a faster
OPERATING INSTRUCTIONS
sweep time. If only a line is displayed, try a slower sweep
time. When the sweep time 1s faster than the waveform being
observed, only part of it will be displayed, which may appear
as a straight line for a square wave or pulse waveform.
MAGNIFIED SWEEP OPERATION
Since merely shortening the sweep time to magnify a
portion of an observed waveform can result in the desired
portion disappearing off the screen, such magnified display
should be performed using magnitied sweep.
Using the <> X POSition control, adjust the desired
portion of waveform to the center of the CRT. Pull out the
PULL X10 knob to magnify the display ten times. For this
type of display the sweep time is the sweep TIME/DIV
setting divided by 10. Rotation of the 4» X POSition
control can then be used to select the desired portion of the
waveforms.
X-Y OPERATION
X-Y operation permits the oscilloscope to perform many
measurements not possible with conventional sweep opera-
tion. The CRT display becomes an electronic graph of two
instantaneous voltages. The display may be a direct com-
parison of the two voltages such as stereoscope display of
stereo signal outputs. However, the X—Y mode can be used
to graph almost any dynamic characteristic if a transducer
1s used to change the characteristic (frequency, temperature,
velocity, etc.) into a voltage. One common application is
frequency response measurements, where the Y axis corre-
sponds to signal amplitude and the X axis corresponds to
frequency.
|. Press the X—-Y switch. In this mode, channel 1 be-
comes the Y axis input and channel 2 becomes the X
axis input. All VERTICAL MODE switches should
be disengaged for X—Y operation.
2. The X and Y positions are now adjusted using the
«<> X POSition and the channel 1 y POSition controls
respectively.
14
3. Adjust the amount of vertical (Y axis) deflection with
the CH 1 VOLTS/DIV and VARiable controls.
4. Adjust the amount of horizontal (X axis) deflection
with the CH 2 VOLTS/DIV and VARiable controls.
VIDEO SIGNAL OBSERVATION
Setting the COUPLING switch to the TV H or TV V
position permits selection of horizontal or vertical sync
pulses for sweep triggering when viewing composite video
waveforms.
When the TV H mode 1s selected, horizontal sync pulses
are selected as triggers to permit viewing of horizontal lines
of video. A sweep time of about 10 jus/div 1s appropriate for
displaying lines of video. The VAR SWEEP control can be
set to display the exact number of waveforms desired.
When the TV V mode is selected, vertical sync pulses are
selected as triggers to permit viewing of vertical fields and
frames of video. A sweep time of 2 ms/div 1s appropriate for
viewing fields of video and 5 ms/div for complete frames
(two interlaced fields) of video.
At most points of measurement, a composite video signal
is of the (—) polarity, that 1s, the sync pulses are negative and
the video is positive. In this case, use (=) SLOPE. If the
waveform 1s taken at a circuit point where the video wave-
form is inverted, the sync pulses are positive and the video
is negative. In this case, use (+) SLOPE.
APPLICATIONS
B+K Precision offers a “Guidebook to Oscilloscopes”
which describes numerous applications for this instrument
and important considerations about probes. It also includes
a glossary of oscilloscope terminology and an under-
standing of how oscilloscopes operate. It may be obtained
free of charge by fillinog out the postage-free coupon card
enclosed with this instrument.
MAINTENANCE
| WARNING |
The following instructions are for use by
qualified service personnel only. To avoid
electrical shock, do not perform any serv-
icing other than contained in the operat-
ing instructions unless you are qualified
to do so.
High voltage up to 2,000 volts is present
when covers are removed and the unit is
operating. Remember that high voltage
may be retained indefinitely on high volt-
age capacitors. Also remember that ac
line voltage is present on line voltage
input circuits any time the instrument is
plugged into an ac outlet, even if turned
off. Unplug the oscilloscope and dis-
charge high voltage capacitors before
performing service procedures.
FUSE REPLACEMENT
If the fuse blows, the pilot light will go out and the
oscilloscope will not operate. The fuse should not normally
open unless a problem has developed in the unit. Try to
determine and correct the cause of the blown fuse, then
replace only with the correct value fuse. For 120 V line
voltage operation, use a 630 mA, 250 V fuse. For 230 V line
voltage operation, use a 315 mA, 250 V fuse. The fuse is
located on the rear panel adjacent to the power cord recep-
tacle.
Remove the fuseholder assembly as follows:
|. Unplug the power cord from the rear of scope.
2. Insert a small screwdriver in fuseholder slot (located
between fuseholder and receptacle). Pry fuseholder
away trom receptacle.
3. When reinstalling fuseholder, be sure that the fuse-
holder in installed so that the correct line voltage is
selected (see LINE VOLTAGE SELECTION).
LINE VOLTAGE SELECTION
To select the desired line voltage, simply insert the fuse
and fuse holder so that the appropriate voltage 1s at the top
(pointed to by the arrow). Be sure to use the proper value
fuse (see label on rear panel).
PERIODIC ADJUSTMENTS
Screwdriver adjustments only need to be checked and
adjusted periodically. Probe compensation and trace rota-
tion adjustments are included in this category. Procedures
are given below.
Probe Compensation
1. Connect probes to CH 1 and CH 2 input jacks. Repeat
procedure for each probe.
2. Touch tip of probe to CAL terminal.
3. Adjust oscilloscope controls to display 3 or 4 cycles of
CAL square wave at 5 or 6 divisions amplitude.
4. Adjust compensation trimmer on probe for optimum
square wave {minimum overshoot, rounding off, and
tilt). Refer to Fig. 5.
Correct
compensation
Over
compensation
Insufficient
compensation
Fig. 5. Probe Compensation Adjustment.
Trace Rotation Adjustment
1. Set oscilloscope controls for a single trace display in
CH 1 mode, and with the channel 1 AC-GND-DC
switch set to GND.
ID
Use the channel 1 $ POSition control to position the
trace over the center horizontal line on the graticule
scale. The trace should be exactly parallel with the
horizontal line.
3. Usethe TRACE ROTATION adjustment on the front
panel to eliminate any trace tilt,
MAINTENANCE
CALIBRATION CHECK
A general check of calibration accuracy may be made by
displaying the output of the CAL terminal on the screen.
This terminal provides a square wave of 0.2 V p-p. This
signal should produce a displayed waveform amplitude of
four divisions at 50 mV/div sensitivity for both channel 1
and 2 (with probes set for direct). With probes set for 10:1,
there should be four divsions amplitude at 5 mV/div sensi-
tivity. The VARiable controls must be set to CAL during
this check.
The CAL signal may be used only as a general check of
calibration accuracy, not as a signal source for performing
recalibration adjustments; a signal source of 0.5% or better
accuracy is required for calibration adjustments.
INSTRUMENT REPAIR SERVICE
Because of the specialized skills and test equipment re-
quired for instrument repair and calibration, many custom-
ers prefer to rely upon B+K Precision for this service. We
maintain a network of B+K Precision authorized service
agencies for this purpose. To use this service, even 1f the
oscilloscope is no longer under warranty, follow the instruc-
tions given in the WARRANTY SERVICE INSTRUCTION
portion of this manual. There 1s a nominal charge for instru-
ments out of warranty.
APPENDIX |
IMPORTANT CONSIDERATIONS FOR RISE TIME AND
FALL TIME MEASUREMENTS
Error In Observed Measurement
The observed rise time (or fall time) as seen on the CRT
is actually the cascaded rise time of the pulse being meas-
ured and the oscilloscope’s own risetime. The two rise times
are combined in square law addition as follows:
Tobserved = V(T pulse)” + (Tscope)”
The effect of the oscilloscope’s rise time 1s aimost negli-
gible when its rise time is at least 3 times as fast as that of
the pulse being measured. Thus, slower rise times may be
measured directly from the CRT. However, for faster rise
time pulses, an error is introduced that increases progres-
sively as the pulse rise time approaches that of the oscillo-
scope. Accurate measurements can still be obtained by
calculation as described below.
Direct Measurements
The Model 2120 Oscilloscope has a rated rise time of
17.5 ns at all attenuator ranges. Thus, pulse rise times of
about 53 ns or greater can be measured directly. Most rise
times are measured at the fastest sweep speed and using X10
magnification. For Model 2120, this sweep rate 1s 50 ns/div.
À rise time measurement of less than about | division should
be calculated.
Calculated Measurements
For observed rise times of less than 53 ns, the puise rise
time should be calculated to eliminate the error introduced
by the cascaded oscilloscope rise time. Calculate pulse rise
time as follows:
2 2
pulse — V(Tobserved) + (Tscope)
Limits Of Measurement
Measurements of pulse rise times that are faster than the
oscilloscope’s rated rise time are not recommended because
a very small reading error introduces significant error into
the calculation. This limit is reached when the “observed”
rise time 1s about 1.3 times greater than the scope's rated rise
time, about 23 ns.
Probe Considerations
For fast rise time measurements which approach the limits
of measurement, direct connection via 50 © coaxial cable
and 50 Q termination is recommended where possible.
When a probe is used, its rise time is also cascaded in square
law addition. Thus the probe rating should be considerably
faster than the oscilloscope if it 1s to be disregarded in the
measurement.
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