Model 120B Section III
Paragraphs 3- 1 to 3-16
SECTION Ill
OPERATION
CAUTION
When using ac coupling, do not ex-
3-2. This section contains operating instructions for
ceed a dc level input of 600 volts.
the Model 120B Oscilloscope. Included are descrip-
tions of the Model 120B controls and indicators, and
operation of the Model 120B as a general-purpose 3-12. When pulse or square waves having a frequen-
oscilloscope. cy less than 200 cps are being measured, dc coupling
is recommended (AC-DC switch-in DC position).
3-3. CONTROLS AND INDICATORS.
3-13. BEAM FINDER OPERATION. The crt trace
3-4. Figure 3-1 illustrates the controls and indica-
may frequently be deflected off the crt face by exces-
tors along with a short description of the particular
sive dc input levels or by misadjustment of the verti-
function of each.
cal POSITION and horizontal POSITION controls.
The BEAM FINDER pushbutton is extremely useful
3-5, GENERAL OPERATING
under these conditions. When the BEAM FINDER is
SUGGESTIONS. depressed, the beam is confined to the face of the
crt, brightened, and defocused to prevent burning of
3-6. The following paragraphs, 3-7 through 3-16,
the crt phosphor. If the crt trace is centered with the
provide suggestions for expediting and simplifying
POSITION controls when the BEAM FINDER is de-
operation of the Model 120B.
pressed, the trace will remain on the crt face when
the BEAM FINDER is released.
3-7. SYNCHRONIZING THE SWEEP. The horizontal
sweep can be synchronized with the vertical input
3-14. VERTICAL SENSITIVITY SELECTION. When
signal (INT positions of TRIGGER SOURCE switch),
the vertical VERNIER control is in CAL position, the
the ac line frequency (LINE position), or an external
VERTICAL SENSITIVITY switch provides attenuation
sync signal (EXT position).
of the vertical input signal in four calibrated steps,
3-8. When the TRIGGER LEVEL control is in AUTO 10 mv/cm, 100 mv/cm, 1 v/cm, and 10 v/cm. Ro-
position, sweep a appears on the crt without applica- tating the vertical VERNIER control in a counter-
tion of any type of synchronizing signal; however, clockwise direction permits continuous adjustment of
when a synchronizing signal above approximately 50 sensitivity between steps, and extends 10 v/cm step
cps is applied, the sweep automatically synchronizes to at least 100 v/cm. When the VERTICAL SENSITI-
with this signal and the sweep is triggered at the VITY switch is in CAL position, a calibrating signal
point where the signal crosses the zero axis (average is automatically connected to the vertical amplifier.
dc level of synchronization signal). If a synchroniz-
ing signal below approximately 50 cps is being used, 3 - 15. COMMON-MODE REJECTION. Balanced in-
the TRIGGER LEVEL control should be out of AUTO put to the vertical amplifier is obtained by removing
position. the ground jumper across two of the vertical input
terminals and applying a balanced signal input. Bal-
3-9. Rotating the TRIGGER LEVEL control in a anced input is useful in applications where it is de-
clockwise direction permits the trigger point to be sired to simultaneously amplify the out-of-phase (dif-
set between rt2 cm along the positive or negative- ferential) signal and attenuate in-phase the (common
going portion of a vertical input signal, depending on mode) signals, such as hum, noise, etc.
whether the TRIGGER SOURCE switch is in INT+ or
INT- position, respectively. When the TRIGGER 3-16. A change in the relative position of the Model
SOURCE switch is in EXT position, rotating the TRIG- 120B Oscilloscope with respect the to earth's mag-
GER LEVEL control in a clockwise direction permits netic field could result in the trace becoming mis-
the trigger point to be set between rt7 volts along the aligned. re-align To the trace with the graticule,
negative-going portion of the synchronizing signal. adjust SCALE, screwdriver adjustment ,on the front
panel (Figure 3-1).
3-10. The particular type of synchronization best
Notes
suited depends on the type of measurement being made
and the type of crt display desired.
Figures 3-2 through 3-5 assume
that the FOCUS, POSITION, and IN-
3-11. AC/DC COUPLING. Ac coupling (AC - DC
TENSITY controls are preset by the
switch in AC position) removes any dc level present
operator for the desired display.
in the vertical or horizontal input signals. This pre-
vents excessive levels dc from deflecting the crt trace If in doubt as to the exact function
off the face of the crt, often to the point where the of a switch listed in figures 3-2
POSITION controls cannot bring the crt trace within through 3-5, refer to figure 3-1
view. for a functional description. |
ACEC
