HP 120A - General Descripti N; General Information

Sect. I Page 1
SECTION I
GENERAL DESCRIPTION
1-1 GENERAL INFORMATION
The Model 120A de to 200 kc oscilloscope is a general
purpose oscilloscope employing a 5-AQP mono-accel 
erator precision type cathode-ray tube. It can be used
with either internal or external sweeps which can be
either internally or externally synchronized and it can
be obtained in either the cabinet or rack type mount 
ing. Because of its high sensitivity and balanced in 
put, the Model 120A may often be used directly with
transducers, enabling you to see a direct presenta 
tion of phenomena desired without having to resort to
preamplifiers. The balanced vertical amplifier may
also be used as a differential amplifier amplifying the
desired signals and rejecting extraneous induced sig 
nals.
Since the control layout on the front panel has been
carefully organized and labeled for convenient opera 
tion, most controls will be self-explanitory. How 
ever, all external controls are discussed completely
in Section II of this manual. A large fold-out view of
the panel is included in Section II with all operating
controls described.
Some of the special features of this oscilloscope are
as follows:
15 DIRECT READING SWEEP TIMES ACCURATE
WITHIN 5%
When you are using the 120A computations are avoid 
ed and possibilities of error are reduced by direct
reading, calibrated sweeps. A single knob selects
15 calibrated sweeps from 5 microseconds/cm to 200
milliseconds/cm or determines the calibrated sen 
sitivity of the horizontal amplifier. Continuous con 
trol of sweep time and horizontal sensitivity between
calibrated steps is provided by a vernier control
which also extends the 200 milliseconds/cm sweep
time to at least 0. 5 sec/cm and lowers the sensi 
tivity of the 10 volt/cm step of the horizontal am 
plifier to at least 100 volts/cm.
LINEAR INTEGRATOR SWEEP GENERATOR
The accurate direct reading sweeps are obtained from
a feedback type integrator which also insures a high
order linearity and stability. This type sweep gener 
ator is much more reliable and independent of tube
characteristics than other types of sawtooth volt 
age generators because negative feedback is inherent
in its design, stabilizing its operation.
X5 SWEEP EXPANSION
You speed observation and analysis of transients by
expanding any two centimeter segments of a trace to
10 centimeters for easy viewing of detail. This X5
sweep expander, usually found only in more costly
oscilloscopes, may be used on all sweep time set 
tings and expands the fastest sweep time to 1 micro -
second/cm.
UNIQUE AUTOMATIC TRIGGERING
No time is wasted adjusting trigger controls on the
<$)Model 120A, it ’ s automatic, just connect the syn -
chronizing signal to obtain a stable, steady trace.
Nor is that all, the automatic trigger ends hunting
for the spot and facilitates establishing a base line
when a synchronizing signal is not present because
this circuit triggers the sweep generator to provide
a baseline on the CRT in the absence of a synchroniz 
ing signal. In applications where it would be more
convenient to have a baseline only in response to an
applied trigger, as in photographic work involving
transients, the automatic baseline provision may be
easily and quickly locked-out and a trigger level es 
tablished which is adjustable from at least -10 volts
to +10 volts of an external trigger. This lockout can
not be accidentally or inadvertantly actuated because
it is located just behind the front panel where it is
easily accessible with a screwdriver.
CALIBRATED AMPLIFIERS FOR MEASUREMENT
AS WELL AS OBSERVATION
Accurate voltage measurements on all kinds of wave 
forms are quickly made with the 120A, the amplifiers
are calibrated and accurate within ±5%. Reliability
and confidence is assured by a built-in calibrator
which is accurate within ±2% and so permits quick
verification and standardization of vertical amplifier