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Section 3-2215A Operators
OPERATORS FAMILIARIZATION
GENERAL OPERATING INFORMATION
GRATICULE
The graticule
is
internally
marked on the
faceplate
of the
crt to enable accurate measurements without parallax error
(see Figure 3-1
).
It is marked with eight vertical
and ten
hori-
zontal major divisions. Each major division is divided
into
five subdivisions. The vertical deflection factors and
horizon-
tal timing are calibrated to the graticule so that accurate
measurements can be made directly from
the
crt. Also, per-
centage markers
for
the measurement of rise and fall times
are located on the left side of the graticule.
GROUNDING
The
most reliable
signal
measurements
are made when
the 2215A and
the unit
under
test are
connected by
a com-
mon reference (ground lead),
in
addition
to
the signal lead
or
probe.
The
probe's ground
lead provides the best grounding
method for
signal
interconnection and ensures
the
maxi-
mum
amount
of signal-lead
shielding
in
the probe cable.
A separate ground lead can also
be
connected
from
the
unit
under
test
to
the
oscilloscope
GND connector
located on
the
front panel.
SIGNAL CONNECTIONS
Generally,
probes
offer the
most
convenient means of
connecting an input signal
to the
instrument. They are
shielded to prevent pickup of electromagnetic interference,
and the supplied
1
OX probe offers a high input impedance
that minimizes circuit loading. This allows the circuit under
test to operate with a minimum of change from its
normal
condition as
measurements
are being
made.
Coaxial cables may also be used to connect signals to
the
input connectors,
but
they
may have considerable effect
on
the
accuracy of a displayed waveform. To maintain the
original frequency characteristics of an
applied
signal, only
high-quality,
low-loss coaxial cables should be used. Coax-
ial
cables should be terminated at both ends
in their
charac-
teristic impedance. If this is
not
possible,
use suitable
impedance-matching devices.
INPUT
COUPLING
CAPACITOR PRECHARGING
When the Input Coupling switch is set to GND,
the
input
signal is connected to ground through the
input
coupling
capacitor in series with a
1 þÿM© resistor
to form a
precharging network. This network allows
the
input coupling
capacitor to charge to the average de-voltage level of the
signal applied to the probe. Thus any large voltage
transients that may accidentally be generated will not be
applied to
the
amplifier input
when the
Input
Coupling
switch
is moved from GND to
AC. The
precharging network also
provides a measure of
protection
to
the
external
circuitry
by
reducing
the
current
levels
that can be drawn
from the ex-
ternal
circuitry during
capacitor
charging.
1
ST
OR LEFT
11TH OR
R
IGHT
VERTICAL
VERTICAL
GRATICULE
G RA
TICULE
..
·
_
·
- j
"" ....... .
I
CENTER
RISE AND
FALL TIME
MEASU REMENT
PERCENTAGE
MARKERS
CENTER
VERTICAL
GRATICULE
LINE
HORIZONTAL
GRATICULE
LINE
C4207-09
Figure
3-1. Graticule
measurement
markings.
3-1
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