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Section 4— 2221 Operators
O
OPERATING
CONSIDERATIONS
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GROUNDING
This section contains basic operating information and
techniques that should be considered before attempting to
make any measurements with the instrument .
GRATICULE
The most reliable signal measurements are made when
the oscilloscope and the unit under test are connected by
a common 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 maximum 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 receptacle
located on the front panel.
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The graticule is internally marked on the faceplate of
the crt to eliminate parallax -viewing errors and to enable
measurements ( see Figure 4-1). The graticule is marked
with eight vertical and ten horizontal major divisions . In
addition , each major division is divided into five subdivi
sions . The vertical deflection factors and horizontal timing
are calibrated to the graticule so that accurate measure
ments can be made directly from the crt. Also , percentage
marks for the measurement of rise and fall times are
located on the left side of the graticule.
SIGNAL CONNECTIONS
Probes
Generally,
the accessory
probes supplied with
the
instrument provide the most convenient means of connect
ing a signal to the vertical inputs of the instrument. The
probe and probe lead are shielded to prevent pickup of
electromagnetic interference, and the 10X attenuation fac
tor of the probe offers a high input impedance that mini
mizes signal loading in the circuitry under test .
1ST OR LEFT
VERTICAL
GRATICULE
LINE
11TH OR RIGHT
VERTICAL
GRATICULE
LINE
Both the probe and the probe accessories should be
handled carefully at all times to prevent damage to them .
Avoid dropping the probe body. Striking a hard surface
can cause damage to both the probe body and the probe
tip . Exercise care to prevent the cable from being crushed
or kinked . Do not place excessive strain on the cable by
pulling.
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RISE AND
FALL TIME
MEASUREMENT
PERCENTAGE
MARKERS
CENTER
VERTICAL
GRATICULE
LINE
CENTER
HORIZONTAL
GRATICULE
LINE
The standard - accessory probe is a compensated 10X
voltage divider. It is a resistive voltage divider for low fre
quencies
and
a
capacitive
voltage
divider
for
high
frequency signal components . Inductance introduced by
long signal or ground leads forms a series-resonant circuit .
This circuit will affect system bandwidth and will
driven by a signal containing significant frequency
ponents at or near the circuit's resonant frequency. Oscil
lations ( ringing) can then appear on the oscilloscope
waveform display and distort the true signal waveshape .
Always keep both the ground lead and the probe signal
4207-09
Figure 4-1 . Graticule measurement markings.
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4-1
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