Operating Considerations; Graticule; Grounding; Signal Connections - Tektronix 2235A Instruction Manual

Operating lnstructlons- 2235A Instruction
OPERATING CONSIDERATIONS
GRATICULE
best grounding method for signal interconnection and
ensures the maximum amount of signal-lead shielding
The graticule is internally marked on the faceplate of the
in the probe cable. A separate ground lead can be
crt to enable accurate measurements without parallax
connected from the unit under test to the
O S C ~ ~ ~ O S C O ~ ~
error (see Figure 2-8). It is marked with eight vertical and
GND
located
On
the front panel.
ten horizontal major divisions. Each major division is
divided into five subdivisions. ' T he vertical deflection
factors and horizontal timing are calibrated to the
graticule so that accurate measurements can be made
SIGNAL CONNECTIONS
directly from the crt. Also, percentage markers for the
measurement of rise and fall times are located on the left
Generally, probes offer the most convenient means of
side of the graticule.
connecting an input signal to the instrument. They are
shielded to prevent pickup of electromagnetic inter-
1 ST OR LEFT 11TH OR RIGHT
VERTICAL VERTICAL
GRATICULE GRATICULE
LINE LINE
1 1
RISE AND CENTER CENTER
FALL TIME VERTICAL HORIZONTAL
MEASUREMENT GRATICULE GRATICULE
PERCENTAGE LINE LINE
MARKERS
7683-21
ference, and the supplied 10X 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. T o main-
tain the original frequency characteristics of an applied
signal, only high-quality, low-loss coaxial cables
should be used. Coaxial cables should be terminated at
both ends in their characteristic impedance. If this is not
possible, use suitable impedance-matching devices.
INPUT COUPLING CAPACITOR
PRECHARGING
When the lnput Coupling switch is set to GND, the input
signal is connected to ground through the input coupling
capacitor in series with a 1
Ma
resistor to form a
precharging network. This network allows the input
coupling capacitor to charge to the average dc-voltage
level of the signal applied to the probe. Thus any large
Figure 2-8. Graticule measurement markings. voltage transients that may accidentally be generated
will not be applied to the amplifier input when the lnput
Coupling switch is moved from GND to AC. The pre-
charging network also provides a measure of protection
GROUNDING
to the external circuitry by reducing the current levels that
can be drawn from the external circuitry during capacitor
charging.
The most reliable signal measurements are made when
this instrument and the unit under test are connected by a
common reference (ground lead), in addition to the sig-
The following procedure should be used whenever the
nal lead or probe. The probe's ground lead provides the
probe tip is connected to a signal source having a
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AR TEK MEDU
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