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OPERATING CONSIDERATIONS
2215 Operators
This section contains basic operating information and
techniques that should be considered before attempting
any measurements.
GRATICULE
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 connector
located on the front panel.
The graticule is internally marked on the faceplate of
the crt to enable accurate measurements without parallax
error (see Figure 8). It is marked with eight vertical and ten
horizontal major divisions. Each major division is divided
into five subdivisions. The vertical deflection factors and
horizontal timing are calibrated to the graticule so that
accurate measurements can be made directly from the crt.
Also, percentage markers for the measurement of rise and
fail times are located on the left side of the graticule.
GROUNDING
The most reliable signal measurements are made when
the 2215 and the .unit under test are connected by a com¬
mon reference (ground lead), in addition to the signal lead
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 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. To maintain 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 input coupling switch is set to GND, the input
signal is connected to ground through the input coupling
capacitor in series with a 1-M12 resistor to form a pre¬
charging 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 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 net¬
work also provides a measure of protection to the externa!
circuitry by reducing the current levels that can be drawn
from the external circuitry during capacitor charging.
Figure 8. Graticule measurement markings.
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