Operating Considerations; Graticule; Grounding; Signal Connections - Tektronix 2215A Instruction Manual

Operating instructions— 2215A Service

OPERATING CONSIDERATIONS

The following basic operating information and techniques
should be considered before attempting to make any mea­
surements with your instrument.

GRATICULE

The graticule is internally marked on the faceplate of the
crt to enable accurate measurements without parallax error
(see Figure 2-8). 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 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. Coax­
ial cables should be terminated at both ends in their charac­
teristic impedance. If this is not possible, use suitable
impedance-matching devices.
2-8
1ST OR LEFT
VERTICAL
GRATICULE
LINE
/
RISE AIN ID
FALL Till
YIENT w * l" :
MEASURE!
AGE VER1
PERCENT
RS
g r a t
MARKE
Figure 2-8. Graticule measurement markings.
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-Mfi 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 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.
The following procedure should be used whenever the
probe tip is connected to a signal source having a different
dc level than that previously applied, especially if the dc-
11TH OR RIGHT
VERTICAL
GRATICULE
L IN E /
)
CENTER
HORIZONTAL
J 5 ? . GRATICULE
RCAL
l in e
ICULE
NE
C4207-09