Tektronix 47E5A

APPLICATIONS AND MEASUREMENTS
Refer to Basic Oscilloscope Displays as needed to obtain correct displays.
PRELIMINARY
Signal Ground
~
Avoid cross-grounding because instrument damage
may occur .
The most reliable measurements are made when the
oscilloscope ground is connected to the ground of the unit
under test by the ground strap on the signal probe. Also a
ground lead can be connected to the ground banana jack
on the oscilloscope chassis to establish a common ground
with the unit under test.
Input Coupling Capacitor Precharging
In the GND position , the input signal is connected to
ground through a one-megohm 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
accidentally generated will not be
applied to the
amplifier input. The precharge network also
provides a measure
of protection to the external ci rcu itry
by reducing the current levels that can be drawn from the
external
circuitry during capacitor charging.
The following procedure should be used whenever the
probe tip is connected to a signal sou rce having a different
dc level than that previously applied, especially if the dc
level difference is more than 10 times the VOL TS/ DIV
setting.
1. Before
connecting the probe tip to a signal source,
set the
Input Coupling switch to GND.
2. Touch the probe tip to oscilloscope chassis ground .
Wait several
seconds for the Input Coupling capacitor to
discharge.
3.
Connect the probe tip to the signal source .
4. Wait several seconds for the Input Coupling
capacitor to charge.
5.
Set the Input Coupling Switch to AC . The display
will remain on the screen so the ac component of the
signal can
be measured in the normal manner.
28 475A/OM44 Operators
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