Applications - Tektronix 7A19 Instruction Manual

Operating Instructions—
7A19
If
the
P6201 Probe
is
used,
a
one
megohm
input
impedance
may
be achieved. Consult
your
local
TEK-
TRONIX
Field
Engineer or Representative
for
further
information.
Vertical
Gain
Check and Adjustment
To
check the gain of the
7A19,
set
the
VOLTS/DIV
switch to
10
mV
and connect 20
mV,
1
kHz
signal
from
the
oscilloscope
Calibrator to the
INPUT
connector.
The
vertical deflection
should be exactly
two
divisions.
If
not,
adjust the front
panel
GAIN
control for exactly
two
vertical divisions.
Input Coupling
The
input coupling switch allows
a
choice
of input
coupling methods.
The
type of display desired and the
applied signal will
determine
the coupling to
use.
The
DC
coupling
position
can be used for
most
applications.
For
AC
signals
with frequencies
below about
1
kHz, and
square
waves
whose
low-frequency compxDnents
are
important
to the display,
it is
necessary to use
DC
coupling
to obtain a satisfactory presentation.
DC
GND
position disconnects the
signal
source
from
the
amplifier
and connects
it
to a resistive
50
ohm
termination,
thus providing the
same
type
of load to the
signal
source.
The
input
to
the amplifier
is
also
provided with
a
ground
reference.
In
the
AC
coupling position, the
DC
component
of the
signal
is
blocked
by
a
capacitor
in
the input
circuit.
The
AC
coupling position
provides the best display of
signals
with
a
DC
component much
larger
than the
AC
comp>onent.
The
PRE-CHG
feature
should be
used
when
there
is
a
possibility
of having a
residual
charge
on
the input
capacitor of the opposite polarity to the intended input,
and
when
the algebraic
sum
of the charges
may
be greater
than the
maximum
input limitations of the amplifier.
To
use
this feature,
first
set
the coupling switch
to
PRE-CHG,
then
connect
the
signal
source
to
the
INPUT
arnd
wait
about
two
seconds
for
the coupling capacitor
to charge,
set
the coupling switch to
AC.
Another
useful
feature of the
PRE-CHG
position
is
that
it
can be
used as a calibrated
100X
attenuator having an
input
impedance
of
five
kilohms
in
series
with
two
microfarads. This
extends
the
Low
Frequency
response
to
less
than
20
Hz. Input
power
should be
limited to 1/8
watt
in
this
mode.
The
AC
GND
position disconnects the
signal
source
from
the amplifier
and connects
it
to a capacitive coupled
50
ohm
termination, thus providing the
same
type
of load to
the
signal
source.
The
input to the amplifier
is
also pro-
vided
with
a
ground
reference.
VO
LfS/D
IV Switch
The amount
of deflection
produced by
a signal
is
determined by
the
signal
amplitude, the attenuation
factor
of the probe, the
setting
of the
VOLTS/DIV
switch,
and
the
setting
of the
Input Coupling
switch. Calibrated
deflection factors represented
by
the
VOLTS/DIV
switch
apply only
when
the
probe
attenuation
is
XI and
when
the
Input Coupling wvitch
is
not
in
the
PRE-CHG
position (the
PRE-CHG
pxasition
has an attenuation of 100X).
POLARITY
Switch
The
POLAR
IT
Y
switch provides a
means
of inverting the
displayed
signal.
With the
POLARITY
switch
set
to
^UP,
a
positive-going
signal at
the
INPUT
produces an upward
deflection of the
CRT
display.
With
the
POLARITY
switch
set to
INVERT,
a
positive-going signal will
produce
a
downward
deflection of the
CRT
display.
Trace
Identification
and Readout Functions
When
the
IDENTIFY
button
is
pressed,
the
trace
is
deflected
upward
about
0.3 division to identify the
7A19
trace. This feature
is
particularly useful
when
multiple
traces
are
displayed
on
the
CRT.
In
mainframes with
readout,
it
also
replaces the deflection
factor
readout with
the
word "IDENTIFY".
The
7A19
is
equipped with probe encoding
circuitry
that,
when
used with
a
coded
probe, corrects the deflection
factor
readout.
VARIABLE DELAY
(Option
4)
The
optional
VARIABLE DELAY
line
provides
a
means
for delaying the
signal
applied to the
INPUT
for
up
to
±500
ps.
APPLICATIONS
General
The
following information describes the
procedures and
techniques for
making measurements with
a
7A19
and the
associated
TEKTRONIX
oscilloscope
and
time-base.
These
applications
are
not
described
in detail,
since
each
application
must
be adapted to the
requirements
of the
individual
measurements.
This instrument can also
be used
for
many
applications
which
are
not described
in this
2-2