Tektronix 7A19 Instruction Manual page 10

Operating lnstructions-7A19
trace to the top
graticule
line.
Do
not
move
the
POSITION
control
after this reference
line
has
been
established.
4.
Set the
Coupling
switch
to
DC.
The
ground reference
line
can
be checked
at
any time by
switching to the
GND
position.
NOTE
To
measure
a voltage level
with respect
to
another
voltage rather
than ground,
make
the following
changes
to
Step
4.
Set
the
Coupling
switch
to
DC
and
apply the reference voltage
to
the
INPUT
connector.
Then
position the trace to the reference
line
and
disconnect the reference
voltage.
5.
Set the time-base Triggering controls for a stable
display. Set the
Time
Base sweep
rate for an
optimum
display of the
waveform.
6.
Measure
the
distance
in
divisions
between
the
reference
line
and the point on
the
waveform
at
which
the
DC
level
is
to
be measured. For example,
in Fig.
2 2 the
measurement
is
between
the reference
line
and point A.
7. Establish
the polarity of the
waveform. With
the
POLARITY
switch
in
the
NORM
position,
any point above
the reference
line
is
positive.
8.
Multiply the distance
measured
in
step 6
by
the
VOLTS/D
IV switch setting.
Include the attenuation factor
of the probe,
if
used.
Po
r— -
nt
A
If
.
._
u
/
"
'
'
-M-f f
m
•«
1
1
-H-++
4-H-f
Vertical
distance
..L,
\
Reference
line
Fig.
2-2. Measuring
instantaneous voltage with
respect to
same
reference.
With high speed
signals,
the
transit
times of the probes and
amplifiers can
distort
the true time
relationship of the
two
signals.
By
using the
VARIABLE DELAY
(Option
4),
the
transit
times
between two
units
can be
matched
to within
50
ps,
thus
giving a true
time
relationship of
the
signals
being viewed.
For matching
transit
times of
two 7A19
with
probes,
proceed
as
follows:
EXAMPLE:
Assume
the vertical distance
measured
is
3.6 divisions
(see Fig.
2-2)
and
the
waveform
is
above
the
reference
line,
using
a
lOX
probe with
a
VOLTS/DIV
switch
setting
of 0.5
V.
Using the formula:
Instan-
vertical
VOLTS/
probe
taneous =
distance
X
polarity
X DIV X
attenuation
voltage
(divisions)
setting
factor
Substituting the given
values:
Instantaneous Voltage
=
3.6
XIX
0.5
V X
10
The
instantaneous
voltage
is
18
volts.
Matching
transit
times using
two
7A19's,
one
having
VARIABLE DELAY
(Option
4)
In
some
applications
it is
necessary to
view
the
time
relationship of
two
signals,
one with
respect to the other.
1.
Install
the
7A19
without
the
VARIABLE DELAY
option
in
the
left
vertical plug-in
compartment.
2.
Install
the
7A19
with
VARIABLE DELAY
option
in
the
right vertical plug-in
compartment.
3.
Connect
the probes
to a
common
signal
source
of
greater than 100
kHz
and
adjust the
time-base
unit for
the
fastest
sweep
available.
4.
Set the Trigger
Source
switch
to left
Vert, and
Vertical
Mode
to Alternate.
5.
Set
both 7A19's
to
the
same
deflection
factor
settings.
6.
Center both
displays
vertically.
7.
Adjust
VARIABLE DELAY
so that the
two
displays
are
superimposed.
The
transit
times of
both
units are
now
matched.
24