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ModeIS31SA/B
Operation
which
allows
the
adjustable Trigger
Leve
l
to
be
positioned at
t
he
optimum point.
Set the
Trigger Level control to
the
approximate
center of the trigger ing range
ind
icated
by
the trigger
light (see
Figure
3-
7).
Figure
3-7.
DC
Coupled Mea5urements
3.
When input loading
is
a
problem
(i.e.,
1
MO
load
or cable
capacitance)
or
when
a
more
conve
nient method
of probing is
desirable,
use
a 10:1 Scope Probe. A
probe
is
recom-
mended
for all
logic
applications.
4.
For
sine wave
measurements
<100
kHz,
always use the low pass filter,
selectable
on
the
front
panel.
Norma
lly
the
input
signal
is int
egrated
over
t
he
ent
ire
100
M
Hz
bandwidth.
Use
of
t
he Filter effectively removes
noise
and
harmonics
(above
100
kHz), t
hat
may
affect the correct measurement.
5.
When
measuring
Power
Line
frequencies,
be
extremely
carefu
l
and
alw ays use a
step-
down isolation transformer
(w
ith
"'lOV output).
The
counter's panel is typically at signal
ground,
so
NEVER
try
to
measure
the 50 or
60 Hz line
w
ithout
an iso lation
transformer.
Fifty
percent
of the t ime, you will get
the
connection reversed and
the
cou nter
will go up
in
smoke,
and maybe the operator.
too.
6.
Be
very
careful
w ith
input
levels at higher frequencies (greater than
5
MHz ).
The counter
front
end can take on
ly
6
volts
rms
at
these
frequencies.
J..51.
Time Interval Measurements
1.
To insure
waveform fidelity during T.I. measurements, always use dc coupling.
2.
Meaurements of pulse w
idth,
and time between
pulses, are
more conven iently made
in
the
COM
A
(common
)
position.
3.
Measuring extreme
ly
fast
rise
times is not
recommended
because
of
the
d ifficu
lty
of
setting precise trigger
levels.
4.
T.I.
Average measurements on
synch
ronous frequencies
(any
10
M
H
z,
or
harmonic
of,
w
it
h stability
similar
or better
than
t
he internal
clock
)
are not
recommended because
of a
possible lock-up condition.
5.
In genera
l,
use
the GATE
TIME
co ntro
l
to
vary
the amount of resolution
di spla
yed
.
This
cont
rol
does not affect accuracy.
It
basically
trades
off
longer measurement
t
ime
for
more
resolution.
3-9
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