HOW
TO
MINIMIZE
SCOPE
/PROBE
COMBINATION
ERRORS
Hewlett- Packard
1125A
active
probe.
Choosing
the
right probe
for
a particular
application
can
reduce
measurement
errors
50% or more.
MOST
of
us tend
to
assume
that
an
oscilloscope
display
is
a
"perfect" representation
of what is
occurring in
a given
circuit.
Actually,
when you
apply
a
signal
to the input
of
a scope,
you
can lose
a
large
percen-
tage
of
what
is really
there if
the
signal
source is
not
carefully matched
to the
scope's
input
impedance.
Since
the
main
reason
for paying
big money
for
54
BY THOMAS
R.
SEAR
a wideband
scope is that you
need
the
bandwidth, it
is important
that nothing
be allowed
to
compromise
its
performance
-least of
all something
as "simple"
as
a probe connected
to
the input.
If
you
select
the
wrong type
of
probe
for
a given measurement,
the
signal
that reaches
the
scope
may
not have
some
of
the
characteristics that
are
of
interest
to
you. Unless certain precau-
tions
are observed, especially
at
high
frequencies,
getting the
signal
to the
input
of the
scope
may
become
the
most
critical part
of
any measurement
you are making.
There
are times when
a plain
piece
of wire will
suffice
for
coupling a
sig-
nal
to a
scope.
Also,
the passive types
of attenuator
probes
that
are sold
with
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