Probes
Now you
are
ready to
connect
a probe
to your
oscilloscope.
It is
important
to use a
probe
designed
to work
with
your
oscilloscope.
A probe
is more
than a
cable
with a
clip-on
tip. It
is a
high-quality
connector,
carefully
designed
not to
pick up
stray
radio
and
power
line
noise.
Probes
are
designed
not to
influence
the
behavior
of the
circuit
you are
testing.
However,
no
measurement
device
can act
as a
perfectly
invisible
observer.
The
unintentional
interaction
of the
probe
and
oscilloscope
with the
circuit
being
tested
is
called
circuit
loading.
To
minimize
circuit
loading,
you will
probably
use a
10X
attenuator
(passive)
probe.
Your
oscilloscope
probably
arrived
with a
passive
probe as
a
standard
accessory.
Passive
probes
provide
you with
an
excellent
tool for
general-purpose
testing
and
troubleshooting.
For more
specific
measurements
or
tests,
many
other
types of
probes
exist.
Two
examples
are
active
and
current
probes.
Descriptions
of these
probes
follow,
with
more
emphasis
given to
the
passive
probe
since
this is
the
probe
type
that
allows
you the
most
flexibility
of use.
Using
Passive
Probes
Most
passive
probes
have
some
degree
of
attenuation
factor,
such as
10X,
100X,
and so
on. By
convention,
attenuation
factors,
such as
for the
10X
attenuator
probe,
have the
X after
the
factor.
In
contrast,
magnification
factors
like X10
have the
X first.
The
10X
(read as
"ten
times")
attenuator
probe
minimizes
circuit
loading
and is
an
excellent
general-purpose
passive
probe.
Circuit
loading
becomes
more
pronounced
at
higher
frequencies,
so be
sure to
use this
type of
probe
when
measuring
signals
above 5
kHz. The
10X
attenuator
probe
improves
the
accuracy
of your
measurements,
but it
also
reduces
the
amplitude
of the
signal
seen on
the
screen
by a
factor
of 10.
Because
it
attenuates
the
signal,
the 10X
attenuator
probe
makes it
difficult
to look
at
signals
less
than 10
millivolts.
The 1X
probe is
similar
to the
10X
attenuator
probe
but
lacks
the
attenuation
circuitry.
Without
this
circuitry,
more
interference
is
introduced
to the
circuit
being
tested.
Use the
10X
attenuator
probe as
your
standard
probe,
but keep
the 1X
probe
handy
for
measuring
weak
signals.
Some
probes
have a
convenient
feature
for
switching
between
1X and
10X
attenuation
at the
probe
tip. If
your
probe
has this
feature,
make
sure you
are
using
the
correct
setting
before
taking
measurements.
Many
oscilloscopes
can
detect
whether
you are
using a
1X or
10X
probe
and
adjust
their
screen
readouts
accordingly.
However
with
some
oscilloscopes,
you must
set the
type of
probe
you are
using or
read
from the
proper
1X or
10X
marking
on the
volts/div
control.
The
10X
attenuator
probe
works by
balancing
the
probe's
electrical
properties
against
the
oscilloscope's
electrical
properties.
Before
using a
10X
attenuator
probe
you need
to
adjust
this
balance
for your
particular
oscilloscope.
This
adjustment
is
called
compensating
the
probe
and is
further
described
in the
next
section.
Following
Figure
shows a
simple
diagram
of the
internal
workings
of a
probe,
its
adjustment,
and the
input of
an
oscilloscope.
