Voltage
Measurements
Voltage
is the
amount
of
electric
potential,
expressed
in
volts,
between
two
points
in a
circuit.
Usually
one of
these
points
is
ground
(zero
volts)
but not
always.
Voltages
can also
be
measured
from
peak-to-peak
- from
the
maximum
point of
a signal
to its
minimum
point.
You must
be
careful
to
specify
which
voltage
you
mean.
The
oscilloscope
is
primarily
a
voltage-measuring
device.
Once you
have
measured
the
voltage,
other
quantities
are just
a
calculation
away.
For
example,
Ohm's
law
states
that
voltage
between
two
points
in a
circuit
equals
the
current
times
the
resistance.
From any
two of
these
quantities
you can
calculate
the
third.
Another
handy
formula
is the
power
law: the
power of
a DC
signal
equals
the
voltage
times
the
current.
Calculations
are more
complicated
for AC
signals,
but the
point
here is
that
measuring
the
voltage
is the
first
step
towards
calculating
other
quantities.
Following
figure
shows
the
voltage
of one
peak -
V[p] -
and the
peak-to-peak
voltage
- V[p-p]
-, which
is
usually
twice
V[p].
Use the
RMS
(root-mean-square)
voltage
- V[RMS]
- to
calculate
the
power of
an AC
signal.
Voltage
Peak and
Peak-to-peak
Voltage
You
take
voltage
measurements
by
counting
the
number
of
divisions
a
waveform
spans on
the
oscilloscope's
vertical
scale.
Adjusting
the
signal
to cover
most of
the
screen
vertically,
then
taking
the
measurement
along
the
center
vertical
graticule
line
having
the
smaller
divisions,
makes
for the
best
voltage
measurements.
The more
screen
area you
use, the
more
accurately
you can
read
from the
screen.
Measure
Voltage
on the
Center
Vertical
Graticule
Line
Many
oscilloscopes
have
on-screen
cursors
that let
you take
waveform
measurements
automatically
on-screen,
without
having
to count
graticule
marks.
Basically,
cursors
are two
horizontal
lines
for
voltage
measurements
and two
vertical
lines
for time
measurements
that you
can move
around
the
screen.
A
readout
shows
the
voltage
or time
at their
positions. |
